Wednesday, November 15, 2006

Antarctic Blows Hot and Cold on Climate Change.

Glaciers around the world are retreating, either by melting or because a drier local climate results in less water in the air to be deposited on them in the form of ice and snow. As a personal experience, I was shocked on visiting Switzerland a few months ago, to observe the diminution in ice-cover on the Jungfraujoch plateau and indeed on the Eiger and other mountains in the Bernese Oberland, where I have visited for over 20 years. If I had any residual scepticism, this largely dispelled it. I am convinced finally that the climate is changing. Scenes of Antarctica and the Southern Ocean are frequently displayed as the supreme and most visual evidence that the Earth is warming... and that it's all our fault - "Anthropogenic Global Warming", i.e. human-made - is the rallying cry. There remains a considerable scepticism among a large body of respectable scientists that while climate change is undeniable, its causes remain a matter of speculation, but those who exhibit the temerity to speculate are regarded as Global Warming "Deniers", just as surely as members of Fascist groups who challenge the evidence of the Holocaust.

Science should always be open to speculation in the light of evidence, otherwise it is not science but self-interest or hysteria. New discoveries about nature will continue to be unravelled, but in my humble opinion, even if there are natural trends (as the geologic record shows) that act to warm the Earth on a roughly 100,000 year cycle, and so climate change is not entirely our fault, it is still madness to continue burning for no real purpose beyond inertia and self-interest those remaining reserves of oil and natural gas in a vain attempt to preserve a lifestyle that will prove ultimately untenable. So, CO2 emissions and their consequent heating of the globe notwithstanding, reductions in burning precious and irreplaceable resources of fossil fuels remain the order of the day. We must act now to use them in driving some sustainable long term strategy of living on this world, which in all probability will involve renewables and nuclear power (if it is so implemented that supplies of uranium and thorium can be eked-out to last for hundreds of years).

Antarctica has shown two new and unexpected features. In the first place, although the "floating" northern peninsular is indeed melting as is shown in the media, this will not influence sea-levels directly. Imagine a glass of "something" with three large ice-cubes floating in it, and filled to the brim. When the ice melts, will the liquid overflow the glass? Counter-intuitively, it will not, because the density of ice is only about 90% that of liquid water (hence just 10% of icebergs are visible - above surface - due to the buoyancy factor), and so when it melts the total volume of water stays the same. Put another way, the water displaced by the ice has the same volume as the total ice when it is melted into liquid water. However, the East Antarctic Ice Sheet - a 2 mile thick, 2.7 million square mile prairie of land bigger than Australia - has increased its mass every year between 1992 and 2003 from increased snowfall, according to satellite radar measurements. Since it is normally too cold to snow there (i.e. the air is too dry to carry much water to be precipitated as snow), it is thought that global warming is to blame, presumably that there is therefore more evaporation of water into the air which falls as snow. This additional snowfall is sufficient to increase the ice-sheet by an extra 45 billion tonnes per year, which is about the same as the amount of water flowing into the oceans from the melting of the Greenland ice cap; an interesting coincidence, which may help to keep sea-levels steady. Sea level is believed (by some) to be rising worldwide by an average of 1.8 millimeters a year due to the expansion of water as the oceans warm, and from the additional outwash from glaciers melting in Greenland, Alaska, tropical highlands and elsewhere in Antarctica. Each millimeter (mm) of increased sea level corresponds to about 350 billion tonnes of water. The growth of the East Antarctic ice cap is thought enough to slow down sea level rise by around 0.12 mm a year, i.e about 6% of the total.

Now, is the melting northern/western Antarctic ice or the growing eastern ice-sheet due to global warming, as thought? Here comes the second discovery, namely an active undersea volcano, previously unknown in the Antarctic Sound, at the northernmost tip of Antarctica (where we usually see the ice melting in torrents). Evidence for the volcano was dredged-up in a study aimed at investigating why a massive ice-sheet known as the Larsen B collapsed and broke-up several years ago. The find corroborated mariners' observations that the seas in this region were "discoloured", which is consistent with an active undersea volcano. Highly sensitive temperature sensors moving continuously across the seabed of the volcano also revealed signs of geothermal heating of seawater, especially near the edges where the most freshly deposited rock was observed. Could undersea heating be a factor in enhancing evaporation of water in the region, and enhancing snowfall on the Eastern ice-sheet, not or only in addition to, global warming?

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