Real Global Temperature Trend, p20 – Combining thermal inertia & carbon cycle inertia: 1 decade extra warming after emissions stop

Apart of course from the amount of greenhouse gases we keep pumping into the atmosphere, there are mainly three factors that determine the amount of warming we will experience in the near future: CO2 climate sensitivity, ocean thermal inertia, and carbon cycle inertia. Here we try to make better sense of their combination.

Climate inertia atmospheric warming
In our attempt to uncover the ‘Real’ Global Temperature Trend we’ve tried to better understand all three factors: Ocean thermal inertia is in the order of 25-50 years. Meaning if CO2 remains constant, warming continues for some 37.5 years (adding some 0.6 degrees Celsius to global average temperature). Carbon cycle inertia teaches us something different: once emissions drop to zero, atmospheric CO2 does not remain constant, but rather slowly declines (thanks to (declining but) continued ocean CO2 absorption) – compensating much of the bad news of ocean thermal inertia. And climate sensitivity. Well. Our expert survey confirms where established climate science has pointed to for a long time. It’s probably ‘close to 3 degrees’ – and perhaps sooner a bit higher than 3 (6 out of 15 experts) than below (3 out of 15).

Now it’s time to combine these factors – to get to an attempted net climate system inertia. Big question: will warming continue once we reduce our emissions to zero? Well, you’ve read the title of this piece. And the above graph helps.

It comes from an interesting two-year-old paper, written by Katharine Ricke and Ken Caldeira of the Carnegie Institution for Science and published in Environmental Research Letters.

Narrowing uncertainty in 21st century warming means narrowing uncertainty in climate sensitivity, ocean thermal inertia and carbon cycle responses, the authors write. Their conclusion is rather optimistic: although maximum warming occurs a decade (10.1 years to be precise) after emissions, ‘the benefit of avoided climate damage from avoided CO2 emissions will be manifested within the lifetimes of people who acted to avoid that emission.’

Judging by this study atmospheric warming rapidly increases in the first couple of years after emissions – and then remains almost constant for the rest of the century, and beyond.

“Carbon dioxide emissions are long-lasting and generate multi-century and multi-millennial commitments,” Ricke and Caldeira write in their conclusion.

Climate system inertia: combining climate sensitivity, thermal inertia and carbon cycle inertia
Above graph show three inert climate processes – and their modelled interplay. Firstly it takes time for equilibrium climate sensitivity to set in, mostly due to relatively fast-acting climate feedbacks (amplifying water and cloud responses to warming). Meanwhile we’re used to living in a climate in which the oceans absorb a large chunk of the extra energy elevated atmospheric CO2 adds to system Earth. As the oceans warm themselves during that process, this negative feedback is declining – so atmospheric temperatures will rise over decades to come (thermal inertia) if atmospheric CO2 is kept constant. But it isn’t. Because oceans also absorb CO2 – the Bordeaux red line.

It’s complicated stuff. Or rather: model runs of complicated stuff. The good news is probably that we witness most of the warming we create more rapidly than many people (in the climate community) think. The bad news is, we’re stuck with that warming for as long as our children’s children live.

Climate warming inertia is small, climate damage inertia is monstrous

Meanwhile other Earth system responses, which are much slower, add there own definitions of climate inertia to this equation. Stuff like sea level rise. Ocean current collapse. Ecosystem disintegration. We may witness the atmospheric warming our emissions create within a couple of years. But we won’t see the full extent of the damage we create until this century is through. Here’s climate-induced intraspecific biodiversity loss by 2080 to give one indication. Here’s ‘equilibrium sea level rise’ to 2 degrees warming to give another.

We need to stop emitting – in the here & now.

© Rolf Schuttenhelm |

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