4.6 Global climate change continued
Box 3: Some impacts of global climate change
Record global temperatures
The global mean surface temperature of our planet has been rising steadily for 30 years. According to climate scientists, who have constructed a reliable global temperature series from 1860, nine of the ten warmest years in this long record have occurred in the last ten years, i.e. up to and including 2004. Global temperatures are now 0.7°C higher than a century ago. This may not sound much but climate scientists are now confident they are detecting the first signs of induced climate change.
Global climate models, such as those used by the Meteorological Office's Hadley Centre, show clearly that global temperature rise during the twenty-first century depends in large part on the greenhouse gases emitted as a consequence of human activity over the next few decades. Projections for the additional temperature rise this century suggest a range from about 2 to 5°C is likely (but will be higher over land than the oceans). What are the consequences of such an outcome? For simplicity we'll concentrate on one region, Europe.
Regional impacts: Europe
In recent years Europe has experienced a series of extreme weather events. In December 1999, northern and central Europe were hit by three intense windstorms, resulting in widespread damage, 200 fatalities and losses estimated at 18 billion euros. In 2002, 15 major floods occurred in Europe, most notably the August floods in central Europe, leading to 250 fatalities. In 2003 an unprecedented heatwave hit western Europe from June to August. Temperatures over 40°C were common and even reached 38.5°C (1O1.3°F) in Kent on 11 August, the highest temperature ever recorded in the UK. The summer heat lead to widespread forest fires and agricultural losses, and to an estimated 201,000 excess deaths, including 2100 in the UK, mostly amongst the vulnerable elderly population.
Are these events a sign of climate change? Not necessarily, although more frequent heatwaves and summer droughts and more incidents of intense rainfall are predicted for much of Europe. Wetter winters are also expected in the north, but whether this will lead to more storms is not clear. However, several points about climate change are illustrated. Firstly, extremes of weather can be more significant for both natural ecosystems and society than changes to the mean. Secondly, climate change is not only about warming, changes to rainfall patterns and water availability can often be more important. Thirdly, in both natural ecosystems and society some sectors are more sensitive and vulnerable to climate change than others, although there will often be winners as well as losers: for example, elderly people are less likely to die in Europe during milder winters.
The summer of 2003 was 2.3°C above the 1960–1990 mean. Without climate change it could be expected to occur once in a thousand years. With climate change it is only a matter of time before a 2003-type summer becomes the average, and this could occur as soon as the 2040s if nothing is done to reduce emissions. What would a hot summer then be like?
Changing the climate system
At some stage, if climate change is allowed to proceed, tipping points will be reached in the climate system – a system that links oceans, ice, atmosphere and biosphere – leading possibly to irreversible changes. Two specific dangers in the northern hemisphere have been identified: the melting of the Greenland ice cap, which would raise sea-levels by 7 metres, and closing down the thermohaline circulation, the ocean conveyor that drives the warm currents in the North Atlantic. Best estimates are that the former is almost certain to happen (but over many hundreds of years), while the latter will only partially close down and its effects will only slow the warming over Europe, not lead to colder conditions. None of this is known with any great confidence, but it is clear that the more climate change proceeds the greater the risk of permanent alterations to the climate system.
There is another reason why global climate change is difficult to deal with, and that is the length of time most greenhouse gases persist in the atmosphere, which for carbon dioxide and most other greenhouse gases is of the order of a hundred years. This means that our grandchildren, and their grandchildren, will suffer the climatic consequences of the emissions that we are producing now. It can be difficult for policy makers to act decisively now when the effects of such changes are both uncertain and likely to have most impact long after they have gone. There is also a judgement to be made between acting now and bearing the costs, and delaying – with the risk of harm to future generations if the delay is too long – in the hope of being able to take more effective action later. There is no simple answer to this type of situation, but there is an historical precedent in the precautionary principle approach taken by the international agreement to protect the ozone layer, where, as we saw in Case Study 1, another group of long-lived chemicals, CFCs, posed a direct threat to the global environment.
I have used the first two case studies to look in some detail at two difficult global environmental problems, with occasional forays into the past to get a better perspective of where we are now. In the process we have also had to explore some technical matters, and confront a few fundamental concepts. For the last case study I am again going into the past, this time to look for some wider and perhaps less familiar consequences of the Industrial Revolution. Although many of its immediate effects were local, other influences spread across the world as new forms of transport and communication allowed international trade to flourish. Together, trade and technology transformed the agriculture and economies of much of the world in the nineteenth century. Part of that story is linked to the early history of refrigeration, and, in the final case study, to its effect on a distant country not usually associated with the Industrial Revolution.