Decades of drought in central Africa reached their worst point in the 1980s, causing Lake Chad, a shallow lake used to water crops in neighboring countries, to almost dry out completely.
The shrinking lake and prolonged drought were initially blamed on overgrazing and bad agricultural practices. More recently, Lake Chad became an example of global warming.
U.S. Library of Congress
Sulfate-laden aerosols coming out of a U.S. smokestack in 1942. Emissions rose steadily until legislation was passed in the late 1960s and ’70s.
New University of Washington research, to be published in Geophysical Research Letters, shows that the drought was caused at least in part by Northern Hemisphere air pollution.
Aerosols emanating from coal-burning factories in the United States and Europe during the 1960s, ’70s and ’80s cooled the entire Northern Hemisphere, shifting tropical rain bands south. Rains no longer reached the Sahel region, a band that spans the African continent just below the Sahara desert.
When clean-air legislation passed in the U.S. and Europe, the rain band shifted back, and the drought lessened.
Related research by the UW researchers and their collaborators shows that global warming is now causing the land-covered Northern Hemisphere to warm faster than the Southern Hemisphere, further reversing the pre-1980s trend.
Previous research has suggested a connection between coal-burning and the Sahel drought, but this was the first study that used decades of historical observations to find that this drought was part of a global shift in tropical rainfall, and then used multiple climate models to determine why.
“One of our research strategies is to zoom out,” said lead author Yen-Ting Hwang, a UW doctoral student in atmospheric sciences. “Instead of studying rainfall at a particular place, we try to look for the larger-scale patterns.”
Wikimedia / Annabel Symington
The road to Timbuktu, in the Sahel region, during more normal conditions.
To determine that the Sahel drought was part of a broader shift, the authors looked at precipitation from all rain gauges that had continuous readings between 1930 and 1990. Other places on the northern edge of the tropical rain band, including northern India and South America, also experienced dryer climates in the 1970s and ’80s. Meanwhile, places on the southern edge of the rain band, such as northeast Brazil and the African Great Lakes, were wetter than normal.
To understand the reason, authors looked at all 26 climate models used by the Intergovernmental Panel on Climate Change. Researchers discovered that almost all the models also showed some southward shift, and that cooling from sulfate aerosols in the Northern Hemisphere was the primary cause.
“We think people should know that these particles not only pollute air locally, but they also have these remote climate effects,” Hwang said.
Light-colored sulfate aerosols are emitted mainly by dirty burning of coal. They create hazy air that reflects sunlight, and also lead to more reflective, longer-lasting clouds.
People living in the Northern Hemisphere did not notice the cooling, the authors said, because it balanced the heating associated with the greenhouse effect from increased carbon dioxide, so temperatures were steady.
UW / Y.-T. Hwang
Global precipitation change between 1931-1950 and 1961-1980. The African Sahel, center, is much drier, while east Africa and east Brazil are wetter.
“To some extent, science messed this one up the first time around,” said co-author Dargan Frierson, a UW associate professor of atmospheric sciences. “People thought that a large part of that drought was due to bad farming practices and desertification. But over the last 20 years or so we’ve realized that that was quite wrong, and that large-scale ocean and atmosphere patterns are significantly more powerful in terms of shaping where the rains fall.”
The models did not show as strong a shift as the observations, Frierson said, suggesting that ocean circulation also played a role in the drought.
The good news is that the U.S. Clean Air Act and its European counterpart had an unintended positive effect beyond improved air quality and related health benefits. Although shorter-term droughts continue to affect the Sahel, the long-term drought began to recover in the 1980s.
“We were able to do something that was good for us, and it also benefited people elsewhere,” Frierson said.
The work was funded by the National Science Foundation. Sarah Kang at the Ulsan National Institute of Science and Technology in South Korea was a co-author.
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Is there any observational data to support this idea, or is all just models? What happened to the Sahel with gigantic volcanic eruptions in the 1800s? I agree with previous posters. This is just a way to divert the issue and intensify the pressure on power generation if the global warming gig doesn’t work out.
We are back to witch trials and the time when humans were sacrificed to placate some malevolent god who caused the crops not to grow and the rivers to dry up. Don’t laugh. That statement could become true unless more voters from the other side shed the wool over their eyes. The scary part is that I believe the politicians on the other side are more than willing to buy votes with free phones and other giveaways.
Buyer beware. In exchange for those trinkets, your heating bill, food bill, and transportation costs will sky rocket.
“… then used multiple climate models to determine why.”
Even if the model outputs corresponded to the observed temperatures, that would not demonstrate the models to be a faithful representation of the reality.
The fact that the models cannot even replicate the observations tells, for sure and certain, that the models are wrong.
1) We were rising in the 1980s from the minimum (1978) of a cold phase.
2) We were lowering aerosol emissions as of the CLean Air Act of 1970 and again in 1990.
3) Grazing and farm practices were clearly major contributors to desertification. Recent developments in grazing and farming strategies have significantly altered plant survivability and increased ground cover.
4) Rising CO2 has been allowing plants to be more temperature tolerant in both directions and be more efficient with water and nutrients.
There is no way that these factors can be separated as they all occurred at the same time. The first two both reached their extremes at roughly the same time and all four have contributed since 1980. Making proportional attribution here is no better than a crap shoot.
“Related research by the UW researchers and their collaborators shows that global warming is now causing the land-covered Northern Hemisphere to warm faster than the Southern Hemisphere, further reversing the pre-1980s trend.”
This “related research” totally ignores the natural 60 cycle caused by ocean currents, the PDO and NAO. They attribute everything to human caused air pollution and claim that we cooled up to the late 1970s due to air pollution and then warmed after we cleaned up emissions.
They simply ignore all cycles and focus on only greenhouse gases warming and aerosols cooling
Ah, and it’s down with MODELS! This is not science.
Soooooo, I guess global warming is a good thing. Thanks. Could you please pass that along to the politicians.
I think whatever happened could be successfully graphed against the cumulative age of baby boomers and a valid correlation shown — and that’s all the help I am going to give them!
Blaming a disaster caused by African mismanagement on the West. IPCC models used for racist purposes. Notice how China and India are not mentioned. Only United States and Europe are cited. RACISM, RACISM, RACISM!
Posts-sanity science! Frightening!
I thought those effects in the 60s to 80s were the negative PDO phase. Why would the article refer to particulate pollution as “global warming”? The warmists use the pollution as an excuse for the current lack of warming. Or am I just confused?
Was it cooling from sulfides, or the cool phase of the PDO?
Manfred says:
June 7, 2013 at 1:18 am
They may have modelled not this world, as there appears to exist no AMO and PDO in their model world.
—-
Basic assumption does seeem to be that, absent man, the world doesn’t change.
Pamela Gray on June 7, 2013 at 5:30 am
‘Buyer beware. In exchange for those trinkets, your heating bill, food bill, and transportation costs will sky rocket.’
Well said.
“Aerosols emanating from coal-burning factories in the United States and Europe during the 1960s, ’70s and ’80s cooled the entire Northern Hemisphere, shifting tropical rain bands south. Rains no longer reached the Sahel region, a band that spans the African continent just below the Sahara desert.”
“For hundreds of years, the Sahel region has experienced regular droughts and megadroughts. One megadrought, from 1450 to 1700, lasted 250 years.[3] There was a major drought in the Sahel in 1914, caused by annual rains far below average, that caused a large-scale famine. From 1951 to 2004, the Sahel experienced some of the most consistent and severe droughts in Africa.[4] The 1960s saw a large increase in rainfall in the region, making the northern drier region more accessible. There was a push, supported by governments, for people to move northwards. As the long drought-period from 1968 through 1974 began, the grazing quickly became unsustainable, and large-scale denuding of the terrain followed. ” Wikipedia
What coal-burning factories were around between 1450 and 1700?
What caused the large increase in rainfall in the 1960s?
And why was this not noticed in the Washington University paper?
And the second go round will be a mess up too, and the third and the fourth. It was perfectly clear to everyone from the beginning that climate models were not ready for prime time, but the alarmists, that was a feature, not a bug. They could frame the models to do whatever they wanted in support of their pre-conceived political agenda, then had the chutzpah to call those who refused to put creedence in their unfounded claims “anti-scientific.”
Pamela Gray says:
We are back to witch trials and the time when humans were sacrificed to placate some malevolent god who caused the crops not to grow and the rivers to dry up. Don’t laugh.
Not laughing. That is absolutely true.
For the vast majority of human history, making shit up has been one of the primary sources of political power. Scary stories of gods and devils and saints and witches that are conveniently aligned for and against the political goals of the person telling the story have been a means to herd the sheep and eliminate competing shepherds for millennia.
The Enlightenment temporarily reigned that in, by introducing the scientific method and the principal of separating church from state. But politics abhors a power vacuum, and the hole in the power structure once occupied by priests and shamans is now being recolonized by story tellers in caps and gowns instead of mitres and robes. “The Science tells us” is the new “The Lord thy God commands”.
This article is a fine example …
B as is BARBARA, S as in Streisand…B.S.
Adults get PAID for this nonsense? Just reading a book, “The Forth Part of the World”, about the history of MAPS and “exploration”. Interesting how much PURE GARBAGE existed as “reliable information”, and how the true INFORMATION came out by ONE WAY…empirical observation. Still true today. EITHER DIRECT EXPERIMENT, or modeling which is BACKED BY DIRECT EXPERIMENT or, virtually WORTHLESS in all accounts!
(Don’t forget however, it was some of the “mis-information” which drove some folks to the “experimentation” or “exploration” that resulted in the TRUE information…so MAYBE that is the value of this nonsense!)
This is obviously the work of some of the 97%’ers.
Why do these things always have the feel of watching a small child with his new Etch- A Sketch in a made- for- TV movie: “Look Daddy, see what I made”? Layers and layers of fiction…
Who are these people that want to make life more difficult than it is? It appears that they want all industrialization to stop, and be reversed. No cars, no electricity, no transportation, no food, no hot water except for the “politically connected” “top of the heap”. Do you seriously believe that any of the U.N. representatives don’t live like KINGS. They are above all U.S. laws, “Diplomatic Immunity”. They have their own concubines. But that is not enough, so under “Climate Change” they want more power, more control.
They will have it all and we [the few who remain] will live in stick huts, gather our own food, and basically starve. OR, we will be direct slave to the owners given the table scraps.
There has always been a hatred for the middle class life style of the West that came about due to industrialization! Now they have a reason for their hatred: we are the cause of all of the worlds problems, including Climate Change!
Sounds like aerosols are the up and coming CYA tool of preference to explain away the failure of CO2 alarmist climate models. I’m sure there is some effect from aerosols and CO2, but when the models appear to not account for natural variability and known cycles like the PDO…it looks like more junk science we’ll have to pay for decades to disprove. Are we seeing the CO2/CAGW grant gravy train transfer over to the aerosol grant gravy train, with past model failures gradually consigned to the memory hole?
I think we need to assign more money to study natural variability to try to establish processes and parameters for “what is the range of normal?”. More effort should go into observation and evidence collection, less on model simulations and runs. I’m all for supporting real science, but this stuff frequently sounds like scare story shake downs of the tax payer.
If true, we will get to see real soon.
Love the way China and India have left the Northern Hemisphere.
Perhaps someone close to these “dear Leader” authors could enquire as to their current location .
Lake Chad is, like Lake Eyre in Australia, a residual of a larger lake formed during the last Pluvial (from the Latin pluvium for rainy) period. Its formation and size are determined by the longer climate cycles of the Ice Ages and the shorter drought cycles of its latitude.
When there is a Glacial Period in polar latitudes the desert zones formed on the poleward side of the Hadley cell shrink and the regions become grassland and parkland. So a Glacial period is accompanied by a Pluvial period and an Interglacial by an Interpluvial period.
Evidence includes everything from the massive aquifers under the Sahara created during the Pluvial period to variations in the organic content of sediments off the African coast,
http://www.columbia.edu/cu/pr/95/18727.html
http://www.gps.caltech.edu/~als/research_articles/2010/niedermeyer-et-al-2010.pdf
These are confirmed by rock paintings of people hunting grassland species in around the Tibesti Mountain range in the central Sahara.
http://www.africanrockart.org/index.php?option=com_content&view=article&id=83&Itemid=83
In the 1980s a proposal was made to divert water from the Congo basin to replenish waters in Lake Chad.
El-Chichon dominated the climate during the 80’s, more so than anyone will ever realize.
Lake Chad is a small remnant of one of several ‘megalakes’ (much larger than the modern Great Lakes) that existed at the end of the last glaciation.
http://climatesanity.files.wordpress.com/2007/11/africa_with_megalakes.jpg
It is a small fraction of its former size The other three have already completely dried up.
http://climatesanity.wordpress.com/2007/11/18/the-shrinking-of-lake-chad-cannot-be-blamed-on-anthropogenic-co2/
The advent of ‘air pollution’ with industrialization can hardly be blamed for the massive evaporation of the lakes which preceded it.
I’m not following. Aerosols from fossil fuel burning cooled the northern hemisphere but then CO2 from fossil fuel burning cancelled out the effect so nobody noticed but the cooling part caused lake Chad to dry up? How perceptive of lake Chad.