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James Hansen on pacts with the devil

By Liz Kalaugher

We are increasing the stakes of the climate Faustian bargain, believes James Hansen, who retires from NASA this week, through higher levels of fossil-fuel particulate and nitrogen pollution, which mask greenhouse-gas warming in the short term. The Faustian bargain sees aerosols reduce the net human-made climate forcing; they only maintain this level of reduction, however, if we allow air pollution to increase as emissions rise. Once people decide to reduce particulate air pollution for health reasons, the “devil’s payment” will be extracted via increased global warming.

The original Faust, the story goes, entered a pact with the devil and received magic powers for 24 years before the devil claimed his soul, leaving Faust in eternal damnation.

“The more we allow the Faustian debt to build, the more unmanageable the eventual consequences will be,” writes Hansen in a perspective article (PDF) in Environmental Research Letters (ERL), adding that plans to build more than 1000 coal-fired power plants and develop some of the dirtiest oil sources on the planet should be “vigorously resisted”. According to Hansen, we are already in a deep hole and it is time to stop digging.

As a result of increased coal use, annual carbon emissions from fossil fuels have risen at about 3% per year over the last decade, double the rate of the 30 years before. But the airborne fraction of carbon dioxide – the ratio of annual carbon-dioxide increase in the air divided by annual fossil-fuel emissions – has declined since 2000, say Hansen and colleagues, who believe this is due to an increase in carbon sink uptake linked to the rise in coal use. The nitrogen emitted by burning coal can fertilize the biosphere and boost carbon uptake by vegetation, and the aerosols released can also make sunlight more diffuse, aiding photosynthesis.

An addition of 5 Tg of nitrogen per year from fossil fuels, with an increase in net ecosystem productivity of 200 kg of carbon per kg of nitrogen, would give an annual carbon drawdown of 1 gigatonne per year, calculate the researchers. This would roughly explain the post-2000 anomaly in airborne carbon dioxide.

Hansen says that if greenhouse gases were the only climate forcing, he and his colleagues’ conclusion that actual greenhouse-gas forcings are slightly smaller than IPCC scenarios, along with Rahmstorf’s conclusions that actual climate change has exceeded IPCC projections, would tempt the team to infer that climate sensitivity is on the high side of what’s generally been assumed. “Although that may be a valid inference, the evidence is weakened by the fact that other climate forcings are not negligible in comparison to the greenhouse gases and must be accounted for,” he writes, along with co-authors Pushker Kharecha and Makiko Sato from the NASA Goddard Institute for Space Studies and Columbia Earth Institute.

Human-made aerosols are the key culprits as it’s not easy to sharpen up their effect. That said, under Hansen’s “Faustian bargain”, it looks like aerosols are reducing the net climate forcing of the past century by about half.

At first glance the increase in fertilization of the biosphere and additional aerosol cooling from the Far East seem to be good news, say the researchers. “Both effects work to limit global warming and thus help explain why the rate of global warming seems to be less this decade than it had been during the prior quarter century,” they write. But increased carbon dioxide doesn’t necessarily mean that the biosphere is healthier or that the higher carbon uptake will continue indefinitely. “Fertilization of the biosphere affects the distribution of the fossil fuel carbon among these reservoirs [atmosphere, ocean, soil, biosphere], at least in the short run, but it does not alter the fact that the fossil carbon will remain in these reservoirs for millenia.”

Since deleterious effects of warming are apparent even though mankind has only burned a small portion of total fossil-fuel reserves, and only about half of the warming due to gases now in the air has appeared because of inertia in the climate system, it seems difficult to avoid passing the “guardrail” of no more than 2 °C of warming agreed in the Copenhagen Accord, say the researchers. “What is clear is that most of the remaining fossil fuels must be left in the ground if we are to avoid dangerous human-made interference with climate,” they write.

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