“What is the optimum temperature for man?” asked Virginia Rep. Morgan Griffith at yesterday’s Congressional hearings on a bill that would remove the EPA’s ability to regulate greenhouse gas emissions “Have we looked at that? These are questions that, believe it or not, I lay awake at night trying to figure out.”

Call me crazy, but I don’t believe it. I worry about climate change every day of my life and this is not something that keeps me awake at night. Although, if I understood as little about the basic facts of human history as you, who knows what would keep me up night?

The truth is, we have looked at it. So in the interests of helping Mr. Griffith get some obviously much-need sleep (maybe that’s why he’s having trouble understood the science), here’s a precis of the answer for the benefit of Mr. Griffith:

Humans have been around as a species for a couple of hundred thousand years. Human civilization arose over the last 10,000, which just happened to be a period known as the latest interglacial, during which temperatures averaged about 59 degrees Fahrenheit (15 C), more or less, globally speaking. We were able to domesticate crops and livestock that thrived in conditions similar to those associated with the current climate.

Civilization did not arise during the most recent ice age when it was several degrees cooler , nor did any species learn to make fire and iPads millions years ago when it was several degrees warmer. It’s actually surprising how small a change in temperature can change the ecological conditions on which we depend. We can reasonably conclude that the global average temperature that works best for us is about 59 F.

NASA has actually written about this very issue and conveniently made its analysis available free of charge on something we call the world wide web:

Life on Earth depends on energy coming from the sun. About half the light reaching Earth’s atmosphere passes through the air and clouds to the surface, where it is absorbed and then radiated upward in the form of infrared heat. About 90 percent of this heat is then absorbed by the greenhouse gases and radiated back toward the surface, which is warmed to a life-supporting average of 59 degrees Fahrenheit (15 degrees Celsius).

I would suggest that “life supporting” is a bit inaccurate, in that life has been around on Earth for about 3.75 billion years in some form, and has survived incredible changes in temperature and other environmental conditions. But humans, and specifically human civilization seems to prefer a global average of 59 degrees.

We can, of course, adapt to warmer temperatures. At least, those of us in the developed world with plenty of extra money and resources to throw around can. But at some point, even the might United States of America will find it difficult to handle decreased agricultural output. Maybe you missed the relevant testimony during yesterday’s hearing (nodded off perhaps?):

One witness, Christopher B. Field, director of global ecology at the Carnegie Institution for Science, piqued the interest of members on both sides of the aisle by detailing new research on the adverse effects of rising temperatures on agriculture. Dr. Field said crops had certain temperature thresholds above which yields dropped sharply. For corn, he said, that temperature is 84 degrees, and a single day of 104 degrees causes a 7 percent drop in yield.

Dr. Field said that extreme warming could reduce crop yields by more than 60 percent. “This new information is quite striking,” he said. “Major food crops and cotton show little sensitivity to rising temperatures until you reach a threshold. That’s why people are generally not aware of these sensitivities.”

You also probably missed the release this week of yet another study that concluded previous estimates of sea level rise are hopelessly optimistic:

The magnitude of the acceleration suggests that ice sheets will be the dominant contributors to sea level rise in forthcoming decades, and will likely exceed the IPCC projections for the contribution of ice sheets to sea level rise in the 21st century. [GEOPHYSICAL RESEARCH LETTERS, VOL. 38, L05503, 5 PP., 2011
doi:10.1029/2011GL046583]

How much?

The authors conclude that, if current ice sheet melting rates continue for the next four decades, their cumulative loss could raise sea level by 15 centimeters (5.9 inches) by 2050. When this is added to the predicted sea level contribution of 8 centimeters (3.1 inches) from glacial ice caps and 9 centimeters (3.5 inches) from ocean thermal expansion, total sea level rise could reach 32 centimeters (12.6 inches). [AGU press release, 8 March 2011]

That’s just by 2050. By 2100 we’re probably looking at something between 80 and 200 cm. (200 cm is more than 6 feet). Given how many people live within three or four feet of sea level, I wouldn’t use the term “optimum” to describe the fiscal and physical challenges that comes with such a change.

Glad I could help clear this up. Not get some sleep. Can’t have you napping on the job.

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Rignot, E., Velicogna, I., van den Broeke, M., Monaghan, A., & Lenaerts, J. (2011). Acceleration of the contribution of the Greenland and Antarctic ice sheets to sea level rise Geophysical Research Letters, 38 (5) DOI: 10.1029/2011GL046583