years ago; it was the time of ‘Snowball Earth’, just before multi-cellular life forms appeared. The period of Snowball Earth was followed by several million years of warming.
The finding of fossil remains of gastropods in the trans-Antarctic mountains near the south pole is good evidence that the Antarctic was much warmer than today – indeed, warm enough to support animal life – about 15 million years ago. This means that the huge glaciation that formed the Antarctic must have occurred when the CO2 levels in the atmosphere were over 0.5 to 1.0 per cent. Although no one can be certain of the CO2 level at this time or the exact extent or duration of the glaciation, it is evident that, in the past, Earth has cooled to very low temperatures in spite of very much higher levels of CO2 than is present today.
None of this is proof that CO2 has not been important as a global greenhouse gas in the past or that it does not play a part in determining the present temperature of our planet. However, it does indicate that high levels of CO2 in the atmosphere are not incompatible with global cooling. It must be borne in mind that many of the figures quoted are based on assumptions and calculations. This is why much of the argument about global warming has centred on what is happening now and how this relates to the period that we can measure with some accuracy, the past 1,000–2,000 years (see Figure 3.2).
Figure 3.2: Temperatures on the surface of the Sargasso Sea over 3,000 years – evidence from isotope studies of marine organisms
Evidence from ice-core samples
Information about the levels of CO2 and temperature dating back hundreds of thousands of years has come from cores drilled in the ice in the Antarctic. Bubbles of air trapped in the ice at the time it was formed give surprisingly reproducible measurements of the CO2 levels. The temperature at those times is calculated from probes inserted into the ice which measured isotope ratios.*
They reveal that, for the past 500,000 years, the level of CO2 has been roughly stable at around the present levels of less than 0.04 per cent. Over this period of 100,000 years the Earth has cooled slightly, although from time to time the temperatures have fluctuated through swings of 3–4ºC.
In order to get some idea of what the conditions were like further back in time we have to make assumptions based on the changes that we know took place. Primitive cellular animal life evolved between 500 and 300 million years ago. As life developed and photosynthesis occurred, large amounts of the CO2 were rapidly sequestrated from the atmosphere by plant and animal life and deposited as chalk, peat, shale, coal and oil. This produced a fall in CO2 concentration from a high of 4.0 per cent to the 0.038 per cent found today. The white cliffs of Dover were made of their calcified carcasses, and they contributed to many of our hills and to the coral of tropical islands. Throughout this time, the Earth was cooling and, although the CO2 levels were falling, they were many times higher than today.
The CO2 produced today when we burn fossil fuels is merely returning into the atmosphere a minute part of the CO2 sequestrated by plant and animal life over hundreds of thousands of years. It is not new CO2 that we have produced. It is CO2 that is being recycled. If we were to hold a huge bonfire and burn all the available fossil fuel, coal, oil and gas in the world at one go, it would raise the atmospheric CO2 by only a small amount, to nowhere near the level it was 500 million years ago, when global cooling caused much of the Earth’s surface to be covered with ice.
Predicting future global temperatures
It was almost entirely due to the apparent link between the temperature and CO2 levels over the past few hundred thousand years, revealed by the analysis of ice cores drilled in the ice caps, that the present concern about the effect of human activity on the CO2 levels in the atmosphere has been given some scientific credence (see Figure 3.3).
Figure 3.3: Ice-core date from Vostok, Antarctica (after Raynaud et al., Science 259, 1993)
The indirect information obtained from the ice-core samples in the Antarctic give us a picture of the CO2 levels and temperatures over the past 600,000 years. However, they can tell us only about the CO2 levels and temperatures locally; they do not tell us what was happening to the rest of the world. While it is likely that the CO2 levels measured in one place, such as Mount Mauna Loa in Hawaii, will not differ significantly from that in the rest of the world, the same cannot be said for the temperature. It would be a nonsense to suggest that a period of hot summers in Manchester meant that there was also a period of excessive heat in Botswana. It is unlikely that the relative hot and cold spells found in the Antarctic ice-core samples accurately reflect what was happening in the rest of the world.
Although the results are largely reproducible, their absolute accuracy cannot be verified, as there are no standard measurements with which to compare them. However, we have direct and anecdotal historical evidence of the temperature changes in the past 1,000 years from various areas around the world (see Figure 3.4).
Figure 3.4: Over 1,000 years there is little change in the temperature of northern Europe
Nevertheless, it is only in the past 50 years that advances in technology have allowed us to measure the change in CO2 levels accurately and record temperatures continuously. In the past 15 years, thanks to the use of Earth-orbiting satellites, we are now able to obtain accurate, reproducible data on ocean levels, global temperatures and the behaviour of clouds.
Global-warming predictions
It is largely due to the gaps in our knowledge and the indirect nature of the information about events in the remote past that people have interpreted the same information in different ways. There is no doubt that some have seen political and personal advantage in filling in these gaps with the most absurd, scary guesses and projections; others have minimised their importance or ignored the potential problem; while some have used the information selectively in order to advance a preconceived hypothesis. The information has been misinterpreted and wildly exaggerated by some in order to make political points. Some pressure groups justify this as being necessary to alert the public to the perceived dangers of global warming. They echo St Paul, who in his letter to the Corinthians appeared to license such scare tactics when he wrote, ‘If the trumpet give an uncertain sound who shall prepare himself for battle?’ Indeed, Sir John Houghton, the first chairman of the International Panel on Climate Change (IPCC), is reported to have said, ‘Unless we announce disasters no one will listen to us.’
There is no doubt that the evangelical nature and the scary exaggerations of many who claim the environmental banner – and their insistence that ‘all reputable scientists agree with them’ when, clearly, many do not (the Oregon petition had more than 33,000 signatures of scientists disagreeing with the theory of manmade global warming, more than 9,000 of whom have PhDs) – has done a grave disservice to science and made many question the basis of all the work linking anthropogenic CO2 to global warming.
The most alarming suggestion of the doomsday environmentalists, that the oceans are rising at an alarming rate, has been proved wrong. Islands that were due to be submerged, according to their forecasts, are actually seeing the seas receding. Their prophecies have been
