One of our geologist friends keeps raising exactly the point of this article in our discussions of climate change policy.
The interglacial we have enjoyed throughout recorded human history, called the Holocene, began 11,000 years ago, so the ice is overdue. We also know that glaciation can occur quickly: the required decline in global temperature is about 12C and it can happen in 20 years.
The next descent into an ice age is inevitable but may not happen for another 1000 years. On the other hand, it must be noted that the cooling in 2007 was even faster than in typical glacial transitions. If it continued for 20 years, the temperature would be 14C cooler in 2027.
By then, most of the advanced nations would have ceased to exist, vanishing under the ice, and the rest of the world would be faced with a catastrophe beyond imagining.
Australia may escape total annihilation but would surely be overrun by millions of refugees. Once the glaciation starts, it will last 1000 centuries, an incomprehensible stretch of time.
If the ice age is coming, there is a small chance that we could prevent or at least delay the transition, if we are prepared to take action soon enough and on a large enough scale.
This is by Phil Chapman, a geophysicist and astronautical engineer who lives in San Francisco. He was the first Australian to become a NASA astronaut.
Chapman and my geologist friend may both be correct. But as Glenn Reynolds emphasizes in this excellent op-ed, there are many good reasons to stop burning fossil fuels with all deliberate speed. As we’ve discussed here in Seekerblog there are a wide range of no-regrets policies that are excellent insurance against the possibility of global warming — or global cooling. Robust economic growth will be a major contributor in either case.
UPDATE: See this post for a persuasive rebuttal.
I read Chapman’s article. I think the problem with his thesis is the timescale mismatch. Though we may indeed be “overdue” for a glaciation the timescale on this process is on the order of tens of thousands of years, whereas the GHG buildup is occurring over ~200 years. And although he is correct that, in general, Pleistocene interlgacial intervals have lasted ~ 10,000 years, their duration has varied. And the last time the earth’s orbital geometry in its orbit around the sun was similar to its geometry “now” (”now” meaning the past ~50,000 years and next ~50,000 years) the earth went through a relatively prolonged interglaciation. I wrote a short review article on this:
Howard, W. R., 1997, A warm future in the past: Nature, v. 388, p. 418-419.
The other problem, more difficult to assess, is that the Pleistocene cycles Chapman is referring to occurred in a context of atmospheric CO2 and CH4 (methane) varying (cyclically) in a band which we have now exceeded by about the amplitude of those cycles. So we may be dealing with different boundary conditions than those associated with the glacial-interglacial cycles. There are a variety of views of how, or if, our addition of GHGs may have forestalled the next glaciation.
For a fairly accessible treatment of this question, see Bill Ruddiman’s Scientific American article:
Ruddiman, W. F., 2005, How did humans first alter global climate?: Scientific American, p. 46-53.
Free preview online at: http://www.sciam.com/article.cfm?id=how-did-humans-first-alte
For more scientifically detailed treatment see Bill’s “Overdue Glaciation” paper:
Ruddiman, W. F., Vavrus, S. J., and Kutzbach, J. E., 2005, A test of the overdue-glaciation hypothesis: Quaternary Science Reviews, v. 24, p. 1-10. doi:10.1016/j.quascirev.2004.07.010
or
Dave Archer’s “Moveable Trigger” paper:
Archer, D., and Ganopolski, A., 2005, A movable trigger: Fossil fuel CO2 and the onset of the next ice age: Geochemistry Geophysics Geosystems, v. 6, p. Q05003. doi:10.1029/2004GC000891
Both Dave and Bill make the case that we already have or soon will, “short-circuit” the next glacial cycle with GHGs. Time will tell.
Thanks for taking the time to put together your comments and references. Your identification of MIS 11 as perhaps the more comparable historical record is fascinating.
If we take the long view is it likely that “short-circuiting” the next glacial cycle could turn out to be net positive? I guess the bottom line is as you said “time will tell”.
The magnitude of “what we don’t know” is what compels me to focus on seeking out “no regrets policies”. We don’t know how GHG and future glaciation will interact over the range of plausible GHG concentrations. We don’t know what future glaciation will look like if GHG concentrations were held constant at any given value.
I do wish the scientific advocates would begin to give a balanced view of the priorities for both management and mitigation. A big investment in management is going to be required regardless of GHG concentrations over next 200 hundred years, and similar to mitigation, is much cheaper when addressed sooner.
“If we take the long view is it likely that ’short-circuiting’ the next glacial cycle could turn out to be net positive?”
Possibly. Indeed in the late ’60s and early ’70s there was actually concern that the input of aerosols into the atmosphere due to industrial pollution was accelerating the onset of the next ice age. At this point in (scientific) history, it was becoming clear that the Pleistocene ice-age cycles were driven (or at least paced) by orbital variations. The implication was clear even then: we should have been on our way into the next ice age. And this concern was part of what drove the development of climate models to investigate the radiative impact of aerosols. And of course the radiative impact of the CO2 that accompanied them could not be ignored either. One key insight from understanding both radiative physics and atmospheric chemistry of aerosols and CO2 was that the sulfate aerosols were relatively short-lived in the atmosphere whereas the CO2 would persist for centuries or more.
There were papers, symposia, and a number of articles in the popular media (Time, Saturday Review, etc.) talking about the possibility of a coming ice age. And remember that at the time, there had been a ~ 30-year cooling trend that began around the late ’30s-early ’40s.
From this perspective global warming would indeed look like a “net positive.”