Saturday, October 24, 2015

Beware of Correlations! They are NOT Causation!

In a recent Nature article the authors contend that "Global Warming" will result in drastic drops in certain national GDPs.

They state:

If societies continue to function as they have in the recent past, climate change is expected to reshape the global economy by substantially reducing global economic output and possibly amplifying existing global economic inequalities, relative to a world without climate change. Adaptations such as unprecedented innovation or defensive investments25 might reduce these effects, but social conflict or disrupted trade—either from political restrictions or correlated losses around the world—could exacerbate them.

As best as I can tell their analysis is predicate on the following chart:

Namely they plotted GDP versus average temperature for countries. They then contend that if say the US were to rise in temperature then we will look like Nigeria. Huh?

The also state:

Growing evidence demonstrates that climatic conditions can have a profound impact on the functioning of modern human societies, but effects on economic activity appear inconsistent. Fundamental productive elements of modern economies, such as workers and crops, exhibit highly non-linear responses to local temperature even in wealthy countries,. In contrast, aggregate macroeconomic productivity of entire wealthy countries is reported not to respond to temperature, while poor countries respond only linearly. Resolving this conflict between micro and macro observations is critical to understanding the role of wealth in coupled human–natural systems, and to anticipating the global impact of climate change, . Here we unify these seemingly contradictory results by accounting for non-linearity at the macro scale. We show that overall economic productivity is non-linear in temperature for all countries, with productivity peaking at an annual average temperature of 13 °C and declining strongly at higher temperatures.

But wait. They do not as far as I can tell demonstrate direct causation. Alabama is hotter than Maine but we have lots of factories in Alabama and few in Maine. Texas is hotter than North Dakota but there is a much higher GDP there than in North Dakota. There does not appear to be any causal relationship established.

This is pure abject conjecture in my opinion. I guess we shall see this paper referenced in the weeks and months to come. In my opinion it is at the very best abject conjecture and at the very worst poorly crafted propaganda.