Oceans cover more of the planet than anything else. So it makes sense that we need to know what’s happening to them to understand how humans are changing the climate.
If you follow climate science, you’d be forgiven for being a little confused recently by different news reports suggesting the oceans are warming , slightly cooling or doing nothing at all.
So are the oceans hotting up or aren’t they? And how does what happens beneath the waves influence what we feel up here on earth’s surface? Here’s our top to bottom look at the oceans and climate change.
More heat in, less heat out
Scientists have known for centuries that greenhouse gases in the atmosphere, such as carbon dioxide and methane, trap heat and warm the planet. This is known as the greenhouse effect.
Scientists use satellite measurements to monitor how much of the sun’s energy enters earth’s atmosphere. A different set of measurements tells them how much finds its way out again.
The difference between those numbers is increasing, which means the earth is trapping more heat than it used to. And that means the planet must be warming.
A hiatus in surface warming
An interesting question is why temperatures at earth’s surface – that’s the air above land and the very top of the ocean – don’t always reflect what’s happening to the planet as a whole.
Over the last 15 years or so, surface temperatures have risen much slower than in previous decades, even though we’re emitting greenhouse gases faster than we were before.
This is what’s become known as the “hiatus”, “slowdown” or even “pause” in surface warming.
This raises an obvious question. If earth is gaining heat but the surface isn’t warming very much, where is the heat going instead?
Where does the heat go?
The scientific literature is full of discussions about where the extra heat might be ending up.
We tend to be most interested in what temperatures at earth’s surface are doing, because that’s where humans live.
But actually only about one per cent of trapped heat stays in the earth’s atmosphere.
As the oceans absorb more than 90 per cent of the heat the planet traps, it makes sense to begin looking there for explanations of the changes we’re seeing at earth’s surface.
Rearranging heat
As the biggest absorber of heat, it make sense that understanding climate change should mean understanding the oceans.And the oceans aren’t an amorphous blue blob. Piecing together what’s happening at different depths and in different parts of the globe is critical.
The hiatus is likely to be a product of several factors, each carrying its own uncertainties. Unravelling how different influences compare will take some time yet – if it’s possible at all.
There are still gaps in scientists’ knowledge of how the climate system behaves in response to greenhouse gases, and how natural factors alter that behaviour from one decade to the next.
But the bottom line is that understanding what’s happening to surface temperatures means focusing not just on the parts of the climate system we’re most familiar with, but also on how the earth rearranges heat out of sight.