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knows whether the rise in global temperature in the past century is the result of human activity or just another blip in the history of our planet is tantamount to claiming that they have the answer to the conundrum: how long is a piece of string?

      Carbon dioxide

      Carbon dioxide, or CO₂, is a colourless odourless gas that is heavier than air. It dissolves in water, which is why the oceans of the world are such an important buffer against a rapid rise in CO₂. The amount that will dissolve in water depends upon its concentration in the atmosphere and the temperature of the water. As the temperature of the seas increases, their capacity to dissolve CO₂ decreases. The effect is similar to warming up a bottle of champagne: it causes the fizz of CO₂ to come out of the wine, causing it to froth.

      When the world was formed, many billions of years ago, it came packaged with a finite content of minerals and gases, which have changed very little over all those years. What change there has been is the result of accretion from cosmic dust, asteroids and comets and as a result of radioactive transformation. These are believed to have produced a large addition to the total amount of water and minerals on the planet. As Earth cooled from the primitive molten mass, violent volcanic eruptions occurred during which vast extra amounts of carbon, in the form of carbon dioxide and carbon monoxide, were spewed into the atmosphere from the depths of the planet. Had nothing happened, the concentration of carbon dioxide in the atmosphere would have remained high, possibly reaching 20 per cent, approaching that found on other planets.

      What has changed since that time is the chemical form in which the carbon is found. Over the ages, huge amounts of carbon dioxide have been taken out of the atmosphere and transformed into chalk and coral, into the hydrocarbons of coal, peat, methane and oil, into graphite, diamonds and charcoal. We are not producing any new carbon when we burn fossil fuels We are merely recycling atmospheric carbon dioxide in various chemical guises. The atmospheric CO₂ is constantly being taken up by plants in the process of photosynthesis. The plants are then eaten by animals and the carbon they contain is then given off when the animals metabolise fuels, such as sugar and fat, in order to produce energy. The energy used by a person on a bicycle is produced by burning a carbon-based fuel in the same way as a car burns petrol (but man is less efficient as a machine than an internal-combustion engine).

      Carbon dioxide is not a pollutant (although the US Supreme Court ruled by five to four that it is). Like oxygen, it is part of our atmosphere and it is essential for life. Without CO₂, plant life would cease to exist and most species of animal life, including man, would die out. Ignoring the effects of industrial activity, the amount of CO₂ in the atmosphere is, in biological terms, a balance between animal and plant life. An increase in the amount of animal life, relative to plants, will increase the CO₂, while a relative increase in plant life will reduce it. The giant rainforests of the world take up some 30–40 per cent of carbon dioxide produced. Contrary to what has been portrayed in the media by pressure groups, 85 per cent of the Amazonian rain forests are intact and a further 12 per cent are in a state of ‘recovering’. In the recovering state, the rapidly growing saplings are more efficient sinks of CO₂ than mature trees. Human activity and industrialisation contribute 2.5–3 per cent to the total CO₂ output. There is no doubt that this amount is increasing.

      The concentration of CO₂ in the atmosphere is, in geological terms, historically low at 380 parts per million (0.038 per cent). As a result of this low concentration, it requires only very small additional amounts of CO₂ to cause a large percentage increase in its concentration. There is evidence to suggest that even at this tiny level it is about 0.008 per cent higher than it was a hundred years ago. Some of this increase is due to CO₂ that is given off by the oceans as their surface waters warm up, and a little comes from volcanoes, but most is attributed to human activity – the so-called anthropogenic CO₂. However, the actual total amount of CO₂ in the atmosphere is still tiny. It is estimated that, if no new CO₂ were added to the atmosphere, it would take only five years to reduce its level below what would sustain plant life; if plant life did adapt and continue at this low level of CO₂, all the gas would be used up in about seven or eight years. The CO₂ level found in our blood is essential to our wellbeing. A sudden reduction would cause many people to feel sick and faint and to develop headaches due to a constriction in the blood vessels supplying vital organs. We are physiologically far better adapted to dealing with a rise in CO₂ than with an acute reduction. This may be an evolutionary footprint reflecting the fact that animal evolution occurred during periods of higher, rather than lower, atmospheric CO₂.

      To regard CO₂ as a pollutant is dangerous nonsense. It is less toxic than oxygen and it is present in the atmosphere at levels that are historically low. The problem that has to be faced is that we do not know with any degree of certainty what would happen if the levels were to be increased dramatically over the next century.

* Although these measurements have been fairly consistent and reproducible it is impossible to verify their absolute accuracy as there is no standard measurement with which they can be compared. It is inevitable that some CO₂, which is a soluble gas, will leach out of a bubble into ice, albeit at a very slow rate at these low temperatures. The magnitude of this effect must increase with time. What we can say with some certainty is that the levels of CO₂ recorded in these bubbles is the very lowest that would have been possible. They probably underestimate the actual values that were present all those years ago. It is probable that the actual CO₂ at the time they were formed would have been higher. Similar criticism can be levied against estimates of the temperature that pertained millions of years ago. These are not absolute measurements but are relative.

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       IS GLOBAL WARMING MANMADE?

      STANLEY FELDMAN

      DOGMA

      Man is destroying the planet.

      IF ONE ACCEPTS that the world has become warmer over the past century and this is a threat to our way of life, then it is necessary to examine the evidence that this is due to an increase in the amount of atmospheric CO₂ produced by man.

      The only compelling evidence that CO₂ is linked to the recent rise in the Earth’s temperature due to its greenhouse-gas effect comes from the studies of ice-core samples drilled in the ice caps. Although this may seem a somewhat inexact science, the picture they reveal is surprisingly reproducible. The temperatures at various depths can be measured and recorded, and the CO₂ content of the bubbles of trapped gas, while subject to a little variation, is also remarkably consistent. The dating of the samples is liable to small errors as the decay rate of the various isotopes measured can be influenced by outside events. Although these measurements cannot be considered definitive, our confidence in them is greatly enhanced because they have proved to be reproducible in different ice cores from varying sites made by different investigators. However, one should be cautious in interpreting these values as accurately reflecting the actual temperatures and CO₂ content of the atmosphere at the time the bubbles became trapped in the ice, since it is probable that some CO₂ will have leached out, over thousands of years, even into frozen ice.

      The results of these investigations have been presented, in various forms, for up to 50 million years, but over 500,000 years their accuracy becomes increasingly questionable. It is the general close parallel, the casual association between the rise in temperature and the rise in CO₂ over the past 10,000 years, that has led to the present persuasion that the temperature change is driven by atmospheric CO₂. However, close examination of the samples from the Vostok Lake area of Antarctica over this period shows that in many instances the temperature increase occurred some 600 to 1000 years before the increase in CO₂.

      Exactly

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