Yes,
it could; there are two basic ways, and they could happen either together or separately. The Azolla Event put enormous
reserves of ‘fossil fuels’ in the
Arctic region. This probably includes coal, oil
and natural gas. There are certainly massive
reserves of Methane
Hydrates. The slow way for
the Azolla Event to be reversed is for some
of these reserves to be used, and in being used, produce Carbon
Dioxide.
The increased greenhouse effect from this would warm the
atmosphere and slowly melt the
icecaps.
However,
there is another and potentially much faster way for it to happen:
When
a gun fires, the explosive in the bullet
is set off. The reaction
spreads throughout the explosive so fast that
to us it appears instantaneous, and the bullet is accelerated so
fast
that it comes out of the end of the barrel, in some cases, faster
than
the speed of sound.
The Arctic has huge amounts of Methane. Most of it is combined with
water molecules to form
‘Methane Hydrates’. These Methane
Hydrates are quite unstable in many conditions.
They are stable if they are cold enough or held under high
pressure. In many oceans there are deposits of Methane Hydrates held stable by the
pressure of the water above.
In the Arctic
there are Methane
Hydrates on land as well as in the Ocean.
The ones on land, in places
like Alaska and Siberia, are held in the hydrate form by the
‘permafrost’. This is a
layer of ‘soil’ which is ‘permanently’ frozen.
In this case, we should remember that this ‘permafrost’ has not
always
been there. It formed on
top of huge deposits of vegetation, including
Azolla (See “The
Azolla Event”). This is mostly not frozen and has
decayed over millions of years, producing Methane
which has combined with
water to form Methane Hydrates.
If
permafrost melted, the Methane Hydrates would not longer
be held
and the Methane released.
Of course it would not all melt at once.
If part of the permafrost melted, some of the Methane would be released.
We hear a lot about greenhouse gases.
The one we hear about most is Carbon Dioxide. This greenhouse
gas is the second most important one in keeping the Earth nice and
warm. The most important
one is Water Vapour. As the
temperature of
the Earth’s atmosphere increases, generally, the amount of Water
Vapour
in it increases. So the
Water Vapour tends to increase the effect of
any increase from other causes.
The third most important of the greenhouse
gases is Methane.
This is many times as effective as either Carbon Dioxide
or Water Vapour, but because of its low concentration in the atmosphere it is less important at the
moment. However, it is
the one that is increasing at the fastest rate:
In
1750 the Methane concentration of the atmosphere
was about 700 parts per billion (ppb).
This increased to 1754 ppb in
1998. This increase
appeared to be levelling out around 2005, but in
2007 it started to increase again.
We do not know what it will do next
although there are many (often opposing) ideas about this. At present,
the increase in Methane concentration is responsible for
about a third of the effect of the increase in Carbon Dioxide concentration.
Methane does not last very long in the atmosphere. It gets oxidised to Carbon Dioxide
and water. However although
an often quoted average length of time
before this happens is seven years, this depends on the
concentration
in the
atmosphere. As the concentration increases, the
rate of oxidation goes down. So
if more is released, the rate of oxidation slows.
As the Earth warms, some of the
permafrost will melt, not only on land, but also in the Arctic Ocean. The Arctic
Ocean is mostly not deep enough for the pressure to keep the Methane Hydrates stable; in this case it is
mainly cold that is doing it.
There is evidence that the ice on the surface of the Arctic
Ocean is melting. The
temperature of the water has started rising and may be allowing the Methane Hydrates to release Methane which will lead to further rises in
temperature. This will also
increase the amount of Water Vapour in the atmosphere
and further increase the temperature; releasing more Methane.
Also, less ice means less reflection of the Sun’s rays, meaning more
warming.
These effects are a
‘positive reinforcement’. If it
happens it will be hard to stop unless we catch it very early on. In
geological terms this could be almost ‘instantaneous’ in the sense
of
someone looking back in the distant future.
If we are alive when this
happens it will not seem so fast.
However, in geological terms the
effect will be like the firing of a gun.
Has
this happened before in the Earth’s (Geological) history?
Yes,
it has, quite a few times, although, as
usual, people will argue about this statement. There is evidence that
for a period of over 100 million years the Earth was very cold. The
surface of land and sea was covered by ice over the whole Earth. Then
it got warmer. Probably by
some of the ice sheets becoming unstable
and releasing Methane.
The Earth ‘suddenly’ changed from one of its coldest periods to a very
warm one.
And
how long did this take to happen?
No one really knows. Some
people who have studied this think it
happened in as little as one hundred years.
Others think it took
longer.
Could it happen again?
Yes, of course it could.
Is
there evidence that it has already started?
It
depends on who is interpreting the evidence.
There have been places on the floor of the Arctic
Ocean where large amounts of Methane are being released, but it is not
clear if there has been a recent large increase in the amount being
released.
Could it happen in, say, the next 20 years?
Yes it could, but my guess
is that it will not.
However, this illustrates a major problem.
We simply do not know
enough to make reliable predictions.
For
an overview of greenhouse gasses on Earth and other planets,
see Greenhouse
Gasses
Steve Challis
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