Posted: 20 May 2013 09:35 AM PDT
It would be good news if the climate’s sensitivity to carbon pollution were on the low side. No, that wouldn’t save us from catastrophic global warming — 7°F warming or higher — if we stay anywhere near our current emissions path (as I explain here).
But a low sensitivity would mean that aggressive action to reduce CO2 emissions starting now would have a modestly higher chance of keeping total warming below 4°F and averting the worst impacts. That’s the point of New Scientist‘s article, “A second chance to save the climate” on a new sensitivity study in Nature Geoscience:
“If we are lucky and the climate sensitivity is at the low end, and we have a strong agreement in 2015, then I think we stand a chance to limit climate change to 2 °C,” says Corinne Le Quéré of the Tyndall Centre for Climate Change Research in Norwich, UK. “But there’s a lot of ifs.”If this new study is accurate, then near-term surface warming might be less than expected. But as the lead author Oxford’s Dr. Alexander Otto told the BBC, “We would all like climate sensitivity to be lower but it isn’t.”
The researchers say the difference between the lower short-term estimate and the more consistent long-term picture can be explained by the fact that the heat from the last decade has been absorbed into and is being stored by the world’s oceans.Recent studies make clear the ocean is warming quite fast, as (see “Global Warming Has Accelerated In Past 15 Years, New Study Of Oceans Confirms” and here). If, as many climatologists believe, some of that ocean heat is released to the surface in the next decade or two, that would reverse the recent slowdown in the rate of surface warming.
Also, many other recent studies find that the climate is more sensitive than we expected:
- Last Time CO2 Levels Hit 400 Parts Per Million The Arctic Was 14°F Warmer!
- Observations Support Predictions Of Extreme Warming And Worse Droughts This Century
Another related source of confusion is conflating “climate sensitivity” — which generally refers to the change in the global surface temperatures (absent major feedbacks) — with how sensitive the climate itself is to changes in temperature.
For instance, our climate models wildly underestimate what’s happening in the Arctic right now:
Arctic sea ice is melting much, much faster than even the best climate models had projected (actual observations in red). The reason is most likely unmodeled amplifying feedbacks. The image (from Climate Crocks via Arctic Sea Ice Blog) comes from a 2007 GRL research paper by Stroeve et al.And considerable recent research suggests that our climate in turn is much more sensitive to Arctic ice loss than we ever thought:
- Arctic Warming Favors Extreme, Prolonged Weather Events ‘Such As Drought, Flooding, Cold Spells And Heat Waves’
- NOAA Bombshell: Warming-Driven Arctic Ice Loss Is Boosting Chance of Extreme U.S. Weather
- How Arctic Ice Loss Amplified Superstorm Sandy — Oceanography Journal
- The so-called “equilibrium climate sensitivity” – the sensitivity of the climate to fast feedbacks like sea ice and water vapor. The ECS, which is typically the focus of modeling studies like the new one discussed above, is how much warming you get if we suddenly adopt a super-aggressive effort to cut carbon pollution and only double CO2 emissions to 560 ppm — and there are no major “slow” feedbacks. We know the fast feedbacks, like water vapor, are strong by themselves (see Study: Water-vapor feedback is “strong and positive,” so we face “warming of several degrees Celsius” and Skeptical Science piece here).
- The actual CO2 concentration level we hit, which on our current emissions path is far, far beyond 550 ppm (see U.S. media largely ignores latest warning from climate scientists: “Recent observations confirm … the worst-case IPCC scenario trajectories are being realised” — 1000 ppm).
- The real-world slower (decade-scale) feedbacks, such as tundra melt (see “Carbon Feedback From Thawing Permafrost Will Likely Add 0.4°F – 1.5°F To Total Global Warming By 2100“).
- Where they live — since people who live in the mid-latitudes (like most Americans) are projected to warm considerably more than the global average.
Actual warming this century on our current emissions path is all but certain to be catastrophic, even if ECS is closer to 2°C than 3°C or more.