I video-taped and posted all the lectures from my Global Warming class this quarter. The class is part of our core science curriculum for non-science majors at the University of Chicago, and interest has been strong enough that the class has kind of taken over my teaching life. The lectures are based on my textbook, Understanding the Forecast, written for the class a few years ago. The students found it useful, I think, to be able to skip lectures and watch them later, but mostly I taped them for y’all, thinking someone might them useful. cheers, David.
Two degrees
The countries of the G8 today approved a target of 2° C rise in global average temperature above the natural, preanthropogenic climate, that they resolve should be avoided. The Europeans have been pushing for 2 degrees as a target maximum temperature for several years, but this is something of a development for the Americans. We posted recently on two new papers about what it would take to limit global average warming, finding that it would require fairly strong change in trajectory. About 2° C as a target, we wrote,
… even a “moderate” warming of 2°C stands a strong chance of provoking drought and storm responses that could challenge civilized society, leading potentially to the conflict and suffering that go with failed states and mass migrations. Global warming of 2°C would leave the Earth warmer than it has been in millions of years, a disruption of climate conditions that have been stable for longer than the history of human agriculture. Given the drought that already afflicts Australia, the crumbling of the sea ice in the Arctic, and the increasing storm damage after only 0.8°C of warming so far, a target of 2°C seems almost cavalier.
Nevertheless, we view today’s development as a constructive step.
Irreversible Does Not Mean Unstoppable
Susan Solomon, ozone hole luminary and Nobel Prize winning chair of IPCC, and her colleagues, have just published a paper entitled “Irreversible climate change because of carbon dioxide emissions” in the Proceedings of the National Academy of Sciences. We at realclimate have been getting a lot of calls from journalists about this paper, and some of them seem to have gone all doomsday on us. Dennis Avery and Fred Singer used the word Unstoppable as a battle flag a few years ago, over the argument that the observed warming is natural and therefore there is nothing that humanity can do to alter its course. So in terms of its intended rhetorical association, Unstoppable = Burn Baby Burn. But let’s not confuse Irreversible with Unstoppable. One means no turning back, while the other means no slowing down. They are very different words. Despair not!
Freeman Dyson’s selective vision
In the New York Review of Books, Freeman Dyson reviews two recent ones about global warming, but his review is mostly shaped by his own rather selective vision.
1. Carbon emissions are not a problem because in a few years genetic engineers will develop “carbon-eating trees” that will sequester carbon in soils. Ah, the famed Dyson vision thing, this is what we came for. The seasonal cycle in atmospheric CO2 shows that the lifetime of a CO2 molecule in the air before it is exchanged with another in the land biosphere is about 12 years. Therefore if the trees could simply be persuaded to drop diamonds instead of leaves, repairing the damage to the atmosphere could be fast, I suppose. The problem here, unrecognized by Dyson, is that the business-as-usual he’s defending would release almost as much carbon to the air by the end of the century as the entire reservoir of carbon stored on land, in living things and in soils combined. The land carbon reservoir would have to double in size in order keep up with us. This is too visionary for me to bet the farm on.
The Forecast in the Streets
The physical impacts of the global warming forecast can be bracketed with some degree of statistical confidence. Biological effects are more difficult to gauge, except in special cases such as the likely demise of polar bears that would result from the demise of Arctic sea ice. The societal effects, however, are nearly uncharted territory, at least to me. Perhaps the topic of global warming suffers from the same sort of cultural divide as university faculties, between the techies and the touchies; that is the sciences and the humanities. A new report (pdf) called The Age of Consequences, just released by the Center for Strategic and International Studies and the Center for a New American Security, tries to bring the social sciences, in particular history, geography, and political science, into the forecast of climate change in the coming century. It makes for fascinating if frightening reading. More »
