Those Other Tipping Points That Go Unnoticed

It's become customary in climate change reports to mention "tipping points." Anyone who has learned to handle a canoe knows there is a point at which the vessel lists far enough left or right that water begins to pour in over the gunwale at which point the canoe tends to go right over.  In the context of climate change, tipping points usually refer to natural feedback loops that take many forms including the loss of Arctic sea ice, the melting of ice caps and the retreat of the glaciers, the thawing and release of once safely sequestered CO2 and methane. The whole idea about holding man-made global warming to 2 degrees Celsius, 1.5C if possible, is to avoid triggering too many of these feedback loops that could lead to runaway global warming and utter catastrophe.

Rarely do we think of our oceans, that cover 70 per cent of the Earth's surface, in the context of tipping points.  Yet oceans are the repository for much man-made warming and man-made CO2. The oceans absorb half of our greenhouse gas emissions and 90 per cent of the heat they generate.  That leads to two changes - ocean acidification and ocean warming.

Ocean acidification is a tipping point we don't talk about in polite company. We know enough to deeply worry some scientists because the past few decades have taught us that climate changes are not linear. They can be abrupt and very fast in their onset triggering other changes (knock-on effects) that can catch us unprepared.

While ocean warming and the effects that may have on everything from sea level rise to ocean currents and circulation, ENSO (the el nino southern oscillation) and PDO (the Pacific decadal oscillation), the "Blob" of unduly warm water in the North Pacific are far better understood today than they were in the not distant past there's an enormous amount yet to learn.

Atmospheric temperature rise generally mirrors atmospheric greenhouse gas loading. Oceans, however, have a more complex warming pattern. Surface heat energy behaves much differently than the heat that reaches the deep ocean. What we've discovered in recent years is that a lot of the heat the oceans have been absorbing lately has gone to the deep ocean.

The reason global warming has been relatively tame over the past two decades, despite all the severe weather events of increasing frequency, intensity and duration, is because so much of the heating has gone into the ocean depths. It's not gone for good. The first law of thermodynamics, the law of conservation of energy, holds that energy can neither be created nor destroyed, merely transformed from one form to another. Put simply, that deep ocean "heat bomb" is waiting for a change in surface wind patterns to come back to the ocean surface and be released back into the atmosphere.

The oceans may be reaching a saturation point. Science has found that the oceans are losing their capacity to absorb atmospheric carbon and heat. They're getting full. That's physics.

A new report finds that, for the past 150 years, the heat energy from global warming absorbed by oceans has been the equivalent of 1.5 nuclear bombs per second. That's averaged out over the last 150 years.

A Guardian calculation found the average heating across that 150-year period was equivalent to about 1.5 Hiroshima-size atomic bombs per second. But the heating has accelerated over that time as carbon emissions have risen, and was now the equivalent of between three and six atomic bombs per second. 

“I try not to make this type of calculation, simply because I find it worrisome,” said Prof Laure Zanna, at the University of Oxford, who led the new research. “We usually try to compare the heating to [human] energy use, to make it less scary.” 

She added: “But obviously, we are putting a lot of excess energy into the climate system and a lot of that ends up in the ocean,. There is no doubt.” The total heat taken up by the oceans over the past 150 years was about 1,000 times the annual energy use of the entire global population.

There are big questions, plenty of them, and few concrete answers, at least at this point.  The heat energy we're putting into the ocean systems is going up while the capacity of the oceans to absorb heat energy is declining.  What happens when the oceans absorb less of our atmospheric heat? What does it mean for the atmosphere if, instead of 90 per cent, the oceans are able to absorb just 80 per cent or 70 per cent of the heat we're pouring into the atmosphere? And what happens to that deep ocean heat energy when/if it is returned to the surface and released into the atmosphere?

Humans, of course, are terrestrial creatures and it is only natural that we tend to see climate change in the context of its terrestrial impacts - tornadoes and hurricanes, sea level rise and coastal erosion/salination, heatwaves, droughts and floods. Yet our wellbeing, even in the most landlocked areas, is more dependent on the health of our oceans than most of us imagine. And so the oceanic tipping points go generally unnoticed and what's out of sight is indeed out of mind and off the political agenda.  Hell, we can't get past our squabbles over a penny ante carbon tax. As Professor Zanna remarks, it's "worrisome."