Claim: The Optimum Average Annual Temperature for Humans is 13c (55F)

Guest essay by Eric Worrall

A new study claims that people who live in tropical climates can’t be as productive as people who live in temperate climates – that 13c (55F) is the optimum temperature for human productivity. In the press release, the researchers further claim that warmer temperatures lead to poorer school results and more violence.

The abstract of the study;

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. The relationship is globally generalizable, unchanged since 1960, and apparent for agricultural and non-agricultural activity in both rich and poor countries. These results provide the first evidence that economic activity in all regions is coupled to the global climate and establish a new empirical foundation for modelling economic loss in response to climate change, with important implications. If future adaptation mimics past adaptation, unmitigated warming is expected to reshape the global economy by reducing average global incomes roughly 23% by 2100 and widening global income inequality, relative to scenarios without climate change. In contrast to prior estimates, expected global losses are approximately linear in global mean temperature, with median losses many times larger than leading models indicate.

Read more: http://www.nature.com/nature/journal/vaop/ncurrent/full/nature15725.html

According to the Washington Post;

Culling together economic and temperature data for over 100 wealthy and poorer countries alike over 50 years, the researchers assert that the optimum temperature for human productivity is seems to be around 13 degrees Celsius or roughly 55 degrees Fahrenheit, as an annual average for a particular place. Once things get a lot hotter than that, the researchers add, economic productivity declines “strongly.”

“The relationship is globally generalizable, unchanged since 1960, and apparent for agricultural and non-agricultural activity in both rich and poor countries,” write the authors, led by Marshall Burke of Stanford’s Department of Earth System Science, who call their study “the first evidence that economic activity in all regions is coupled to the global climate.” Burke published the study with Solomon Hsiang and Edward Miguel, economists at the University of California, Berkeley.

…

Assuming this relationship between temperature and productivity is correct, that naturally leads to deep questions about its cause. The researchers locate them in two chief places: agriculture and people. In relation to rising temperature, Burke says, “We see that agricultural productivity declines, labor productivity declines, kids do worse on tests, and we see more violence.”

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However, the new work has already drawn criticism — University of Sussex economist Richard Tol called it “hugely problematic” in an email to the Post — so it remains to be seen what other researchers make of the work.

Read more: http://www.washingtonpost.com/news/energy-environment/wp/2015/10/21/sweeping-study-claims-that-rising-temperatures-will-sharply-cut-economic-productivity/

Even if we accept the study at face value, according to the abstract, unmitigated warming is expected to reshape the global economy by reducing average global incomes roughly 23% by 2100 and widening global income inequality, relative to scenarios without climate change.

Given that the global economy is growing at around 1% per annum per capita, a simple projection still yields a 130% increase in per capita income by 2100 under BAU. A 23% reduction to a 130% gain doesn’t seem such a big deal, in the scheme of things.

(1 + 0.01)^{85 years} = 2.3

2.3 (230%) – the original 100% = 130% gain

I’m concerned that this study may be ignoring a lot of political and historical context. If an equivalent study was performed in the age of the Roman Empire, when much of the world’s economic activity centred on warm countries like Italy and Egypt, it seems likely that the calculated “optimum economic temperature” would have been significantly higher than 13c (55F)

However the simplest criticism of the study is the irrefutable fact that humans are physiologically optimised to extreme tropical conditions.

How would you feel, right now, if you took all your clothes off outdoors? You might feel embarrassed – but that is a cultural response. What you would most likely feel is cold, unless it was a hot day.

We all wear clothes, for comfort, style, and most importantly, to protect ourselves from the cold. Even in my home town on the edge of the tropics, certainly in winter, and for at least part of the Summer, people have to wear clothes, otherwise they get uncomfortably cold.

If you become too hot, such as when performing outdoor physical labour on a hot day, you can adjust your clothing to optimise your body temperature, say by swapping a long sleeve shirt for a t-shirt, wearing shorts, or in extreme cases by peeling down to not much clothing at all. I’ve mowed a large hilly multi-acre lawn with a petrol push mower, on days when the temperature exceeded 110F (45c). I’ll spare you the image of what I was wearing on those days.

My point is, humans are physiologically well adjusted to handling very hot weather, without adverse effects, providing we are acclimatised, providing we stay hydrated, and providing we dress appropriately for the weather. In any climate cooler than the extreme tropics where humans evolved, we have to wear clothes pretty much continuously, to protect ourselves from the cold.

Suggesting that productivity inevitably drops off, as we approach our physiological optimum environmental temperature, in my opinion is just plain silly.

As for the productivity of other plants and animals on which we depend, tropical countries are characterised by their superabundance of natural life, including food plants and animals. Some staple crops such as oats might like it cold – but there is plenty of edible farm produce which thrives in the heat.