The
accelerated global warming described in article
1 could lead to a runaway methane global warming effect due
to the release of methane currently trapped in unstable methane
hydrate deposits in the arctic that could be destabilised by accelerated
global warming effects.
Core
samples taken from old ocean sediment layers have been used to
trace back in time the climate changes that have occurred over
the past tens of millions of years. By analysing the incidence
of different fossil shell remains of sea creatures occurring in
these sediments it is possible to track the changes in the sea
water temperatures and levels of atmospheric CO2 occurring at
the time the shells were formed and deposited. These shells contain
carbon from the CO2 in the atmosphere which was dissolved in the
sea water in which the creatures lived just as takes place today.
From
these records it appears that there have been short periods of
only a few hundred years in the geological past when rapid increases
of the Earth's temperature have occurred superimposed on top of
the rise and fall of average temperatures over the longer term.
For these short periods temperature rises of up to 8 degrees centigrade
appear to have occurred on top of existing long term rises of
5 to 7 degrees to give temperatures up to 15 degrees centigrade
warmer than today. Temperatures then fell back to the long term
trend, the whole rise and fall only lasting a few hundred years.
The
most likely cause of this rapid global warming over such a short
period is the release of methane into the atmosphere. Methane
is 60 times more powerful than CO2 as a greenhouse gas but only
remains in the atmosphere for about ten years and so looses it's
greenhouse effect quickly compared to CO2 which remains in the
atmosphere for 100 years. CO2 would not be available in sufficient
quantities to achieve the rapid warming and if CO2 was the cause
then the raised temperatures would last a lot longer.
Methane
hydrates occur extensively today all over the world. They consist
of methane stored within unstable water bound deposits that if
disturbed release the methane. They occur in major river deltas
such as the Amazon delta and in old delta areas such as the Gulf
of Mexico. Major rivers carry millions of tons of silt containing
vegetable matter that continues to decay after the silt is deposited
in the river delta. This anaerobic decay produces methane which
gets trapped in the silt as methane hydrates until the conditions
of water temperature and pressure change which can release the
methane in vast quantities very quickly. Another form is a frozen
slush/ice methane hydrate where the methane is trapped in an ice/water
mixture which releases the methane when it warms up or the pressure
on the ice is reduced. Frozen methane hydrates can contain 170
times their own volume of methane. These frozen hydrates occur
in the seabed deposits of the Arctic Ocean.
Methane
can also be trapped by permafrost layers which over-lay lower
unfrozen layers of vegetable material that is decaying and producing
methane which remains trapped by the frozen permafrost on top.
If the permafrost layer were to melt then the methane in the layers
below would escape into the atmosphere. Given the vast areas of
permafrost in northern latitudes there is a significant potential
for methane to be trapped that would be released if the permafrost
melted as a result of global warming.
The
theory for these rapid rises and falls of temperature, based on
the geological records from 55 million years ago, is that gradual
global warming due to some natural cause had resulted in temperatures
5 to 7 degrees centigrade higher than average ( i.e. higher than
today's temperatures). At this point methane trapped in methane
hydrate deposits started to be released into the atmosphere and
accelerated the rate of warming. This would result in further
warming releasing more methane. As the atmosphere warmed different
types of methane deposits would start to be released and so a
cycle of methane release leading to increased warming leading
to more methane release from other areas of methane deposits elsewhere
in the world would become established as global warming effected
different areas of the world.
There
is an intriguing photograph of what appears to be a methane plume
coming up out of the Arctic ice sheet which indicates that the
phenomenon described above can occur. There have also been incidences
of oil drilling inadvertently triggering large releases of methane
from hydrate deposits. One theory to explain the loss of ships
in the so called Bermuda triangle is that they have been engulfed
in a sudden methane release which reduces the buoyancy of the
sea water so that the ship sinks.
So,
does methane pose a threat today? Let us review the situation.
We know there are extensive methane hydrate and permafrost deposits
all around the world. We have evidence that we are at the beginning
of a period of global warming that is probably being made worse
by the continuing build up of CO2 in the atmosphere due to fossil
fuel burning. Recent computer modelling incorporating the feed
back effects of global warming that has already occurred suggests
that by about 2050 we may start to loose the beneficial effects
of the Amazon rain forest as a carbon sink. This could lead to
temperature rises of 5 to 8 degrees centigrade by 2100. This would
be uncharted territory and no one really knows at present how
the world's environmental systems would change but we now have
the evidence from the geological past. On the basis of this evidence
global warming can lead to methane releases which once started
would escalate. This would be the worst possible thing to happen
because once started there would be no way of stopping a runaway
methane global warming event. We CAN reduce our CO2 emissions
from fossil fuels but we COULD NOT reduce methane emissions once
they started, huge natural forces would take over and change our
world. This would probably result in the melting of the Antarctic
icecap which would raise sea levels by 50 metres and would completely
change the climates of the world.
So
what should we do? We should be careful and not risk starting
the sequence events described above. To do this we must reduce
total CO2 emissions from now onwards and take measures to protect
carbon sinks such as the Amazon rainforest.
This
is the third of this series of articles describing scenarios resulting
from CO2 induced global warming over the next100 years. If we
all carry on burning so much fossil fuel as we do now we will
be running the risk of starting an unstoppable runaway methane
global warming event within the foreseeable future. Only major
absolute reductions in CO2 emissions NOW will avoid this risk,
hence the need for Hydrogen NOW!
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