Yesterday I looked briefly at the major impacts of anthropogenic global warming observed so far. The most notable impacts are changes in the climate in the Arctic region and modest sea level rise that nonetheless contributes to damages during severe storms on coastal areas.
Today I would like to advance a hypothetical scenario for climate between now and 2075. This isn’t science–I’m not a scientist. But it isn’t science fiction, either. I’ve been following this for a while and have done the sums.
Global warming has proceeded very unevenly, with short bursts of warming followed by periods of stasis. The 0.8C of observed global average temperature rise since 1880 has actually occurred in two sharply defined periods–from 1910 through 1940 and from 1975 through 1998.
I will assume that this pattern will continue.
Global average temperatures have risen 0.8C since 1880, as I said. As a Lukewarmer, I believe atmospheric sensitivity is low, around 2C. I expect to see something close to 2C warming this century over what would otherwise be the case, but some part of that warming will come from other contributions from deforestation, black carbon and other human causes, mostly related to land use changes.
For the sake of this hypothetical exercise I will assume that the static period in temperatures that started in 1998 will continue for about 25 years–much the same as previous periods of stasis. I therefore assume that temperatures will begin rising again in about 10 years, or 2023. (By that time we’ll have all forgotten about it and Judith Curry and Michael Tobis will be laughing about all the blogfights over a drink in a bar in West Texas.)
By that time the world’s CO2 emissions will have increased from 31.6 billion tons of CO2 to 42.5 billion tons each year, an average growth rate of 3% that is probably too conservative. And eventually it will overcome the inertia that characterizes global average temperatures now.
It will be helped by the behavior of other factors that influence climate–phenomena like the alphabet soup of ENSO, AMO and PDO ‘pseudocycles’, (events that can look cyclical from the outside but probably are not–they’re just periodic). Currently some of them are probably pushing temps down. Solar activity is low–although we really don’t know how much of an effect solar variation has, whatever effect it has right now is moving in a different direction than during the warming of 1975-1998. And at some point these phenomena will return to pushing temperatures up. And that’s where temperatures will go.
And I honestly think, in my Lukewarm heart of hearts, that temperatures will rise another 0.5C between 2025 and 2050 (give or take five years either way). And I think that then temperatures will pause again–maybe until 2075.
I think using history, combined with lower math analysis of credible numbers, is actually a useful guide to looking at the near term. (I actually think higher math often does a poorer job in forecasting, tempting as it is.)
I don’t actually know if temperatures will take the same path as that which I describe here. But I don’t think my scenario does violence towards history, what we know of the present and what we can confidently project about the near term future.
My big fear is what happens after 2075–by that time energy consumption will have climbed dramatically, possibly reaching six times the total energy the world used in 2010. Because we’re not planning for it, most of that consumption will be powered by coal.
And at that point my crystal ball goes black.