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Ice ages

Whilst considering past, present, and potential future natural ‘disasters’, I should at least include a mention of ice and ice ages. They have been a frequent part of Earth’s climatic history, although, fortunately, we are currently enjoying a warm interglacial period. Their recurrent pattern, as measured from the ice core records from earlier ice ages, suggests they are partially predictable. Ice ages occur for a number of reasons, including small fluctuations in solar activity, and minor deviations in the orbit of the earth that have taken us slightly farther from the sun. We know the scale of these periodic orbital variations; we also know that the angle at which Earth is tilted relative to the axis of rotation steadily changes in a fixed pattern (termed precession).

Precession is not a new discovery—it was appreciated from the early astronomical observations of a few thousand years ago. It was detected because the direction to the Pole Star is not quite constant. The precession is quite slow, so this influence on the climate is of no immediate concern. However, the timescale before the next ice age occurs is difficult to predict because of the number of minor orbital oddities that need to combine to cause it. The estimates therefore vary between a pessimistic one—with another ice age happening in 2,000 years—to a more optimistic estimate of 30,000 years. No matter which is correct, for our generation, it is not a pressing problem.

Instead, we should be more concerned about survival in a world that is steadily heating. Confusingly, with a complex situation of many inputs to the earth’s climate, some models suggest that heating contributes to ice melting, which may in turn influence a shift in the rotation axis and tilt, leading to a more imminent ice age. No matter which models are correct, glacial events will certainly reoccur. If civilization is well organized, we should survive, but with a greatly reduced sustainable population, ideally achieved intentionally rather than by war and chaos.

Rather than worry about the next ice age, it would be more instructive to consider current changes in ice coverage around the polar regions, as these will certainly influence our lives in the more immediate future. Satellite images and ground observations unequivocally show that over recent years, the Arctic has progressively had far less summer ice than had ever previously recorded by human explorers. This is extremely bad news for polar bears, but possibly a real bonus in that it could open summer shipping routes north of Canada and Russia.

The discussion, opinions, and prejudices on the scale of climate change and global warming are often totally unrelated to evidence, which is well documented, and which can be appreciated by any intelligent person (i.e. without scientific training). Predictions and modelling are far more difficult, as there are many factors and a range of opinions. Even climatologists disagree on the details. Therefore I will not discuss predictive models, but focus just on data that are not in dispute.

In the case of the satellite images of the steadily reducing summer ice cover of the Arctic Ocean, there is no question that they show very dramatically that in this region of the northern hemisphere, warming is taking place. No scientific training is required—just direct observation of the changing yearly photographs. It is clear evidence, even if arguments exist over the cause.

At the opposite end of the world, there are immense glaciers on the Antarctic land mass and also many glaciers stretching out over frozen ocean. Interestingly, because the underlying ocean is heating, it is undermining their stability, so the glacier ice sheets start to flex with tidal movements. One consequence is that large chunks of ice and glacier have broken free and headed out to sea. The only difference between contemporary and former loss of glaciers is the scale, speed, and size of the pieces that are coming from various ice shelves (particularly in the West Antarctic). Satellite data show the current loss is more than 150 billion tons of ice per year. It sounds like a lot of ice, but the earth has a lot of oceans, so in terms of European sea level, this gives a tiny rise of less than a millimetre per year.

Nevertheless, the speed of melting is increasing, so over the next century the change in sea level will certainly influence many low-lying areas across the world. This includes islands, cities such as Venice, and much of Holland. London already needs a tidal barrier to prevent flooding and loss of the underground transport system. It is conceivable, and with current trends probable, that the present Antarctic pattern will result in the loss of all the Amundsen Sea ice, which would raise global sea level by more than a metre within the next two centuries. Other larger glacial areas might follow. In terms of the Antarctic, the confusing factor for predictions is that ice on the solid Antarctic mountain continent is actually increasing in some areas—a feature seized upon by those who do not wish to recognize there is global warming.

A difficulty for the ice scientists, which is not explained in the reports of the popular media, is that there is a need to measure the thickness of the ice, not just the surface level. The entire Antarctic continent is depressed by the weight of the glaciers. Therefore when the glaciers move or melt, the underlying rock can slowly spring upwards, giving a false appearance that the ice surface level has increased. In altitude the surface may have risen, but in terms of thickness it may be less; more complex and detailed data are needed to separate these alternatives.

I suspect this is not the only example of scientific information that has been oversimplified by the media, and indeed may not even be known by those with a scientific background.

 
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