Geoengineering is the deliberate and large-scale
intervention in the Earth’s climatic system with the aim of reducing global
warming. It is most often thought of in terms of carbon dioxide removal or solar
radiation management but a third approach using the cooling of ocean surface
waters and the surrounding atmosphere with cold water brought up from the oceans
depths has also been considered.
Thermodynamic geoengineering is a fourth way.
Thermal stratification of the oceans (Figure 1 to right)
induced by global warming presents the opportunity to convert warming heat to
The oceans are storing about 93 percent of the energy of
climate change. (Firgure 2 to right)
When water is heated it becomes less dense and rises thus
the oceans are increasingly thermally stratified. This stratification presents
the opportunity to create work in accordance with the 2nd law of thermodynamics.
(Figure 3 to right)
The 2nd law dictates that heat flows from warm to cold.
The majority of warming heat is accumulating in tropical waters. The ocean
depths are a vast cold sink but the density issue makes it difficult for
tropical heat to flow into the abyss. The avenue of least resistance is for
tropical heat to move towards the poles where it is melting icecaps and
permafrost that is locking in methane; a potent greenhouse gas the release of
which would create a dangerous warming feedback.
Damaging tropical storms are one of the main mechanisms of
heat transport from tropics to the poles.
Although CO2 emissions have continued to rise (Figure 4 to
right) it is thought that increased ocean heat uptake has caused an atmospheric
warming slowdown this century. The forces believed to have brought about the
mixing of surface heat into deep waters are wind and density issues associated
with the melting of polar ice. Both of these are believed to be temporary
phenomena that when reversed will see much of the so called missing heat
returned to the atmosphere.
Heat pipes are sometimes described as thermal
superconductors because they rapidly move heat through phase changes of a
working fluid. They are a highly efficient way of conducting heat away from a
region where it can do harm, as with the ocean's surface. The heat pipe’s
efficiency stems from the fact they have no moving parts yet they can transport
heat at speeds approaching that of sound. They can move heat counter to the
forces of gravity and when a turbine is situated in the vapor stream heat can be
converted to work.
With enough of these devices the hiatus can be perpetuated
while generating as much energy as is currently derived from fossil fuels.
The efficiency of a heat engine is equal to 1 – the
absolute temperature of the cold reservoir divided by the absolute temperature
of the hot reservoir.
Ocean thermal energy conversion (OTEC) requires a delta T
of at least 20 degrees.
Universally the oceans at a depth of 1000 meters are about
4oC or 277K so the theoretical Carnot efficiency of a minimally operative OTEC
system would be about 6.75%. Realistically 5% is about the best that can be
achieved, which means 20 times as much heat has to be moved away from the
surface of the ocean as energy produced.
It has been estimated the oceans are capable of an output
14 terawatts (TW) of primary energy without creating environmental damage.
This is about what is currently derived from fossil fuels. To convert ocean heat
to that much work would require the transmission of an additional 280 TWth into
the deep through heat pipes and since
NOAA estimated in 2010 that the oceans are accumulating about 330 TWth due
to climate change, virtually all of this excess energy can be converted or
relocated to the safety of the abyss with heat pipe OTEC.
This would short circuit the movement of heat towards the
poles by moving it to an ocean depth where the
coefficient of thermal expansion of sea water (Figure 5 to right) is half
that of the tropical surface. By sapping as well the energy of tropical storms
these systems would ameliorate the two greatest risks of climate change; sea
level rise and storm surge.
estimated that at depths from 500 to 2000 meters, the oceans are warming by
about .002 degrees Celsius every year, and in the top 500 meters, they’re
gaining .005 degrees C. In contrast the atmosphere has been warming about 3
times faster than the deep ocean and the poles 3 times faster than that. It is
apparent therefore that the deep oceans have the greatest capacity to accept the
heat of global warming while producing the least temperature increase because of
their huge heat capacity.
To get ocean derived energy to shore requires the
conversion of electricity to an energy carrier.
Electrolysis of sea water can be done in such a way that not only is
hydrogen produced, carbon dioxide is sequestered with the formation of
carbonates and bicarbonates and these in turn neutralize the increasing acidity
of the oceans brought on by increasing CO2 uptake.
Heat pipe OTEC (Figure 6 to right) addresses both the
cause and effect of climate change.
Heat uptake in the deep oceans is believed to be the
reason for the atmospheric warming slowdown experienced this century. This
natural phenomenon is replicated with heat pipes that are part of a system that
produces energy in a heat engine. Although the natural phenomena are expected to
reverse within a few decades, heat moved to an ocean depth of 1000 meters would
take about 250 years to return given that upwelling in the Pacific is
estimated at about 1cm/day.
As this is an emissions free approach to producing energy,
atmospheric concentrations of CO2 would be reduced by the time the heat
reemerged, at which point it could be returned to the deep with the same
Heat moved into the deep is no longer available to drive
tropical storms or to migrate towards the poles where it would melt icecaps and
The thermal coefficient of expansion of sea water is half
at an ocean depth of 1000 meters that it is at the tropical surface thus sea
level rise would be reduced due to this effect as well.
Thermodynamic geoengineering provides a lot of
environmental wins in a single package.