There is an interesting discussion on going at Andy Revkin’s weglob Dot Earth on the topic Debate Over Climate Risks – Natural or Not, which invites responses to the statement,
“One clear-cut lesson [of this study] seems to be that human-driven warming, for this part of Africa, could be seen as a sideshow given the normal extremes. Tell me why that thought is misplaced if you feel it is.”
This subject was initiated by a Science article by Shanahan et al and subsequent news item on April 16 2009 by Andy Revkin which includes the text
“For at least 3,000 years, a regular drumbeat of potent droughts, far longer and more severe than any experienced recently, have seared a belt of sub-Saharan Africa that is now home to tens of millions of the world’s poorest people, climate researchers reported in a new study.
That sobering finding, published in the April 17th issue of Science magazine emerged from the first study of year-by-year climate conditions in the region over the millenniums, based on layered mud and dead trees in a crater lake in Ghana. “
The abstract of the Science article by Shanahan et al reads
” Although persistent drought in West Africa is well documented from the instrumental record and has been primarily attributed to changing Atlantic sea surface temperatures, little is known about the length, severity, and origin of drought before the 20th century. We combined geomorphic, isotopic, and geochemical evidence from the sediments of Lake Bosumtwi, Ghana, to reconstruct natural variability in the African monsoon over the past three millennia. We find that intervals of severe drought lasting for periods ranging from decades to centuries are characteristic of the monsoon and are linked to natural variations in Atlantic temperatures. Thus the severe drought of recent decades is not anomalous in the context of the past three millennia, indicating that the monsoon is capable of longer and more severe future droughts.”
Climate Science and our research papers have emphasized the large natural variations of climate that have occurred in the paleo-climate record and that these variations dwarf anything we have experienced in the instrumental record.
For example, in
Rial, J., R.A. Pielke Sr., M. Beniston, M. Claussen, J. Canadell, P. Cox, H. Held, N. de Noblet-Ducoudre, R. Prinn, J. Reynolds, and J.D. Salas, 2004: Nonlinearities, feedbacks and critical thresholds within the Earth’s climate system. Climatic Change, 65, 11-38,
our abstract reads
“The Earth’s climate system is highly nonlinear: inputs and outputs are not proportional, change is often episodic and abrupt, rather than slow and gradual, and multiple equilibria are the norm. While this is widely accepted, there is a relatively poor understanding of the different types of nonlinearities, how they manifest under various conditions, and whether they reflect a climate system driven by astronomical forcings, by internal feedbacks, or by a combination of both. In this paper, after a brief tutorial on the basics of climate nonlinearity, we provide a number of illustrative examples and highlight key mechanisms that give rise to nonlinear behavior, address scale and methodological issues, suggest a robust alternative to prediction that is based on using integrated assessments within the framework of vulnerability studies and, lastly, recommend a number of research priorities and the establishment of education programs in Earth Systems Science. It is imperative that the Earth’s climate system research community embraces this nonlinear paradigm if we are to move forward in the assessment of the human influence on climate.”
In an article specifically with respect to drought,
Pielke Sr., R.A., 2008: Global climate models – Many contributing influences. Citizen’s Guide to Colorado Climate Change, Colorado Climate Foundation for Water Education, pp. 28-29,
“A vulnerability perspective, focused on regional and local societal and environmental resources, is a more inclusive, useful and scientifically robust framework to use with policymakers. In contrast to the limited range of possible future risks by current climate models, the vulnerability framework permits the evaluation of the entire spectrum of risks to the water resources associated with all social and environmental threats, including climate variability and change.”
Thus, regardless of the role humans play within the climate system (and it is much more than due to carbon dioxide increases; see), adaptation plans to deal with climate variations, beyond what occurred in the historical record, should be a priority.