A New Climate Frontier

"We anticipate acceleration of the long-term global warming rate by at least 50%"

Fossil fuel consumption and CO2 emissions. Source: http://www.columbia.edu/~jeh1/Documents/PipelinePaper.2023.07.05.pdf

We anticipate acceleration of the long-term global warming rate by at least 50%, i.e., to at least 0.27°C/decade.
—James Hansen, “Oh-Oh. Now What?”

Did I say overlords? I meant protectors.
—Jonathan Coulton, here

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James Hansen has a new piece called “Oh-Oh. Now What?” I’d like to bring you some of its highlights, or lowlights, since there’s not much highness in it. The whole thing is fairly short, but I want to summarize its key points (all emphasis below is mine).

Three metrics are mentioned in the piece:

• The rate of increase in global warming

• EEI (Earth’s energy imbalance) — the difference between energy in and energy out of the Earth climate system

• Equilibrium climate sensitivity (ECS) — a measure of Earth’s responsiveness to change in atmospheric CO2

Accelerating temperature increase

About global temperature itself, Hansen writes:

[T]he 12-month mean global temperature likely will pierce the 1.5°C warming level before this time next year.

About the rate of increase in global temperature, he says this:

Global warming between 1970 and 2010 was 0.18°C/decade (Fig. 2), but the rate increased to 0.24°C/decade between [1997 and 2016]. … We anticipate acceleration of the long-term global warming rate by at least 50%, i.e., to at least 0.27°C/decade.

Increased energy imbalance (EEI)

About Earth’s energy imbalance, Hansen says:

The leap of global temperature … is fueled by the present extraordinarily large Earth’s energy imbalance (EEI). EEI is the proximate cause of global warming. The large imbalance suggests that each month for the rest of the year may be a new record for that month. We are entering a new climate frontier.

When the first author gave a TED talk 10 years ago, EEI was about 0.6 W/m², averaged over six years (that may not sound like much, but it equals the energy in 400,000 Hiroshima atomic bombs per day, every day). Now EEI has approximately doubled.

Here’s a chart of that imbalance from Hansen’s recent paper, “Global warming in the pipeline”:

The mean energy imbalance for July 2005 to June 2015 was 0.71 Watts per square meter, applied over the entire surface of the earth. (A Watt is a measure of the rate of energy transfer.) This means that 0.71 more Watts of sun energy were absorbed by each square meter of the earth than were thrown back into space.

That imbalance is increasing. Note the rate for March 2020 to Feb 2023 was 1.33 W/m2. Almost double. The imbalance isn’t just bad; it’s increasing.

Greater equilibrium climate sensitivity (ECS)

About equilibrium climate sensitivity, Hansen writes:

The recent revelation (Global warming in the pipeline) from paleoclimate data that equilibrium climate sensitivity (ECS) is 4.8°C ± 1.2°C for 2×CO₂ implies that clouds provide a strong amplifying climate feedback, as, without cloud feedbacks, ECS would be ~2.5-3°C for 2×CO₂.

This requires a little explaining. Imagine throwing a basketball against a wall from six feet away with a well-defined force. ECS is, in that metaphor, a measure of how far back the ball bounces, all other things being equal.

If sensitivity is low (a less “bouncy” ball), the response will be small, and the ball will hit the ground maybe two feet from the wall. But if sensitivity is high (a very bouncy ball), it may go flying back, landing maybe five feet from the wall, or eight, or ten.

Equilibrium climate sensitivity says, if you suddenly double atmospheric CO2 (the "well-defined force”), at what higher temperature will the climate system stabilize and reach equilibrium (the “bounce”)?

“ECS = 3°C for doubled CO2” means global warming will stabilize, come to rest, at 3°C higher than it was before the doubling. “ECS = 5°C for doubled CO2” means the system will come to rest at 5°C higher.

And here’s the application. We’re fast approaching doubled atmospheric CO2 since our emergence as a species:

Source: keelingcurve.ucsd.edu

How far will the climate ball bounce? Will we just get 3°C of warming? This is what the climate science community has been assuming for a long time. See here for one example. Keep in mind that three degrees of warming would still be “devastating” according to most accounts.

Or will we get more?

Hansen puts equilibrium climate sensitivity (ECS) at 4.8°C ± 1.2°C — 60% greater than most people now assume. A very bouncy ball indeed.

The world through 2100

Here's what constant warming of 0.27°C per decade looks like through 2100:

Notes:

• I assume we’re at +1.5°C now, which I think is right if we stop finessing the global warming start date.

• I also assume a constant warming rate, not an accelerating one. That’s a generous assumption. See the graph at the top — global energy consumption and global CO2 emissions — for why. Or just consider the greed of those who run world governments.

• Note these are transient temperatures. There’s no guarantee the world won’t continue to heat past 2100.

This is certainly not the world our policymakers, those who control world governments, are anticipating. 

But it's the world your child will live in. If she was born in 2020, she'll see three degrees warming when she's 55.

Hansen’s conclusion

Hansen ends on a note of hope, but not a strong one:

That does not mean that the problem is unsolvable. It is possible to restore Earth’s energy balance. Perhaps, if the public finds the taste of the new climate frontier to be sufficiently disagreeable, we can begin to consider the actions needed to restore a propitious climate.

The problem isn’t his prediction of public awakening. The public will certainly wake. The problem is that the public’s not in charge. Yet.