Ice Core Evidence for Global Warming - an Ice Age is coming
One of the main planks in the global warming theory is the
extraordinary Vostok ice core, dragged 2.5 km out of the Antarctic ice
by the Russians in the '80s and '90s. (Other ice cores and analysis methods tell much the same story, but we will concentrate here on Vostok)
The data from the ice, published in 1999 (see http://www.noe21.org/dvd2/Global%20Warming%20FAQ%20-%A0%20temperature.htm)
, gives snapshots of temperature and CO2 concentrations going
back 400,000 years. Since the two data sets have different time scales, it is a little tricky to graph them together. .
An article on Ice Cores, how they are obtained and what they tell us, is here.
If one sits down to look at the curves, a few things are apparent:
1. Four times in the period, (ie, roughly every 100,000 years) the temperature has quickly shot up to 2°C - 3°C above today's and then slowly slipped back to about 8°C below today's temperature. It looks as though the Earth's complex, non-linear climate system has two stable states and flops rhythmically from one to the other. A possible mechanism is described below - see Flip-flop.
2. We are currently hovering near the top of a cycle and an ice-age seems to be due. However, comparing today's position with the 4 previous peaks suggests that the temperature should have reached 2°C or more some 10,000 years ago, but it hasn't. If anything, the world is now somewhat colder than we might expect.
3. CO2 and temperature track each other well. When one goes up, so does the other and conversely. They show such a strong correlation that one might suspect they are causally connected.
4. But which is the cause? We normally think that causes come first and consequences come after. Over long periods in this data, it is temperature that comes first and and by several thousand years (except for a short period about 340,000 years ago). Al Gore, in his film, seems not to have noticed this detail.
5. One explanation might be: when the world gets warmer, the oceans expel CO2 and, some hundreds to thousands of years later, the gas
concentration rises. When the world get colder the oceans absorb CO2 and, some time later, the concentration falls. For some reason, when the temperature is rising, CO2 tracks quicker than when the temperature is falling.
6. The fashionable theory of gobal warming says that a rise in atmospheric CO2 causes more of the sun's heat to be retained in the atmosphere. This raises the world's temperature and warms the oceans. As the oceans get warmer they
expel more dissolved CO2 and the effect accelerates. This would seem to be a recipe for runaway positive feedback which will raise the world's temperature to an uncomfortable level. We would like to do an experiment to see whether this happens or not.
7. In an area of science where experiments are hard to do, nature has given us 4 repetitions. The Vostock core clearly shows that when the temperature reaches 2°C a mechanism kicks in which sets the temperature falling again and initiates an ice-age. Since this mechanism has repeatedly worked well after 100,000 years of disuse, it seems to be robust.
8. Since the Industrial Revolution, man has contributed increasing amounts of CO2 and other greenhouse gasses to the atmosphere. It is said that these extra greenhouse gasses will change the climate cycle and that this time the temperature will climb far above the historical maximum, plunging the world into disaster.
9. There is about 800 B tonnes of CO2 in the atmosphere and human activities release another 27 B tonnes per year, or 3% of the total . CO2 in the air dissolves in the oceans and there is a lot more in the oceans than there is in the atmosphere. CO2 in the oceans slowly forms limestones, chalk and other rocks. More than 100 times the amount of CO2 in the atmosphere is locked up in these stones (The White Cliffs of Dover are largely CO2). But how much goes where and how long it stays there is not well understood. (See 'non-linear' in para 1). Even if one accepts that man is contributing large amounts of CO2 to the atmosphere, it will dissolve in the sea and then turn to limestone without any help from us.
10. If we consider all greenhouse gasses, not just CO2, the most important by far is water vapour, which contributes 36% of the total effect. Short of wrapping all the oceans in plastic sheet, we can't do much about that.
11. CO2 contributes 9% of the greenhouse effect. Industry currently pumps 3% more CO2 into the atmosphere each year, which is responsible for .27% of the total greenhouse effect. If we shut down all transport and industry tomorrow, it is hard to believe it would have much immediate impact on global warming.
12. A fact that is often overlooked is that the amount of heat radiated by the earth into space varies as the fourth power of the absolute temperature. That is, if the average temperature of the atmosphere rises from 20C to 21C (293K to 294K or .3%), the radiated energy increases by 1.4%. This fourth power law has a strongly stabilising effect on global temperature.
13. It may be true that this small amount of extra greenhouse gas will trigger run-away global warming, but it is hard to find solid evidence for it in the historical record. What evidence there is must come from models of the way the climate works. But models of such complicated mechanisms as the climate are notoriously unreliable until they have been refined and rigorously checked against the historical evidence. Which has not yet happened.
13. I am not a climatologist, but there is a solid looking review paper here. There is a scientific review of Al Gore's film here.
Natural global warming seems to be expected about now in the cycle, but I'm sceptical/skeptical about man-made warming.
Let's start near the top of a warm period, as it were, today. As the world gets warmer (for whatever reason), we would expect the oceans to get hotter and more water to evaporate into the atmosphere. That would produce increased rain and near the poles, increased snow. The ice caps would get bigger, increasing the Earth's total albedo. More of the Sun' heat would be reflected from the enlarged ice-caps and the temperature of the Earth's surface would start to fall. An ice age would begin with the ice ultimately becoming several miles deep. A large part of the globe would be covered by ice and snow and a lot of the Sun's heat would be reflected away into space.
But there is a second source of heat: the earth's hot core, powered by radioactivity. Heat constantly percolates from the core up to the surface. The amount is very small, but ice is an excellent insulator so that heat will accumulate at the earth-ice interface. In time, it could melt the ice to form an ever-enlarging lake under the ice cap. After about 100,000 years the ice would mostly be gone and the climate would become warm again.
A back of an envelope calculation shows that enough heat leaks out of the earth's core to melt enough ice in about 100,000 years, so the idea is not immediately ridiculous, but it does need a more careful calculation. And even then we won't know if it is correct until the ice has come and gone in the manner described.
Richard Waley, whose PhD topic was upper air atmospherics, and I hit on this notion over lunch the at The Marquess of Lorne, an excellent Dorset pub near the village of Powerstock after an archaeological walk.
If the science is hard to understand, the politics is easy. The 'man-made CO2 calamity' gives the developed nations a wonderful stick with which to beat the emerging superpowers of India and China. If the west can persuade them that they have a moral duty to clean up their industries, substantial extra costs are imposed on them which will do something to offset the west's higher wages.
On the campaign level in the west, things work as usual in practical politics. Here is one of several accounts by scientists who changed their views about global warming, from http://www.canadafreepress.com/2007/global-warming051607.htm
"I was on that gravy train, making a high wage in a science job that would not have existed if we didn't believe carbon emissions caused global warming. And so were lots of people around me; and there were international conferences full of such people. And we had political support, the ear of government, big budgets, and we felt fairly important and useful (well, I did anyway). It was great. We were working to save the planet! But starting in about 2000, the last three of the four pieces of evidence outlined above fell away or reversed. The pre-2000 ice core data was the central evidence for believing that atmospheric carbon caused temperature increases. The new ice core data shows that past warmings were *not* initially caused by rises in atmospheric carbon, and says nothing about the strength of any amplification. This piece of evidence casts reasonable doubt that atmospheric carbon had any role in past warmings, while still allowing the possibility that it had a supporting role," he added. "Unfortunately politics and science have become even more entangled. The science of global warming has become a partisan political issue, so positions become more entrenched. Politicians and the public prefer simple and less-nuanced messages. At the moment the political climate strongly supports carbon emissions as the cause of global warming, to the point of sometimes rubbishing or silencing critics."
Have I missed out something important? If so, please email me.
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