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The IPCC doesn’t believe its own models. The 1.5C ambitious target = 400ppm. We’re already there!

Apparently we want to set Earth’s climate control knob at 1.5C above the Little Ice Age. If the IPCC is right, we can use cars, hairdryers and air-conditioners to do it. All we need to know is equilibrium climate sensitivity (ECS) and then we can work out the right atmospheric level of CO2 to aim at. Easy, right?

Now I don’t believe the IPCC claims, but the IPCC believes the IPCC, and therefore they’ve done this calculation. It’s what the whole Paris convention was for, eh? But something doesn’t add up. If the climate modelers are right, and equilibrium climate sensitivity is 3C, the CO2 concentration we need to aim for is … wait… 400 ppm. How many years have we got to change the whole “human emissions” equilibrium and discover 100% clean energy? Answer: No years.

If CO2 is the dominant climate driver, we are already at the “max” set point that 40,000 people in Paris just decided was  the holy grail new ambitious target. Turn off the lights, stop the planes, get on your bike. The warming is in the can already.

Bear in mind that it is “equilibrium” climate sensitivity, so the warming is not all here yet. We’ve warmed some 0.9C since 1910 (and something before that too) , but the rest of the heat  is trolling about in the ocean or somewhere for a few more decades until the system settles down.

Strangely, the rejoicing UN crowd in Paris didn’t mention that the 1.5C target means switching it all off, or doing a massive terraforming kind of global engineering project to pack away CO2 — and it really needs to start sooner than is possible, like, you know, 1990.

400 ppm means 1.5C warming doesn’t it?

It’s a simple equation. C is the CO2 concentration, and C0 is the pre-industrial concentration (280 ppm).Equation for calculating change in temperature from a given CO2 concentrationLately the IPCC has admitted that climate sensitivity could be a bit lower at at 2.5C. But even that doesn’t give us much breathing space to redefine western civilisation. If equilibrium sensitivity is 2.5C, then we are aiming for 430 ppm on the CO2-power-control-knob, which at the current rate will be reached by 2030. In other words, we have to keep global atmospheric CO2 below 430 ppm to limit warming to 1.5C above preindustrial levels. (That is, unless we have to keep it below 400ppm.) Global CO2 levels are rising relentlessly by around 2ppm a year. At this current steady rate of increase, the best case scenario is that we’ve got 15 years to become 100% “carbon neutral”.

Year CO2 (ppm) log2 (C/Co) Warming (ECS of 3°C) Warming (ECS of 2.5°C)
1800 280 0
2015 400 0.51 1.5° 1.25°
2030 430 0.62 1.8° 1.5°
2040 450 0.68 2.04° 1.7°
2047 465 0.73 2.2° 1.82°
2055 480 0.78 2.34° 1.94°
2060 490 0.8 2.4° 2.0°

The IPCC thinks the 1.5C ambitious aim is important. It’s written in four spots in the Glorious Paris Treaty. Here’s one:

Article 2 a. Holding the increase in the global average temperature to well below 2 °C above pre-industrial levels and to pursue efforts to limit the temperature increase to 1.5 °C above pre-industrial levels, recognizing that this would significantly reduce the risks and impacts of climate change;

What does it mean to pursue a target that we’re about to surpass, unless we stop Western Civilization (and East, North and South too)?

So either the IPCC is incompetent, or (golly) maybe the point of the 1.5C label is not really about “global temperature” at all. Think of it from a PR point of view.  1/ It implies we can control the climate. 2/ It looks like an advance on the 2C target. 3/Given that the warming has paused, it’s useful to shift those goal posts closer to where the ball keeps being kicked. ( ;- ).

Or maybe the UN are really serious about the 1.5C target, and they just haven’t done that first most obvious calculation?


*Climate Sensitivity means the equilibrium “sensitivity” to the assumed cause of global warming, CO2

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