Posts Tagged ‘ocean warming’

Warming the Deep Cold Ocean

Wednesday, November 27th, 2013

The global mean surface temperature has been increasing very slowly, if at all, for the past 10-15 years, even though levels of CO2 emissions continue to rise, sea levels continue to rise, Arctic ice continues to thin, and ocean acidification continues to increase.

Sea level measurements have become increasingly detailed and reliable (

Sea level measurements have become increasingly detailed and reliable (

Since global mean surface temperatures aren’t rising as expected, where has the heat gone?

We have known for a while that about 90% of the extra heat energy absorbed by the Earth goes into warming the seas, which then contribute in complex ways to increasing the global mean surface temperatures. So the missing heat has got to be somewhere in the oceans.

Dense, saline, cold water sinks in the North Atlantic and near the West Antarctic Peninsula, driving the global exchange of water and its heat (

Dense, saline, cold water sinks in the North Atlantic and near the West Antarctic Peninsula, driving the global exchange of water and its heat (

The slow global circulation of ocean water, known as the Global Conveyor but also as Thermohaline Circulation and more recently as the Meridional Overturning Circulation, plays a huge role in keeping the planet climate relatively stable and in general equilibrium.

What drives this global circulation? Sea water gets denser as it gets colder, reaching its maximum density not at 4 degrees C like freshwater, but at its coldest unfrozen state at -1.8 degrees C. Only in the very highest latitudes, in the North Atlantic and in the Southern Ocean near the West Antarctic Peninsula, does it remain saline enough and get cold and dense enough to sink into abyssal depths in the deep ocean basins 4km or more below the surface.

View from the South Pole of the Global Conveyor or Meridional Overturning Circulation (

View from the South Pole of the Global Conveyor or Meridional Overturning Circulation (

The sinking of this very cold and saline water drives the global circulation. The deep cold water flows slowly toward lower latitudes, rises or upwells for a variety of reasons and becomes the warmer surface waters, driven into familiar currents by winds and tides.

Very cold saline water (blue) sinks, flows along the basin bottom, is forced toward the surface (green) and then becomes the warm surface current (red) (

Very cold saline water (blue) sinks, flows along the basin bottom, is forced toward the surface (green) and then becomes the warm surface current (red)(

A great deal of data has now been gathered about the temperatures and salinity levels of ocean waters from all depths around the planet, including from the Southern Ocean that rings the Antarctic. They tell us that the deep ocean water mass around Antarctica, particularly near the West Antarctic Peninsula, is getting warmer and it is freshening. This warming and freshening of the deep cold water has now also been tracked north in all directions to around 30 degrees South latitude.

Deep cold water flows north toward the equator in all the oceans (

Deep cold water flows north toward the equator in all the oceans (

So that is what has changed. Much of the missing heat, along with West Antarctic glacial melt water, has gone into the deepest, densest, coldest basins of the oceans, rather that into its surface waters.

It will not stay there for long. Further data indicate the mass of the cold dense bottom water is shrinking, and its rate of flow is slowing. These are not reassuring changes.

Still, we have learned that the increasing heat on planet Earth is not only absorbed by surface waters, resulting in a relatively rapid warming of global mean surface temperatures, but that it can also be absorbed first in the high latitudes by very cold water and transported into deeper layers of the ocean. Surface temperatures may then not rise as soon or quickly, but the planet continues to warm anyway, and the long-term impact will be profound.

Ships and satellites are collecting ever more data. If nothing else, the development of this dramatic change in global climate will be incredibly well documented. Perhaps at some point the weight of evidence will be sufficient to push us into effective response.

Meanwhile, last month 140 boats sailed together from San Francisco to the tip of Baja and back. One of the boats first sailed over from Sweden, taking the Northwest Passage to get to the Pacific.

State of the Oceans

Thursday, September 8th, 2011

Well, this is grim reading.

The International Program on the State of the Ocean – IPSO – has published a summary report of a meeting of late June. Twenty seven fisheries and ocean scientists and other experts from 8 organizations and 6 countries assessed the current state of the oceans. A lot of global expertize resides in this group of people. The ‘long’ summary includes a list of 100 references published in peer reviewed journals, a lot of them from 2010 and 2011 – the report is evidence based, to say the least.

And the evidence indicates that the oceans are well along the way of the worst case scenarios published in the IPCC report of 2007. Ice is melting faster in the Arctic Ocean, Greenland, and Antarctica; ocean surface temperatures are rising; sea levels are rising; increase in ocean acidification is measurable; methane trapped in sediments is beginning to be released; changes are occurring in the distribution and diversity of marine species, in primary production and in harmful algal blooms; and food webs continue to simplify, with jellyfish too often becoming the top predator in the ecosystem.

Sea surface temperatures, measured globally by satellite, are rising. (

The lead-off statement of the summary is clear enough: The biggest threat to our ocean’s health is climate change, with its rising sea temperatures and acidification. Because this has become so difficult to resolve, we must at least reduce the other main stressors on the ocean to give it the best chance of dealing with climate change.

What are the other stresses whose impact we could reduce? They are too familiar: overfishing, habitat destruction, extraction pollution, and alien species introductions.

Negative synergy of these stresses will certainly drive any resilience to climate change ever lower. For example, global coral reefs, coping with rising temperatures and acidification, along with the other stresses, have little chance of surviving this century.

Those parts of the Great Barrier Reef that are most protected appear to be the healthiest, the most resilient (

The IPSO report does have some strong recommendations.
– Reduce CO2 emissions immediately.
– Restore the structure and function of marine ecosystems.
– Reduce and close fisheries, and develop a holistic approach to sustainable fisheries management.
– Establish far more marine protected areas.
– Reduce pollution from agricultural runoff and from resource extraction.
– Apply the precautionary principle that everyone seems to agree with and then ignores.
– Promote effective governance of the high seas through the UN.

And then some stark conclusions:
– Current consumer values coupled with current rates of population increase are not sustainable.
– Timelines are shrinking rapidly – and the longer we wait to act, the greater the cost.
– Core values of human society and its relation to the natural world and the resources on which we all rely must be re-evaluated.

What do you think? In the face of the world’s growing economic and social problems, are we capable of changing our core values? Are we capable of finding the global resolve to meet any of the recommendations before we run out of time, and extreme and irreversible change is upon us?

Opportunities still exist. The IPSO report should be read as an opening salvo, leading up to the next UN Conference on Sustainable Development in Rio in June, 2012. Rio+20, as it also calls itself, apparently without any intended irony.

All the right things get said leading up to Earth Summits.

Reefs at Risk

Saturday, February 26th, 2011

Cyclone Yasi, as big as Katrina, and one of the strongest cyclones in a century, swept across the Great Barrier Reef and on into Queensland on Feb 2. A coral reef has little defense against such a storm.

Crossing the unusually warm Coral Sea before it got to the reef, it grew in strength to Category 5 – just as Katrina grew to Category 5 when it blew across the warm Gulf of Mexico. The Coral Sea has in fact never been warmer, a product of the impact of the current La Nina and the long-term warming of the ocean.

Cyclone Yasi, Category 5, about to hit Queensland on Feb 2 (

Because of the warmer surface waters, this has been another bad year of global coral bleaching on reefs from the Indian Ocean, Thailand, the Maldives, and the Caribbean, probably as bad as 1998, certainly worse than 2002 or 2005. Global bleaching events such as these used to occur every hundred or a thousand years. No longer.

Coral bleaching occurs when water temperatures get too warm and symbiotic algae called zooxanthellae are expelled (

Corals live very close to their upper lethal temperature limits, and a rise in surface temperatures of just 1-2 degrees centigrade is enough to cause extensive coral bleaching. Following the global bleaching of 1998, about 15% of corals failed to recover. We’ll see soon enough how much recovery occurs from the global bleaching of this last year.

At the same time, as atmospheric carbon levels continue to rise, the oceans are becoming more acidic. This is the greatest threat of all: at some point calcareous skeletons of corals will no longer form and the reefs will crumble. Only a reduction in atmospheric levels of CO2 will prevent this, and we all know now how unlikely that is.

As atmospheric CO2 rises, so does the amount of CO2 dissolved in sea water, and the pH gradually drops, making sea water more acidic (

Coral reef scientists around the globe have been warning us for some years that coral reefs are not going to survive global warming. The warnings have now escalated. The World Resources Institute, along with the Nature Conservancy and a diversity of coral reef monitoring organizations, has just published “Reefs at Risk Revisited”, updating its last report of 1998. Local and global stresses now threaten 75% of reefs. Without action on our part, by 2030 that will be 90%, and by 2050, all of them.

Of course, efforts to protect the reefs from overfishing, destructive fishing, pollution, and coastal development are all worthwhile, allowing the corals to be as resistant as possible to the serious global stresses of warming temperatures, coral bleaching, and ocean acidification. But there probably isn’t a single coral reef scientist left who thinks there will still be reefs in existence for our grandchildren to see.

What will the world look like without reefs? This isn’t hard to imagine – we need only go to many parts of the Caribbean and snorkel or dive around reefs that now are dead and crumbling rubble, covered with macroalgae.

A Caribbean coral reef reduced to rubble, abandoned by most fish and all scuba divers (

The costs are huge. A coral reef dies, and those who depend on it leave or die with it – reef fish and their prey and predators, scuba diving operations, recreational visitors, community fishermen, everything is lost. Vulnerable tropical countries, most of them island nations, are now advised to reduce their dependence on coral reefs, and ‘build adaptive capacity’.

We don’t know if life is abundant or rare in the universe, but we can make some reasonable guesses. With 100 billion galaxies, each with its trillion or so stars, life is probably not unusual. But it is probably bacteria-like rather than multicellular, for after all that’s what life on our own very benign planet looked like for a couple of billion years or more.

Stromatolites are mounds of cyanobacteria and look like rocks. They dominated life on Earth for about two billion years. Life on other planets may be no more complex. (

Complex ecosystems like those we find on Earth may be extraordinarily unusual across the universe. And even if complex life has evolved elsewhere, it will be different, contingent on the interacting pressures and planetary events of their own systems. Coral reefs evolved here, on Earth, and probably nowhere else.

Other ecosystems may survive these perilous times through adaptation, resilience, and migration to different latitudes. But not coral reefs. We’ve become familiar, even comfortable, with the extinction of particular species. But the extinction of an ecosystem? That is something very different.

There are no words that I know of to express the depth of such a loss. It is a loss to our universe.

Great Barrier Reef. See it while it's still there. (