Attribution

Michael Glantz
Environmental and Societal Impacts Group

Perhaps the most commonly cited climate impact on the course of history has been Napoleon's march on Moscow in 1812. An extremely cold winter decimated his invading army.

There has been a spate of articles and books in the last few years attributing major turning points to El Niño or El Niño-related impacts. For example, El Niño has been alleged to have influenced: the course of the French Revolution in the late 1780s, the making of the Third World, famines in colonies of major European powers, the collapse of empires, and the defeat of the Incas by Spanish conquistadors. Perhaps these associations with El Niño through atmospheric or oceanic teleconnections in the past are plausible – at least to some degree. Yet, although these suggestions make for interesting reading, I am not really sure how valid they are or how much faith one can put in those linkages.

The reason I raise this issue is the following: many researchers have spent the past 4 years or so trying to identify with some degree of confidence the impacts on ecosystems and on socio-economic systems of the 1997-98 "El Niño of the Century." That event was the most monitored, modeled, and forecast of all previous El Niño events. Yet, many of our studies are filled with caveats because of the difficulty in isolating causal relationships between El Niño in the central equatorial Pacific and adverse or positive impacts around the globe. Although there is often convincing evidence to support some of these proposed linkages, given the many factors that influence the behavior of a society or an economy, only preliminary findings can be offered. Our vision about such impacts of an El Niño of extraordinary magnitude remains cloudy, even though they occurred recently.

When reading about the assertions of El Niño's impacts on previous civilizations or on political changes hundreds of years ago, it appears that our vision and powers of analysis seem to have improved greatly. In fact, to the unsuspecting eye, that vision of El Niño's past impacts appears to be 20/20 vision or better, whereas today's vision remains somewhat blurred.

I would contend that many attributions of socioeconomic impacts to specific climate-related episodes fall into the category of educated speculation. This is not to say that speculation is a bad thing, but that degrees of uncertainty as well as of confidence should accompany that speculation. This applies in general to our attempts to identify climate and climate-related impacts on economy, environment, and society today, as well as in the past.

We (and I include myself) need to be more careful in making such attributions. Perhaps we need to include qualitative error bars with those attributions as we continue to blame climate variability on climate change and weather or climate extremes for the impacts that they seemingly (plausibly) cause. But, not all plausible scenarios will turn into reality.

– Michael Glantz