Hansen's Courage

I hope the IPCC is listening this time ...

Climate Science doyen James Hansen doesn’t mince his words. And he’s not scared to speak out against the collective wisdom of the IPCC either. But, unlike climate deniers, he thinks they’re overly optimistic. He explains why here. I respect his views enormously.

He points out that the gap between the rose-tinted IPCC story and his reality is growing alarmingly, and that we’re currently on a path that more closely matches their most extreme scenario (RCP8.5), than the moderate path (RCP2.6) they prefer to emphasise. The point is illustrated in the plot below, which shows how ‘climate forcing’ from greenhouse gases has changed over the last half century, and how it might be expected to change in the future. Note that it’s still increasing despite all the talk.

Updated annual growth of climate forcing by greenhouse gases. The ‘MPTG + OTG’ category includes Traces Gases like CFCs that are controlled under the Montreal Protocol and Other Trace Gases.

This ‘climate forcing’ is just the difference between incoming energy from the Sun received by planet Earth, and outgoing energy emitted by from Earth, measured in Watts per square meter (Wm-2). From the tapering down of the red region in the plot, you can see that least the Montreal Protocol is doing its bit. Without that landmark agreement, the curves would already have crossed the upper limit in the plot.

What does that imbalance of 0.05 Wm-2 mean as far as global temperatures are concerned? Well, the RCP2.6 scenario shown there (the lowermost curve in yellow) is the one that, if followed, would lead to a temperature rise of 2C. Clearly, that’s not going to happen. At current rates, the projected temperature rise will far exceed that. The gap between that and reality has grown over the last few years. It’s already 0.03 Wm-2, and is rapidly increasing. It’s also increasing compared the intermediate scenarios RCP4.5 and RCP6.0.

Hansen makes the point that temperature changes over the next few years - including the next El Niño - will tell us if the accelerated warming continues, or whether the more optimistic continuation of the increases since 1970 path is followed. To me, it looks as if the rate of increase in the last few years has been much larger than over that longer period, so I’d be surprised future increases didn’t closely match the yellow band. In that case, that 2C temperature rise could be reached sometime next decade. Either way, it looks as if we’ll be well above the 1.5C temperature change by mid-century, with no signs of abatement.

Global temperatures relative to 1900.

It's time for less talk and more action.

But let’s end with some better news. A recent report on the rapid uptake of solar energy tells me that there’s still just a chance that we can stay below that yellow band. Energy sources are now transitioning rapidly in the right direction, though not entirely without their problems.

Note added 26 May 2023: Thanks to my old colleague Keith Lassey for bringing the incorrect units to my attention. The “Energy” imbalance is really a Power imbalance, since its measured in Wm-2. The “per year”on the y-axis of the first graph is not part of the units. Its just to remind the reader that these values are yearly means.