Oceans Don’t Forget

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Ocean Warming

By David Kattenburg

Earth’s oceans are warming at a remarkable rate, a recent scientific report reveals.

It’s perfectly predictable.

 

Almost three quarters of Earth’s surface is covered in oceans, accounting for ninety-seven percent of the planet’s liquid water endowment. An additional 1.7% of Earth’s aqueous inventory is frozen away in its cryosphere — continental ice sheets and glaciers, permafrost and sea ice.

Marshall Islands, central Pacific

Water absorbs lots of heat, and takes its time heating and cooling. In so doing, the Atlantic, Pacific, Indian and great polar oceans, and adjoining terrestrial components of the cryosphere, absorb vast quantities of heat energy, buffering adjoining terrestrial climate.

Earth’s oceans are estimated to have absorbed over ninety percent of the atmospheric heat humans have generated, relentlessly pumping earth-warming carbon dioxide out of their stacks and tail pipes, along with more powerful methane and nitrous oxide through agriculture and other land use changes.

The total amount of heat oceans have absorbed is staggering, quantified in zeta joules. One ZJ is the number one with twenty-one zeros in front of it.

Zeeland, the Netherlands

Thanks to water’s high heat capacity — its heat buffering capacity — this vast amount of absorbed heat has yielded a minute degree of warming: an average 0.075 degrees Celsius in the top two thousand-meter column, with respect to the 1981-2010 period.

Barely a tenth of a degree may seem small, but it’s been arrived at with great confidence, based on a large number of readings throughout the oceans.

According to the authors of this report, “Record-Setting Ocean Warmth Continued in 2019,” oceans have never been warmer than this past year. The past five years have been the warmest years on record.

Warm waters expand, compounding sea level rise due to terrestrial ice melt. The current rate of sea level rise is estimated at 3.1 millimeters/year. Once again, the value seems low. But small, incremental increases are sufficient to drive storm surges and “sunny day flooding.”

South China sea beyond Vietnamese estuary

No one acknowledges this more publicly than the large insurance companies, whose exposure to the financial costs has been as brutal as a rising tide.

Ocean warming is not uniform. The Atlantic and southern polar oceans have been heating up the fastest.

Warm waters circulate, moving the heat around. El Nino, the Indian Ocean dipole and the notorious Pacific ‘blob’ are well known examples of heated surface waters drifting this way and that.

In a classic positive feedback loop, wherever they pool, surface ocean waters warmed by a warming atmosphere turn around and warm the atmosphere above them, releasing both sensible and latent heat — the latter in the form of water vapour, highly energetic, as anyone who’s stuck their finger or soft forearm at the mouth of a steam spout knows.

For each degree of atmospheric warming (Celsius), the atmosphere holds seven percent more water.

Crossing the Mekong

Warm waters move around. Wherever they pool, major energy imbalances ensue: marine heat waves, violent hurricanes and monsoons. Think of the monumental snow dump St. John’s, Newfoundland is now shoveling its way out from beneath.

Hurricane Harvey generated two meters of rainfall for Houston and the Gulf of Mexico coast in 2017.

Hurricane Florence deluged the Carolinas in 2018. Jakarta has just experienced torrential downpours and flood.

As warm waters slosh from one side of the ocean to the other, surface waters on the side they sloshed from grow cool, air dries and droughts ensue. Beneath an oppressively hot, dry atmosphere, wildfires break out. Increasingly strong El Nino and more ‘positive’ Indian Ocean dipole events appear to be linked to wildfires in western North America and eastern Australia respectively. They testify to the future as Earth’s surface warms.

It gets worse. Ocean warming has been a catastrophe for marine biodiversity.

View of Caribbean from Caye Caulker

In surface waters that rarely shift from summer to winter by more than two degrees Celsius, sudden spikes of up to three degrees wipe out macro and microrganisms on an epic scale. Whales, seals, otters and sea birds have all affected. The notorious Pacific blob reportedly wiped out a hundred million cod.

Earth’s coral reefs, nurseries and breeding grounds for legions of marine organisms, are being bleached white by warm waves — damage compounded by waters acidified by rising CO2 levels.

And warm waters hold less oxygen, due both to a drop in oxygen solubility, and reduced mixing as warm water columns stabilize. Marine organisms already stressed out by the heat suffocate.

As if all these details weren’t dismal enough, oceans have a long memory. Water — recall — stores lots and lots of heat, holding heat for a long time and releasing it slowly. Earth’s oceans are its climate memory, storing and registering all the changes humans have introduced at the surface.

Courtesy of Lijing Cheng

Ocean “commitment,” it’s called. Even if we cap warming at two degrees (very unlikely; the consensus is that Earth is hurtling for three or four degrees, post-industrial), atmosphere-ocean ‘coupling’ guarantees that impacts will accumulate over centuries. Perhaps accelerate.

Kevin Trenberth is one of the authors of this study just published in the journal Advances in Atmospheric Sciences. Trenberth is a Distinguished Scholar at the National Center for Atmospheric Research, in Boulder, Colorado, currently on sabbatical in New Zealand.

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