Slashdot Mirror
Extreme CO2 Levels Could Trigger Clouds 'Tipping Point' and 8C of Global Warming (carbonbrief.org)
If atmospheric CO2 levels exceed 1,200 parts per million (ppm), it could push the Earth's climate over a "tipping point", finds a new study. This would see clouds that shade large part of the oceans start to break up. From a report: According to the new paper published in the journal Nature Geoscience, this could trigger a massive 8C rise in global average temperatures -- in addition to the warming from increased CO2. The only similar example of rapid warming at this magnitude in the Earth's recent history is the Paleo-Eocene Thermal Maximum 55m years ago, when global temperatures increased by 5-8C and drove widespread extinction of species on both the oceans and land.
However, scientists not involved in the research caution that the results are still speculative and that other complicating factors could influence if or when a tipping point is reached. The threshold identified by the researchers -- a 1,200ppm concentration of atmospheric CO2 -- is three times current CO2 concentrations. If fossil fuel use continues to rapidly expand over the remainder of the century, it is possible levels could get that high. The Representative Concentration Pathways 8.5 scenario (RCP8.5), a very high emissions scenario examined by climate scientists, has the Earth's atmosphere reaching around 1,100ppm by the year 2100. But this would require the world to massively expand coal use and eschew any climate mitigation over the rest of this century. Further reading: A state-of-the-art supercomputer simulation indicates that a feedback loop between global warming and cloud loss can push Earth's climate past a disastrous tipping point in as little as a century.
However, scientists not involved in the research caution that the results are still speculative and that other complicating factors could influence if or when a tipping point is reached. The threshold identified by the researchers -- a 1,200ppm concentration of atmospheric CO2 -- is three times current CO2 concentrations. If fossil fuel use continues to rapidly expand over the remainder of the century, it is possible levels could get that high. The Representative Concentration Pathways 8.5 scenario (RCP8.5), a very high emissions scenario examined by climate scientists, has the Earth's atmosphere reaching around 1,100ppm by the year 2100. But this would require the world to massively expand coal use and eschew any climate mitigation over the rest of this century. Further reading: A state-of-the-art supercomputer simulation indicates that a feedback loop between global warming and cloud loss can push Earth's climate past a disastrous tipping point in as little as a century.
Climate change is real, but you need to read any single study or model with a bit of a "let's see if this gets confirmed by other groups" before believing it.
This is the flip side of that "scientific consensus" thing that the deniers keep not understanding. Science is about replication, and the real science comes when other scientists look at a result and say "yes, that makes sense, we can confirm it with our own modeling and measurements."
This is one group, with one model. Too early to call it doomsday yet.
From the abstract it looks like a doomsday prediction. Predicting an 8 K increase (+265c) in global temperature is an extraordinary claim and would require extraordinary evidence.
It's not even an extraordinary claim; it's an extraordinary hypothesis.
Past the doomsday headline, the story says :
"The paper emphasises that large uncertainties remain and the results they find are very much preliminary. Because they are using a high-resolution large-eddy simulation their model lacks many other factors contained in global climate models that operate over larger geographic scales.
"Specifically, climate models suggest that large-scale subsidence in the atmosphere – colder air becoming denser and moving towards the ground – weakens as the world warms. This has the effect of lifting up and cooling cloud tops, which counteracts possible stratocumulus breakup. While the paper tries to account for this, the weakening of subsidence that occurs is uncertain and varies across climate models."
Really, I'm not sure why this is even a story making the news. "Here's some scientists trying to figure out feedback loops in a greenhouse regime that is far from where we currently are, and here's an possible result that is interesting but has yet to be rigorously modelled, much less tested."