Monday, September 15, 2014

New paper finds North Carolina sea levels rising < 7 inches per century

A new paper published in Quaternary Research reconstructs sea level rise in North Carolina over the past 1000 years and finds sea level rise since 1845 has been only 1.71 mm/year, equivalent to 6.7 inches per century and in line with many other papers finding global sea level rise of less than 7 inches per century. 

Data from the paper indicates no evidence of acceleration since the end of the Little Ice Age in ~1850. No acceleration of sea level rise means no evidence of a man-made contribution. The data also shows that sea levels "paused" their natural 20,000 year rise during the Little Ice Age from ~1,200 to  ~164 years ago. 




Salt-marsh sediments provide accurate and precise reconstructions of late Holocene relative sea-level changes. However, compaction of salt-marsh stratigraphies can cause post-depositional lowering (PDL) of the samples used to reconstruct sea level, creating an estimation of former sea level that is too low and a rate of rise that is too great. We estimated the contribution of compaction to late Holocene sea-level trends reconstructed at Tump Point, North Carolina, USA. We used a geotechnical model that was empirically calibrated by performing tests on surface sediments from modern depositional environments analogous to those encountered in the sediment core. The model generated depth-specific estimates of PDL, allowing samples to be returned to their depositional altitudes. After removing an estimate of land-level change, error-in-variables changepoint analysis of the decompacted and original sea-level reconstructions identified three trends. Compaction did not generate artificial sea-level trends and cannot be invoked as a causal mechanism for the features in the Tump Point record. The maximum relative contribution of compaction to reconstructed sea-level change was 12%. The decompacted sea-level record shows 1.71 mm yr− 1 of rise since AD 1845.

New paper explains dissipation of ocean heat content

A new paper published in the Journal of Physical Oceanography compiles "high-resolution measurements of ocean mixing collected over the past three decades to reveal how deep ocean waters return to the surface - a process that helps to regulate Earth's climate" via ocean oscillations such as the Atlantic Meridional Overturning Circulation [AMOC], and other natural ocean oscillations.

The AMOC deep ocean overturning oscillation lasts 1000-1500 years and likely explains Earth's unstoppable 1,500 year climate cycle, along with various shorter ocean oscillations explaining other short-term climate cycles. 

The paper discusses dissipation of ocean heat due to turbulence and mixing, which is a substantial 0.4 * 10^12 Watts [Terawatts] necessary to continuously lift dense bottom waters to the ocean surface, generated from a total of ~2 Terawatts potential energy from large internal ocean waves that mix bottom waters back to the surface. 

The large amounts of ocean heat content that is dissipated by these "missing mixing" processes results in heat lost to potential energy and turbulence, thereby decreasing the ability of the oceans to warm from any source, including greenhouse gases. The oceans additionally cannot warm from greenhouse gases due to a number of other physical reasons, explaining why at least 93% of Trenberth's "missing heat" is missing from the oceans [in addition to 100% of Trenberth's heat missing from the atmosphere]. 

Further, dissipated ocean heat and potential energy can not pop out of the oceans and say "Boo!" without violating the 2nd Law of Thermodynamics principle of maximum entropy production. The oceans have warmed only a tiny 0.09C over the past 55 years, and even if that could violate the laws of thermodynamics to pop out and heat the atmosphere, the maximum it could heat the atmosphere is limited to 0.09C. 







Global Patterns of Diapycnal Mixing from Measurements of the Turbulent Dissipation Rate

Amy F. Waterhouse,* Jennifer A. MacKinnon,* Jonathan D. Nash,+ Matthew H. Alford,# Eric Kunze,# Harper L.Simmons,@ Kurt L. Polzin,& Louis C. St. Laurent,& Oliver M. Sun,& Robert Pinkel,* Lynne D. Talley,* Caitlin B.Whalen,* Tycho N. Huussen,* Glenn S. Carter,** Ilker Fer,++ Stephanie Waterman,##,@@Alberto C. Naveira Garabato,&& Thomas B. Sanford,# and Craig M. Lee#
* Scripps Institution of Oceanography, University of California, San Diego, La Jolla, California
+ College of Oceanic and Atmospheric Sciences, Oregon State University, Corvallis, Oregon
# Applied Physics Laboratory and School of Oceanography, University of Washington, Seattle, Washington
@ University of Alaska Fairbanks, Fairbanks, Alaska
& Department of Physical Oceanography, Woods Hole Oceanographic Institution, Woods Hole, Massachusetts
** Department of Oceanography, University of Hawai‘i at Mānoa, Honolulu, Hawaii
++ Geophysical Institute, University of Bergen, Bergen, Norway
## Department of Earth, Ocean and Atmospheric Sciences, University of British Columbia, Vancouver, British Columbia
&& National Oceanography Centre, University of Southampton, Southampton, United Kingdom
Abstract
The authors present inferences of diapycnal diffusivity from a compilation of over 5200 microstructure profiles. As microstructure observations are sparse, these are supplemented with indirect measurements of mixing obtained from (i) Thorpe-scale overturns from moored profilers, a finescale parameterization applied to (ii) shipboard observations of upper-ocean shear, (iii) strain as measured by profiling floats, and (iv) shear and strain from full-depth lowered acoustic Doppler current profilers (LADCP) and CTD profiles. Vertical profiles of the turbulent dissipation rate are bottom enhanced over rough topography and abrupt, isolated ridges. The geography of depth-integrated dissipation rate shows spatial variability related to internal wave generation, suggesting one direct energy pathway to turbulence. The global-averaged diapycnal diffusivity below 1000-m depth is O(10−4) m2 s−1 and above 1000-m depth is O(10−5) m2 s−1. The compiled microstructure observations sample a wide range of internal wave power inputs and topographic roughness, providing a dataset with which to estimate a representative global-averaged dissipation rate and diffusivity. However, there is strong regional variability in the ratio between local internal wave generation and local dissipation. In some regions, the depth-integrated dissipation rate is comparable to the estimated power input into the local internal wave field. In a few cases, more internal wave power is dissipated than locally generated, suggesting remote internal wave sources. However, at most locations the total power lost through turbulent dissipation is less than the input into the local internal wave field. This suggests dissipation elsewhere, such as continental margins.

And then they came for The Holocene: New paper suggests "removing the Holocene Epoch from the geologic timescale"

Is there any limit to the extremes some climate propagandists will go?

The Climategate team removed the warm 1940's "blip", erased the Medieval Warm PeriodHid the Decline, and tortured temperature & sea level data until it confessed, but a paper published today in Earth's Future could take the cake by suggesting removal of "the Holocene Epoch from the geologic timescale" and replacing it with the fictitious, scary-sounding "geologic" timescale "The Anthropocene."
Excerpt from "Hello Anthropocene, Goodbye Holocene": 
: "As the official timescale keepers deliberate the introduction of the Anthropocene and a Holocene-Anthropocene boundary (Anthropocene Working Group of the Subcommission on Quaternary Stratigraphy; Zalasiewicz, J., M. et al., 2010; http://goo.gl/wIm6X0 ), they should consider the alternative: Remove the Holocene Epoch from the geologic timescale. Whereas any timescale change is a contentious issue, let alone changes to an existing epoch, modern human society’s interactions with its planet and ecosystems, embodied by the Anthropocene, are sufficiently large to produce a lasting geologic marker that supports such modification. This new boundary would remain visible in the geologic record of oceans and continents (see also Corcoran et al., 2014 on plastics), meeting the stratigraphic requirements that ultimately underlie the timescale and marking a shift from the Pleistocene’s Milankovitch forcing to the Anthropocene’s human forcing. 
The Holocene is a climate-centric placeholder for change after the latest Quaternary glaciation, but does not, as defined, match the accelerated changes in land, ocean and atmosphere that mark modern times. So, I suggest that (a) we remove the Holocene altogether in favor of a (young) Anthropocene Epoch that reflects planet-wide geologic changes since c. 1900 CE, or (b) we demote the Holocene to Stage/Age status, marking the end of the Pleistocene Epoch. The latter, perhaps more palatable compromise, would recognize historical precedent and allow continued use of Holocene in the literature as a temporal (“Age”) marker. Regardless, slicing the Quaternary Period in ever thinner epochs has no geologic merit. Given the degree and impact of modern, human-induced changes on our planet, a young Pleistocene-Anthropocene boundary seems justified."
The journal titled The Holocene probably isn't going to like this idea.

The fact is the tiny 0.7C recovery since the end of the Little Ice Age in ~1850, which is coincidentally when the global temperature record begins, could easily be natural and 95% explained by solar activity and ocean oscillations, and is not unprecedented or unusual within the past ~10,000 years of the Holocene Epoch. Thousands of paleoclimate papers show the Medieval, Roman, Egyptian, Minoan, and multiple other unnamed warm periods within the Holocene were warmer than the present. In addition, the Pacific Ocean has been significantly warmer than the present throughout vast majority of the Holocene

Further, during the last interglacial ~120,000 years ago, Greenland was up to 8C warmer than the current interglacial warm period, and sea levels were up to 29 feet higher. Therefore, there is no evidence that warmth during the current interglacial warm period is unprecedented, unusual, or unnatural.

Therefore, there is no valid reason whatsoever to remove the Holocene Epoch "blip" from the geological timescale, despite how convenient it would be for the climate propagandists. Kinda bad timing too promoting the silly 
Anthropocene/Mannocene notion that man-made CO2 controls the climate given the 50+ excuses for the absence of global warming for the past 18-26 years despite a steady rise in CO2.


GISP2 Greenland ice core data in blue, the tiny 0.7C "Anthropocene" warming of HADCRU sea surface temperatures to present-day shown in red spliced at end
Above GISP2 Greenland ice core data with labeled warm periods

Present Greenland temperatures haves been exceeded many times over past 4000 yrs Full paper

Temperatures during the last interglacial period ~120,000 years ago [and several other interglacials] were higher than during the present interglacial period.
Holocene Epoch shown at lower right, as well as the lack of correlation on geologic timescales between CO2 and temperature.


On geologic timescales, we are still in an ice age, because there are ice sheets present at both poles

Fracking Update: Improves production 5X & gives US energy boom plenty of room to run, doesn't cause methane leaks



Fracking Gives U.S. Energy Boom Plenty of Room to Run
Current Top Gas Well Produces Five Times as Much as Record Setter a Decade Ago

By RUSSELL GOLD
Sept. 14, 2014 5:04 p.m. ET     THE WALL STREET JOURNAL

Skeptics of the U.S. energy boom say it can't last much longer because it requires drilling an ever-increasing number of wells.

But the boom already has lasted longer than anyone would have imagined just a decade ago and has more room to run. That's because oil and natural-gas wells have become more productive—an unrecognized but potent trend that should keep the fuels flowing.

Back in 2003, the energy industry had just begun combining the techniques of drilling horizontal bores through shale and then using hydraulic fracturing—shooting tons of water, chemicals and sand into the rocks.

Four Sevens Oil Co. drilled the best gas well that year, in the Barnett Shale, just north of Fort Worth, Texas, according to Drillinginfo, an industry data service that searched its records at the request of The Wall Street Journal.

Four Sevens used what was then considered a whopping 2.8 million gallons of liquid and 221,000 pounds of sand in fracking the well, named the Braumbaugh after the family that owned the mineral rights.

At its peak, 5.9 million cubic feet of gas a day rushed up the well. "We were real happy with it," says Four Sevens co-founder Dick Lowe. When the state published the production data, competitors were envious.

Today, the Braumbaugh looks like a pipsqueak.

Cabot Oil & Gas Corp. drilled the best gas well in the U.S. last year, in Susquehanna County, Pa., about 110 miles northwest of Manhattan. Drilling longer horizontal legs and fracking the well repeatedly, Cabot pumped in 12.5 million gallons of liquid, more than four times the amount Four Sevens had employed, and used 13.3 million pounds of sand.

The well produced 30.3 million cubic feet a day—five times as much as the Four Sevens record setter a decade earlier.

"That's a pretty damn good well," Mr. Lowe says. "I might have dreamed of drilling a well that size."

The U.S. oil-and-gas industry no longer spends its time trying to find new shale formations to tap. Instead, it focuses on finding ways to get more out of the formations it has found. And it is succeeding.

As a result, the U.S. has become the world's largest energy producer, natural-gas prices have remained low and U.S. oil output has helped prevent rising crude prices around the world.
...
What's beyond dispute is that the newly drilled wells are better than the ones they are replacing.

The number of rigs drilling in the U.S. is basically flat, but production is rising. The federal Energy Information Administration calls this "drilling productivity" and says it is showing no sign of slowing.

Lynn Westfall, the EIA's director of energy markets and financial analysis, points out that the rig count in South Texas' Eagle Ford Shale "has not changed since 2012, but the production per new well has doubled."

Innovation makes the difference. The federal government recently predicted that oil production would rise through 2019 and then flatten off. But a second scenario in the report assumed that extraction technology would continue to improve, leading crude output to rise through 2040, if not longer.

The recent history of oil wells productivity is similar to that of gas wells.

In 2003, Headington Oil drilled an experimental well into the Bakken Shale in Montana near the North Dakota border. Headington, a private Dallas-area company, pumped in 326,000 gallons of liquid and used 640,000 pounds of sand. The well produced 828 barrels a day in October 2003.

Pat Smith, Headington's chief operating officer, says his approach back then was "to frack the heck out of it."

Turns out he didn't know from big fracks. EOG Resources Corp. last year drilled a well in the Eagle Ford Shale, using 30 times as much liquid. It also used 14.2 million pounds of sand. The result: 2,748 barrels a day.

Headington sold its Montana properties to XTO Energy Inc., now part of Exxon Mobil Corp. , for $1.8 billion in 2008. Founder Tim Headington took some of his earnings and bankrolled Hollywood movies, such as "Hugo" and "Rango."

Mr. Smith is still chasing oil and looking to drill in the Permian Basin. But first, he needs to get up to speed on modern fracking. "I have a big learning curve," he says.



Weak wells not fracking caused US gas leaks into water

A new study suggests that the contamination of drinking water by shale gas is due to faulty wells and not hydraulic fracturing.

Researchers in the US analysed the gas content in 130 water wells in Pennsylvania and Texas.

They were able to trace the methane found in the water to problems with the casing or lining of wells drilled to extract the gas.

The report appears in the Proceedings of the National Academy of Sciences.

In many parts of the US, the migration of gas into drinking water has raised questions about the fracking process.

You need enough inspectors on the ground to keep people honest ”Prof Robert JacksonStanford University

Previous research has detailed the scale of these difficulties without arriving at a satisfactory explanation of how the gas got into the water.

This new study focussed on areas which were well known for elevated levels of methane in drinking wells.Noble experiment

The researchers used noble gases to trace the path of methane as these inert chemicals are not affected by microbial activity or oxidation.

By measuring the ratios of the noble materials to the methane they were able to accurately determine the distance to the likely source.

The scientists analysed content from 113 wells in the Marcellus shale in Pennsylvania and 20 in the Barnett shale in Texas. They found eight clusters of wells with problems.

"The mechanism of contamination looks to be well integrity," said one of the authors, Prof Robert Jackson from Stanford University.

"In about half the cases we believe the contamination came from poor cementing and in the other half it came from well casings that leaked."

Cement is used in the oil and gas extraction industry to fill the spaces between the well casing and the sides of the well.

In one case the methane was linked to the failure of an underground well. In none of the investigated wells was there a direct link to fracking.

Protestors have attempted to disrupt the development of fracking in the UK

"These results appear to rule out the possibility that methane has migrated up into drinking water aquifers because of horizontal drilling or hydraulic fracturing, as some people feared," said Prof Avner Vengosh, from Duke University.

The researchers are concerned that the wells are failing because of the large volumes of water going through them at very high pressure. This is a critical part of the process of extracting gas from the shale rocks.Separation of powers

They also point to the pressure that drillers are under to finish and move on to the next site. The historically low price of gas could also be affecting spending on well integrity as profit margins shrink.

The scientists believe that most of the problems they have identified can be resolved with better enforcement of existing regulations.

"You need strong rules and regulations on well integrity," said Prof Jackson.

"You need generous setbacks that protect homes and schools and water sources from drilling, sometimes farther than the drillers would want. You need enough inspectors on the ground to keep people honest and you need separation between the industry and the inspectors and you don't always have that in the US."

Other researchers say that the latest work shows that the process of fracking is safe - and that with proper regulation it could be a viable proposition in countries like the UK.

"It's important to put this work into a UK/EU perspective," said Prof Quentin Fisher from the University of Leeds.

"The licensing system in the US means that companies have to drill a massive number of wells very quickly. This is not the case in the UK/EU so far more care can be taken to ensure that leakage into groundwater does not occur."

The researchers say that further work in this field could help them predict the likely path of methane if leaks occur in areas where fracking takes place.

Sunday, September 14, 2014

New paper links Arctic sea ice extent to absorption of sunlight by clouds

A new paper published in the Journal of Geophysical Research Atmospheres finds Arctic sea ice concentrations at the low of each summer are related to absorption of sunlight by cloud cover at the top of the atmosphere in early summer, a phenomenon "not represented in most of current climate models."

According to the authors, 
"absorbed solar radiation at the top of the atmosphere in early summer (May–July) plays a precursory role in determining the Arctic sea ice concentration in late summer (August–October)"   
"this intimate delayed...relationship is not represented in most of current climate models. Rather, the models tend to over-emphasize internal sea ice processes in summer."
Alarmists focus on Arctic sea ice as the supposed canary in the coal mine for CAGW, but many papers have demonstrated natural variability is more likely responsible for the trends in Arctic sea ice than man-made CO2, including the natural Atlantic Multidecadal Oscillation, Atlantic Meridional Overturning Circulation [AMOC]wind  & storm activity, and long-term solar variability. This new paper suggests another way that natural variability controls Arctic sea ice extent via cloud cover, another possible solar amplification mechanism  via the cosmic ray theory of climate.

Alarmists ignore the unspeakable all-time record highs in Antarctic sea ice extent broken over each of the past three years, as do climate models, which laughably predicted the opposite of a decrease in Antarctic sea ice extent more so than Arctic sea ice. 

Alarmists also claim current Arctic sea ice changes are "unprecedented" while ignoring proxy data indicating Arctic sea ice was much less than present-day during the Holocene Climate Optimum ~6,000 years ago, Arctic temperatures were warmer than the present multiple times over past 1357 years, the Medieval Warming Period in the Arctic was warmer than the present, Alaskan glaciers are about the same size as during the Medieval Warm Period, etc., etc.



Connecting early summer cloud-controlled sunlight and late summer sea ice in the Arctic


Yong-Sang Choi, Baek-Min Kim, Sun-Kyong Hur, Seong-Joong Kim, Joo-Hong Kim, Chang-Hoi Ho

This study demonstrates that absorbed solar radiation (ASR) at the top of the atmosphere in early summer (May–July) plays a precursory role in determining the Arctic sea ice concentration (SIC) in late summer (August–October). The monthly ASR anomalies are obtained over the Arctic Ocean (65°N–90°N) from the Clouds and the Earth's Radiant Energy System during 2000–2013. The ASR 
[absorbed solar radiation] changes primarily with cloud variation. We found that the ASR [absorbed solar radiation] anomaly in early summer is significantly correlated with the SIC [Arctic sea ice concentration] anomaly in late summer (correlation coefficient, r ≈ −0.8 with a lag of 1 to 4 months). The region exhibiting high (low) ASR anomalies and low (high) SIC anomalies varies yearly. The possible reason is that the solar heat input to ice is most effectively affected by the cloud shielding effect under the maximum TOA solar radiation in June and amplified by the ice-albedo feedback. This intimate delayed ASR-SIC relationship is not represented in most of current climate models. Rather, the models tend to over-emphasize internal sea ice processes in summer.

New paper predicts Antarctica will only contribute a tiny -.87 to +2.5 inches of sea level rise by 2100

A new paper published in Climate Dynamics models the future contribution of the Antarctic ice sheet to global mean sea level in 2100 and predicts a range from a decrease in sea level [due to ice accumulation] of -22 mm or negative 0.87 inches to a slight increase in sea levels of 63 mm or 2.5 inches. The median of this range is a tiny 1.6 inches of sea level contribution from Antarctica by the year 2100, hardly of concern.

Further, this estimate based upon conventional climate model assumptions of climate sensitivity to CO2, falsified as exaggerated at confidence levels exceeding 98%. 

The authors also conclude that "sea-level change has driven the deglaciation of the ice sheet" over the past 21,000 years since the peak of the last ice age. Global sea levels have been naturally rising for ~20,000 years and have decelerated over the past 8,000 years, decelerated over the 20th centurydecelerated 31% since 2002 and decelerated 44% since 2004 to less than 7 inches per century. There is no evidence of an acceleration of sea level rise, thus no evidence of any effect of mankind on sea levels. Since sea-level rise is not man-made, and based upon the findings of this paper, there is therefore no evidence of any effect of man on Antarctic glacier loss in the past. 

Antarctica holds over 80% of the ice on Earth, with most of the remainder in the Greenland ice sheet, which has also been demonstrated to be resistant to thaw and "insensitive" to surface melting from warming, thus further lowering sea level rise projections. Lowered sea level contributions from both Antarctica and Greenland effectively call off the alarm on future sea levels. 



A model study of the effect of climate and sea-level change on the evolution of the Antarctic Ice Sheet from the Last Glacial Maximum to 2100

M. N. A. Maris, J. M. van Wessem, W. J. van de Berg, B. de Boer, J. Oerlemans


Due to a scarcity of observations and its long memory of uncertain past climate, the Antarctic Ice Sheet remains a largely unknown factor in the prediction of global sea level change. As the history of the ice sheet plays a key role in its future evolution, in this study we model the Antarctic Ice Sheet from the Last Glacial Maximum (21 kyr ago) until the year 2100 with the ice-dynamical model ANICE. We force the model with different temperature, surface mass balance and sea-level records to investigate the importance of these different aspects for the evolution of the ice sheet. Additionally, we compare the model output from 21 kyr ago until the present with observations to assess model performance in simulating the total grounded ice volume and the evolution of different regions of the Antarctic Ice Sheet. Although there are some clear limitations of the model, we conclude that sea-level change has driven the deglaciation of the ice sheet, whereas future temperature change and the history of the ice sheet are the primary cause of changes in ice volume in the future. We estimate the change in grounded ice volume between its maximum (around 15 kyr ago) and the present-day to be between 8.4 and 12.5 m sea-level equivalent and the contribution of the Antarctic Ice Sheet to the global mean sea level in 2100, with respect to 2000, to be −22 to 63 mm.

New paper debunks the "wet gets wetter, dry gets drier" meme

A new paper published in Nature Geoscience finds the "wet gets wetter, dry gets drier" meme derived from climate models is an oversimplification of climate change not supported by observational data, and that the opposite pattern of "dry gets wetter, and wet gets drier" is almost as likely to occur. According to the authors,
"assessments of observed continental dryness trends yield contradicting results. The concept that dry regions dry out further, whereas wet regions become wetter as the climate warms has been proposed as a simplified summary of expected as well as observed changes over land, although this concept is mostly based on oceanic data. 
We find that over about three-quarters of the global land area, robust dryness changes cannot be detected. Only 10.8% of the global land area shows a robust ‘dry gets drier, wet gets wetter’ pattern, compared to 9.5% of global land area with the opposite pattern, that is, dry gets wetter, and wet gets drier. We conclude that aridity changes over land, where the potential for direct socio-economic consequences is highest, have not followed a simple intensification of existing patterns."
The paper joins at least one other finding the "wet gets wetter and dry gets drier" meme is false on local scales, although this belief is still commonly held in the climate science community. American Meteorological Society President Dr. Marshall Shepherd tweeted a few months ago that one of his "toughest challenges" is "explaining to linear thinkers that dry/drier, wet/wetter is expected. They want either or" :
  1. one my toughest challenges. Explaining to linear thinkers that dry/drier, wet/wetter is expected. They want either or.

These two papers demonstrate that this meme is a gross oversimplification as about as likely as the reverse to occur, with no change in aridity found in ~80% of global land area observations from 1948-2005. Likewise, the common assumption that dry and wet areas will become more extreme is also premature and potentially false. 

UPDATE: Another paper published in Geophysical Research Letters finds 
"We report a near-zero temporal trend in global mean Precipitation. Unexpectedly we found a reduction in global land Precipitation variance over space and time that was due to a redistribution, where, on average, the dry became wetter while wet became drier."
Thus, at least 3 papers have put the "wet gets wetter, dry gets drier" meme to bed, and the opposite may actually be true [and would be more consistent with natural homeostasis of the hydrological cycle].

Article describing the new paper below




Global assessment of trends in wetting and drying over land


Nature Geoscience
 
 
doi:10.1038/ngeo2247
Received
 
Accepted
 
Published online
 
Changes in the hydrological conditions of the land surface have substantial impacts on society12. Yet assessments of observed continental dryness trends yield contradicting results34567. The concept that dry regions dry out further, whereas wet regions become wetter as the climate warms has been proposed as a simplified summary of expected8910 as well as observed1011121314changes over land, although this concept is mostly based on oceanic data810. Here we present an analysis of more than 300 combinations of various hydrological data sets of historical land dryness changes covering the period from 1948 to 2005. Each combination of data sets is benchmarked against an empirical relationship between evaporation, precipitation and aridity. Those combinations that perform well are used for trend analysis. We find that over about three-quarters of the global land area, robust dryness changes cannot be detected. Only 10.8% of the global land area shows a robust ‘dry gets drier, wet gets wetter pattern, compared to 9.5% of global land area with the opposite pattern, that is, dry gets wetter, and wet gets drier. We conclude that aridity changes over land, where the potential for direct socio-economic consequences is highest, have not followed a simple intensification of existing patterns.


UPDATE: Science Daily article on this paper:

Rules of thumb for climate change turned upside down: Wet and dry regions recalculated

Date:
September 14, 2014
Source:
ETH Zurich
With a new analysis of land regions, ETH climate researcher are challenging the general climate change precept that dry regions are getting drier and wet regions are getting wetter. In some regions they are encountering divergent trends.
Based on models and observations, climate scientists have devised a simplified formula to describe one of the consequences of climate change: regions already marked by droughts will continue to dry out in the future climate. Regions that already have a moist climate will experience additional rainfall. In short: dry gets drier; wet gets wetter (DDWW).
However, this formula is less universally valid than previously assumed. This was demonstrated by a team of ETH climate researchers led by Peter Greve, lead author of a study recently published in Nature Geoscience. Traditional analyses use technology that can comprehensively describe climate characteristics above the ocean, but is problematic over land. While this fact was mentioned in said studies, scientific and public discourse has neglected this aspect so far. In their new study, the ETH researchers in the group headed by Sonia Seneviratne's, professor for land-climate dynamics, take into account the specific climatic properties of land surfaces, where the amount of available water is limited when compared with the ocean.
In her analysis, the climate scientists made use of measured data compiled solely on land, such as rainfall, actual evaporation and potential evaporation. The data derived from various sources was combined by Greve and his co-authors -- this allowed them to extract trends in terms of a region's humidity and dryness. Furthermore, the researchers compared data from between 1948 and 1968 and 1984 to 2004.
Half of the surface areas show divergence
The evaluation shows no obvious trend towards a drier or wetter climate across three-quarters of the land are. There are solid trends for the remaining quarter. However, only half of this surface area follows the DDWW principle, i.e. one-eighth of the total landmass, while the trends seem to contradict this rule over the other half.
In some regions, the climate has developed contrary to the general climate formula 'dry gets drier; wet gets wetter' over the past 70 years. (Chart: from Greve et al, 2014)
Some regions which should have become wetter according to the simple DDWW formula have actually become drier in the past -- this includes parts of the Amazon, Central America, tropical Africa and Asia. On the other hand, there are dry areas that have become wetter: parts of Patagonia, central Australia and the Midwestern United States.
Nevertheless, the 'wet gets wetter' rule is largely confirmed for the Eastern United States, Northern Australia and northern Eurasia. 'Dry gets drier' also corresponds to indications in the Sahel region, the Arabian Peninsula and parts of Central Asia and Australia.
However, the DDWW principle does still applies to the oceans. "Our results emphasise how we should not overly rely on simplifying principles to asses past developments in dryness and humidity," Greve explains. This can be misleading, as it cannot do justice to the complexity of the underlying systems.
Story Source:
The above story is based on materials provided by ETH ZurichNote: Materials may be edited for content and length.
Journal Reference:
  1. Greve P, Orlowsky B, Müller B, Sheffield J, Reichstein M, Seneviratne SI. Global assessment of trends in wetting and drying over landNature Geoscience, 14th September 2014 DOI: 10.1038/ngeo2247