Before we consider the evidence that underlies the various predictions that have been made about the consequences of the present and future levels of CO2, it is necessary to ask the questions, ‘Is the world getting hotter?’ and ‘If so, is it doing so at a historically unusual rate?’ If these two questions give the convincing answer yes, then we must consider the evidence that this is due to an increase in atmospheric CO2 caused by man.
Is the world getting warmer?
The answer to this question is that it all depends upon the length of the period studied.
If one takes a very long timescale – say 400 million years – then the answer is no: Earth is at least 10 degrees colder today. If one takes a shorter period – say 10,000 years – then the answer is yes: the world is slowly getting a little bit warmer. There is good evidence of what has been called the medieval warm period in northern Europe between 700 and 1000 CE, when temperatures soared. This was followed some 600–700 years later by the Little Ice Age when the Thames froze over and Bruegel painted his landscapes of the frozen Dutch countryside. It was probably during this period that there was a great expansion of the Arctic ice cap, extending it almost to the shores of Scotland. It caused the abandonment of the Viking settlements in Greenland, which before this time was covered with forests, and the closing of the Northwest Passage from the Atlantic to the Pacific by pack ice.
Coming nearer to our times, in the hundred years 1900 to 2000, northern Europe and America have warmed up by about 0.8ºC and the whole world by about 0.6ºC. This has occurred mainly as a result of warmer and shorter winters. However, between 1940 and 1975 there was reversal of this warming trend and Europe cooled by about 0.3–0.4ºC. So marked was this cold period that predictions of an impending disastrous ice age abounded in the environmentally conscious ‘green press’.
A word of caution about ‘average temperatures’. Until recent times only maximum and minimum temperatures were recorded in many places. Often the places used as weather stations change over the years, and many are near town centres and may be affected by urban warming. During the breakup of the Soviet Union many stations were closed.
In the 25 years from 1975 the world warmed up by about 0.5ºC, although this started to plateau off in 1998 (see Figure 3.6). In the past nine years, accurate monitoring of global temperature by orbiting satellites has shown that this period of global warming has come to an end. Instead of rising, there has been a fall in temperature of about 0.4ºC.
Figure 3.6: Global estimates of temperature change over 140 years (note the 0.6º rise from 1975 to 1998 that gave rise to the global-warming scare) (Calculation from Met Office Hadley Centre)
The net increase in temperatures, recorded over the past hundred years, appears to have been the result of fewer very cold nights, and only modest increases in the daytime temperatures. Table 3.1 demonstrates that the highest temperatures recorded were reached, in various parts of the world, over 50 years ago. Indeed, the number of days when the summer temperature has exceeded 32ºC in the South of France has decreased markedly.
| Continent | All-time high (ºF) | Place | Date |
| Africa | 136 | El Azizia, Libya | 13 September, 1922 |
| North America | 134 | Death Valley, CA | 10 July, 1913 |
| Asia | 129 | Tirat Tsvi, Israel | 22 June, 1942 |
| Australia | 128 | Cloncurry, Queensland | 16 January, 1889 |
| Europe | 122 | Seville, Spain | 4 August, 1881 |
| South America | 120 | Rivadavia, Argentina | 11 December, 1905 |
| Oceania | 108 | Tuguegarao, Philippines | 29 April, 1912 |
| Antarctica | 59 | Vanda Station, Scott Coast | 5 January, 1974 |
Table 3.1
How the scare started
It was the burst of warming following the cold spell that ended in 1975 that gave rise to the global-warming panic. Statistically, a hundred years of ups and downs of less than 1ºC represents too little change over too short a period to know whether or not this is just another blip on the temperature chart or whether it represents the beginning of a new, potentially dangerous change in the world’s weather. Much of the present anxiety is less to do with the actual increase in world temperature – after all, 0.5ºC is less than the variation between town and countryside – but it is the rate of this increase in the 1980s and 1990s that alarmed the weather watchers and started the global-warming panic.
The question that faces us is this: does the recent increase in global temperature represent a departure from the recurring ups and downs of our weather and presage a permanent and increasingly rapid shift towards a warmer world? If so, can we or should we try to counter the effect?
It is like the problem of asking, ‘How long is a piece of string?’ that is at the core of our present confusion. There are those who paint a frightening picture of totally improbable ‘tipping points’ based on a speculative extrapolation of the most extreme predictions. They see the piece of string as being very short. They tell wild stories of cities under water, an ice-covered Britain and imminent global catastrophe. Every storm, drought or flood is proclaimed to be evidence of global warming.
Few of these claims stand up to scientific scrutiny. Climate changes have occurred from the beginning of time. There have been floods, drought and storms ever since the world began, they are recorded in the Bible and are present in the folklore of the first farmers who settled in Mesopotamia at the very beginning of civilisation.
Others take the view that the string is very long and point out that the world has seen the present changes over and over again during its history. They argue that a modest rise in temperature provides us with an extra source of energy at relatively little cost and, like Arrhenius and Callendar, they see the potential benefit to mankind. To them the string is very long. Unfortunately, good news does not sell newspapers or generate research grants, so one seldom hears their side of the story.
The majority take the view that the changes we are seeing are real and they may possibly be made more severe by industrialisation. They advocate caution, suggesting that we should do what we can to moderate the effects of any anthropogenic changes by anticipating any adverse effects that may ensue.
To claim that anyone,