It is my opinion that humanity’s response to climate change, going forward, should be guided by the assumption that it’s going to keep warming for at least a century. If we can get things under control faster than that, it’ll be a nice surprise, but it would be dangerous and reckless to assume that we’ll be able to do it. That means that we cannot simply focus on reducing emissions. We must also be working to prepare for the warming that we know we can no longer avoid. There are a number of reasons for this belief. Feedback loops like methane from melting permafrost are part of it, as is my view of global politics, but a big part is the fact that air pollution has been keeping the temperature lower than it would otherwise be.

Basically, some air pollution reflects sunlight back into space, reducing the amount of solar energy that actually reaches the planet. As we reduce air pollution, more sunlight hits the planet, and the temperature rises more quickly. This is something we’ve known about for a long time, but apparently worldwide efforts to reduce air pollution since 2000 have been successful, and that has caused a measurable increase in the planet’s temperature:

In a new international analysis, Professor Johannes Quaas, a meteorologist at Leipzig University, and colleagues from across Europe, China, and the US have now documented robust evidence of this effect on the climate of improved air quality. “We analysed data from NASA’s Terra and Aqua satellites. They have been providing comprehensive satellite observations of the Earth since the year 2000, measuring incoming and outgoing radiation, but also clouds and aerosol pollution. The latter has decreased significantly across North America, Europe and East Asia since 2000,” says Professor Johannes Quaas, lead author of the study, which was initiated in a meeting by the two European research projects CONSTRAIN and FORCES.

This has also reduced the cooling effect of aerosols. Compared to the year 2000, it has led to an increase in the warming effect that is up to 50 per cent of the one by CO2 increases in the same period. This means an acceleration of the drivers of global warming compared to the previous period. “Our study should not be interpreted to mean that we should now be emitting more aerosols to cool the climate. On the contrary: aerosols are harmful to human health and the environment, which is why we need to keep reducing emissions,” Quaas concludes. And it is why air quality legislation has become increasingly stringent since the 1970s and is being implemented by more and more countries. Professor Quaas and his colleagues on the new study stress the ever more urgent need for rapid and strong reductions in greenhouse gas emissions.

This effect will continue as we keep reducing air pollution. As the study authors say, reducing air pollution is very important. Not only will it save lives under normal conditions, but the higher temperatures of the coming decades will make air pollution much more dangerous than it already is. While geoengineering projects could change the equation in theory, relying on them to save us seems like a bad idea; at best, they would kick the can down the road. As I’ve said before, I think we’re likely to need the time that would buy us, but only if we’re actually using it to end fossil fuel use and to adapt to those change that are set in stone.

There was a little leeway in the 20th century, but we blew that. Things are more volatile now, and we’re out of time. Still, it’s good that air pollution has been going down, and it’s good to have confirmation that our understanding of how things work is accurate. It’s going to be a bumpy ride no matter what, but we do know what we need to in order to get through it.

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