The Existential Imperative: Ocean Thermal Energy Conversion II

The fourth IPCC assessment report projects that 40 to 70 percent of species could go extinct if Earth warms by 3.5°C.

Ominously, in the light of this projection, a recent study by Australian and French scientists published in Nature, Spread in model climate sensitivity traced to atmospheric convective mixing, predicts that unless greenhouse gas emissions are cut, the planet will heat up by a minimum of 4°C by 2100 and by more than 8°C by 2200.

Compounding the bad news, two German scientists have confirmed the earlier work of a a U.S.-led group that found reducing sunlight by geoengineering – the most widely assumed last line of defence in the face of climate change – will not cool the planet.

It will however disrupt global rainfall patterns.

The Australian/French research indicates that fewer clouds form as the planet warms, meaning less sunlight is reflected back into space, driving temperatures up further.

The way clouds affect global warming has been the biggest mystery surrounding future climate change and the main reason why a doubling of atmospheric carbon dioxide concentration is reflected in various climate models as a rise in temperature ranging between 1.5 to 5 degrees Celsius.

This spread arises largely from differences in the feedback from low clouds, for reasons not yet understood. The study compared 43 different climate models and shows that the differences in the simulated strength of convective mixing between the lower and middle tropical troposphere explain about half of the variance in climate sensitivity. This mixing apparently dehydrates the low-cloud layer at a rate that increases as the climate warms.

As explained by the NASA Earth Observatory low clouds act to cool the Earth due to the albedo effect while high, thin, cirrus, clouds warm the planet because they are virtually transparent to the incoming shortwave radiation from the Sun yet absorb the long infrared wave lengths that radiate heat from the Earth back to space.

As Steven Sherwood of the Climate Change Research Centre and ARC Centre of Excellence for Climate System Science at the University of New South Wales stated in an interview, “4C would likely be catastrophic rather than simply dangerous. . . For example, it would make life difficult, if not impossible, in much of the tropics, and would guarantee the eventual melting of the Greenland ice sheet and some of the Antarctic ice sheet, with sea levels rising by many metres as a result.”

The argument for geoengineering goes that since governments show little inclination to reduce greenhouse gas emissions, in spite of inexorable warming; we should try to find a way to filter, block, absorb or reflect some of the sunlight hitting the Earth in order that we can continue to burn all of the fossil fuels we like.

Axel Kleidon and Maik Renner of the Max Planck Institute for Biogeochemistry show that the world doesn’t work that way and concluded geoengineering approaches to reduce global warming are unlikely to succeed in restoring the original climatic conditions.

If you make the atmosphere warmer, but keep the sunlight the same, evaporation increases by 2 percent per degree of warming. If you keep the atmosphere the same, but increase the level of sunlight, evaporation increases by 3 percent  per degree of warming.

Water is a more powerful greenhouse gas than CO_2.

Kleidon used the analogy of a saucepan on a kitchen stove. “The temperature in the pot is increased by putting on a lid, or by turning up the heat – but these two cases differ by how much energy flows through the pot.”

While in the kitchen you can reduce your energy bill by putting the lid on, with Earth’s system this slows down the water cycle with wide-ranging potential consequences.

That is because evaporation itself, and the movement of water vapour around the planet, plays a powerful role in the making of climate. To change the pattern and degree of evaporation would inevitably disturb weather systems and disrupt agriculture, with unpredictable and potentially catastrophic consequences.

In US patent application 20100300095 Sea Surface Cooling System Utilizing OTEC, Tohihiko Sakurai comes to a similar conclusion to that reached by the Australian and French scientists referred to above. As the sea surface temperature rises due to global warming, the amount of cloud cover above the sea decreases. The essential reason for this is a weakening of atmospheric convection, and hence a weakening of ascending current over the sea, due to the progression of global warming.

Sakurai describes a mechanism of thermal runaway that is effected through a double positive feedback process in which the density of water vapour increases but the amount of cloud cover decreases and postulates that the most cost effective way to counteract this may be to cool the ocean’s surface rather than to reduce CO₂ levels.

His invention would do this using an OTEC system designed solely to produce mechanical energy that would pump cold water from the deep up to the ocean’s surface.

You can move a great deal more heat, much faster, through phase changes of a working fluid rather than in masses of water because the latent heat of vaporization and its inverse the latent heat of condensation of a liquid is much greater than its sensible heat and it is easier to move a light vapour than a heavy liquid.

In light of recent findings it seems advisable that we should be moving surface ocean heat to deep water using an OTEC system with a deep water condenser in view of the ocean’s demonstrated capacity to absorb such heat.

It had been assumed in some circles that the movement of heat from near the ocean’s surface into deeper waters had reduced climate change over the past 15 years by as much as 50 percent.

I and some associates believe that using phase changes of a working fluid is the most appropriate way to produce extraordinarily large amounts of energy from the ocean’s thermal statification as well and in doing so you would cool the ocean’s surface and prevent potential thermal runaway.   

In the first Existential Imperative posting the concern was phytoplankton that are the lungs of the planet and the base of the ocean food chain.

It now seems the odds against our mortality beyond the end of this century may be as low as thirty percent; perhaps even less than that of phytoplankton.

It is time therefore to start doing something with haste and in the most productive way possible.

Photo Credit: Ocean Heat and Energy/shutterstock