Scientists see fingerprint of warming climate on droughts going back to 1900

Scientists see fingerprint of warming climate on droughts going back to 1900
Regions projected to become drier or wetter as the world warms. More intense browns mean more aridity; greens, more moisture. (Gray areas lack sufficient data so far.) A new study shows that observations going back to 1900 confirm projections are largely on target. Credit: Adapted from Marvel et al., Nature, 2019

In an unusual new study, scientists say they have detected the fingerprint of human-driven global warming on patterns of drought and moisture across the world as far back as 1900. Rising temperatures are well documented back at least that far, but this is the first time researchers have identified resulting long-term global effects on the water supplies that feed crops and cities. Among the observations, the researchers documented drying of soils across much of populous North America, central America, Eurasia and the Mediterranean. Other areas, including the Indian subcontinent, have become wetter. They say the trends will continue, with severe consequences for humans. The study appears this week in the leading journal Nature.

In general, scientists agree that as global warming progresses, many now dry regions will become drier, and wet ones will become wetter. Some recent studies suggest that human-induced warming has intensified droughts in particular regions, including a now near 20-year ongoing drought in the southwestern United States. However, the last report by the Intergovernmental Panel on Climate Change says confidence in attributing specific ongoing events directly to humans is still chancy.

The new study combines computer models with long-term observations to suggest that systemic changes in what scientists call the hydroclimate are already underway across the world, and have been for some time. The researchers looked not simply at precipitation, but rather soil moisture, a more subtle measure that balances precipitation against evaporation, and is the quality most directly relevant to farming and forestry. They used tree rings going back 600 to 900 years to estimate trends before human-produced greenhouse gases started rising, then compared this data with 20th-century and modern instrumental observations, to see if they could pick out drought patterns matching those predicted by computer models, amid the noise of natural yearly or decadal regional weather variations.

Global ‘drought atlas’ data derived from tree rings running from 1400-2005. Green is wetter and brown is dryer. No titles. Note that the timing of the frames slows during the years 1900-2005. Credit: NASA's Scientific Visualization Studio

"We asked, does the real world look like what the models tell us to expect?" said study coauthor Benjamin Cook of the NASA Goddard Institute for Space Studies and Columbia University's Lamont-Doherty Earth Observatory. "The answer is yes. The big thing we learned is that climate change started affecting global patterns of drought in the early 20th century. We expect this pattern to keep emerging as continues."

Lead author Kate Marvel, a climate modeler at Goddard and Columbia University, said, "It's mind boggling. There is a really clear signal of the effects of human greenhouse gases on the hydroclimate."

Soil moisture is a complex issue, because precipitation and evaporation can work with each other, or against each other. Warmer air can carry more moisture, and thus more rain or snow. But warmer air can also evaporate more moisture from soil and carry it away, outweighing precipitation. That is probably the factor now at work in the drying western United States, and possibly other locations that have seen recent big droughts. "Precipitation is just the supply side," said study coauthor Jason Smerdon, a Lamont-Doherty paleoclimatologist. "Temperature is on the demand side, the part that dries things out." Which part predominates depends on complex factors including wind patterns, seasons, clouds, topography and proximity to the moisture-giving oceans.

  • Scientists see fingerprint of warming climate on droughts going back to 1900
    Some areas including the Indian subcontinent may get wetter than they already are, but rains may come in extreme bursts. Here, a boy cools off in an irrigation canal in Bangladesh. Credit: Kevin Krajick/Earth Institute, Columbia University
  • Scientists see fingerprint of warming climate on droughts going back to 1900
    This graphic describes how thicker tree rings indicate a wet year, and thinner tree rings indicate dry years. Credit: NASA's Scientific Visualization Studio

The scientists identified three distinct periods in their study. The first was 1900 to 1949, when they say the global-warming fingerprint was the most obvious. During this time, as predicted by models, drying was seen in Australia, much of central America and North America, Europe, the Mediterranean, western Russia and southeast Asia. At the same time, it got wetter in western China, much of central Asia, the Indian subcontinent, Indonesia and central Canada.

From 1950 to 1975, the pattern scattered into seemingly random events. The scientists believe this might be related to enormous amounts of industrial aerosols then being poured into the air without modern pollution controls. These can affect regional cloud formation, rainfall and temperature, by, among other things, blocking solar radiation and providing nuclei for moisture droplets. The researchers believe that the complex effects of aerosols probably threw a monkey wrench into the weather in many places, masking the effects of greenhouse gases, even though those gases continued to rise.

Then, starting in the 1970s, many industrial countries including the United States started instituting progressively stricter clean-air laws. Even though industrial activities continued to grow, aerosols quickly leveled off or slightly declined in many places. But at the same time, greenhouse-gas emissions continued spiraling up, along with temperatures. As a result, the researchers say, the signature on hydroclimate began re-emerging around 1981. The signal is not yet as obvious as it was in the early 20th century, but it continues to rise, especially since around 2000.

  • Scientists see fingerprint of warming climate on droughts going back to 1900
    In a warming world, some regions are expected to get drier, while others will get wetter; a new study suggests this trend is already underway, and has been for more than 100 years. Here, a geologist traverses Petrified Forest National Park in southern Arizona, one of many regions expected to become more arid. Credit: Kevin Krajick/Earth Institute, Columbia University
  • Scientists see fingerprint of warming climate on droughts going back to 1900
    “Fingerprint” still image depicting a global pattern of drought more likely to occur if greenhouse gasses are affecting the climate. Credit: NASA's Scientific Visualization Studio

"If we don't see it coming in stronger in, say, the next 10 years, we might have to wonder whether we are right," said Marvel. "But all the models are projecting that you should see unprecedented drying soon, in a lot of places."

Many of the areas expected to dry out are centers of agricultural production, and could become permanently arid. "The human consequences of this, particularly drying over large parts of North America and Eurasia, will likely be severe," says the study.

Precipitation over much of central America, Mexico the central and western United States and Europe is projected to stay about the same, or even increase. But, according to both the new study and a separate 2018 paper, and resulting evaporation of moisture from soils in those regions will probably predominate. The Mediterranean region is expected to be hit with a double whammy of both less rainfall and more heat-driven evaporation. Adding to the drought dynamics of all the affected areas: populations are expected to continue increasing, adding to water demand. According to an earlier Lamont-Doherty study, a 2006-2010 drought leading up to the disastrous Syrian civil war was probably made more likely by warming climate, and the drought may have helped create the social and economic conditions that sparked the initial rebellion.

Some areas are expected to get wetter, but this may not necessarily be good. India and some surrounding nations are expected to get more rain, because they sit squarely in the path of monsoon winds that pick up moisture from the Pacific and Indian oceans, and those oceans are getting warmer. But the rain may come perhaps more often in overwhelming storms, and not necessarily at times when it is needed.

The new study was made possible in part by recently published atlases of tree-ring chronologies from thousands of sites around the world, going back as far as 2,000 years. These gave the researchers a baseline of how weather varied before humans started heavily affecting it. The atlases are largely the work of Lamont-Doherty scientist Edward Cook, father of study coauthor Benjamin Cook. The North American drought atlas came out in 2004, followed by a Monsoon Asia atlas in 2010, and compilations for Europe and the Mediterranean, Mexico and Australia/New Zealand in 2015. (One for South America is on the way; much of Africa still remains uncovered.)

"This important paper offers new insights into the link between increasing atmospheric and regional droughts, both in the past and increasingly in the future," said Peter Gleick, cofounder of California's Pacific Institute, and expert on climate and water issues. "It also confirms the growing sophistication of our climate models and improves the tools available to detect and identify the fingerprint of human impacts on extreme hydrologic events."


Explore further

How pollution and greenhouse gases affect the climate in the Sahel

More information: Twentieth century hydroclimate changes consistent with human influence, Nature (2019). DOI: 10.1038/s41586-019-1149-8 , https://www.nature.com/articles/s41586-019-1149-8
Journal information: Nature

Citation: Scientists see fingerprint of warming climate on droughts going back to 1900 (2019, May 1) retrieved 26 May 2019 from https://phys.org/news/2019-05-scientists-fingerprint-climate-droughts.html
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May 01, 2019
Does nobody know statistics. Science has turned in shamanism.

May 01, 2019
This "unusual" study, is covered in fingerprints of fecal matter, because we all know from where the AGW Cult pulled it out.

May 01, 2019
"In an unusual new study, scientists say they have detected the fingerprint of human-driven global warming on patterns of drought and moisture across the world as far back as 1900. "

Perhaps Co2 is the wrong target. It seems that the planet will never be saved as long as humans exist. You can all deduce from that what "Their" plan is.

May 01, 2019
@grandpa
@antigoracle
@MR166.

The study of tree-rings is a long-standing, tried-and-true methodology/tool used by archaeologists to date fossilised trees and wooden artefacts. The information to be had from such is invaluable in determining what the local living conditions were like for humans, animals, plantlife and general ecosystems at the time in those areas involved in any particular 'archaeological dig'.

Until a 'world atlas' of such dendrochronological (tree-ring-based chronology) information re thousands of sites/digs was available, this new study was not possible:
The new study was made possible in part by recently published atlases of tree-ring chronologies from thousands of sites around the world, going back as far as 2,000 years. These gave the researchers a baseline of how weather varied before humans started heavily affecting it.
The fact you three again posted uninformed irrelevant BS further betrays your political/troll-factory 'activity' on the net.

May 01, 2019
RC in 1900 carbon emissions were negligible. Thus, to blame mankind for the changes in climate is ridiculous and assumes that the earths climate patterns would never change if man did not inhabit the planet.

May 01, 2019
"RC in 1900 carbon emissions were negligible." As if deforestation, coal burning, and intensive agriculture only started in the twentieth century. Your assertion is false, and the unconnected conclusion you leap to is laughable.

May 01, 2019
It is clear, from this graph, that low carbon dioxide levels, have caused wild temperatures on earth. Humans are bringing back balance to earths temperatures. https://upload.wi...ange.png and
https://ars.els-c...r001.jpg

May 01, 2019
@MR166.
RC in 1900 carbon emissions were negligible. Thus, to blame mankind for the changes in climate is ridiculous and assumes that the earths climate patterns would never change if man did not inhabit the planet.
If you read my climate change posts in relevant threads over the years/recently, you will find I already pointed out the exact same things which @TrollBane has just pointed out (and more: ie, world-wars accelerated/exacerbated mechanisation/coal-oil-burning/industrial plants and vast chemicals-production/land-sea-air-transportation etc etc) for your information. The fact you/other deniers are totally ignorant of and/or intentionally ignoring all these relevant facts and factors, confirms your denialist/troll-factory agendas from Russian/GOP/Fossil troll-factories/lobbies. Give it up; start learning/earning honestly; instead of being ignorant/mercenary stooges (ie, 'weaponised stupids') used by profiteering conmen/crooked politicians betraying humanity. Try.

May 01, 2019
@grandpa.
It is clear, from this graph, that low carbon dioxide levels, have caused wild temperatures on earth. Humans are bringing back balance to earths temperatures. https://upload.wi...ange.png
All I see in your link is a contextless graph. Please explain your point; and then further explain what your graph purports to convey that allegedly supports your point. Thanks.

May 01, 2019
There are two graphs there. One shows carbon dioxide levels the other shows wild swings in temperature. It is clear from the two charts that low carbon dioxide levels lead to wild swings in earth temperatures. It has been show from other studies that, without sufficient carbon dioxide, water vapor cannot keep the temperatures warm on earth. Carbon dioxide levels were getting too low, thus leading to the wide swings in ocean levels and the wide swings in earths temperatures. Having a stable earth, isn't just for humans. Sure we will suffer some by the temperatures increasing on earth, but it will bring overall stability to the earth.

May 01, 2019
I am dubious about changes that far back simply because the rise in CO2 wasn't significant at that point.

One point is however that saying that dry areas will get dryer and wet areas wetter misses the observation that the warmer the air gets the more water it can hold. I suspect that in the next 50 years we will see all kinds of drastic ramifications of this, including unusual amounts of rainfall in previously dry areas,

May 01, 2019
I would like to take a Poll so that all of the AGW believers can itemise everything that you PERSONALLY are/have been doing to mitigate AGW CO2 and other gas emissions into the atmosphere. Just number each one as:
1.
2.
3.
and so on. Thanks for your cooperation.

May 02, 2019
I would like to take a Poll so that all of the AGW believers can itemise everything that you PERSONALLY are/have been doing to mitigate AGW CO2 and other gas emissions into the atmosphere. Just number each one as:
1.
2.
3.
and so on. Thanks for your cooperation.


While many of us are doing lots of things (e.g. offsets for flying, purchasing or establishing renewable energy for the home, electric cars etc etc, the most far reaching thing we can do is to vote in a government that will act to reduce emissions across society. In economic terms - we need to end free riding and encourage cooperation on this internationally.

May 02, 2019
Antigoracle and all his sockpuppets swinging the trees high and low today, barking and chest thumping, that little brain only sees bananas, then the barking goes off the chart.

May 02, 2019
The white supremacist troll MR166 wrote:

RC in 1900 carbon emissions were negligible. Thus, to blame mankind for the changes in climate is ridiculous and assumes that the earths climate patterns would never change if man did not inhabit the planet.


As an historian, I'd like to say that this is one of the stupidest things I've ever read. Not "read on phys.org". Read *anywhere*. And I've seen some pretty stupid writing.

Apparently, this idiotic troll has never for a moment considered what the world in the Victorian era looked like. Here's a little hint: the fact that cities like London were very frequently covered in a thick, yellowish fog that smelled of sulphur could be a sign. The weird (if you think there were few if any carbon emissions) discoloration of brick buildings from that era, clearly visible even on the black-and-white plate photographs from the 19th century, might be another indicator.

And let's not mention the amount of coal used. Didn't happen. Nope.

May 02, 2019
Marcus 'encourage cooperation on this internationally'

Does this mean you are willing to go to war with China over this? Because that is what it will take.

May 02, 2019
In an unusual new study,


That explains it all, what BS.

May 02, 2019
Your socks babble BS, science happens here ;)

May 02, 2019
Nice to see that attribution science has moved on from global to regional trends; it is hard to fulfill the requisite < 5 % uncertainty but apparently it can be done: we now know this!

As an historian, I'd like to say that this is one of the stupidest things I've ever read.


Actually I would like to inflate the context a bit. The anti-science troll (I just blocked it) does not attack the science since the attribution was done on proxies, the carbon claim is just a label for it.

As far as climate fingerprints that can be affected by hydroclimate changes, there is a growing consensus that human climate change goes back to the start of farming/deforestation after the last glacial ended [ http://www.realcl...-update/ ].

In absolute numbers the CO2/CH4 greenhouse gas concentrations were small then and remain a smallish forcing - but it is enough to explain what we see and its imminent dangers (see article).

May 02, 2019
While many of us are doing lots of things (e.g. offsets for flying, purchasing or establishing renewable energy for the home, electric cars etc etc, the most far reaching thing we can do is to vote in a government that will act to reduce emissions across society. In economic terms - we need to end free riding and encourage cooperation on this internationally.


Exactly. I have browsed the evidence to the degree that I know the general issues; I have voted accordingly; I have written to some parties with questions; I have verified that my personal carbon/energy footprint is sustainable (mainly, I bike and keep stuff longer); and since the nation I live in started to change to 100 times more resource effective vegetarian foods I have started to switch over as well* (essentially, share the society interest and effort).

*)We/I have a long way to go, I live in a nation that for historical reasons consume lots of meats and fish. But we see a 40 % increase in vegs over last year.

May 02, 2019
''As if deforestation, coal burning, and intensive agriculture only started in the twentieth century.''

remember when 'global warming ' was all about fossil fuel ?

so if was victorian gas how to explain ,

''Fluctuations of glaciers during the 20th century in Garibaldi Provincial Park, in the southern CoastMountains of British Columbia, were reconstructed from historical documents, aerial photographs,and fieldwork. Over 505 km2or 26%, of the park, was covered by glacier ice at the beginning of the18th century. Ice cover decreased to 297 km2 by 1987–1988 and to 245 km2''

from ;

https://www.resea...mbia.pdf

May 02, 2019
''As if deforestation, coal burning, and intensive agriculture only started in the twentieth century.''

remember when 'global warming ' was all about fossil fuel ?

so if was victorian gas how to explain ,


"victorian gas", also known as coal gas
https://en.wikipe...Coal_gas

May 02, 2019
Holocene glacier fluctuations prior to the `Little Ice Age' in Garibaldi Provincial Park in the British Columbia Coast Mountains were reconstructed from geomorphic mapping and radiocarbon ages on 37 samples of growth-position and detrital wood from glacier forefields. Glaciers in Garibaldi Park were smaller than at present in the early Holocene, although some evidence exists for minor, short-lived advances at this time. The first well-documented advance dates to 7700—7300 14C yr BP. Subsequent advances date to 6400—5100, 4300, 4100—2900 and 1600—1100 14C yr BP. Some glaciers approached their maximum Holocene limits several times during the past 10 000 years. Periods of advance in Garibaldi Park are broadly synchronous with advances elsewhere in the Canadian Cordillera, suggesting a common climatic cause. The Garibaldi Park glacier record is also broadly synchronous with the record of Holocene sunspot numbers, supporting previous research that suggests solar activity may be an important

May 02, 2019
This is pure fake science! Physics proves that neither We, CO2 nor solar energy have anything, whatsoever to do with climate...

May 02, 2019
These scientists are frauds!

May 03, 2019
This is pure fake science! Physics proves that neither We, CO2 nor solar energy have anything, whatsoever to do with climate...


So...when you say 'physics', I take it you mean 'right wing talk radio', and when you say 'proves', I suppose you mean 'screams loudly and aggressively whilst banging the table'.

Meanwhile, in the real world, 'physics' has clearly demonstrated that CO2 absorbs and emits infrared radiation, warming the (lower) atmosphere and thus impacting global climate. None of this is new, or controversial, or even difficult to show in a laboratory setting.

May 03, 2019
Your socks babble BS, science happens here ;)


You're a disgrace to the word science, with your political horsechit.

May 03, 2019
If you mix politics and science you are bound to get erroneous results.

Stick with the science.

In politics shouting loud enough and thumping the table might get you somewhere, though not often because it's pretty transparent. In science it will do nothing but make people laugh at you.

May 04, 2019
I understand that many people doubt that CO2 affects climate. I don't doubt that CO2 affects climate. I just believe that the geometric progression of life will bring balance to the world. It has done so for a billion years. Our knowledge of all these interactions are but a drop in the bucket. All we can is make things worse by pretending that we can make things better, much less figure out what is better. It could be that Gaia has brought humans here, in its wisdom, to help bring balance to the earth again, not by our intelligence, but by our lack of wisdom. For whatever it is worth, we have mixed up the surface of the earth and remixed the life on earth, that will set off a new level of evolution.

May 06, 2019
@grandpa.
I understand that many people doubt that CO2 affects climate. I don't doubt that CO2 affects climate. I just believe that the geometric progression of life will bring balance to the world. It has done so for a billion years. .....It could be that Gaia has brought humans here, in its wisdom, to help bring balance to the earth again, not by our intelligence, but by our lack of wisdom.
While I appreciate your philosophy re Gaia and balance etc; I have to point out the reality that 'balance' existed for millions upon millions of years while DINOSAURS ruled the Earth. We don't want THAT sort of 'balance' NOW, do we?

And if you were fully apprised of the damage/extinction we doing to the Earth's (up-till-then reasonably 'tolerable') climate/ecosystem 'balance' since industrial revolution and its increased CO2/pollution, habitat destruction etc, then you wouldn't trust to (recent) human activity to bring about a 'balance' that you would like/survive in.

May 08, 2019
These scientists are frauds!


Takes one to know one, asshole.

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