So, Nic Lewis, who created a bit of news in the climate change blogosphere for coming up with quite a low estimate of climate sensitivity, has actually got a paper published in a reputable journal.
James Annan, who truly has a tin ear for how fake skeptics will use his words when he is speaking about sensitivity, had already found some grounds for doubting parts of Lewis' approach, but a very detailed look at Lewis' work is now up at Skeptical Science. (See above.)
The comments following are worth reading too.
It certainly does not look like this should be taken as sweeping all other work on the issue away.
But watch the fake skeptics treat it that way.
Update: this passage in the Skeptical Science article caught my attention:
There is very much a tendency for climate change skeptics to not notice how much of the discussion about climate change merely looks to what the situation is likely to be by the end of this century: "Oh, sea level rise of 60cm over a century. That's manageable." There is inadequate discussion by scientists of the longer term consequences, if you ask me.In Figure 3, the PALEOSENS team also illustrates the amount of warming we can expect to see at various atmospheric CO2 levels, based on these paleoclimate studies, using several different approaches. Doubling of CO2 from 280 to 560 parts per million results in close to 3°C global surface warming at equilibrium, when accounting for relatively fast feedbacks. The paper also discusses various estimates of 'Earth System Sensitivity', which includes slower feedbacks that operate over thousands of years. They estimate this longer-term warming in response to doubled CO2 would be closer to 7°C.
Also, a new paper in Nature Climate Change talks about land biosphere feedbacks:
Atmospheric concentrations of the three important greenhouse gases (GHGs) CO2, CH4 and N2O are mediated by processes in the terrestrial biosphere that are sensitive to climate and CO2. This leads to feedbacks between climate and land and has contributed to the sharp rise in atmospheric GHG concentrations since pre-industrial times. Here, we apply a process-based model to reproduce the historical atmospheric N2O and CH4 budgets within their uncertainties and apply future scenarios for climate, land-use change and reactive nitrogen (Nr) inputs to investigate future GHG emissions and their feedbacks with climate in a consistent and comprehensive framework1. Results suggest that in a business-as-usual scenario, terrestrial N2O and CH4 emissions increase by 80 and 45%, respectively, and the land becomes a net source of C by AD 2100. N2O and CH4 feedbacks imply an additional warming of 0.4–0.5 °C by AD 2300; on top of 0.8–1.0 °C caused by terrestrial carbon cycle and Albedo feedbacks. The land biosphere represents an increasingly positive feedback to anthropogenic climate change and amplifies equilibrium climate sensitivity by 22–27%. Strong mitigation limits the increase of terrestrial GHG emissions and prevents the land biosphere from acting as an increasingly strong amplifier to anthropogenic climate change.I'm not sure how much difference that makes to overall long term climate sensitivity estimates, but it sounds as if it might be new and significant.
2 comments:
"There is very much a tendency for climate change skeptics to not notice how much of the discussion about climate change merely looks to what the situation is likely to be by the end of this century: "Oh, sea level rise of 60cm over a century. That's manageable." There is inadequate discussion by scientists of the longer term consequences, if you ask me."
Well of course the fake skeptics don't think past the end of the century, Steve, they don't think past the end of their retirement fund. By then they've made and spent their money. What happens after that is someone else's problem. Certainly not surprising from libertarian fake skeptics, anyway. If it doesn't affect me personally, why should I care?
Climate sensitivity is still a "live" issue in climate change science, with insufficient constraints available to rule out sensitivity estimates at the high or low ends.
Your point about earth system sensitivity is a good one. There's nothing special about the year 2100, or CO2 doubled above preindustrial values, or global temperature 2 degrees above preindustrial. These are convenient metrics by which to think about climate.
Climate change will not stop at 2100 due to a range of processes in the system with very long time scales. These include the dynamics of the big continental ice sheets in Greenland and Antarctica. ALso the geochemical processes in the ocean and on land that will ultimately buffer the fossil fuel GHG input. These have time scales of at least centuries, and probably millennia.
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