Debunking the GWPF Briefing Paper No2 – The Sahel Is Greening

Image Credit : Global Warming Policy Foundation

This article was written by M. A. Rodger and was originally posted at DeSmogBlog and is syndicated by an informal agreement and with the express permission of both the author and DeSmogBlog, without payment or charge.
This is the second in a series of posts on the educational charity and climate sceptic “think-tank” Global Warming Policy Foundation (GWPF). The first post examined GWPF”s organisation and its principles (or lack of them). Here we examine GWPF”s Briefing Paper No2 – The Sahel Is Greening by Philipp Mueller who is the Assistant Director of the GWPF. Coverage of the greening Sahel has been in the media for a decade now, so this cannot be too controversial a subject, can it?

Mueller explains what this Briefing Paper No2 is about in the first three sentences.

“Global warming has both positive and negative impacts. However, very often only the negative consequences are reported and the positive ones omitted. This article will show an example of a positive effect of warming.” 

Mueller then sets out to show how the Sahel is enjoying a “positive impact” of global warming.

Yet already here is a glaring omission. Despite this being an ideal opportunity to list out all the other “positive impacts”, Mueller fails even to hint at what any of the others might be. Never mind. We still have the Sahel. Or do we?

Mueller”s account can be summarised thus:

Between the 1950s and 1980s reducing rainfalls across the Sahel (the region of Africa immediately South of the Sahara Desert) caused severe drought and famine. But, according to Mueller, since the early 1980s this process has gone into reverse with the Sahel greening, harvests more plentiful and the Sahara shrinking.

The reason for this improvement is more than simply increasing rainfall. The climate of the Sahel region is delicate. Additional rainfall results in higher levels of vegetation. This induces yet more rain while reducing soil erosion. However, there is more at work than just this one “feedback” mechanism. Mueller says the extra factor that might be responsible is “the rise of atmospheric CO2 levels.” It seems the elevated levels of atmospheric CO2 let plants grow better, especially in arid regions. Clever stuff, that!

Mueller does not leave it there. He discusses the cause of the underlying increase in rainfall citing papers that suggest the rainfall was due to a warmer climate in the Sahara or a warmer North Atlantic, a process “partially caused by greenhouse gas emissions.”

Mueller”s shrinking Sahara is not unprecedented. In the past the Sahara, far from being a desert, was once a grass-covered savannah. This was over 6,000 years ago during the Holocene Climate Optimum (when temperatures were 2-5 deg C hotter than now according to Mueller but not according to others) and also during two other times in last 120,000 years.

Mueller says the future isn”t certain. The Sahel may become wetter or it may become drier. But, he concludes, today the Sahel is undoubtedly wetter and suddenly Mueller becomes far more certain about those speculative causes of the greening of the Sahel.  “The increase in rainfall, which was probably caused by rising temperatures, and rising CO2 concentrations, might even – if sustained for a few more decades – green the Sahara. This would be a truly tremendous prospect.”

This account makes bold statements but can it all be true?

Mueller”s account contains many omissions and misrepresentations. The list is so long that the full account of Mueller”s errors are appended to the bottom of this post and just a summary is presented here.

After droughts end, things grow greener. That is natural. The Sahel has a delicate climate and research shows that increased human emissions were more likely the cause of the initial drought rather than the cause of the re-greening. The recovery is also very patchy. Drought and famine, declining crops as well as encroaching deserts continue to plague parts of the Sahel, to the point that the description “greening” remains a subject for debate. Mueller”s rosy account fails to tell us any of this.

It is wild speculation to assert that any recovery in the Sahel is a result of global warming and to dangle the prospect of a future green Sahara is the exact opposite of the message provided by Mueller”s reference on the matter. However welcome the re-greening of parts of the Sahel, it cannot be relied on.

Mueller does mention this in passing but he fails to mention the confident scientific finding that any re-greening will eventually be reversed in the future. So if this greening of the Sahel is the prime example of the “positive impacts” of global warming, it is no surprise that Mueller fails to list any of the others.

GWPF Briefing paper No2 is an entirely flawed document. The views it expresses are those of the author (as the disclaimer on the cover says), not those views of the GWPF. Yet the author works with a “distinguished team of GWPF Academic Advisors.” Further, it remains a wonder that a registered charity whose task is to educate the public on global warming could ever put its name on such a report. If this is representative of GWPF Briefing Papers as a whole, it would be a cause of grave concern.

A second GWPF Briefing Paper will be the subject of the next post in this series. Hopefully it will prove to be more factual in nature than Briefing Paper No2.

APPENDIX – Details of Omissions & Misrepresentations within Mueller”s paper.

Mueller”s account began with mention of a drought between the 1950s & 1980s. This drought requires greater consideration than just a mention. Would we not expect a region to become greener in the period following a drought? Strangely, while Mueller discusses theories for the greening, he fails to mention the causes of the initial drought and its continuing legacy. This is not some minor event. The drought has been described as “…among the most undisputed and largest recent climate changes recognized by the climate research community.”

The causes of the drought have slowly become better understood. Rising population and over-grazing by livestock was the first theory but studies now show the drought resulted from changes in ocean surface temperatures Folland et al (1986) Giannini et al (2003)which are likely due in part to the sulphate aerosol pollution of Europe and North America Rotstayn & Lohmann (2002) Biasutti & Gainnini (2006) and thus it is the cleaning of emissions from power stations that has likely allowed the rains to return.

Mueller remains entirely silent about the potential role of sulphate aerosols in causing the drought and the subsequent greening. It is difficult to understand his silence as these findings are well known. Perhaps the potential role of human pollution in causing a “devastating drought” sits too uncomfortably with the intended message of “positive impacts” from global warming.

To emphasis his “positive impact”, Mueller tells us the greening is “a very welcome and very beneficial development for the people living in the Sahel.” What Mueller omits to tell us is that conditions have yet to return to the levels seen in the 1950s and that drought and famine still stalk the Sahel. His rosy reporting is even used by one sceptical commentator as proof that the continuing drought in the Sahel is but a “pseudo-catastrophe.”

Climatology may not provide the best reports of the events but the Sahel drought is reported in newspapers and the humanitarian aid networks. “In 2005, drought and famine hit the Sahel, claiming many lives. The pattern was repeated in 2010 with the crisis most acute in Niger. And now the early warning signs are there for problems again in 2012.” For Mueller to entirely miss such prominent reporting in the age of the internet is truly remarkable!

It is also remarkable how Mueller writes of improving agricultural outputs across the Sahel. Mueller cites the findings of Chris Reij in a small region of Burkina Faso and also Olsson (2008), from where he quotes half a sentence about improved agricultural output in Burkina Faso and Mali.

What Mueller totally misses in Olsson”s paper is the preceding sentence and the following half sentence which says – “After many years of dwindling food production in the Sahel, only two countries show signs of improved agricultural performance. …while the other Sahelian countries show decreases in their production.” So Mueller omits to mention the situation in the other nine countries of the Sahel, instead concentrating on the two countries where the evidence doesn”t directly contradict his theorizing.

To reinforce his greening Sahel message Mueller strays geographically. He embellishes part of a Heartland Institute report that quotes a second-hand report from geologist Stephan Kropelin.

This concerns greening within the deserts of Western Sahara, a much-troubled country that is in Africa but definitely not part of the Sahel! It is from the same Heartland report that Mueller times the start of the greening as “since the early 1980s” when if he had read the other more reliable references he cited he would have known the greening began in 1994.

The entirety of the Sahel is not greening as Mueller would have us believe. It is patchy and there remains enough areas still suffering encroaching desert to make the term "greening" debatable. Somehow Mueller fails to notice.

Mueller does manage to notice that there are signs of greening even in some areas where rainfall is still decreasing. Mueller asserts this might well be due to increased levels of atmospheric CO2. To support his CO2 claim Muller cites Sherwood Idso who has long espoused such theories and claims certain forest studies show evidence of it

But when it comes to the greening of the Sahel, Idso makes clear the CO2 link is only speculation and makes do with pointing out where researchers fail to mention his brave theorising.
There is one logical problem with Mueller”s claim which may be why Idso does not pursue a similar argument. It is difficult to reconcile patchy Sahel greening with a widespread (indeed worldwide) phenomenon like rising CO2 levels. The most likely reason for patchy greening (other than patchy rainfall) is very, very, widely discussed and observed on the ground. It is farmers changing their methods of cultivation, something Mueller fails to even mention, preferring instead to advance his ridiculous CO2 claim

The prehistoric green Sahara of the mid-Holocene with its lakes and rivers is used by Mueller to reinforce his argument that global warming may trigger a return to such conditions and so provide a truly tremendous “positive impact” from global warming. Again he manages to misrepresent the words of others. On this matter Mueller concludes “(Professor Martin) Claussen has considered the likelihood of a greening of the Sahara due to global warming and concluded that an expansion of vegetation into today”s Sahara is possible as a consequence of CO2 emissions.”

This is an exceedingly bizarre interpretation of the source document! Claussen”s quote actually says “some expansion of vegetation into today”s Sahara is theoretically possible”,(end quote, emphasis added) words too pessimistic for Mueller so he changed them.

Not only does Mueller misquote Claussen, he wholly ignores the explicit warning that Claussen makes against any belief in a future green Sahara. “But he(Claussen) warns against believing the mid-Holocene climate optimum will be recreated.” This source document continues by pointing to the continuing tree-loss in the Sahel and the shrinkage of Lake Chad; this despite the improved levels of rainfall.

Indeed, Claussen is not alone in dismissing a green Sahara.  Yet Mueller”s report concludes that a green Sahara is a distinct possibility, the exact opposite of the very authority that he claims is supporting his conclusions.

Finally, Mueller is silent about one “negative impact” of a greening Sahel. He intimates that any greening due to global warming will be permanent but this is incorrect. Climatology shows that the Sahel has a very sensitive climate such that it can be stated “with confidence” that “any greening of the Sahel and Sahara in the near future will eventually be reversed.”  The greening is unreliable. It is thus hardly an encouraging example of a “positive impact” from global warming.


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