James Hansen study

Hansen Study: Climate Sensitivity Is High, Burning All Fossil Fuels Would Make Most Of Planet ‘Uninhabitable’

ThinkProgress,

17 September, 2013

James Hansen, the country’s most prescient climatologist, is out with another must-read paper, “Climate sensitivity, sea level and atmospheric carbon dioxide.” The paper, co-authored by a number of Hansen’s former colleagues at NASA, is an antidote to the rosy scenarios the mainstream media have recently been pushing.

The key findings are:

The Earth’s actual sensitivity to a doubling of CO2 levels from preindustrial levels (to 550 ppm) — including slow feedbacks — is likely to be larger than 3–4°C (5.4-7.2°F).

Given that we are headed towards a tripling (820 ppm) or quadrupling (1100 ppm) of atmospheric CO2 levels, inaction is untenable.

“Burning all fossil fuels” would warm land areas on average about 20°C (36°F) and warm the poles a stunning 30°C (54°F). This “would make most of the planet uninhabitable by humans, thus calling into question strategies that emphasize adaptation to climate change.”

Burning all or even most fossil fuels would be a true scorched Earth policy.

Given that James Hansen has been right about global warming for more than 3 decades, his climate warnings need to be taken seriously.

The article makes two crucial point that so many media reports on climate sensitivity ignore. First, we are headed well past a doubling of CO2 levels. 

Second, “slow feedbacks, especially change of ice sheet size and atmospheric CO2, amplify the total Earth system sensitivity by an amount that depends on the time scale considered.” We know from recent research that two CO2 feedbacks alone — thawing permafrost and ocean acidification — have been projected to increase total global warming by 2100 as much as 2°F!

If we stay anywhere near our current emissions path, we face catastrophic levels of warming. Indeed, if we ultimately burn all of fossil fuels, Hansen et al find almost unimaginable consequences:

Our calculated global warming in this case is 16°C, with warming at the poles approximately 30°C. Calculated warming over land areas averages approximately 20°C. Such temperatures would eliminate grain production in almost all agricultural regions in the world. Increased stratospheric water vapour would diminish the stratospheric ozone layer.

More ominously, global warming of that magnitude would make most of the planet uninhabitable by humans. The human body generates about 100 W of metabolic heat that must be carried away to maintain a core body temperature near 37°C, which implies that sustained wet bulb temperatures above 35°C can result in lethal hyperthermia. Today, the summer temperature varies widely over the Earth’s surface, but wet bulb temperature is more narrowly confined by the effect of humidity, with the most common value of approximately 26–27°C and the highest approximately of 31°C. A warming of 10–12°C would put most of today’s world population in regions with wet a bulb temperature above 35°C…. Note also that increased heat stress due to warming of the past few decades is already enough to affect health and workplace productivity at low latitudes, where the impact falls most heavily on low- and middle-income countries

Climate Progress has previously written on the literature projecting a collapse in labor productivity from business as usual global warming. But the scorched Earth would have a vastly smaller carrying capacity than our current one, and avoiding mass starvation would become the primary task of humanity.

Hansen et al. note that this may not even require burning all of fossil fuels. It could happen on our current emissions path — if the slower (decadal) feedbacks are as strong as some paleoclimate analysis suggests. Back in 2011 we reported on a paleoclimate paper in Science that found we are headed towards CO2 levels in 2100 last seen when the Earth was 29°F (16°C) hotter.

In that sense, Hansen et al. is a conservative analysis. Their whole paper is worth reading. The authors conclude:

Most of the remaining fossil fuel carbon is in coal and unconventional oil and gas. Thus, it seems, humanity stands at a fork in the road. As conventional oil and gas are depleted, will we move to carbon-free energy and efficiency—or to unconventional fossil fuels and coal? If fossil fuels were made to pay their costs to society, costs of pollution and climate change, carbon-free alternatives might supplant fossil fuels over a period of decades. However, if governments force the public to bear the external costs and even subsidize fossil fuels, carbon emissions are likely to continue to grow, with deleterious consequences for young people and future generations.

It seems implausible that humanity will not alter its energy course as consequences of burning all fossil fuels become clearer. Yet strong evidence about the dangers of human-made climate change have so far had little effect. 

Whether governments continue to be so foolhardy as to allow or encourage development of all fossil fuels may determine the fate of humanity.