Monday, September 12, 2016

As Oceans Continue to Warm, Consequences Grow More Dire, Study Says

By Nicholas Kusnetz
Sept. 7, 2016

The coming century will likely bring dangerous and dramatic changes to the planet's oceans, with ever strengthening storms, annual bleaching of almost all coral reefs, loss of biodiversity and severe impacts on fisheries and aquaculture unless humans slash greenhouse gas emissions.

These are the findings of a comprehensive review of the effects of warming oceans, issued Monday by International Union for the Conservation of Nature (IUCN) and compiled by more than 80 scientists from 12 countries. The report chronicles how the seas have absorbed the vast majority of the excess heat trapped in the atmosphere by carbon emissions in recent decades, and how that energy is already altering the planet's weather systems and ecology, from deep ocean trenches to alpine glaciers.

"Ocean warming is one of this generation's greatest hidden challenges—and one for which we are completely unprepared," Inger Andersen, IUCN's director general, said in a statement. "The only way to preserve the rich diversity of marine life, and to safeguard the protection and resources the ocean provides us with, is to cut greenhouse gas emissions rapidly and substantially."


In many ways, the oceans have helped mitigate the effects of carbon dioxide emitted into the atmosphere. They've absorbed more than 90 percent of the excess heat since the 1970s. If all the warmth that went into the top 1.25 miles of the ocean between 1955-2010 had instead gone into the air, the earth would have warmed 36 degrees Celsius.

[I looked this up in the original document, and that's right, a rise of 36C = 65F!]

Unfortunately, the report explained, the oceans are beginning to catapult that heat back into the atmosphere, with often dire consequences.

The unusually intense El Niño weather pattern in recent years—which has contributed to strong monsoons, droughts and wildfires across the globe—may be an example of a sudden release of stored energy to the surface in the Pacific Ocean. The seas are likely to warm 1 to 4 degrees Celsius by 2100, and models suggest that will translate into stronger, more frequent El Niño events, more intense hurricanes and a general amping up of the hydrological cycle, which brings moisture into the atmosphere from the ocean and then back down as precipitation.


The study, which the authors said is meant to build on the 2013 Intergovernmental Panel on Climate Change report, covered other issues as well, including ocean acidification and the potential links between warming waters and increased spread of tropical diseases. If that wasn't bad enough, the report also warned that increased ocean temperatures could unleash some 2.5 billion tons of methane hydrate—a potent greenhouse gas currently frozen into the sea floor.


The original study. It is a pdf, and I don't have time to fix the short line lengths.

[from p. 375]

Ocean warming and associated stressor

As stated above around 90% of the extra heat now
trapped within the earth system is now in the ocean
(Johnson and Lyman, 2014), a consequence of the
vastly higher heat capacity of the ocean relative to the
atmosphere and the rapid transfer of water that has
recently been in contact with the atmosphere into the
deep ocean interior.

[from p. 3780 Deoxygenation
Ocean deoxygenation is occurring now, partly as a direct
consequence of the warming (that makes oxygen less
soluble in warmer waters and which is ongoing) and partly
as a consequence of the reduced circulation rates (that
decrease the transport of oxygen into the subsurface
ocean from the atmosphere) (Keeling
et al
., 2010). The
latter appears to be happening as predicted by state-
of-the-art IPCC class models although not quite at the
same rate. Reduced oxygen levels have been observed
in much of the ocean (e.g. the Mauritanian upwelling by
west Africa, the Benguela upwelling by south-west Africa,
the Arabian Sea, the Peruvian upwelling, the equatorial
Pacific, Ulloa
et al
., 2012) and it seems likely that these
areas will expand. Aside from the direct consequences
of these zones expanding (fish mortality, species shift,
etc.) there are at least two important consequences of
these expansions which have the capacity to impact on
ocean functioning in a major way.

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