No Virginia, we didn’t Avoid another Ice Age
January 10, 2012
Did you hear the one about how great it is that we are emitting heat trapping gases? Turns out, the story goes, that we are warding off an impending ice age. Thank God for Peabody Coal!!
Notwithstanding the obviously inconsistent narrative (greenhouse gases have no effect/thank god they’re saving us from an ice age), this is yet another of those peripheral news stories that takes on a life of its own thru the climate denial magic mirror megaphone. Someone asked me this at a sports bar last night, so apparently its gotten a little traction.
Since this has potential to be another pesky BS denial meme, let’s nip it in the bud right now. First listen to the BBC Today Show interview with study author, Luke Skinner, above. Then read on.
Human emissions of carbon dioxide will defer the next Ice Age, say scientists.
The last Ice Age ended about 11,500 years ago, and when the next one should begin has not been entirely clear.
Researchers used data on the Earth’s orbit and other things to find the historical warm interglacial period that looks most like the current one.
In the journal Nature Geoscience, they write that the next Ice Age would begin within 1,500 years – but emissions have been so high that it will not.
“At current levels of CO2, even if emissions stopped now we’d probably have a long interglacial duration determined by whatever long-term processes could kick in and bring [atmospheric] CO2 down,” said Luke Skinner from Cambridge University.
Dr Skinner’s group – which also included scientists from University College London, the University of Florida and Norway’s Bergen University – calculates that the atmospheric concentration of CO2 would have to fall below about 240 parts per million (ppm) before the glaciation could begin.
The current level is around 390ppm.
My first question when I heard the news was, “Where did the 1500 years come from?”, since the most recent word from IPCC has this .. ” The next large reduction in northern summer insolation, similar to those that started past Ice Ages, is due to begin in 30,000 years.”
Most readers of this blog will be familiar with the prevailing idea, put forth by mathematician Milutin Malankovic, that subtle changes in the earth’s orbit and axial tilt over tens of thousands of years are the driver that takes the planet into, and out of, glacial periods. (review the BBC article for a quick reminder if needed)
The parameters of these orbital changes have been fuzzy enough that estimates for the onset of the next ice age are kind of all over the map, and I’ve seen estimates from 1000, to 30,000 years in the future. Important also to recognize the the “onset of an ice age” is a 5 to 10 thousand year process, and not something like an instantaneous “Day After Tomorrow” scenario that some would have you believe.
The current study is useful in that it specifically aims to nail down a little more closely the conditions that instigate the onset of glaciation, and focuses on a particular interglacial some 800,000 odd years ago that was similar in many ways to our own.
Using analysis of orbital data as well as samples from rock cores drilled in the ocean floor, Dr Skinner’s team identified an episode called Marine Isotope Stage 19c (or MIS19c), dating from about 780,000 years ago, as the one most closely resembling the present.
The transition to the Ice Age was signalled, they believe, by a period when cooling and warming seesawed between the northern and southern hemispheres, triggered by disruptions to the global circulation of ocean currents.
If the analogy to MIS19c holds up, this transition ought to begin within 1,500 years, the researchers say, if CO2 concentrations were at “natural” levels.
As things stand, they believe, it will not.
The study’s bottom line is that, for a glaciation to occur, carbon dioxide levels would have to get back down to 240 parts per million (ppm), from the current 390. Given the very slow drawdown of co2 from natural processes, even if we were to stop emitting today, that would not be happening for some millennia in the future.
Even the very slight rise in co2 that took place in the pre-industrial era, possibly due to human agriculture and deforestation practices, might have been enough to head off the very weak orbital forcing.
“The thing to underline” Dr. Skinner told the Today interviewer, is that, “..if anything, the study kind of suggests that the climate system is quite sensitive to small changes in co2, let alone the huge change that we’ve been responsible for in the last 200 years.”
The study’s conclusion is aimed directly at a popular climate denial shibboleth, that somehow the long, slow orbital processes that initiate ice ages could save us from the consequences of the current emissions.
“…it is important to reiterate that the current insolation forcing and lack of new ice growth mean that orbital-scale variability will not be moderating the effects of anthropogenically induced global warming. “