As it turns out, there is a near-linear relationship between cumulative emissions and global warming
Very interesting. Thanks!
What role would potential tipping points like permafrost loss play on the “near-linear relationship between cumulative emissions and global warming”? As far as I understood, there was a lot of uncertainty on that.
I had a similar question. I’ve been reading some sources arguing for strong action on climate change recently, and they tend to emphasise tipping points.
My understanding is that the probability of tipping points is also accounted for in the estimates of eq climate sensitivity, and is one of the bigger reasons why the 95% confidence interval is wide.
It also seems like if ultimately the best guess relationship is linear, then the expectation is that tipping points aren’t decisive (or that negative feedbacks are just as likely as positive feedbacks).
The new models account for potential feedbacks from permafrost carbon. I’m also not especially worried about that feedback or the one from methane clathrates. The world was about 4 degrees warmer a few million years ago, and we didn’t get a rapid carbon input from these sources. And the models and basic physics suggest that these would be slow acting multi-centennial scale feedbacks.
The Sherwood et al (2020) paper accounts for evidence from the paleoclimate which should in principle pick up some tipping points from the past, though what we are doing now is not a perfect analogue for past climate change in various ways, and paleoclimate proxies are imperfect. Our confidence in the linear relationship between cumulative emissions and warming is lower the higher emissions get. The IPCC is less sure it holds once we get past 1,000 billion tonnes of carbon (on top of the 650 billion tonnes we have already emitted). The Sherwood et al (2020) paper only estimates ECS for up to two doublings of CO2 concentrations, so 1,100ppm. Beyond that, we have less of a clue, especially as CO2 concentrations wouldn’t have been that high for tens of millions of years.
I am worried about feedbacks if emissions do get that high. Imo, the most worrying thing about climate change is the potential for unexpected surprises, especially from cloud feedbacks, eg here. That is the first time a fast feedback has shown up in the models. But that is something we reach when we get to 1,300ppm, which is probably several centuries away.
There is some stuff from the planetary boundaries people arguing that we are on the brink of massive and disastrous tipping points even at 2 degrees, eg this widely cited paper from 2018. That paper fits the planetary boundaries pattern of arguing that there is a potentially significant environmental tipping point close by, on the basis of limited or non-existent evidence and argument.
Very interesting. Thanks!
What role would potential tipping points like permafrost loss play on the “near-linear relationship between cumulative emissions and global warming”?
As far as I understood, there was a lot of uncertainty on that.
I had a similar question. I’ve been reading some sources arguing for strong action on climate change recently, and they tend to emphasise tipping points.
My understanding is that the probability of tipping points is also accounted for in the estimates of eq climate sensitivity, and is one of the bigger reasons why the 95% confidence interval is wide.
It also seems like if ultimately the best guess relationship is linear, then the expectation is that tipping points aren’t decisive (or that negative feedbacks are just as likely as positive feedbacks).
Does that seem right?
The new models account for potential feedbacks from permafrost carbon. I’m also not especially worried about that feedback or the one from methane clathrates. The world was about 4 degrees warmer a few million years ago, and we didn’t get a rapid carbon input from these sources. And the models and basic physics suggest that these would be slow acting multi-centennial scale feedbacks.
The Sherwood et al (2020) paper accounts for evidence from the paleoclimate which should in principle pick up some tipping points from the past, though what we are doing now is not a perfect analogue for past climate change in various ways, and paleoclimate proxies are imperfect. Our confidence in the linear relationship between cumulative emissions and warming is lower the higher emissions get. The IPCC is less sure it holds once we get past 1,000 billion tonnes of carbon (on top of the 650 billion tonnes we have already emitted). The Sherwood et al (2020) paper only estimates ECS for up to two doublings of CO2 concentrations, so 1,100ppm. Beyond that, we have less of a clue, especially as CO2 concentrations wouldn’t have been that high for tens of millions of years.
I am worried about feedbacks if emissions do get that high. Imo, the most worrying thing about climate change is the potential for unexpected surprises, especially from cloud feedbacks, eg here. That is the first time a fast feedback has shown up in the models. But that is something we reach when we get to 1,300ppm, which is probably several centuries away.
There is some stuff from the planetary boundaries people arguing that we are on the brink of massive and disastrous tipping points even at 2 degrees, eg this widely cited paper from 2018. That paper fits the planetary boundaries pattern of arguing that there is a potentially significant environmental tipping point close by, on the basis of limited or non-existent evidence and argument.