Climate-change sceptics would have you think that global warming has paused, but this is only surface warming. Beneath the waves, heat is building.
Sceptics cite a clever bit of mathematical trickery where they "prove" that temperatures have not increased in the last 15 years. They then combine this with the fact that temperature increases in the last decade have not been as rapid as were predicted, and sell the narrative that global warming has paused.
This is done by taking a very warm point in 1998 and showing that this has not been exceeded by much in recent years. It's an easy way to distract from real debate. And it has led to sensational headlines that might lead people to think scientists are no longer sure that global warming is happening.
In part, it is the fault of trying to make science simple for the sake of journalism. We tend to interchange phrases like global warming and climate change to make things easier to read. This meant that in the 1990s and early 2000s the media reported on the increases in air temperatures. A slowing down of this increase – in the context of this simplified narrative – allows critics to then easily say global warming has stopped or has paused.
What all of this ignores is that a fraction – only 2% – of all the warming makes the atmosphere where we are hotter. The biggest chunk – 90% – is soaked up by the ocean. And until very recently we have not been very good at measuring the temperatures in the lower levels of our ocean. So we don't have records stretching far back that we can compare with, and we haven't known how much warming is happening deeper than 700m.
But the scary truth is that it has not. It is continuing to accelerate, and it is the rate of change that is the problem. Heat is, quite simply, energy. More heat means more energy being pushed into the ocean, which slowly increases its temperatures. By burning things we are pumping once dormant energy into this system. The greenhouse gases that are also released during this process then trap more heat in the atmosphere, accelerating the warming. This means more of the sun's heat—which previously used to escape back out into space—is trapped.
This increasing energy has been equated to how much energy would be released if we detonated four Hiroshima-scale atomic weapons every second. Although the world is quite big, that's a profound change cumulatively.
'Fifteen years of no warming'
Several recent studies have begun to look at where the heat is going. One of these, published in the peer-reviewed journal, Nature Climate Change, found that average surface temperatures have not increased at the predicted rate because we are experiencing more La Niña weather events.
This is an ocean phenomenon where more heat than normal is absorbed into the ocean, which keeps surface temperatures cool. The opposite effect, El Niño, was the predominant force in the 1990s. And 1998, the year sceptics use in their "15 years of no warming" arguments, was one of the strongest El Niño's in a century.
All this has scared scientists, and in these studies they have raised concerns about what happens when we go into another prolonged spate of El Niños. Then the current heat being pumped into the system will come out in surface air temperatures.
The fact is that human activity is creating energy. That energy has nowhere to go, and so is warming the planet. A warming planet means the earth systems that we have relied on to be relatively predictable are already changing.
In its most recent report on this, "Turn Down the Heat: Why a 4C warmer world must be avoided", the World Bank said increasing temperatures "will pose unprecedented risks for humanity". It also said climate change was happening already, and was being driven by human activity.
To say global warming has paused is to mislead people based on a fraction of information. What we need to be doing is putting less energy into the system than we are now and adapting to a changing climate.