Wednesday, April 23, 2014

WSJ Book Review: "Given uncertainties of climate-change forecasting & urgency portrayed by "alarmists," expect the "deniers" to hold their ground"

Book Review: 'A Climate of Crisis' by Patrick Allitt

Before climate change, 'alarmists' and 'deniers' had it out over hazardous waste, acid rain, the ozone layer and rain forests.

By JAMES HUFFMAN 

April 23, 2014 7:06 p.m. ET    THE WALL STREET JOURNAL

Climate change has been the dominant environmental concern of the 21st century. Public discussion of the topic is less an informed exchange of ideas than a strident debate pitting alarmists against deniers—at least that is how each side labels the other. Both are secure in the knowledge that truth, reason and the moral high ground undergird their positions.

And thus it has always been with environmental policy. There was a brief period of productive collaboration during the Johnson and Nixon administrations, but thereafter "green" politics settled into a stark polarization as issues like hazardous waste, environmental racism, acid rain, the ozone layer and the Amazonian rain forest each came to the fore. Climate change is just the latest chapter.

It is this larger story that Patrick Allitt tells in "A Climate of Crisis: America in the Age of Environmentalism." In recounting partisan battles, Mr. Allitt's objectivity is refreshing.

His account begins with the environmental initiatives inspired by Rachel Carson's
"Silent Spring" (1962) and more apocalyptic writings, like Paul Ehrlich's "The Population Bomb" (1968) and Barry Commoner's "The Closing Circle" (1971). In Mr. Allitt's telling, these books inspired such strong public responses because the public was already attuned to the existential threats of the Cold War and the nuclear arms race. In the 1960s and early 1970s, there was broad national support for the Wilderness Act, the National Environmental Policy Act, the Endangered Species Act, the Clean Air Act, the Federal Water Pollution Control Act and the creation of the Environmental Protection Agency.



A Climate of Crisis  By Patrick Allitt (Penguin, 384 pages, $29.95)

There were dramatic reductions in pollution, expansions of national parks and wilderness areas, and the restoration of several threatened species. Even so, environmentalists continued to cry wolf and were undeterred when their doom-saying forecasts of global famine and ecological ruin failed to materialize. The consensus collapsed, and the public grew skeptical, especially the people bearing the significant and often unintended costs of regulation. The acid-rain and environmental-racism scares, writes Mr. Allitt, "turned out to be evanescent." Yet companies had spent hundreds of millions on regulatory compliance. 
Many apple farmers were put out of business in 1989 by what proved to be baseless claims that the chemical Alar was causing cancer in schoolchildren. And numerous Northwest communities were devastated in the 1990s by a 90% cut in public-land timber harvests, which crippled the timber industry to save the Northern Spotted Owl. Scientists later found that the greatest threat to this owl was its cousin, the Barred Owl.

The environmental lobby seldom acknowledged its failures—or even its successes. Since 1990, there has been a 90% reduction in automobile emissions (and a 99% reduction since 1960), yet the car remains public enemy No. 1. Despite widespread recognition that ethanol has few if any environmental benefits, subsidies and mandated use persist—and food prices have been driven higher by the diversion of corn from food to fuel production.


Environmentalism has grown into an industry of interest groups, lobbyists, litigators, impact assessors and bureaucrats who rely on warnings of impending disaster to sustain and expand their enterprises.
It is much the same with their opponents, for whom the wolf is always at the door—notwithstanding numerous examples of their somehow surviving what they had vehemently insisted were business-killing regulations. Both sides reacted in predictable ways when climate change reared its political head in the early 1990s.

Mr. Allitt covers this ground well and fairly presents the views of everyone from "Deep Ecologist" Arne Naess, who believed that humans must regard plants and animals as our equals, to Helen Chenoweth, the Idaho congresswoman who called environmentalism "a cloudy mixture of New Age mysticism, Native American folklore, and primitive earth worship." Mr. Allitt's critique of the relentless crisis mentality will lead many environmentalists to dismiss the book as anti-environmental, while anti-environmentalists will object to his conclusion that much conservation has been achieved at little cost to ordinary Americans.

Yet for all its balance, Mr. Allitt's account falls short in two important respects. He misunderstands "free-market environmentalists" and bundles them with the "Sagebrush Rebellion" of the late 1970s and the "Wise Use" movement of the late 1980s. There is little that connects them. While the last two, like today's protesters at Cliven Bundy's ranch in Nevada, advocated for state rather than federal control of the vast public lands of the West, they were dependent on the largess of a friendly public landlord. Free-market environmentalists urged property-based solutions, spurring tradable emission permits, congestion pricing on roadways, volume-based trash-collection fees, transferable ocean-fisheries quotas, and numerous other market approaches. Even EPA administrators "eventually realized," in Mr. Allitt's words, "that it would be better to allow manufacturers to trade in the right to pollute."

Mr. Allitt also pays little heed to the large role that environmental litigation (as well as the threat of litigation) has played over the past half-century. Nowhere has our divisive environmental politics been more apparent and influential. Thanks to bipartisan legislation of the 1960s and '70s, which opened the courthouse doors to both sides of the environmental divide, scarcely a timber sale or urban-development plan moves forward without courts being asked to assess whether the developer or the government has properly weighed the pros and cons. The judge as policy maker is thus a central part of the story.

Given the uncertainties of climate-change forecasting and the urgency portrayed by "alarmists," expect the "deniers" to hold their ground—and our environmental politics to remain in a climate of crisis.


Mr. Huffman, dean emeritus of the Lewis & Clark Law School, is a visiting fellow at the Hoover Institution. He is the author of "Private Property and State Power" and "Private Property and the Constitution."

New paper finds natural Pacific Decadal Oscillation controlled Myanmar climate during 20th century

A paper published today in the International Journal of Climatology finds evidence of a strong influence of the natural Pacific Decadal Oscillation [PDO] on the climate of Myanmar over the 20th century. The authors reconstruct the Myanmar climate using tree ring data, producing another non-hockey-stick with temperatures warmer during the 1930's-1940s than at the end of the 20th century and end of the record in 2007. 

According to the authors, negative PDO phases correspond to dry conditions, due to reduced moisture flux into central Myanmar, and vice-versa. Many other peer-reviewed papers similarly demonstrate the major ocean oscillations are the primary "control knob" of climate, not CO2. 


It is well known that climate models are unable to reproduce any of the major ocean oscillations including the PDO, ENSO, AMO, etc., which is one of the primary reasons why climate models have little to no skill reproducing or projecting climate. 

The PDO, ENSO, AMO and other natural ocean oscillations have been linked to solar activity, and represent only one category of potential solar amplification mechanisms described in the scientific literature, and which continue to be ignored by climate modelers. 



Climate reconstruction from Teak tree rings shown in top graph demonstrates warmer temperatures during the 1930's-1940's than at the end of the record in 2007. Also shown is a close correspondence with the natural Pacific Decadal Oscillation in bottom graph 
Full paper available here

The climate of Myanmar: evidence for effects of the Pacific Decadal Oscillation

Rosanne D'Arrigo and Caroline C. Ummenhofer

We show evidence for the influence of the Pacific Decadal Oscillation (PDO) on Myanmar's monsoonal hydroclimate using both instrumental and 20th century reanalysis data, and a tree-ring width chronology from Myanmar's central Dry Zone. The ‘regime shifts’ identified in the instrumental PDO for the past century are clearly evident in the Myanmar teak. The teak record and PDO index correlate most significantly and positively during December–May, at r = 0.41 (0.002, n = 109). We generated composite climate anomalies for southern Asia and adjacent ocean areas during negative and positive PDO phases and above/below average teak growth for the May–September wet monsoon season. They show that negative (positive) PDO phases correspond to dry (wet) conditions, due to reduced (enhanced) moisture flux into central Myanmar. Multitaper Method (MTM) and Singular Spectrum Analysis (SSA) spectral analyses reveal considerable multidecadal variability over the past several centuries of the teak chronology, consistent with the PDO.

New paper in Nature finds increased CO2 & warming both enhance plant growing seasons

A paper published today in Nature finds that elevated CO2 in combination with warming further lengthens plant growing seasons, by helping to "conserve water, which enabled most species to remain active longer." In other words, increased CO2 and warming both independently and in combination improve the length and magnitude of plant productivity cycles, a win-win for the biosphere, and a truism well-known by greenhouse operators for a long time. 

According to the authors, "Our results suggest that a longer growing season, especially in years or biomes where water is a limiting factor, is not due to warming alone, but also to higher atmospheric CO2 concentrations that extend the active period of plant annual life cycles." The paper adds to many others finding increased CO2 improves plant resistance to drought.

The biosphere needs more CO2, not less.


Elevated CO2 further lengthens growing season under warming conditions


Nature advance online publication 23 April 2014. doi:10.1038/nature13207

Authors: Melissa Reyes-Fox, Heidi Steltzer, M. J. Trlica, Gregory S. McMaster, Allan A. Andales, Dan R. LeCain & Jack A. Morgan


Observations of a longer growing season through earlier plant growth in temperate to polar regions have been thought to be a response to climate warming. However, data from experimental warming studies indicate that many species that initiate leaf growth and flowering earlier also reach seed maturation and senesce earlier, shortening their active and reproductive periods. A conceptual model to explain this apparent contradiction, and an analysis of the effect of elevated CO2—which can delay annual life cycle events—on changing season length, have not been tested. Here we show that experimental warming in a temperate grassland led to a longer growing season through earlier leaf emergence by the first species to leaf, often a grass, and constant or delayed senescence by other species that were the last to senesce, supporting the conceptual model. Elevated CO2 further extended growing, but not reproductive, season length in the warmed grassland by conserving water, which enabled most species to remain active longer. Our results suggest that a longer growing season, especially in years or biomes where water is a limiting factor, is not due to warming alone, but also to higher atmospheric CO2 concentrations that extend the active period of plant annual life cycles.

Tuesday, April 22, 2014

New paper finds solar UV is correlated to global mean temperature

A paper published today in Methods in Ecology and Evolution describes a new satellite dataset of solar UV-B radiation for use in ecological studies. According to the authors, "UV-B surfaces were correlated with global mean temperature and annual mean radiation data, but exhibited variable spatial associations across the globe." The finding is notable, since climate scientists dismiss the role of the Sun in climate change by only looking at the tiny 0.1% variations in total solar irradiance [TSI] over solar cycles, ignoring the large variations in solar UV of up to 100% over solar cycles, and which according to this paper, correlates to global mean temperature. Thus, the role of the Sun and solar amplification mechanisms on climate is only at the earliest stages of understanding. 

glUV: a global UV-B radiation data set for macroecological studies

Michael Beckmann et al


Macroecology has prospered in recent years due in part to the wide array of climatic data, such as those provided by the WorldClim and CliMond data sets, which has become available for research. However, important environmental variables have still been missing, including spatial data sets on UV-B radiation, an increasingly recognized driver of ecological processes.

We developed a set of global UV-B surfaces (glUV) suitable to match common spatial scales in macroecology. Our data set is based on remotely sensed records from NASA's Ozone Monitoring Instrument (Aura-OMI). Following a similar approach as for the WorldClim and CliMond data sets, we processed daily UV-B measurements acquired over a period of eight years into monthly mean UV-B data and six ecologically meaningful UV-B variables with a 15-arc minute resolution. These bioclimatic variables represent Annual Mean UV-B, UV-B Seasonality, Mean UV-B of Highest Month, Mean UV-B of Lowest Month, Sum of Monthly Mean UV-B during Highest Quarter and Sum of Monthly Mean UV-B during Lowest Quarter. We correlated our data sets with selected variables of existing bioclimatic surfaces for land and with Terra–MODIS Sea Surface Temperature for ocean regions to test for relations to known gradients and patterns.

UV-B surfaces showed a distinct seasonal variance at a global scale, while the intensity of UV-B radiation decreased towards higher latitudes and was modified by topographic and climatic heterogeneity. UV-B surfaces were correlated with global mean temperature and annual mean radiation data, but exhibited variable spatial associations across the globe. UV-B surfaces were otherwise widely independent of existing bioclimatic surfaces.

Our data set provides new climatological information relevant for macroecological analyses. As UV-B is a known driver of numerous biological patterns and processes, our data set offers the potential to generate a better understanding of these dynamics in macroecology, biogeography, global change research and beyond. The glUV data set containing monthly mean UV-B data and six derived UV-B surfaces is freely available for download at: http://www.ufz.de/gluv.

UV-radiation data to help ecological research

UPDATE: see comment below 4/24/14

New paper finds Alpine glaciers were of similar size during the Medieval Warm Period

A new paper published in The Cryosphere reconstructs Alpine glacier fluctuations over the past 1600 years and finds glacier lengths of 7 Alpine glaciers were similar during the Medieval Warm Period and the end of the 20th century. 

The paper uses a combination of observations shown as the black dots in Fig 1 below and modeled glacier lengths shown as the red lines. Lengths of the seven modeled glaciers are approximately the same or slightly less during the Medieval Warm Period 1000 years ago as compared to the end of the 20th century:


The author also finds a link between the Atlantic Multidecadal Oscillation [AMO] and reconstructed Alpine summer temperatures and glacier lengths. The AMO, in turn, has been linked to solar activity variation. 

The Cryosphere, 8, 639-650, 2014
www.the-cryosphere.net/8/639/2014/
doi:10.5194/tc-8-639-2014



M. P. Lüthi
1VAW Glaciology, ETH Zürich, 8093 Zurich, Switzerland
*now at: University of Zürich, 8057 Zurich, Switzerland

Abstract. Mountain glaciers sample a combination of climate fields – temperature, precipitation and radiation – by accumulation and melting of ice. Flow dynamics acts as a transfer function that maps volume changes to a length response of the glacier terminus. Long histories of terminus positions have been assembled for several glaciers in the Alps. Here I analyze terminus position histories from an ensemble of seven glaciers in the Alps with a macroscopic model of glacier dynamics to derive a history of glacier equilibrium line altitude (ELA) for the time span 400–2010 C.E. The resulting climatic reconstruction depends only on records of glacier variations. The reconstructed ELA history is similar to recent reconstructions of Alpine summer temperature and Atlantic Multidecadal Oscillation (AMO) index, but bears little resemblance to reconstructed precipitation variations. Most reconstructed low-ELA periods coincide with large explosive volcano eruptions, hinting at a direct effect of volcanic radiative cooling on mass balance. The glacier advances during the LIA, and the retreat after 1860, can thus be mainly attributed to temperature and volcanic radiative cooling.

New paper finds huge erroneous assumption in climate models on how solar radiation is averaged in space & time

A paper published today in the Journal of the Atmospheric Sciences finds an astonishing bias of climate models with regard to "an important decision about how to average solar radiation in space and time" by choice of the solar zenith angle [the angle measured from directly overhead to the geometric centre of the sun's disc]. According to the authors, the bias errors in choice of solar zenith angle upon the Earth's energy budget can be as great as the effect of a 12-fold [1200%] change in CO2 concentrations.

According to the paper, "Use of daytime-average zenith angle may lead to a high bias in planetary albedo of ~3%, equivalent to a deficit in shortwave absorption of ~10 W m−2 in the global energy budget (comparable to the radiative forcing of a roughly sixfold change in CO2 concentration). Other studies that have used general circulation models with spatially constant insolation have underestimated the global-mean zenith angle, with a consequent low bias in planetary albedo of ~2-6%, or a surplus in shortwave absorption of ~7-20 W m−2 [comparable to the radiative forcing of up to a roughly 12-fold change in CO2 concentration] in the global energy budget."

As noted by Dr. Roy Spencer, a change in planetary albedo of only 1-2% alone can account for global warming or global cooling, but this paper finds climate model planetary albedo may be biased as much as 6% due to errors of the solar zenith angle alone!

Whoops

On the Choice of Average Solar Zenith Angle

Timothy W. Cronin*
Program in Atmospheres, Oceans, and Climate, Massachusetts Institute of Technology, Cambridge, Massachusetts
Abstract
Idealized climate modeling studies often choose to neglect spatiotemporal variations in solar radiation, but doing so comes with an important decision about how to average solar radiation in space and time. Since both clear-sky and cloud albedo are increasing functions of the solar zenith angle, one can choose an absorption-weighted zenith angle which reproduces the spatial- or time-mean absorbed solar radiation. Here, we perform calculations for a pure scattering atmosphere and with a more detailed radiative transfer model, and find that the absorption-weighted zenith angle is usually between the daytime-weighted and insolation-weighted zenith angles, but much closer to the insolation-weighted zenith angle in most cases, especially if clouds are responsible for much of the shortwave reflection. Use of daytime-average zenith angle may lead to a high bias in planetary albedo of ~3%, equivalent to a deficit in shortwave absorption of ~10 W m−2 in the global energy budget (comparable to the radiative forcing of a roughly sixfold change in CO2 concentration). Other studies that have used general circulation models with spatially constant insolation have underestimated the global-mean zenith angle, with a consequent low bias in planetary albedo of ~2-6%, or a surplus in shortwave absorption of ~7-20 W m−2 [comparable to the radiative forcing of a roughly 12-fold change in CO2 concentration] in the global energy budget.

New paper finds many positive benefits of climate change in the 'untouched areas of Russia'

A paper published on Earth Day today in Global Change Biology examines the impact of climate change since 1900 on "untouched areas of Russia" in the Urals mountain range and finds significant positive effects including ongoing forest expansion, high density of seedlings and saplings, a "more favorable microclimate", increased precipitation and snow while "summer temperatures have only changed slightly (~0.05°C/decade)", and growth forms of trees indicating less severe winter conditions.

That is, none of the changes since 1900 in the Urals described by the authors would be considered a negative impact of climate change and are instead considered improved winter conditions.

Treeline advances along the Urals mountain range – driven by improved winter conditions?



Global Change Biology by Frank Hagedorn, Stepan G. Shiyatov, Valeriy S. Mazepa, Nadezhda M. Devi, Andrey A. Grigor'ev, Alexandr A. Bartish, Valeriy V. Fomin, Denis S. Kapralov, Maxim Terent'ev, Harald Bugman, Andreas Rigling, Pavel A. Moiseev

Abstract

High-altitude treelines are temperature-limited vegetation boundaries, but little quantitative evidence exists about the impact of climate change on treelines in untouched areas of Russia. Here, we estimated how forest-tundra ecotones have changed during the last century along the Ural mountains. In the South, North, Sub-Polar and Polar Urals, we compared 450 historical and recent photographs and determined the ages of 11,100 trees along 16 altitudinal gradients. In these four regions, boundaries of open and closed forests (crown covers above 20 and 40%) expanded upwards by 4 to 8 m in altitude per decade. Results strongly suggest that snow was an important driver for these forest advances: (1) Winter precipitation has increased substantially throughout the Urals (~7 mm/decade), which corresponds to almost a doubling in the Polar Urals, while summer temperatures have only changed slightly (~0.05°C/decade). (2) There was a positive correlation between canopy cover, snow height and soil temperatures, suggesting that an increasing canopy cover promotes snow accumulation and, hence, a more favorable microclimate. (3) Tree age analysis showed that forest expansion mainly began around the year 1900 on concave wind-sheltered slopes with thick snow covers, while it started in the 1950s and 1970s on slopes with shallower snow covers. (4) During the 20th century, dominant growth forms of trees have changed from multi-stemmed trees, resulting from harsh winter conditions, to single-stemmed trees. While 87, 31, and 93% of stems appearing before 1950 were from multi-stemmed trees in the South, North and Polar Urals, more than 95% of the younger trees had a single stem. Currently, there is a high density of seedlings and saplings in the forest-tundra ecotone, indicating that forest expansion is ongoing and that alpine tundra vegetation will disappear from most mountains of the South and North Urals where treeline is already close to the highest peaks.

Monday, April 21, 2014

Study predicts sea levels in India will rise only 1.57 inches over next 100 years

In a new report from The Energy and Resources Institute (TERI), a "not-for-profit" organization also headed by IPCC Chairman Rajendra Pachauri, the mean sea level along Mumbai, the most populous city in India, is predicted to rise a horrifying 4 cm or 1.57 inches over the next 100 years. 

The prediction for sea level rise in Mumbai is oddly less than half the average rate of rise over the past 203 years of only ~4 inches per century.

Meanwhile, Pachauri's other organization the IPCC predicts, on the basis of highly-flawed and overheated climate models, that global sea level rise will be 52-98 cm by 2100, a rate of 23.8 - 38.6 inches per century, more than 24 times faster than for Mumbai. How is that possible?

Mean sea level along Mumbai to rise by 4 cm in 100 yrs: Study


Written by Anjali Lukose | Mumbai | April 17, 2014 3:43 am

In the 2050s, the increase in the mean sea level along the Mumbai coast may be around 2 cm and it would increase to around 4 cm by 2100.

SUMMARY
The study was conducted by The Energy and Resources Institute (TERI), an environmental research institute.

The mean sea level along Mumbai’s coast is likely to rise by around 4 cm while warmer nights, increased rainfall, decline in crop productivity and health issues stare Maharashtra in the next 100 years, finds a study on “Assessing climate change vulnerabilities and adaptation strategies for Maharashtra”.

The study was conducted by The Energy and Resources Institute (TERI), an environmental research institute, in partnership with Met Office Hadley Centre, United Kingdom’s climate change research centre for the state environment department.

Coastal flooding, the report warned, could lead to reduction in availability of fresh water due to saltwater intrusion as well as contamination of water supply through pollutants from submerged waste dumps. The temperature in Mumbai and the rest of Maharashtra is likely to increase by 1 to 3 degrees in the next 50 years, and evening or nights would be warmer by 1.5 to 2 degrees.

The study is part of the state environment department’s project to study impact of climate change in Maharashtra and devise district-wise plans. “It is important for the state to develop its own strategy and be prepared to meet challenges posed by climate change,” said R A Rajeev, principal secretary, environment department. “TERI has submitted a draft report and we had some queries so they are finalizing the report.”

In the 2030s , TERI has predicted that the state’s coastal regions, which include Mumbai, Navi Mumbai and Thane and eastern Maharashtra, will have higher ambient temperature compared to central Maharashtra.

“If the rainfall increases as predicted, combined with an increase in sea levels, construction close to the sea could be affected because of heavy flooding, which is a grave situation for a coastal city like Mumbai,” said Subimal Ghosh, an associate professor in IIT-B’s civil engineering department and researcher on climate change. “We need to conserve our water resources and come up with better alerting systems during extreme climate events in Mumbai.”

In the 2050s, the increase in the mean sea level along the Mumbai coast may be around 2 cm and it would increase to around 4 cm by 2100, according to the executive summary report of the study. Due to increasing temperature and rainfall, coastal and eastern Maharashtra are vulnerable to malaria outbreaks in the future, predicts the study. Even rainfall shows an increasing trend with TERI’s prediction of a 20-40 per cent increase in rainfall through the state.

However, the mean temperature in the state has risen only between 0.5 to 2 degrees and rainfall showed a significant increase only in the Konkan region in the past 100 years, according to A K Srivastava, director of National Climate Centre, Indian Meteorological Department (IMD) Pune.

Across Maharashtra, Nandurbar was found to be the district that would be the most vulnerable to climate change, followed by Dhule and Buldhana, while Satara followed by Ratnagiri and Sindhudurg would be the least vulnerable districts.

Review paper finds the Medieval Warm Period was global and its peak warmth likely significantly greater than the present

A new paper from SPPI and CO2 Science reviews the scientific literature on the Medieval Warm Period in Upper North America, and concludes, "these published results now join the many other similar results, from all around the world, where it can be seen that the Medieval Warm Period was not only a global phenomenon, but that its peak warmth was very likely significantly greater than that of the Current Warm Period."

mwp_upper_n_america
[Illustrations, footnotes and references available in PDF version]
Excerpts:

Climate alarmists claim that rising atmospheric CO2 concentrations due to the burning of fossil fuels, such as coal, gas and oil, have raised global air temperatures to their highest level in the past one to two millennia. And, therefore, investigating the possibility of a period of equal global warmth within the past one to two thousand years has become a high-priority enterprise; for if such a period could be shown to have existed, when the atmosphere's CO2 concentration was far less than it is today, there would be no compelling reason to attribute the warmth of our day to the CO2 released to the air by mankind since the beginning of the Industrial Revolution. Thus, in this review of the pertinent scientific literature, results of the search for such knowledge are presented for studies conducted within the borders of Canada and other regions north of the lower 48 states of the United States of America.
There is nothing unusual or unnatural about climate change. It happens on decadal scales, centennial scales and millennial scales. And over the past century or two, the earth has experienced a natural and not-unexpected millennial-scale climatic shift that may or may not have yet run its course.
The fact that the air's CO2 content increased in phase with this shift is simply due to the coincidental concurrent development of the Industrial Revolution and its subsequent transformative impact on humanity.
Since the peak warmth of the Medieval Warm Period was caused by something quite apart from elevated levels of atmospheric CO2, or any other greenhouse gas for that matter, there is no reason to not believe that a return engagement of that same factor or group of factors is responsible for the even lesser “peak” warmth of today.

But if not CO2, then what? According to Luckman and Wilson, some solar-related phenomenon may well be the main driver of the low frequency temperature trends.

The same story is also told by tree ring-width anomalies from the adjacent Wrangell Mountains of Alaska. Hence, it can be concluded from two different data bases that the region's current temperature is, in fact, lower than it was during the warmest part of the Medieval Warm Period, adding more weight to the growing mountain of evidence that indicates there is nothing unusual about the planet's current level of warmth.

These results now join the many other similar results, from all around the world, which have been archived in the databases of co2science.org's Medieval Warm Period Project29, where it can be seen that the Medieval Warm Period was not only a global phenomenon, but that its peak warmth was very likely significantly greater than that of the Current Warm Period.

Thursday, April 17, 2014

New paper finds solar activity controlled the East Asian Monsoon over past 6,000 years

A new paper published in Earth and Planetary Science Letters finds solar variability is the "fundamental forcing" that has produced large scale changes in the East Asian winter monsoon [EAWM] over the past 6,000 years. The paper finds low solar activity correlated to a strong EAWM and cold periods, and high solar activity correlated to weak EAWM and warm periods. The EAWM has large-scale effects on climate and interacts with other global atmospheric oscillations, thus may represent another solar amplification mechanism by which tiny changes in solar activity have large-scale effects on global climate. 


Graph b shows a significant cooling of sea surface temperatures from the Holocene Climate Optimum 6,000 years ago until the end of the record ~400 years ago during the Little Ice Age

Total Solar Irradiance in bottom graph is shown to correlate with changes in the East Asian winter monsoon strength in graphs b and c. Total Solar Irradiance was at relatively high levels at the end of the record in the late 20th century, and increased ~4 W/m2 over the past 400 years. 

We provide high-resolution record of Holocene EAWM from the western North Pacific.
Centennial-scale variations in summer and winter monsoons are inversely correlated.
East–west climate linkage across the North Pacific is proposed.
Solar variability is proposed as a fundamental forcing of EAWM [East Asian Winter Monsoon] change.
EAWM change possibly linked to climate change in tropical Pacific and Europe.

Abstract

Centennial-scale variability of the East Asian winter monsoon during the Holocene is poorly understood because suitable archives and proxies are lacking. Here we present a high-resolution (∼30-yr spacing) planktonic foraminiferal View the MathML source record of Neogloboquadrina incompta   (dextral form), which reflects sea surface temperature during the winter season, for the last 6000 yrs from marine sediments in the western North Pacific. Stronger winter monsoons indicated by cooler winter SSTs correspond to weaker summer monsoons indicated by the cave oxygen isotopes in centennial-scale variability. The variability also shows good correlation with View the MathML source records in lake sediments and ice cores from the Yukon Territory, Canada, spanning the last 4500 yrs, suggesting east–west climate coupling across the North Pacific. Furthermore, the climate changes across the North Pacific co-vary over widespread regions, such as the eastern tropical Pacific and the northern Red Sea, and the reconstructed solar activity. The cross-spectral and wavelet analyses show that the East Asian winter monsoon shares some cyclicity with the solar variability. Our results suggest that the solar activity is a fundamental forcing producing the centennial-scale EAWM variability mediated by the large-scale climate linkages.

New paper finds ancient forest tundra under 2 miles of ice, Greenland ice sheet resistant to melt

In a new paper published in Science, the Greenland ice sheet has been found to be much more stable and resistant to melt than previously believed, having survived many episodes of warming over the past 2.7 million years to much higher temperatures [8C or higher temperatures than the present]. Thus, the alarmist notion of a tipping point and runaway melt of the Greenland ice sheet appears unfounded. 

The "scientists were greatly surprised to discover an ancient tundra [with partial forest] landscape preserved under the Greenland Ice Sheet, below two miles of ice. "We found organic soil that has been frozen to the bottom of the ice sheet for 2.7 million years," said University of Vermont geologist Paul Bierman -- providing strong evidence that the Greenland Ice Sheet has persisted much longer than previously known, enduring through many past periods of global warming."

"The new discovery indicates that even during the warmest periods since the ice sheet formed, the center of Greenland remained stable; "it's likely that it did not fully melt at any time," Vermont's Bierman said. This allowed a tundra landscape to be locked away, unmodified, under ice through millions of years of global warming and cooling."

Related: Why Antarctica also doesn't need 'saving'


There's something ancient in the icebox: Three-million-year-old landscape beneath Greenland Ice Sheet


Date: April 17, 2014


This is a piece of the GISP2 ice core showing silt and sand embedded in ice. Soon after this picture was taken, the ice was crushed in the University of Vermont clean lab and the sediment was isolated for analysis.
Glaciers are commonly thought to work like a belt sander. As they move over the land they scrape off everything -- vegetation, soil, and even the top layer of bedrock. So scientists were greatly surprised to discover an ancient tundra landscape preserved under the Greenland Ice Sheet, below two miles of ice.

"We found organic soil that has been frozen to the bottom of the ice sheet for 2.7 million years,"
said University of Vermont geologist Paul Bierman -- providing strong evidence that the Greenland Ice Sheet has persisted much longer than previously known, enduring through many past periods of global warming.

He led an international team of scientists that reported their discovery on April 17 in the journal Science.

Antique landscapes

Greenland is a place of great interest to scientists and policymakers since the future stability of its huge ice sheet -- the size of Alaska, and second only to Antarctica -- will have a fundamental influence on how fast and high global sea levels rise from human-caused climate change.

"The ancient soil under the Greenland ice sheet helps to unravel an important mystery surrounding climate change," said Dylan Rood a co-author on the new study from the Scottish Universities Environmental Research Centre and the University of California, Santa Barbara, "how did big ice sheets melt and grow in response to changes in temperature?"

The new discovery indicates that even during the warmest periods since the ice sheet formed, the center of Greenland remained stable; "it's likely that it did not fully melt at any time," Vermont's Bierman said. This allowed a tundra landscape to be locked away, unmodified, under ice through millions of years of global warming and cooling.

"The traditional knowledge about glaciers is that they are very powerful agents of erosion and can effectively strip a landscape clean," said study co-author Lee Corbett, a UVM graduate student who prepared the silty ice samples for analysis. Instead, "we demonstrate that the Greenland Ice Sheet is not acting as an agent of erosion; in fact, at it's center, it has performed incredibly little erosion since its inception almost three million years ago."
Rather than scraping and sculpting the landscape, the ice sheet has been frozen to the ground, "a refrigerator that's preserved this antique landscape," Bierman said.

Cosmic signal

The scientists tested seventeen "dirty ice" samples from the bottommost forty feet of the 10,019-foot GISP2 ice core extracted from Summit, Greenland, in 1993. "Over twenty years, only a few people had looked hard at the sediments from the bottom of the core," Bierman said. From this sediment, he and a team at the University of Vermont's Cosmogenic Nuclide Laboratory extracted a rare form of the element beryllium, an isotope called beryllium-10. Formed by cosmic rays, it falls from the sky and sticks to rock and soil. The longer soil is exposed at Earth's surface, the more beryllium-10 it accumulates. Measuring how much is in soil or a rock gives geologists a kind of exposure clock.

The researchers expected to only find soil eroded from glacier-scoured bedrock in the sediment at the bottom of the ice core. "So we thought we were going looking for a needle in haystack," Bierman said. They planned to work diligently to find vanishingly small amounts of the beryllium -- since the landscape under the ice sheet would have not been exposed to the sky. "It turned out that we found an elephant in a haystack," he said; the silt had very high concentrations of the isotope when the team measured it on a particle accelerator at Lawrence Livermore National Laboratory.

"On a global basis, we only find these sorts of beryllium concentrations in soils that have developed over hundreds of thousands to millions of years," said Joseph Graly, who analyzed the beryllium data while at the University of Vermont.

The new research, supported by funding from the National Science Foundation, shows that "the soil had been stable and exposed at the surface for somewhere between 200,000 and one million years before being covered by ice," notes Ben Crosby, a member of the research team from Idaho State University.

To help interpret these unexpected findings, the team also measured nitrogen and carbon that could have been left by plant material in the core sample. "The fact that measurable amounts of organic material were found in the silty ice indicates that soil must have been present under the ice," said co-author Andrea Lini at the University of Vermont -- and its composition suggests that the pre-glacial landscape may have been a partially forested tundra.

"Greenland really was green! However, it was millions of years ago," said Rood, "Greenland looked like the green Alaskan tundra, before it was covered by the second largest body of ice on Earth."
To confirm their findings about this ancient landscape, the researchers also measured beryllium levels in a modern permafrost tundra soil on the North Slope of Alaska. "The values were very similar," said Bierman, "which made us more confident that what we found under Greenland was tundra soil."

Future tense

Many geologists are seeking a long-term view of the history of the Greenland Ice Sheet, including how it moves and has shaped the landscape beneath it -- with an eye toward better understanding its future behavior. It's 656,000 square miles of ice, containing enough water, if fully melted, to raise global sea levels twenty-three feet -- "yet we have very little information about what is happening at the bed with regards to erosion and landscape formation," said Corbett.

What is clear, however, from an abundance of worldwide indicators, is that global temperatures are on a path to be "far warmer than the warmest interglacials in millions of years," said Bierman [False - Greenland was 8C warmer than the present during the last [Eemain] interglacial ~120,000 years ago, and many other interglacials were much warmer than the present with sea levels up to 50 meters higher]. "There is a 2.7-million-year-old soil sitting under Greenland. The ice sheet on top of it has not disappeared in the time in which humans became a species. But if we keep on our current trajectory, the ice sheet will not survive. And once you clear it off, it's really hard to put it back on."

Journal Reference:

Paul R. Bierman, Lee B. Corbett, Joseph A. Graly, Thomas A. Neumann, Andrea Lini, Benjamin T. Crosby, Dylan H. Rood.Preservation of a Preglacial Landscape Under the Center of the Greenland Ice Sheet. Science, 2014 DOI:10.1126/science.1249047

New paper finds current abrupt changes in Arctic are typical of the past 66 million years

An important review paper published today in Quaternary Science Reviews demonstrates that the rapid changes in the Arctic which have been blamed on man by alarmists are in fact within the norm of frequent, large and abrupt changes for the entire Cenozoic Era [past 66 million years].

According to the paper, "Globally, the general trend of increasing air surface temperature over the last 15 years has slowed in recent years, and is currently four times less than predicted by simulations [of the latest IPCC climate models] (Fyfe et al., 2013). However, over the same interval, global atmospheric CO2 level has continued to increase (Francey et al., 2013) and the Arctic Ocean has experienced a rapid decline in summer sea ice extent and thickness (Stroeve et al., 2012) (Fig. 1). The lack of a strong correlation between global average air temperature, atmospheric CO2 and Arctic summer sea ice provides one example that shows that Arctic environmental changes are heavily influenced by complex interplays between different feedback mechanisms." i.e. not the simplistic explanation by warmists that all changes in the Arctic are man-made.

According to the authors, "Instead of interpreting changes almost exclusively as near linear responses to external forcing (e.g. orbitally-forced climate change [or man-made greenhouse gases]), research is now concentrated on the importance of strong feedback mechanisms that in our palaeo-archives often border on chaotic behaviour. The last decade of research has revealed the importance of on-off switching of ice streams, strong feedbacks between sea level and ice sheets, spatial and temporal changes in ice shelves and perennial sea ice, as well as alterations in ice sheet dynamics caused by shifting centres of mass in multi-dome ice sheets."

The paper states, "Perhaps the next paradigm shift is towards recognising the unstable nature of Arctic cryosphere and Arctic environmental change more widely? That instability likely makes predicting the future a real challenge."

The dynamic Arctic
Research campaigns over the last decade have yielded a growing stream of data that highlight the dynamic nature of Arctic cryosphere and climate change over a range of time scales. As a consequence, rather than seeing the Arctic as a near static environment in which large scale changes occur slowly, we now view the Arctic as a system that is typified by frequent, large and abrupt changes. The traditional focus on end members in the system – glacial versus interglacial periods – has been replaced by a new interest in understanding the patterns and causes of such dynamic change. Instead of interpreting changes almost exclusively as near linear responses to external forcing (e.g. orbitally-forced climate change [or man-made greenhouse gases]), research is now concentrated on the importance of strong feedback mechanisms that in our palaeo-archives often border on chaotic behaviour. The last decade of research has revealed the importance of on-off switching of ice streams, strong feedbacks between sea level and ice sheets, spatial and temporal changes in ice shelves and perennial sea ice, as well as alterations in ice sheet dynamics caused by shifting centres of mass in multi-dome ice sheets. Recent advances in dating techniques and modelling have improved our understanding of leads and lags that exist in different Arctic systems, on their interactions and the driving mechanisms of change. Future Arctic research challenges include further emphases on rapid transitions and untangling the feedback mechanisms as well as the time scales they operate on.

1. Introduction

The Arctic has a prominent role in scientific debate on global change. This is a consequence from that the region is changing faster than almost anywhere on Earth and from that such dynamic change in the Arctic has been a characteristic of the entire Cenozoic Era. Thus, quantitative palaeoclimate reconstructions suggest that Arctic temperature changes have been three or four times the corresponding hemispheric or globally averaged changes over the past 4 Ma (Miller et al., 2010).
Globally, the general trend of increasing air surface temperature over the last 15 years has slowed in recent years, and is currently four times less than predicted by simulations within Phase 5 of the Coupled Model Intercomparison Project (CMIP5) (Fyfe et al., 2013). However, over the same interval, global atmospheric CO2 level has continued to increase (Francey et al., 2013) and the Arctic Ocean has experienced a rapid decline in summer sea ice extent and thickness (Stroeve et al., 2012) (Fig. 1). The lack of a strong correlation between global average air temperature, atmospheric CO2 and Arctic summer sea ice provides one example that shows that Arctic environmental changes are heavily influenced by complex interplays between different feedback mechanisms. These include changes in glacier/ice sheet extent, snow cover and sea ice distribution that affect surface albedo, and atmospheric and oceanic circulation patterns. The Arctic also influences environmental change at lower latitudes, primarily through the global thermohaline circulation and modulation of atmospheric CO2 and CH4 concentrations (Overpeck et al., 1997).
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Fig. 1. 
The dynamic Arctic illustrated on different time scales. Orbital forcing (g) constitutes the main overarching climate driver on millennial time scales. Considering this parameter alone, the present interglacial is likely to last at least another 50,000 years (Berger and Loutre, 2002), although the net effect from feedbacks is far from known and remains a research challenge. On millennial time scales the sea level record follows from a build-up and decay of large ice sheets (f) with large feedback effects from, for example, changes of land/ocean distribution. The sea ice (a–e) is perhaps the Arctic component that best illustrates how the dynamics of the climate system is operating on different time scales.
Environmental variability in the Arctic is increasingly viewed as the norm, and there is a growing recognition that today's Arctic cryosphere (glaciers, sea ice, permafrost, gas hydrates) and biosphere (terrestrial, lacustrine, and marine) are not in steady state; they have changed and will continue to change in response to climate and other perturbations. Recognition that the Arctic has likely never been in steady state is a challenge to those of interested in reconstructing past change. What, for example, is the purpose of seeking to define a reconstruction of the maximum extent of an entire ice sheet, such as at the Last Glacial Maximum (LGM), if the age of that maximum extent was diachronous and the ice sheet was not in equilibrium with its climate?
The Arctic Palaeoclimate and Its Extremes (APEX) program was initiated in October 2004 in Brorfelde, Denmark, with the aim of better understanding the magnitude and frequency of past Arctic climate variability, especially the “extremes” versus the “normal” conditions of the climate system. The goal has been to highlight Arctic palaeoclimate changes through an interdisciplinary approach that integrates marine and terrestrial science, and through using modelling that is constrained by boundary conditions set by field observations.
It is the nature of the subject that research completed under APEX, as under its predecessors PONAM (Polar North Atlantic Margin: Late Cenozoic Evolution) (Elverhøi et al., 1998) and QUEEN (Quaternary Environments of the Eurasian North) (Thiede et al., 2004), has gravitated towards understanding end-member records of extreme events rather than signatures of transitions, be they gradual or abrupt, or indeed dynamic change within a particular state. Indeed, notwithstanding the attraction of such end-members, including our growing ability to apply reliable tools to identify maximum and minimum situations (e.g. maximum extent of ice, climate optimum, episodes of high relative or global sea level) in both time and space, we are increasingly appreciative of the fact that Arctic cryospheric and oceanic changes are time-transgressive.
From the perspective of Earth's orbit around the Sun, the present interglacial is expected to last for an exceptionally long interval, perhaps more than another 50,000 years (Berger and Loutre, 2002) (Fig. 1). The implication is that CO2 forcing and dynamic feedback mechanisms will dictate climate change long into the future, and for this reason the forcing and feedbacks that link these processes are important future targets for Arctic research in the years to come.
This special issue contains a suite of articles that mark the completion of the APEX program. Collectively they provide a state-of-the-art record of current knowledge regarding Arctic Quaternary environmental change, and here we aim to review progress achieved under the PONAM-QUEEN-APEX programs and highlight the main scientific challenges that they have left us with.

2. History and current status

2.1. Palaeoglaciology

The year 1875 was a break-through year for Agassiz' (1840) Ice Age Theory, with the work of Croll (1875) on multiple ice ages through time marking the birth of palaeoglaciology as a scientific subject. Palaeoglaciology aims to outline the history of former ice sheets and cast light on their dynamics through time (Andersen and Borns, 1994), and over the past 120 years there have been ever more sophisticated reconstructions that seek to define the former extents of the Eurasian ice sheets e.g., Andersen, 1981Hughes et al., 1981 and Svendsen et al., 2004; see also reviews in Fastook and Hughes (2013) and Ingólfsson and Landvik (2013).
It is interesting to ask the question “How far have we advanced our understanding of palaeoglaciology sinceGeikie (1894) published his maps of ice sheet extents over Europe, the British Isles and Scandinavia?” A partial answer to this question can be found by comparing these original maps with current versions, as we do in Fig. 2. What is astounding from this exercise is how remarkably similar Geikie's map from 1894 is to, by example, the recent reconstructions by QUEEN (Fig. 2). Such a comparison begs the question as to whether this means that the discipline has been treading water for much of the last century? We argue that it does not; that there are good reasons why the general maximum extents on base maps are little changed and there have indeed been major advances in our understanding of former ice sheet extents and in their dynamics. However, we also argue that we must now make a greater effort to illustrate the dynamics of these glacial system on maps and in other media; a far from trivial task!
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Fig. 2. 
Ice sheet extent published on the “Glacial Map of Asia” by Geikie (1894) compared with the Last Glacial Maximum (LGM) and Saalian ice sheet margins by the QUEEN program (Svendsen et al., 2004).
As pointed out by Ingólfsson and Landvik (2013), there is a fundamental problem with regional palaeoglacial reconstructions because they synthesise large amounts of field data that contain problems, notably different spatial resolutions and often problematic age controls. The outcome of such efforts is therefore commonly a compromise of best fit reconstructions that simplify or over-look time-transgressive changes and ignore ice sheet dynamics; the ice sheets are reconstructed as if they are always close to steady-state equilibrium. In Europe and Eurasia, the resulting reconstructions tend to depict the ice sheets as relatively stable, concentric or single-domed rather than unstable and multi-domed, and, although ice streams may be acknowledged, the dynamic linking of the ice sheets to global and regional sea levels is often not accounted for. These reconstructions do not allow for the understanding that marine-based ice streams are inherently unstable (Jamieson et al., 2012) nor do they fully recognise that different sectors of an ice sheet experienced different histories, depending on the topography/bathymetry, sub-glacial conditions and glacial dynamics, as well as climate and sea-level forcing. These problems are particularly evident for the marine sectors of former ice sheets, because ice shelves and floating ice tongues are highly dynamic, yet do not leave clearly identifiable imprints of their maximum extents (Jakobsson et al., 2014). Landvik et al. (2014) also note that the distribution of glacigenic bedforms, which are used as the main data source for reconstructing past ice flows, are most informative about the most recent events with older landforms susceptible to erosion. There is, therefore, considerable work to be done to reconcile glacial geomorphology data with the dynamic ice margin behaviour predicted by ice sheet models (Kirchner et al., 2011). This includes reconciling the resolution of ice sheet models with the temporal and spatial complexities of the glacial geomorphological evidence that documents ice sheet build-up and decay (Evans et al., 2009).
A growing appreciation of the dynamic nature of Arctic glacier and ice sheet change also challenges the traditional view of the link between palaeoglaciology and climate change, across glacial–interglacial and stadial–interstadial transitions. Climatostratigraphic concepts are relatively easy to use at mid and low latitudes where glacial landforms and biostratigraphic indicators define end-members, but such concepts are much harder to use at higher latitudes (Backman et al., 2004 and Alexanderson et al., 2014). Consequently, ice sheet advances and retreats are all too often interpreted as evidence for climate events, disregarding the possibility that they may reflect changes in ice dynamics, e.g., rapid changes in grounding-line position in response to sea-level oscillations. For this reason, whilst some suggest that over past glacial–interglacial cycles, continental ice volume kept pace with slow, multi millennial-scale changes in climate forcing (Rohling et al., 2013b), there is an increasingly recognition that system feedbacks (Fig. 1) can readily cause ice sheet collapse, independent of strong climate forcing (Hughes, 2011Ó Cofaigh, 2012Mangerud et al., 2013 and O'Leary et al., 2013). Understanding causal links that lead to such “tipping point” behaviour is a major challenge of Arctic palaeoglaciology.
There are several important advances in our understanding of Quaternary ice sheet extents and behaviour that extend beyond the one dimensional representation of an isochronous ice limit drawn on a map. First, the development of new dating methods, notable cosmogenic exposure dating, combined with improved understanding of the basal thermal regime of ice sheets, has enabled reconstructions of the former temporal dimension of the vertical extent of former ice sheets (Alexanderson et al., 2014 and Stroeven et al., 2014). This has challenged long-standing paradigms that interpreted trim lines as evidence for the upper limits of ice sheets and instead has led to a more nuanced appreciation of the importance of cold-based ice, and the recognition that former ice thicknesses were greater than previously thought. This knowledge has important implications for reconstructions of down-ice flow lines, as well as overall ice volume at glacial maxima.
A second advance is the appreciation of the important role of ice streams and their geometry in controlling the dynamic behaviour of large parts of an ice sheet (e.g. Andreassen et al., 2014Batchelor and Dowdeswell, 2014 and Kleman and Applegate, 2014). Recent observations and reconstructions show that large-scale reorganizations of ice streams can significantly affect ice sheet dynamics over relatively short time scales (Winsborrow et al., 2012). In Greenland today, we see three or four major ice streams dominating the dynamic mass loss from the ice sheet, and that these ice streams can accelerate or slow-down in an unpredictable manner (Joughin et al., 2011). By thinning and accelerating, West Antarctic ice streams are contributing about 10% of the observed global sea level rise, and much of this ice loss is from Pine Island Glacier alone (Dutrieux et al., 2013). Such is the importance of ice streams to our understanding of the overall dynamics of the former ice sheets, during ice build-up and decay, that considerable effort is directed at unravelling their sensitivity to different forcing.
Conventional theory suggests that ice sheets and ice streams that are grounded below sea level are especially vulnerable to sea-level forcing, with the potential that sea-level jumps caused by ice sheet collapse can trigger further ice sheet instabilities. However, recent work is painting a more complex picture and challenging this long-held paradigm. For example, it has long been known that as an ice sheet loses mass, so the gravitational force of that ice mass on the adjacent ocean surface weakens (Simpson et al., 2009 and Woodroffe et al., 2014). This so-called “direct effect” causes relative sea level close to an ice sheet or ice stream that is losing mass to fall and, in theory, help stabilise the ice sheet margin by reducing water depths. In addition, removal of ice mass from a retreating ice sheet is often associated with glacio-isostatic rebound, a process that also causes relative sea level to fall. On the other hand, an example of a destabilizing effect is the sudden loss of an ice shelf that extends in front of an ice stream, that may result in rapid ice stream acceleration as the buttressing force the ice shelf exerted is lost (Rignot et al., 2004). We begin to map traces of abrupt ice stream break-ups and retreats from glacial landforms preserved in the seafloor of both the Antarctic (Jakobsson et al., 2011) and the Arctic (Andreassen et al., 2014 and Bjarnadóttir et al., 2014), that may well be the effects of former ice shelf collapses.
A third area of major advance is in our understanding of the dynamic effects of ocean forcing on ice sheet margin stability, especially those marine-based sections that are directly impacted by ocean temperatures. Warm water flowing beneath calving margins promotes significantly enhanced rates of basal melting, increased buoyancy and can lead to accelerated mass loss. This process is most clearly illustrated in the accelerated flow and retreat of Jakobshavns Isbrae (Greenland) in the last 15 years, during a period of time when warm Atlantic-sourced waters penetrated deep into the fjord system (Holland et al., 2008). A similar pattern of events is contributing the rapid collapse of Pine Island Glacier in Antarctica (Jacobs et al., 2011). This ocean coupling does not over-ride the importance of air temperature forcing, which remains a widely recognised control on ice sheet mass balance, including through the enhanced supply of meltwater to the base of ice sheets that may accelerate ice velocities. It does, though, exemplify the complex controls that combined to influence marine terminating ice sheets today.
A fourth advance is the significant progress made in reconstructing ice limits offshore, using remotely sensed imagery as well as sea bed sediment cores. Within the APEX project, we report important new understanding of the spatial extent of, for example, the Greenland Ice Sheet in West Greenland (Dowdeswell et al., 2014 and Lane et al., 2014). This is an essential development if we are to reconstruct how this ice sheet, and others that were grounded on the current continental shelf during initial deglaciation, responded to short-lived climate forcing such as the Younger Dryas (Ó Cofaigh et al., 2013).
In summary, the broad similarity between maps of Eurasian ice sheet extents drawn today and that of a hundred years ago or more masks significant advances in our understanding of the dynamic nature of ice sheet behaviour over a range of spatial and temporal scales. It is also true, however, that modern glaciological and oceanographic studies are not always appropriate analogues for the past, including previous interglacial (minima) ice-sheet configurations and during ice build-up and collapse. There is significant scope to improve our understanding of how ice sheets build during periods of high sea-level, whether the same atmosphere-ocean forcing that we see today operated in previous interglacials, or indeed whether the controls on ice sheet collapse during the exit from, for example, the LGM was typical of previous terminations or not.

2.2. Palaeoceanography

Reconstructions of oceanographic conditions in the central Arctic Ocean did not really begin until nearly half a century after Fridtjof Nansen compiled a bathymetric map that portrayed the central Arctic Ocean as a single deep featureless basin from a handful of lead line soundings acquired during the Fram Expedition1893–1896 ( Nansen, 1907). Extensive pack ice has prevented efficient mapping the Arctic Ocean seafloor, and each published map has systematically revealed a more complex seafloor, shaped by tectonics, ocean currents, and the glacial history, than the preceding one (e.g. Atlasov et al., 1964Johnson et al., 1979Perry et al., 1986 and Jakobsson et al., 2012). While the bathymetry provides a long-term paleoceanographic record of the interactions of bottom currents, ice, geochemical processes, and biological activity with the seafloor, sediment cores are required to decipher the palaeoceanography in detail.
Sediment core studies within the APEX program published in this special issue provide a range of new insights into the Arctic Ocean palaeoceanography (Chauhan et al., 2014Gibb et al., 2014Immonen et al., 2014Löwemark et al., 2014 and Werner et al., 2014). These studies demonstrate how far we have progressed, specifically regarding the use of paleoceanographic proxies, since the first short cores raised from drifting ice islands in the 1950s and 1960s captured near surface sediments from the Arctic Ocean floor (Ericson et al., 1964 and Hunkins and Tiemann, 1977). Only the construction of research icebreakers in the 1980s allowed targeted expeditions to the Arctic to obtain long, large-volume sediment cores for palaeoceanographic reconstructions. During the QUEEN project, we learned that earlier ideas of extremely low sedimentation rates (Clark, 1970) were based on a misinterpretation of the palaeomagnetic pattern in the sedimentary record and that the rates were rather on the scale of centimetres per kiloyear than millimetres (Backman et al., 2004). While this finding substantially advanced our ability to use sediment cores to study palaeoceanography, the central Arctic Ocean sedimentation rate of centimetres per kiloyear is far from capturing the full dynamics and ongoing rate of change in the Arctic. It is also difficult to know what we capture with a proxy study of a sediment core; is what we reconstruct the extremes of paleoceanographic changes or a blurred averaged view? There is certainly not one answer to this questions, it will depend on several factors such as for example the proxy and core location.
The important role of the Arctic Ocean in driving the modern (interglacial) ocean circulation and heat transport was recognized by Nansen (1907), but due to the nearly land-locked Arctic Ocean physiographic configuration it was assigned a rather passive role during interglacials. It should be noted that Nansen's map from 1907 did not depict a deep Fram Strait simply because no soundings from the strait at that time had been collected. The CLIMAP reconstruction of the surface of the ice-age earth (CLIMAP Project Members, 1976) showed the Nordic Seas as perennially ice covered in the LGM and assumed that the Arctic Ocean had experienced the severest cold conditions. The last decades have seen a slow maceration of this contrasting view between glacial and interglacials. Evidence for a relatively strong advection of Atlantic Water to the Arctic in the LGM was found in the eastern Fram Strait where the associated moisture transfer from the sea surface to the atmosphere may have enhanced ice sheet growth on the Barents Sea (Hebbeln et al., 1994), and Hald et al. (2001) showed that Atlantic water repeatedly reached the polar North Atlantic during the Last Interglacial–Glacial cycle. It was assumed that this water mass reached only parts of the Eurasian Arctic (Sarnthein et al., 2003). This is in stark contrast to the interglacial Arctic Ocean, including present day conditions, when Atlantic Water contributes to the intermediate depth water masses well into the Makarov and Canada basins on the Amerasian side of the Arctic (Rudels et al., 2013).
Seafloor mapping, which began during the QUEEN program and continued during APEX, has revealed glacigenic landforms and ice grounded seabed in the central Arctic Ocean at depths >1000 m below present sea level, indicating the existence of marine based ice sheets including huge ice shelves (e.g. Polyak et al., 2001Spielhagen et al., 2004Niessen et al., 2013Dove et al., 2014 and Jakobsson et al., 2014). How could these have existed if warm Atlantic Water entered the Arctic Ocean during glacials as well as interglacials? A conceptual model has been developed that now reconciles both the influx of Atlantic Water and the existence of deep drafting ice. This model suggests that the glacial palaeoceanography of the glacial Arctic was characterized by less fresh water influx resulting in a more diffuse and deeper halocline than today that forced the Atlantic Water deeper (Jakobsson et al., 2010). This model is supported by geochemical data from ostracods, as reported by Cronin et al. (2012). Their trace metal analyses of ostracod shells suggest that Atlantic Water penetrated basin-wide during the coldest phases of the Last Glacial, albeit at deeper depth than present. In addition, Hoffmann et al. (2013) showed that a persistent deep water exchange existed between the Arctic Ocean and North Atlantic during the last 35 ka. Apparently, the Arctic Ocean never lost the oceanographic connection to the rest of the World's ocean during the Last Glacial, and it thus contributed to the global ocean circulation over this time period.
Sea ice is one of the most dynamic components of the cryosphere as illustrated recently by the large yearly variation in the spatial extent of the Arctic Ocean summer sea ice (Comiso, 2011) (Fig. 1). The question most often asked is “When will there be sea ice free summers in the Arctic?” (Overland and Wang, 2013). The follow-up question is “Has the Arctic recently experienced sea ice free summers?” While the high frequency dynamic sea ice swings cannot be fully captured in sediment core studies, the general trends may be revealed from studies of various types of proxies for sea ice (Polyak et al., 2010 and de Vernal et al., 2013). Several studies suggest that the Early Holocene (∼6000–10,000 years BP) experienced less summer-sea ice than at present (e.g. Polyak et al., 2010Funder et al., 2011 and Müller et al., 2012), although not all studies are showing the exact same pattern (Dyke and England, 2003). Stranne et al. (2014) show, using numerical modelling, that the sea ice during the Early Holocene potentially could have moved over to a seasonal regime with sea ice-free summers due to the insolation maxima the Earth experienced at that time (Fig. 1).

3. Discussions and future challenges

The history of Quaternary geology contains numerous examples of revolutions in our approaches to science that resulted from anomalies that could not be explained by the universally accepted paradigm. In glacial geology, Agassiz's (1840) Ice Age theory and Croll's (1875) and Milankovitch's (1920) astronomical theory mark paradigm shifts that fundamentally changed our views of how ice sheets and climate evolved over time (Hays et al., 1976). Our perception of how the large Quaternary ice sheets and the cryospheric system evolved over interglacial–glacial cycles has, however, changed slowly in recent decades. We find evidence from ice core and marine oxygen isotope data that the Late Pleistocene continental ice sheets were characterised by slow growth and rapid decay. Palaeoglaciological reconstructions typically reflect this pattern with continuous, isochronuous ice margins reconstructed by connecting geomorphological features, especially end moraines, to define events in ice expansion and retreat (Lüthgens and Böse, 2012). However, as we note above, the glacial landform record is strongly biased towards extreme events and terminations, whilst records of ice sheet dynamics during their growth phase are poorly preserved or not preserved at all.
As outlined above, the focus of Arctic palaeoglaciology has over the past few decades been on the LGM. The extents of LGM ice sheets are now reasonably well understood (Clark and Mix, 2002 and Clark et al., 2009) and we now know that growth of the ice sheets to their maximum positions occurred between 33.0 and 26.5 ka, and that nearly all ice sheets were at their LGM positions from 26.5 ka to 19–20 ka (Clark et al., 2009). We are now developing ever more sophisticated records of the dynamics of the deglaciations/terminations. Much of this new knowledge in the Arctic is drawn from newly collected marine geological data that reveals clear spatial and temporal variations in ice dynamics, with evidence for both active ice streaming and frozen-bed conditions at the maximum and during deglaciation (Ottesen and Dowdeswell, 2009Winsborrow et al., 2010Andreassen et al., 2014Jakobsson et al., 2014 and Landvik et al., 2014). However, there is most likely much more information about the dynamics of the Arctic still to be extracted from palaeorecords as we improve our methods. In view of the advances in our understanding of the Arctic cryospheric system made during the International Polar Year (IPY) 2007–08 and the APEX program 2004–12, several challenges and research tasks stand out:
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We need to focus on ice streams. The importance of ice streams for the geometry and stability of ice sheets has made the identification, location, and timing of ice stream activity essential for the reconstruction of palaeo-ice sheets and the interpretation of the associated landform record (Stokes and Clark, 2001Bennett, 2003 and Batchelor and Dowdeswell, 2014);
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We need to acknowledge in our reconstructions that the datasets that we work with tend to be strongly biased towards extreme events and terminations. This calls for a holistic approach where it is recognized that apparent mismatches and enigmatic data may be caused by the complexity and chaotic nature of the system rather than poor chronological or quality control of the data;
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We need to focus on internal forcing and feedbacks in the Arctic system, particularly those that result in non-linear or chaotic behaviour such as changes in sea ice extent and ocean circulation;
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We need to focus on rapid transitions and mode shifts, which in turn demands robust, high resolution chronologies;
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We need to search for ultra-high resolution records (decadal to century-scale) that enable us to reconstruct past environmental change on time scales comparable to current and near-future environmental change;
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We need to understand what were the leads and lags between different parts of the Arctic cryosphere/ocean, what caused them and how did they link to changes in the Southern Hemisphere?
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We need to understand if Arctic ice sheets can grow quickly, during “warm” periods and if this can explain the high frequency sea-level variations seen in archives from low latitudes (Rohling et al., 2013a).
Perhaps the next paradigm shift is towards recognising the unstable nature of Arctic cryosphere and Arctic environmental change more widely? That instability likely makes predicting the future a real challenge.