The following schematic shows how heat is typically added, is mixed, and is lost in the major oceans.
Near the equator heat warms the ocean’s surface, with some of the heat mixing to deeper water, while the rest migrates towards the poles. There heat is radiated back to the atmosphere and space, and the chilled water, which becomes denser as it gets colder, then sinks and circulates back towards the equator as part of the Thermohaline circulation that governs much of the world’s climate.
Global warming is the trapping of more heat than is being radiated back to space by greenhouse gases in the atmosphere.
The latest work of James Hansen and 16 of his colleagues adds a new and troubling wrinkle to the cycle pictured above and to global warming in general. Hansen et al. think that increased melting of ice around the coasts of Greenland and Antartica will create a fresh water blanket that will flow over the warm layer moving towards the poles. This blanket prevents the loss of heat to the air and the trapped heat then works on the underside of the ice shelves and glaciers; increasing their melt rate and sea level rise.
This accumulating cold water on the surface will also shut down the Thermohaline with the result tropical waters will get warmer and produce stronger storms, while higher latitudes will be cooled by the melt water on the surface.
Effectively the oceans are experiencing a greenhouse effect of their own which has ramifications for waste heat and Hansen’s call for nuclear power as a global warming remedy.
If the potential for waste heat from sources like nuclear power to radiate into space is impaired then it probably shouldn’t be produced at all since it will primarily increase the melting of the icecaps.
While the Hansen group says the icecaps are being eroded from below, another current study by a team lead by Samuel Doyle of Aberystwyth University, says the melting of the Greenland ice sheet is being amplified by rainfall on the ice surface driven by late-summer cyclones. Since this too will produce the effects Hansen notes, including stronger storms that will in turn produce more late summer rainfall in Greenland, this doubly negative feedback will likely produce far greater and faster sea level rise than is currently anticipated?
Most climate scientists agree with Hansen that if carbon emissions are not dramatically reduced there will be irreversible catastrophic climate change by mid century.
Vaclav Smil however has pointed out that typically it takes 50 to 60 years for the world to transition from one energy source to another.
Since it is unlikely the world can transition away from fossil fuels much faster than it transitioned to them, in spite of the urgency to do so, it is imperative that the greatest environmental benefit be derived from every dollar spent on replacement technologies.
From 1998 to 2012, the rate of atmospheric warming slowed from the 1984 to 1998 decadal average of 0.26 °C per decade to about 0.04 °C per decade, according to the last International Panel on Climate Change report. A new NASA study of ocean temperature measurements shows the heat wasn’t missing it was simply trapped in the waters of the Pacific and Indian oceans to a depth of about 300 meters. NASA found the Pacific Ocean is the primary source of the subsurface warming as unusually strong trade winds piled up warm water in the western Pacific, pinning it against Asia and Australia but these waters became so warm some of the heat leaked into the Indian Ocean.
Kevin Trenberth of the National Center for Atmospheric Research in Boulder, Colorado says however that “There’s a good chance the hiatus is over.” Last year was the hottest since records began and with an El Niño now under way the warm surface waters of the Pacific are releasing heat into the atmosphere with the result 2015 is likely to break last year’s record and the global average surface temperature could jump by as much as 0.1 °C this year alone. This would bring global surface temperatures increases above 1°C relative to the average of the second half of the 19th century and half way towards the 2°C limit most governments have promised we will not pass.
It has to be noted that the Hansen study says that 2C global warming is highly dangerous and points to evidence from the paleoclimate record that shows that less than 1C previously precipitated sea level rise due to icecap melting of between 5 and 9 meters and extreme storms.
In order to prevent such an outcome the hiatus should serve as the example. Warming heat moved away from the surface reduces atmospheric warming, can not melt polar ice nor drive storms.
A heat pipe is a device that moves heat away from locations where it can do damage to somewhere benign. It does this with phase changes of a working fluid and energy can be produced by inserting a turbine into the vapor stream of such a device.
This design would move warming heat to an ocean depth of 1000 meters from where, with an estimated return rate of 4 meters per year, it would take 250 years to return to the surface as opposed to the less than two decades the wind driven hiatus kept global warming at bay.
Energy would be generated by this process remote from most markets in North America and Europe but close to those in Asia.
In order to get this power to most markets it would be necessary to convert electricity to an energy carrier like hydrogen. Other carriers, like ammonia, have been proposed but hydrogen would be ideal because it is as much a water carrier as it is an energy carrier and water is even more vital than energy.
Hydrogen is the ideal energy carrier because compressed it has the highest specific energy of any non fissionable material. It produces over 3 times the amount of energy as an equal weight of gasoline and when burned or is converted to electricity in fuel cells water is the only by-product.
It is also an ideal water carrier with diverse energy potential.
Hydrogen’s drawbacks are the energy required to compress it to the 350 to 700 bar (atmospheres) needed for volume and range considerations in most transportation applications and the CO2 produced by steam reforming of natural gas, which is the principal way the gas is produced commercially.
Steam reforming is used because electrolysis is between 3 and 10 times more costly but the CO2 negates much of the environmental potential of hydrogen when both are produced by this process.
High-pressure electrolysis is the cheapest form of electrolysis because it eliminates the need for further compression of the gas.
At 1000 meters, the deepest extent of a heat pipe OTEC system, the water pressure is 100 bar and electrolysis performed there would bring hydrogen to the surface at that pressure. Further when the electrolysis is performed with the technique developed by a team of Lawrence Livermore scientists, atmospheric and dissolved ocean CO2 is sequestered and ocean acidification is neutralized.
This is another way to buy the time necessary to avoid climate catastrophe and to transitions away from fossil fuels.
If climate catastrophe is imminent, we should be prepared to address the problem regardless of the cost. That is the primal human response to existential threats but as was pointed out here heat pipe OTEC may be the renewable energy with the lowest levelized cost and therefore should be transitioned to on that basis alone.
Cost it not the only reason however we should develop this approach. As my colleague Paul Curto, former chief technologist with NASA, points out, “using the ocean’s heat sink to dump the ocean surface heat may become one of the very few feasible methods to reverse global warming before all major species on earth become part of the sixth mass extinction.”