Monday, December 14, 2015

The Paris Climate Conundrum — Three Facts and a Question


He's been to London and to Gay Paree. A fine live performance (source)

by Gaius Publius

I'll publish a fuller analysis of the Paris climate agreement in due time — yes, climate negotiators in Paris did reach an agreement — but for those fresh to the news, I'd like you to put three facts together, then ask a question. Note: This is not a "give up" post. It's a "what the right next move" post. First, the three facts. 

1. World Leaders Agree — Two Degrees Warming Is Too Much

I'll let Bill McKibben tell this part of the story:
In the agreement, the world promises to hold the rise in the planet’s temperature to below 2 degrees Celsius. Heck, it promises to aim for 1.5 degrees, which is extraordinary. It’s what actually needs to be done; if we succeeded, it might just head off complete calamity. (We’re now at 1 degree above average pre-industrial temperatures, and considering what that’s already done in terms of melt, flood, and drought, 1.5 C will still be trouble, but maybe manageable trouble.)
He quotes the preamble to the Paris agreement (pdf):
Emphasizing with serious concern the urgent need to address the significant gap between the aggregate effect of Parties’ mitigation pledges in terms of global annual emissions of greenhouse gases by 2020 and aggregate emission pathways consistent with holding the increase in the global average temperature to well below 2 °C above pre-industrial levels and pursuing efforts to limit the temperature increase to 1.5 °C …
So that's fact one, and your first major takeaway. World leaders want to hold global warming to "well below 2 °C above pre-industrial levels" and are shooting to "limit the temperature increase to 1.5 °C".

2. If We Stop Emissions Today, 1.5 Degrees Is Still Guaranteed

If your car is moving at 60 mph and you slam on the brakes, will it stop instantly? Of course not. It will continue to move a certain amount. That "certain amount" in the world of DMV tests is called the "braking distance" for a given speed. You'd be foolish not to take it into account. If you put take a roast out of a hot oven and set it on a cool surface, it will continue to cook for a while, and a meat thermometer would show that. (Same with your hand, by the way, if you touch a hot stove. Done that.)

In the climate world, the tendency to continue to cook is called "in the pipeline" warming, and it reflects what they call "climate latency" — the lag between a force applied (a single-pulse emission of a greenhouse gas, say) and the final effect on surface temperature after equilibrium is reached. It's the temperature at equilibrium that counts, since that's the world we'll be living in. (Other temperatures, such as "global warming by 2100," are called transient temperatures, since they're on the way to something else.)

Turns out, if we stop today, most best-estimates of the equilibrium temperature — the temperature after everything still "in the pipeline" is accounted for — is 1.5°C. Let's look at just a few of the people saying this:

Scientific American (my emphasis throughout):
It is still difficult to say how much temperatures will rise by 2050 or 2100 due to the carbon dioxide that is already in the atmosphere known as the warming in the pipeline. There is a lag between any rise in CO2 levels and the heating that results, so the planet is locked in to further warming and to the chief repercussions such as further sea level rise. But the IPCC has released good estimates of the pipeline: the best case is that the average global temperature at the Earths surface will rise 1.5 degrees C by 2100, compared with 1990 levels. The worst case is 4.5 degrees C, and the most likely case is 3 degrees C.

In his own assessment of the numbers, Dana Nuccitelli, a physicist who writes at the Skeptical Science blog known for deep analysis of these matters notes that the 1.5 degrees C case would only be possible if the world stopped increasing emissions by 2020 and then began reducing them by 3.5 percent a year. As he notes, that scenario involves extremely aggressive greenhouse gas emissions reductions.
Skeptical Science:
[Climate skeptic (!) Christopher] Monckton, on the other hand, is calculating how much surface warming remains "in the pipeline" from the CO2 we've already emitted, due to the thermal lag of warming the oceans, and the fact that there is still a planetary energy imbalance. We can calculate this by instead plugging in the current CO2 concentration (390 ppm [at that time]) into the formula above:

dT = 0.8*5.35*ln(390/280) = 1.4°C

Since the surface air has warmed about 0.8°C above pre-industrial levels thus far, there remains approximately 0.6°C warming "in the pipeline" from the CO2 we've emitted to this point, roughly consistent with Monckton's calculations (0.7°C).
That was written in 2011, and we've certainly emitted a lot more since then, so the "pipeline"' number has moved. If you recalculate the formula with 400 ppm instead of 390, you get 1.526°C. Note that our emissions are also accelerating.

Finally, Dr. Michael Mann, from an interview I did with him in October 2014 (listen here). His best estimate of the "in the pipeline" number gives us a Stop Now equilibrium temperature of ... 1.5°C. Remember, the final number depends on the climate system reaching equilibrium — "settling down," in other words, after period of imbalance due to the force of new atmospheric CO2.

3. If We Never Stop Emissions, the In-the-Pipeline Number Keeps Going Up

And finally, to just say the obvious, the equilibrium number keeps going up with each new ton of atmospheric CO2 we add. Global carbon emissions are currently at 10 GtC (gigatons of carbon) per year. Our atmospheric concentration (ppm) is at 400 ppm and rising at more than 2.1 ppm per year. Our current "stop now" equilibrium number is already 1.5°C. We haven't stopped, and Paris, so far, isn't an agreement to stop emitting CO2, simply to slow down.

Those are simply facts. So...

Question: What Should We Do In Response?

This is the question. I don't mean "what should world leaders do in response?" We know what they will do — the best the owners of the world's wealth will let them.

The question is — what should we do, the ones who will be left behind when they take their corporate jets to Sweden and Canada forever, to inhabit their new, climate-safe homes and leave the wreck to us? We have time — I give us a window of 5-10 years unless truly catastrophic tipping points are reached. What should we do with that time?

I think the climate movement is clear on half the answer: We should do everything we can. I don't think it's as clear on the schedule: The press for the end result — zero emissions — has to start immediately and be pursued more aggressively than the "free market" will allow. Otherwise, the math is against us.

With that in mind, I challenge you — what next steps would you consider, assuming you chose to help, if you knew we had five years, and only that?

As I said, I'll have a fuller analysis of Paris in due time. These are the big ones, though; three facts and a question. (If your answer to the question tends toward the electoral, you might consider supporting this guy, the only viable candidate who seems to get it; adjust the split any way you like at the link.)


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At 11:42 AM, Anonymous Lewis Gannett said...

1.5 equilibrium "if we stop now" doesn't include a "global dimming" bump, right? "Dimming" refers to blocked sunlight because of particulates (soot mostly I think, also the occasional volcanic eruption) suspended in the atmosphere. I see different numbers about how much warming uptick we'll get if particulates clear out (pollution control, industrial collapse). Is there a recognized authority on this? Gaius: thank you for clarifying "in the pipeline." I've been wondering about this with reference to the professed Paris 1.5C cap. It's disingenuous to talk about a cap that's already been reached, more so if the cap has been exceeded.

At 10:40 AM, Blogger Gaius Publius said...

Lewis, you're right about the numbers being tighter if we get off of coal, because some coal particulates ("aerosols" in the literature) have a cooling effect ... some of them reflect the sun's energy back into space.

Estimates of how much of an effect depend on a lot of assumptions, but you can get Michael Mann's take on that here:

My explainer of this is here:

Bottom line, for Mann we get to 450 ppm and 2 degrees "on the ground" in about 2036 under the most likely scenario. (For reference, we're increasing at about 2.1 ppm/year at the moment and we're at 400 ppm CO2.) But if we get off of coal, the ppm we need to hold at is ... 405, just about where we are now.

One person's view, but not a nobody on this subject.




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