From UC Berkeley: Rising temperature difference between hemispheres could dramatically shift rainfall patterns in tropics
By Robert Sanders, Media Relations
BERKELEY —
One often ignored consequence of global climate change is that the Northern Hemisphere is becoming warmer than the Southern Hemisphere, which could significantly alter tropical precipitation patterns, according to a new study by climatologists from the University of California, Berkeley, and the University of Washington, Seattle.
Such a shift could increase or decrease seasonal rainfall in areas such as the Amazon, sub-Saharan Africa or East Asia, leaving some areas wetter and some drier than today.
“A key finding is a tendency to shift tropical rainfall northward, which could mean increases in monsoon weather systems in Asia or shifts of the wet season from south to north in Africa and South America,” said UC Berkeley graduate student Andrew R. Friedman, who led the analysis.
“Tropical rainfall likes the warmer hemisphere,” summed up John Chiang, UC Berkeley associate professor of geography and a member of the Berkeley Atmospheric Sciences Center. “As a result, tropical rainfall cares a lot about the temperature difference between the two hemispheres.”
Chiang and Friedman, along with University of Washington colleagues Dargan M. W. Frierson and graduate student Yen-Ting Hwang, report their findings in a paper now accepted by the Journal of Climate, a publication of the American Meteorological Society. It will appear in an upcoming issue.
Generally, rainfall patterns fall into bands at specific latitudes, such as the Intertropical Convergence Zone. The researchers say that a warmer northern hemisphere causes atmospheric overturning to weaken in the north and strengthen in the south, shifting rain bands northward.
Impact of the Clean Air Act
Even though greenhouse gas warming of Earth has been going up since the 19th century, Chiang, Friedman and their team found no significant overall upward or downward trend in interhemispheric temperature differences last century until a steady increase beginning in the 1980s.
The researchers attribute this to human emissions of aerosols, in particular sulfates – from coal-burning power plants, for example – which cooled the Northern Hemisphere and apparently counteracted the warming effect of rising greenhouse gases until the 1970 U.S. Clean Air Act led to a downward trend in sulfur emissions. The act reduced pollution and saved more than 200,000 lives and prevented some 700,000 cases of chronic bronchitis, according to 2010 figures from the Environmental Protection Agency.
“Greenhouse gases and aerosols act in opposite directions, so for much of the 20th century they essentially canceled one another out in the Northern Hemisphere,” Chiang said. “When we started cleaning up aerosols we essentially leveled off the aerosol influence and allowed the greenhouse gases to express themselves.”
The regions most affected by this shift are likely to be on the bands’ north and south edges, Frierson said.
“It really is these borderline regions that will be most affected, which, not coincidentally, are some of the most vulnerable places: areas like the Sahel where rainfall is variable from year to year and the people tend to be dependent on subsistence agriculture,” said Frierson, associate professor of atmospheric sciences. “We are making major climate changes to the planet and to expect that rainfall patterns would stay the same is very naïve.”
20th century rainfall patterns
Many discussions of climate change focus on long-term trends in the average global temperature. The UC Berkeley and University of Washington researchers went a step further to determine how the temperature difference between the two hemispheres changed over the last century and how that may have affected tropical rainfall patterns.
Using more than 100 years of data and model simulations, they compared the yearly average temperature difference between the Northern and Southern hemispheres with rainfall throughout the 20th century and noticed that abrupt changes coincided with rainfall disruptions in the equatorial tropics.
The largest was a drop of about one-quarter degree Celsius (about one-half degree Fahrenheit) in the temperature difference in the late 1960s, which coincided with a 30-year drought in the African Sahel that caused famines and increased desertification across North Africa, as well as decreases in the monsoons in East Asia and India.
“If what we see in the last century is true, even small changes in the temperature difference between the Northern and Southern hemispheres could cause measureable changes in tropical rainfall,” Chiang said.
This bodes ill for the future, he said. The team found that most computer models simulating past and future climate predict a steadily rising interhemispheric temperature difference through the end of the century. Even if humans begin to lower their greenhouse gas emissions, the models predict about a 1 degree Celsius (2° F) increase in this difference by 2099.
As global temperatures rose over the course of the 20th century (top), the temperature between the two hemispheres changed little until the 1980s, though it has been rising since. Courtesy of Andrew Friedman.While the average temperature of the Earth is increasing as a result of dramatic increases in atmospheric greenhouse gases, primarily carbon dioxide, the Earth is not warming uniformly. In particular, the greater amount of land mass in the north warms up faster than the ocean-dominated south, Chiang said. He and his colleagues argue that climate scientists should not only focus on the rising global mean temperature, but also the regional patterns of global warming. As their study shows, the interhemispheric temperature difference has an apparent impact on atmospheric circulation and rainfall in the tropics.
“Global mean temperature is great for detecting climate change, but it is not terribly useful if you want to know what is happening to rainfall over California, for example,” Chiang said. “We think this simple index, interhemispheric temperature, is very relevant on a hemispheric and perhaps regional level. It provides a different perspective on climate change and also highlights the effect of aerosols on weather patterns.”
The research was supported by the U.S. Department of Energy and the National Science Foundation.
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I read the word ‘could’ in the headline and stopped right there.
Hmm, what could be the difference between hemispheres? It could be as simple as something like this – with far less major cities in the Southern Hemisphere, and thus less weather stations located in and around them, there is far less of a UHI (Urban heat island) effect skewing the recorded temperature higher.
So the difference may be nothing but an indicator of a systemic error of measurement. In fact, I think that hypothesis is far more likely than the idea that just 1/2 of the world is warming.
“The research was supported by the U.S. Department of Energy and the National Science Foundation.”
,,,which explains why the resulting press release reads as if it originated at the EPA. Follow the money. Res ipsa loquitur.
Not even worth reading, what a bunch of crap.
I just could not keep reading.I am glad i was not alone.
Alfred
Cause/Effect
I see the usual plethora of weasel words like “if,” “could,” “might,” “possibly,” “in the future,” etc. topped-off by this Alice in Wonderland summary:
Such a shift could increase or decrease seasonal rainfall in areas such as the Amazon, sub-Saharan Africa or East Asia, leaving some areas wetter and some drier than today.”
“The team found that most computer models simulating past and future climate predict a steadily rising interhemispheric temperature difference through the end of the century.”
And those would be the same computer models that have shown no predictive skill. What a load of manure.
I did a similar exercise just recently and posted it at Tallblokes.
http://i279.photobucket.com/albums/kk145/pochas_2008/NoExt_SoExt.png
My motivation was to see if a periodicity is evident that could arise from tidal effects. My eventual conclusion is nothing evident from my graphic except a possible connection with PDO, and the simplest explanation is that when we’re warming the northern hemisphere warms fastest and when we’re cooling the northern hemisphere cools fastest, possibly due to effective heat capacity although there are other explanations.
I think it’s a stretch to think this phenomena has anything to do with multi-decadal Global Warming beyond its attention-getting value. I do think my graphic shows recent cooling better than Friedmans’.
at Tallblokes:
http://tallbloke.wordpress.com/2013/03/21/roy-martin-how-do-the-planets-affect-the-sun-updated/comment-page-1/#comment-47543
Computer models, really? Can they model the rainfall pattern changes over what s now Ethiopia which lead to the drying of Geza in Egypt ~4500ya? More GIGO = CO2 doom = more funding!
Good/bad.
Another paper that simply suggests change is bad, if man may be a factor. Instead of discussing cause/ effect and how to take advantage of observed dynamics.
The aerosol-greenhouse gas relationship is pure speculation, They have no data, much less physical evidence. They would have done better by using the known laws of thermodynamics and kinetics to explain the regional and time diferences in the processes of evaporation, condensation, freezing, and thawing. Any possible aerosol-greenhouse effects on the loss of energy to space are small compared to these water related effects. http://www.kidswincom.net/CO2OLR.pdf.
Joseph Bastardi says:
April 3, 2013 at 3:50 am
I think you nailed it. From 1996 to 2013, and obviously beyond, how many climatists will continue to rediscover the AMO/PDO?
Enough handwaving to make the director of the show jump up and yell about Jazz hands.
UC Berkeley says:
“Generally, rainfall patterns fall into bands at specific latitudes, such as the Intertropical Convergence Zone.”
In the real world, in January, the intertropical convergence zone is found south of the equator.
During July, the intertropical convergence zone (ITCZ) is generally found north of the equator.
Looks to me like yet another in a long line of tales promoting a consistent theme. Whatever it may be, if it’s bad, man caused it and the Gods are angry. We’ve shifted from the age of reason and man’s dominion over nature to “nature worship”. The high priests of this new religion reside in academia. Under this new order, ordinary citizens can trust neither their thermometer readings nor their tide gauges. They must rely on the high priests to interpret such readings using “sophisticated statistical manipulations” of mysterious origins.
Ring any bells?
Word count:
could – 5
if – 3
should – 1
may have – 1
think – 1
That’s 1 weasel word out of every 89 words in the document.
” One often ignored consequence of global climate change…” the point I lost interest. If that’s how it starts it only gets worse thereafter. We should substitute such phrases with ‘…consequence of the moon being made of cheese’*
* I have no links with Big Cheese
/sarc
Is there no end to the nonsense coming out of computer models etc.?vanloon@ucar.edu
Such gibberish. The System is Broken, and so is this site’s standards for articles.
‘“Tropical rainfall likes the warmer hemisphere,” summed up John Chiang, UC Berkeley associate professor of geography and a member of the Berkeley Atmospheric Sciences Center.’
Really? I would’ve thought that ‘Tropical’ rainfall would’ve liked ‘colder’ hemispheres instead of ‘warmer’ hemispheres, and Arctic rainfall would’ve liked warmer hemispheres instead. Who would’ve known?
‘…1970 U.S. Clean Air Act led to a downward trend in sulfur emissions. The act reduced pollution and saved more than 200,000 lives and prevented some 700,000 cases of chronic bronchitis, according to 2010 figures from the Environmental Protection Agency.’
So the EPA’s a medical agency? I have lung disease and I’d think I’d quibble a little bit with those numbers. Take away their air conditioning, EPA, and you can add a few extra zeroes behind those numbers.
“Greenhouse gases and aerosols act in opposite directions, so for much of the 20th century they essentially canceled one another out in the Northern Hemisphere,” Chiang said. “When we started cleaning up aerosols we essentially leveled off the aerosol influence and allowed the greenhouse gases to express themselves.”
I’m surprised this old cheating trick still works. People still fall for this ace up the sleeve? Maybe Wigley can consider himself proud of this nonsense.
“Global mean temperature is great for detecting climate change…”
I’ll let the stupidity of the foregoing statement speak for itself.
‘The research was supported by the U.S. Department of Energy and the National Science Foundation.’
Where’s the sequester when you need it.
I lost interest at “could”. ” Rising temperature difference between hemispheres could dramatically shift rainfall patterns in tropics”. Yeah, and humans could grow wings and fly like birds in the future. I’m sure the must be mention of computer models somewhere in the report.Reckon there must be a standard template for this kind of stuff, and the “scientists” just need to fill in the blank spaces between the vague and doom laden standard text.
Aerosols are the latest “climate change” wrinkle to continue blaming humanity for natural processes, along with “extreme WX” despite any actual warming for about two decades (& in any case an Arctic warming more rapidly than temperate & tropic zones should produce less extreme WX).
Back to the future, since it’s reminiscent of the Antarctic ozone hole, except that that phenomenon probably does actually have an anthropogenic component. And sulfuric aerosols do tend to cool (as shown by volcanoes), which means science can’t even be sure of the sign of the negligible man-made contribution to climate, ie whether warming or cooling.
Hemispherical differences are normal & to be expected. If you think Holocene differences are bad, check out MIS 13:
http://www.clim-past.net/5/21/2009/cp-5-21-2009.html
@Claude Harvey says:
April 3, 2013 at 6:32 am
“[…] Ring any bells?”
==========================
Call “Rent-A-Shaman” if you wish, but I prefer the oracle of Delphi myself. Much more accurate.
And thank you, Doug (April 3, 2013 at 6:33 am) for the word count. Ratio of 1:89, eh? I think that measure should go along with Willis’ “# of Authors” rating.
it works here?
cn
Why do alarmists always bleat that we should insist on achieving a static climate?
Climate change is the norm, it is not a threat. Climate is always changing; our world does not mind, only goofy greenies seem fixated that the climate norm was in the year 1946, 1954 or whenever and we must return to the conditions prevailing then, or else.
If it gets warmer, the rainfall patterns will change – that’s obvious.
If it gets cooler, the rainfall patterns will change and decline – that’s the really scary part.
When the ice sheets advance, the tropical rain forests almost disappear.
During the Holocene Optimum, circa 7,500 years ago when it was around 1.0 dedree C warmer than today, the Sahara Desert was mostly grassland.
So this clearly needs more research and more grant money.