Over-selling West African ‘megadroughts’

A recent report by Richard Black on the BBC’s Science & Environment website is headed ‘West Africa faces ‘megadroughts’. Most climate sceptics who visit blogs like Harmless Sky will anticipate what is coming next – but in this case things aren’t quite so simple.

The article refers to a new research paper published in Science by a team from the University of Texas. They have been sampling sediments from Lake Bosumtwi in Ghana which indicate that this area is regularly subject to severe droughts which last not just for years, or even decades, but for centuries.  The most recent one ended about 250 years ago, comfortably before human activity can be blamed for climate change.

Apparently the researchers are baffled about what causes these phenomena. Recurrent droughts lasting a decade of so are thought to be associated with variations in ocean currents, which in turn influence the intensity of rainfall. But these ‘megadroughts’ are on an altogether different scale and no explanation of the cause is being offered.

Such events should not be confused with the appalling drought in the Sahel during the 1970s and 1980s which is estimated to have claimed hundreds of thousands of lives.

Here is what one of the scientists has to say:

“It’s disconcerting – it suggests we’re vulnerable to a longer-lasting drought than we’ve seen in our lifetime,” said Tim Shanahan from the University of Texas in Austin, who led the research team.

Now why would Professor Shanahan be disconcerted (or possibly even discombobulated) because a century long drought has not occurred ‘in our lifetime’? Perhaps it’s because he is a palaeoclimatologist and, at the moment, this field of study seems to be fixated on climate events of the last thirty years or so – particularly the apparent need to link them to human activity – rather than actually trying to research how the climate has behaved in the past. This seems to have distorted the thinking of scientists who should be concerned with the broad sweep of geological time-scales in which the lifespan of humans is insignificant. The professor’s remark reveals a very disturbing degree of myopia.

What this paper is telling us is that previously unsuspected large scale climate events take place without human intervention, and that we still do not have complete knowledge of what tricks the natural world has up its sleeve. The BBC’s story is, in essence, a simple and very interesting one; there are major aspects of natural climate variability that we still do not know about or understand.

Of course, had there been a ‘megadrought’ during the last century, there can be little doubt that by now this would be represented as incontrovertible evidence of human induced climate change.

Unfortunately, given that this is a climate story, and written by Richard Black of the BBC, it is too much to hope that anthropogenic global warming might not be dragged into the picture even though it is irrelevant to what is being reported. A powerful quote that would provide the link was not too hard to find:

However, the cause of the longer, muti-century droughts is not clear.

“That’s one of the scary aspects – we have no idea what causes them,” said Jonathan Overpeck from the University of Arizona, who oversaw the research effort.

“In Africa, we could cross the threshold, driving the system into one of these droughts, without even knowing why.”

Professor Overpeck has featured on this blog before, in connection with an extremely generous estimate of increased sea levels. Now it would seem that he is prepared to characterise this new paper as ‘scary’ in the interests of promoting climate alarmism. But it certainly is scary when you see an influential scientist, who has played a leading roll in the IPCC’s assessments of climate research, claiming that human activity may trigger a ‘megadrought’ while admitting that their cause is completely unknown. But there is more:

Michael Schlesinger, who first characterised the AMO [Atlantic Multidecadal Oscillation] a decade ago but was not involved in the current study, suggested a similarity between the outlook for West Africa and the southwestern portion of the US.

There, research has also shown a history of shorter and longer droughts.

“There are two things that need to be done, one of which California and Arizona and so on have done – and that is put in the water collection and distribution infrastructure to deal with the short periods of not very intense water stress,” the University of Illinois at Urbana-Champaign scientist told BBC News.

“What West Africa won’t handle – and neither will California – is the 100-year-long, deep megadrought.

“The only way I can see of dealing with that is desalination; if push comes to shove and these megadroughts appear – and they will, and it’ll probably be exacerbated by man-made global warming – that will be the only thing to do.”

What started out as a perfectly innocuous story about the discovery of a previously unknown phenomenon – cause unknown – which clearly predates large scale emissions of carbon dioxide by humans, has become a means of reinforcing public belief in anthropogenic global warming.

If we take the bare facts, that analysis of lake sediments has revealed droughts in the comparatively recent past on a previously unimagined scale, then this is certainly interesting. It indicates that there is still a very great deal – totally unrelated to human activity – that we do not know about inconvenient variations in the climate system.

Lastly, Lake Bosumtwi occupies a ten-kilometre wide meteorite crater dating from about a million years ago. It is certainly safe to say that the arrival of this comparatively modest piece of stela detritus would have been heralded by a cataclysmic bang far greater than anything that we have experienced in our lifetimes, with devastating consequences for the biosphere. Such impacts have occurred regularly throughout earth’s history, and there is absolutely no reason to think that they will cease just because it would be inconvenient for one highly developed species, some of whom are now under the impression that Homo sapiens is in control of the vast chaotic system which is the earth’s climate. The natural world is not under our control.

The natural world will continue to surprise us, and those surprises will not always be pleasant or convenient for human beings.