It's an interesting article in more ways then you imagine. But that's a different story.
You are aware that I am a climatologist, you may also be aware that a considerable amount of my work in recent years has been in West Africa where I have extensively studied the effects of climate change and have worked with experts from a broad base of scientific disciplines, most notably for various government's Depts of Agric.
We have conducted extensive research into the effects and mitigation of a changing climate in desert and semi-desert environments.
Our primary control experiments have been running since June 2006 and are located in Bawku in UER, Ghana, in the grounds of Pantang and Aburi to the north of Accra, near Ouagadougou in Burkina, at Paga on the BF border and Arlit in the Niger Sahara. Early indications are that our work will be successful and thus of benefit to the inhabitants of arid regions.
The test sites are producing yields of 98% and 113% compared to the long term average whereas the controls have produced yields of between 92% and 101%. It's early days yet but preliminary indications are that we can increase yields by about 11% (106% for test sites, 95% in control sites).
We use our own Stephenson's screens for recording met data. Although 4 years is too short a period of time to draw conclusions it appears that, if trends continue, there has been a slight decline in rainfall and a steady rise in temperatures (as compared to the 1976 to 2005 base period). An unusual Harmattan in 07/08 and extended drought affecting the late millet in 2006 have added a lot of 'noise' to the results thus adding to the uncertainty.
Another problem is the scarcity of long term, unbroken, weather records for the West African region. There are good records for many of the larger towns and cities but not that many for the desert regions. Up to the 1950's there are detailed records and these were compiled at a time when much of the region was colonised by the UK and France. Upon gaining independence many countries ceased to maintain detailed records until recent years. All of which means that there is a lot of uncertainty and an unsatisfactorily high amount of interpolation and extrapolation is required - not ideal but it's the best that can be done.
So, turning to each of the points you raised...
<< It has been assumed that global warming would cause an expansion of the world's deserts,>>
Overall this is what is being observed and the region which has been hardest hit is China where more than a million people have been forced from their homes as a result of desertification. We have seen the same thing happen in other regions including Darfur, where conflicts have raged over who controls the remaining agriculturally viable land.
<< but now some scientists are predicting a contrary scenario in which water and life slowly reclaim these arid places. >>
This is also true. Warmer temperatures increase the rate of evapouration from the seas and oceans and in turn this causes an overall rise in levels of precipitation. Being in the UK you hardly need me to tell you this. Globally precipitation has increased by around 10% but there have been some strange anomalies. Cherrapunjee in India is often cited as the wettest place on Earth but in recent years it’s been suffering from drought conditions. Conversely, in parts of Antarctica where it’s ‘too cold to snow’ there have been significant increases in precipitation levels, Antarctica is the driest continent (it seems odd but the ice that is there is the accumulation of millions of years).
<< They think vast, dry regions like the Sahara might soon begin shrinking.
The evidence is limited and definitive conclusions are impossible to reach but recent satellite pictures of North Africa seem to show areas of the Sahara in retreat.>>
Shrinkage is a distinct possibility and the evidence suggests that some peripheral regions are now receiving more rainfall and have the potential to sustain limited agricultural growth. However, I think that rather than describe the Sahara as ‘shrinking’ it would be better to say it is ‘shifting’. Whilst some parts are terraforming there are other places outwith the established Saharan boundary that have been evacuated and agricultural land has been lost to encroachment of the desert.
<< It could be that an increase in rainfall has caused this effect.
Farouk el-Baz, director of the Centre for Remote Sensing at Boston University, believes the Sahara is experiencing a shift from dryer to wetter conditions.>>
I would like to elaborate further but off the top of my head I’m not aware that a collation of Sahara wide rainfall data has been undertaken, I’m sure someone will have done it and the datasets will be out there but I’m not at work so can’t locate them. However, there is definitely a logic to the points made by el-Baz.
<< The Intergovernmental Panel on Climate Change warned recently that rising global temperatures could cut West African agricultural production by up to 50% by the year 2020.>>
The findings aren’t perhaps as wide ranging as your comment suggests. The 50% reduction relates only to specific forms of agriculture in certain parts of West Africa. The overall picture is one of a 20% reduction by the year 2020. As mentioned earlier, our research has indicated a 5% reduction in 4 years, which if continued to 2020 would equate to an overall reduction in yields of 17.5%.
<< But satellite images from the last 15 years do seem to show a recovery of vegetation in the Southern Sahara, although the Sahel Belt, the semi-arid tropical savannah to the south of the desert, remains fragile."">>
The Sahel is one of the greener areas of Africa. It consists of predominantly low-lying land comprising semi-arid grass, steppe and savannah transitional ecosystems. It is particularly sensitive to the effects of climate change. Several thousand years ago it experienced a climate shift resulting in extensive desertification and the loss of river systems, lakes and much agricultural land. Many of the inhabitants of present day West Africa are the descendants of people forced to migrate from the Sahel. Extensive hunting has decimated the populations of wild animals and today the Sahel has neither the fauna or flora to support anything other than transitory populations.
<< The report notes that it's a very complex subject,t pointing out that,>>
Anything to do with the climate always is complex, there are hundreds, if not thousands, of component factors interacting with each other.
<< ""You would have to look at a record of several hundred years to maybe say that things are getting greener or dryer. For the last few years there has been higher than average rainfall."">>
Maybe not hundreds of years but certainly a few decades. As I pointed out earlier, one of the problems is a trough in the climate and met records for West Africa covering the years when we really need to know what was going on. As a consequence, even the best observations have a comparatively high uncertainty to them.
<< ~ what's your view on this BBC report?>>
Hmmm
<< Please note that i;m not asking whether or not global warming is happening or whether or not it's man-made, but whether this specific effect is caused by global warming. Thank you. >>
Are these changes caused by global warming? It’s safe to say that global warming is having an effect, it’s probable that these effects include the shifting of the desert and arid regions, it’s also probable that rainfall variations can largely be attributed to global warming. It’s not possible to say that any one specific event has been caused by global warming or that in the future X, Y or Z will happen. It comes down to probabilities – if you toss a coin you’ve got a 50% chance that it will be heads, if you toss the coin dozens of times and it always shows heads then it would be reasonable to assume that you’ve got a double-headed coin. It’s a similar situation with the climate in West Africa, each individual event may or may not be caused by global warming, but the fact that there’s hundreds of such events is a clear indication that something is going on.
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If you’d have asked this question a year ago I would have suggested you visit us at Ouagadougou last April to coincide with the World Met Office’s Commission for Agricultural Meteorology AGM where you could have asked any questions to a large number of experts in the field of Agric Met.
PS - As a skeptic can you please educate some of the... how shall I put this... some of the 'less enlightened skeptics' in an attempt to stem the barrage of nonsense that is polluting this forum.