Unprecedented warming could be ocean feedback

“Just like this year, last year the heat wave extended from parts of India to Bangladesh and Myanmar, and all the way to Thailand. This year it went further east, into the Philippines. So, it's the same pattern,” said Prof. Krishna Achutarao, of the Indian Institute of Technology. “I do not particularly buy into this idea that El Niño is the cause.”

That is the burning question. A heat wave is a random phenomenon that comes and goes in certain seasons for a period of some days. A climate feedback is forever.

The average global temperature for each of the last 11 months has been the hottest the world has experienced in that month.

So, obviously something big is happening, but what? Is it just El Niño, a heating of the surface waters of the eastern Pacific that happens every three to seven years? That would be nice, because it would mean it's cyclical and will go away in due course.

Or, is it confirmation of climate scientist Jim Hansen's claim the average global temperature is going to jump half a Celsius degree? He says new rules on pollution are cutting back hard on the sulphur dioxide emissions that used to reflect a lot of sunlight back into space and therefore cool the planet.

Or have we triggered a big feedback in some natural system of which we were not aware? There's about a dozen potential tipping points about which we do know — the collapse of the West Antarctic ice sheet, the melting of the permafrost, a switch from rainforest to savannah in the Amazon — but there may be a few about which we don't know, yet.

We may be about to find out where the limit is, and it could be the mother of all feedbacks.

So, which is it? It's unlikely El Niño, because this one was not particularly strong. Besides, it peaked in December and has been fading since, while global temperatures go on breaking records.

Hansen's proposed explanation is a contender, because the “brown clouds” that used to hang over big Chinese cities and the “ship track” clouds from the exhaust gases of 60,000 giant tankers and container ships did reflect enough sunlight to have a significant cooling effect. Cleaning up those emissions was bound to drive up the temperature.

Alas, the dates don't match very well.

The emissions from Chinese factories and ocean-going ships were reduced during a period of about 15 years, whereas the non-linear jump in average global temperature began a year ago. Moreover, some scientists doubt the amount of cooling that was lost is big enough to explain the scale of the heating.

This leaves us with the least desirable explanation. The heating humans already have caused carries us across a tipping point we cannot see, and unleashes a feedback: warming from non-human sources that we cannot turn off.

The likeliest candidate for a new mystery feedback is the world's oceans. Since we began burning fossil fuels in a big way two centuries ago, they have absorbed around a quarter of the carbon dioxide humans emitted. More importantly, they have soaked up about 90 per cent of the excess heat.

Now, they may be giving some of it back. In the last 13 months, the average sea surface temperature worldwide has soared. According to the European Union's Copernicus Climate Service, it is now at an all-time global high of 21.09 C.

There was not enough data about deep ocean currents to put the ocean heat sink on most climate scientists' list of potential feedbacks. However, many always feared there would be a limit to how much heat the oceans could contain.

We may be about to find out where the limit is, and it could be the mother of all feedbacks. Or maybe it will turn out to be a false alarm.

The fact we don't even know which yet illustrates the depth of our ignorance, and the scale of our peril.