The IPCC report
“Climate Change 2014: Impacts, Adaptation, and Vulnerability”
ranks the risk of death, injury, ill-health, or disrupted livelihoods in
low-lying coastal zones and small island developing states and other small
islands, due to storm surges, coastal flooding, and sea-level rise as the number
one threat posed by climate change.
Stefan Rahmstorf notes in a RealClimate post
What makes sea-level rise? “The causes of global sea
level rise can be roughly split into three categories: (1) thermal expansion of
sea water as it warms up, (2) melting of land ice and (3) changes in the amount
of water stored on land.”
Each of these causes is mitigated with technology that
produces as much energy as is currently derived from fossil fuels as outlined in
the Natural Analogies section of this
The heat accumulating in the oceans due to climate change
excites the water molecules causing an increase in their average separation and
thermal expansion. This effect however is not manifest at a constant rate
throughout the depths of the ocean. The greatest expansion occurs at the surface
and then decrease to a depth of 1000 meters, beyond which it slowing increases
again until at 8000 meters the rate returns to close to what it is at the
The greatest potential for sea level rise exists in the
polar icecaps, which if melted entirely would raise the oceans by a total of 68
meters. About 61 meters of this rise would come from Antarctica, where the
average temperature is -37°C, so it seems unlikely all of this will melt.
It is estimated however that warming will occur at a rate 2.5x greater in
Antarctica than the tropics and 4x greater in the Arctic where the ice is
floating and will not effect sea levels when it melts.
Greenland on the other hand would add 7 meters to ocean
levels if all of its ice melts. Since it is closer to the equator than
Antarctica, the temperatures are higher and there is a greater likelihood
this will happen.
The question is, how fast will any of this occur?
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, sinks and circulates back towards the
equator as part of the Thermohaline circulation that governs much of the global
Global warming is the trapping of more heat than is being
radiated back to space by greenhouse gases in the atmosphere.
latest work of James Hansen and 16 of his colleagues adds a 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
Antarctica 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 the calls by Hansen and others
for nuclear power as the remedy for global warming.
If the potential for waste heat, which are as high as
twice as much as the energy produced, from thermal 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
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?
In a Nature
article, “Model estimates of sea-level change due to anthropogenic impacts on
terrestrial water storage”, Yadu Pohkrel et al. postulates, “climate-driven
changes in terrestrial water storage and the loss of water from closed basins
have contributed a sea-level rise of about 0.77 mm yr−1 between 1961 and 2003,
about 42 percent of the observed sea-level rise.”
conditions persist in regions like California the pumping of aquifers, which
have taken thousands of years to fill in many cases is being increasingly relied
on because the alternative for many farmers is to stop producing crops.
It is a stark
proposition, starve or contribute to the inundation of the land.
These sea level consequences are
addressed with energy production that moves the heat accumulating due to global
warming though a heat engine to produce energy.