This study from the University of Pittsburgh and SUNY-Albany set out to illustrate how rainfall patterns changes with global temperature in South America. They found the link they were looking for. At the same time, they validated the existence of the Medeival Warm Period and the Little Ice Age effects in the Southern hemisphere, which is interesting since many claim the effects were regional, not global. See the image at left and press release below.
Pitt-led Team Unearths 2,300-Year Climate Record Suggesting Severe Tropical Droughts as Northern Temperatures Rise
A sediment core from a South American lake revealed a steady, sharp drop in crucial monsoon rainfall since 1900, leading to the driest conditions in 1,000 years as of 2007 and threatening tropical populations with water shortages, a team from Pitt, Union College, and SUNY-Albany reports in PNAS
PITTSBURGH—A 2,300-year climate record University of Pittsburgh researchers recovered from an Andes Mountains lake reveals that as temperatures in the Northern Hemisphere rise, the planet’s densely populated tropical regions will most likely experience severe water shortages as the crucial summer monsoons become drier. The Pitt team found that equatorial regions of South America already are receiving less rainfall than at any point in the past millennium.Laguna Pumacocha in the Peruvian Andes.
The researchers report in the Proceedings of the National Academy of Sciences (PNAS) that a nearly 6-foot-long sediment core from Laguna Pumacocha in Peru contains the most detailed geochemical record of tropical climate fluctuations yet uncovered. The core shows pronounced dry and wet phases of the South American summer monsoons and corresponds with existing geological data of precipitation changes in the surrounding regions.
Paired with these sources, the sediment record illustrated that rainfall during the South American summer monsoon has dropped sharply since 1900—exhibiting the greatest shift in precipitation since around 300 BCE—while the Northern Hemisphere has experienced warmer temperatures.
Study coauthor Mark Abbott, a professor of geology and planetary science in Pitt’s School of Arts and Sciences who also codesigned the project, said that he and his colleagues did not anticipate the rapid decrease in 20th-century rainfall that they observed. Abbott worked with lead author and recent Pitt graduate Broxton Bird; Don Rodbell, study codesigner and a geology professor at Union College in Schenectady, N.Y.; recent Pitt graduate Nathan Stansell; Pitt professor of geology and planetary science Mike Rosenmeier; and Mathias Vuille, a professor of atmospheric and environmental science at the State University of New York at Albany. Both Bird and Stansell received their PhD degrees in geology from Pitt in 2009.
“This model suggests that tropical regions are dry to a point we would not have predicted,” Abbott said. “If the monsoons that are so critical to the water supply in tropical areas continue to diminish at this pace, it will have devastating implications for the water resources of a huge swath of the planet.”
The study compared the record in the Pumacocha sediment core (PC) to various geological records from South America—Cascayunga Cave (CC), the Quelccaya ice Cap (QIC), and the Cariaco Basin (CB)—as well as the annual position of the Intertropical Convergence Zone (ITCZ).
The sediment core shows regular fluctuations in rainfall from 300 BCE to 900 CE, with notably heavy precipitation around 550. Beginning in 900, however, a severe drought set in for the next three centuries, with the driest period falling between 1000 and 1040. This period correlates with the well-known demise of regional Native American populations, Abbott explained, including the Tiwanaku and Wari that inhabited present-day Boliva, Chile, and Peru.
After 1300, monsoons increasingly drenched the South American tropics. The wettest period of the past 2,300 years lasted from roughly 1500 to the 1750s during the time span known as the Little Ice Age, a period of cooler global temperatures. Around 1820, a dry cycle crept in briefly, but quickly gave way to a wet phase before the rain began waning again in 1900. By July 2007, when the sediment core was collected, there had been a steep, steady increase in dry conditions to a high point not surpassed since 1000.
To create a climate record from the sediment core, the team analyzed the ratio of the oxygen isotope delta-O-18 in each annual layer of lake-bed mud. This ratio has a negative relationship with rainfall: Levels of delta-O-18 are low during the wetter seasons and high when monsoon rain is light. The team found that the rainfall history suggested by the lake core matched that established by delta-O-18 analyses from Cascayunga Cave in the Peruvian lowlands and the Quelccaya Ice Cap located high in the Andes. The Pumacocha core followed the climatological narrative of these sources between the years 980 and 2006, but provided much more detail, Abbott said.
The team then established a connection between rainfall and Northern Hemisphere temperatures by comparing their core to the movement of the Intertropical Convergence Zone (ITCZ), a balmy strip of thunderstorms near the equator where winds from the Northern and Southern Hemispheres meet. Abbott and his colleagues concluded that warm Northern temperatures such as those currently recorded lure the ITCZ—the main source of monsoons—north and ultimately reduce the rainfall on which tropical areas rely.
The historical presence of the ITCZ has been gauged by measuring the titanium concentrations of sea sediment, according to the PNAS report. High levels of titanium in the Cariaco Basin north of Venezuela show that the ITCZ lingered in the upper climes at the same time the South American monsoon was at its driest, between 900 and 1100. On the other hand, the wettest period at Pumacocha—between 1400 and 1820, which coincided with the Little Ice Age—correlates with the ITCZ’s sojourn to far south of the equator as Northern Hemisphere temperatures cooled.
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Levels of the oxygen isotope delta-O-18 from Pumacocha overlaid with corresponding levels from Cascayunga Cave (red) and Quelccaya Ice Cap (blue).h/t to reader Dennis via emailDiscover more from Watts Up With That?
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“The conditions during the peak of the Eemian were only a few degrees more than present, and if projections of the likely physical effect of the increased CO2 are close to correct that temperature will be reached in the next century.
Then as the past shows the sea level rise will be likely to reach ~20 ft higher than the present.
There may also be arid deserts over large inland areas of the continents.”
During the Eemian most deserts actually disappeared. There were lakes in the driest parts of Sahara and Rub al-Khali and Lake Eyre was a permanent lake rather than a playa.
@-Smokey says:
May 24, 2011 at 7:03 am
“Unfortunately for the believers in CO2=CAGW, the planet isn’t cooperating.”
Perhaps it is, this appears to be the first time since the Holocene maximum that ice-fields and glaciers are LOSING mass, that more ice is melting from the surface than is being added.
There is no evidence in the ice-cores that this has ever happened before since the melt at the end of the last ice-age.
http://researchnews.osu.edu/archive/radsignl.htm
http://e360.yale.edu/feature/unlocking_secrets_from_the_ice_in_a_rapidly_warming_region/2268/
Out of all the hundreds of predictions that purport to show that CAGW is happening – accelerating sea level rise, tropospheric hot spot, permanent coral bleaching, hurricanes increasing, disappearing polar ice caps, ocean acidification, frog extinctions, rapidly rising global temperature, etc., etc., etc. – none of them have actually happened. None.
A broken clock is still right twice a day, and the climate alarmist claque is currently arm-waving over the natural variability of the Arctic [not mentioning the Antarctic, of course], the only event that even comes close to their hundreds of failed predictions. But Arctic ice has been even lower in the early 1800’s, well before industry started emitting significant amounts of CO2. Taking Occam’s Razor into account, the simplest explanation is that the Arctic ice cover is naturally variable. There is no evidence that CO2 has anything to do with Arctic ice.
In any branch of the hard sciences a completely failed conjecture that has zero supporting evidence, and that cannot make correct predictions, and that has reams of contrary evidence would be universally ridiculed, and its funding would be cut off. The reason that the falsified claims of the “carbon” cultists are not laughed off stage is because CAGW is political, not scientific.
Folks like Izen, who has at least some science background, apparently do not realize how ridiculous they sound making predictions of 20-foot sea level rises, and predictions that Eemian temps will be reached next century – conveniently far enough in the future that they can’t be proven wrong now. But the declining temperature trend over the past decade makes their unscientific claims of runaway global warming based on a harmless trace gas sound increasingly preposterous.
Interesting thread here in the form of a he said, she said debate. I don’t mean to demean the intellect here, for I myself am limited to BS Degree in Geology with over 25 years of environmental consulting and compliance. Not as much as most of you here I am sure. Through my work, I investigate/research issues and provide solutions, just as some of you do in your work. Root causes of local events/issues are important to identify to prevent recurrence. Why an event occurred can not be overemphasized as we seek understanding.
In climate we all seek to understand as well. It really is simplistic to me (and you can rip me if you want) that the Earth warms up, cools down, and goes through wet and dry periods – sometimes extremes. I think we can all agree on that. Here is the issue so pay attention. How are we going to control the Earth’s processes and the relationship with the Sun’s processes? Ding Ding Ding. The answer is we can not on such a grand scale. All the information presented above and all the other information presented elsewhere, accurate/true or inaccurate/false, has no bearing on what Earth’s climate will do. It will do so as it has before our existence and will do so after our existence. That’s the bottom line on a grand scale of things. On a smaller scale we can prepare and react to climate changes (see investigate events/issues above).
The past couple of years in the North, I have prepared by looking to the Southern Hemisphere. Surprisingly it was somewhat accurate looking back. Tough cold winters and floods. Will it work again? I have know idea as I can not control the Earths processes.
So please, quit wasting taxpayer money and using AGW (its a punchline to me), as a means to line your pockets. Don’t tell me how to live my life. After all, this really is about obtaining wealth and power over others. Recorded human history tells us such.
izen says:
May 24, 2011 at 6:50 am
…The conditions during the peak of the Eemian were only a few degrees more than present, and if projections of the likely physical effect of the increased CO2 are close to correct that temperature will be reached in the next century.
Then as the past shows the sea level rise will be likely to reach ~20 ft higher than the present.
There may also be arid deserts over large inland areas of the continents.
Does a warmer world always mean more arid? Putting the CAGW hypothesis in a palaeo-climate context always seems problematic for the hypothesis. For most of the history of multicellular life (from the Cambrian onwards, the Phanerozoic eon) the earth has been much warmer than now. And it has not been arid. The Silurian, Devonian and Carboniferous gave us our oil and coal organic fossil deposits, with rich vegetation over most continents including Antarctica.
Plus of course CO2 was through the roof then compared to now. If anything, life on earth appears to have been MORE vibrant, fecund and verdant then than now. Not less.
I keep coming back to this graph:
http://img801.imageshack.us/img801/289/logwarmingpaleoclimate.png
There is a message in this graphic to any with an open mind – to me it seems to suggest clearly that we are in fact at the low, not the high – end of a “healthy” range of atmospheric CO2 concentrations which is wide and extends up to 8,000 ppm and maybe further. We know for instance that somewhere below 150-180 ppm CO2 plant photosynthesis starts to be limited and then we’re all up a gum tree.
It is quite possible that a future, more enlightened and less politicised scientific community will welcome CO2 emission as a beneficial medicine for the planet’s thermal well being, and remain incredulous of the historic period of the dominance of the CAGW catastrophist alarmism driven by misanthropic Luddite politics.
Smokey,
You’ve correctly identified the Arctic as the one region that we should be seeing the earliest signs of global warming and that you feel might even come close to the “failed” predictions of the AGW “alarmists”, but then you make this claim:
“Arctic ice has been even lower in the early 1800′s…”
Please substantiate this with lots of scienfiically verified studies with complete references and links, which will need to be extraordinary since your claim is quite extraordinary.
Response to phlogiston:
May 24, 2011 at 1:38 pm
____
It is absurd to think that a world of several thousand ppm of CO2 would be more conducive to supporting the 7+ billion human beings who largely rely on the millions upon millions of cultivated grain crops for their daily food supply in one way or another. Tropical rain forests may enjoy higher CO2 levels, at least some species of plants, but the vast open wheat fields of N. America, Russia, southern Brazil, Australia, etc. might be serioiusly threatened by such higher levels and the rather disputive weather changes that would probably ensue. Far from bringing a great bonanza of increased food supplies, CO2 levels at several thousand ppm would probably even further restrict the ability of humanity to feed itself.
R. Gates says: May 24, 2011 at 4:30 pm
Response to phlogiston: May 24, 2011 at 1:38 pm
____
It is absurd to think that a world […] might be serioiusly threatened […] would probably even further […]
You really nailed this time Gates! Do you have anything to “substantiate this with lots of scienfiically verified studies with complete references and links, which will need to be extraordinary since your claim is quite extraordinary.”?
We know 2000 ppm of CO2 is more typical for life on this planet, and we currently reside in a time of historically low CO2.
http://i55.tinypic.com/11awzg8.jpg
http://i46.tinypic.com/2582sg6.jpg
R. Gates says:
May 24, 2011 at 4:30 pm
Steve Keohane says:
May 25, 2011 at 6:36 am
Response to phlogiston:
May 24, 2011 at 1:38 pm
I’m not suggesting that several thousand ppm CO2 is a desirable end. But as Steve K reiterated, the palaeo record makes it a challenge, to say the least, for the AGW camp to justify alarm over CO2 levels a few hundred ppm higher than today.
Of course data on both temperature and CO2 from deep time – 10^8-10^9 yrs ago, has to be taken with a pinch of salt. We only have indirect estimates. But enough of them seem to agree for a probable picture to emerge.
In any case even if industrial CO2 emissions continue as today indefinitely, atmospheric CO2 will not increase indefinitely but will equilibrate depending on the lifetime of CO2 in the atmosphere, which is finite; probably at somewhere in the 1000-2000 range. Grasses evolved in the late cretaceous in such CO2 levels so grasses such as wheat, barley etc should not find a problem to back-evolve a little to such levels, Dollo’s Law notwithstanding.
I believe a worse problem than CO2 is loss of vegetation. Photosynthesis by plants and the effect of natural vegetation on water tables and the hydrological cycle are such that the artificial desertification that extensive urbanisation represents, is a threat to the homeostasis of the biosphere. Plant metabolism over the Phanerozoic have reduced both temperature and CO2 concentration to levels conducive of a healthy biosphere (I happen to believe that Lovelock’s Gaia is a serious scientific hypothesis, and largely correct, and should not be ridiculed).
BTW deforestation in this context is a red herring. If Brazilian farmers cut down forest and replace them with grasses for agriculture, the end result is not less photosynthesis but more, due to the more efficient c4 photosynthesis of grasses and other monocots. But if they use the land for shopping malls and car parks – then that’s a problem…