Non-linear climate emergency

If you spend a lot of time talking to scientists about climate change, there's one word you'll hear time and time again, and yet it's hardly ever mentioned in the public discussion of climate change. The word is "non-linear."

Most people think of global warming as an incremental thing. It may be inexorable, but it's also predictable. Alas, most people are wrong. The climate is a very complex system, and complex systems can change in non-linear ways.

In other words, you cannot count on the average global temperature rising steadily but slowly as we pump more and more greenhouse gases into the atmosphere. It may do that - but there may also be a sudden jump in the average global temperature that lands you in a world of hurt. That may be happening now.

"We are moving into uncharted territory with frightening speed," said Michel Jarraud, secretary-general of the World Meteorological Organization, last November. He was referring to the fact that global warming is now accelerating in an unprecedented way.

2014 was the hottest year ever - until 2015 beat it by a wide margin. 2016 may beat that record by an even wider margin. It was the hottest January ever - and then the average global temperature in February was a full fifth of a degree Celsius higher than January. 

That was a huge jump, since the "average global temperature" is an average of all the temperatures over the seas and the land in both the summer hemisphere and the winter hemisphere. It is normally a very stable figure, changing no more than a few hundredths of a degree from year to year.

But March was not only hotter than February. It was hotter by an even wider margin than February was over January. Indeed, each of the past 11 months has beaten the highest...