In my first column on climate change I discussed what responsibilities it might impose on us as Christians. The latest assessment by the Intergovernmental Panel on Climate Change (IPCC), from 2007, claimed that there was a 90 per cent probability that human activity was the main agent. Given the complexity of the factors there is room to question aspects of this assessment but I think it to be prudent to take the most comprehensive and broadly accepted evidence. I am not qualified to judge between the experts.
The first, and rather dramatic, clue is a graph which shows the growth in the greenhouse gases over the last 10,000 years. (Historical measurements are made through the analysis of ice cores.) It shows a nearly horizontal line until about 200 years ago, coinciding with the Industrial Revolution, which led to a sustained, sharp vertical upturn. Carbon dioxide, which is the major element, shows an increase of 35 per cent over pre-industrial levels; it is growing at its fastest recorded rate. Methane and nitrous oxide have also increased. Halocarbons, resulting from refrigerators and spray propellants, are a man-made new arrival. Our contribution to this is confirmed by the analyses which show that the major source is the burning of fossil fuels, and that the hotspots are located over the areas of high industrialisation.
There are, of course, factors which alleviate the situation: some result from human activity and some from natural conditions. Aerosols, which are airborne particles from sources such as dust storms, forest fire and volcanoes, help in reflecting sunlight back to source, although the process is not fully understood. Solar energy has made a contribution to warming but the effect is small at around a 10th of the whole. Land management has good and bad effects. Measurements taken in 2005 show that the contribution of human activities to climate change outweigh the other factors by a large margin.
Naturally we should expect to see changes caused by these factors: 11 out the last 12 years up to 2006 have been the warmest since 1850, when good records began. The upwards trend in global temperatures measured over the 20th century is accelerating, and the majority of the increase has occurred over the last 50 years. We now experience fewer frosty days and more warm days and nights. This is further confirmed by tree-ring data: the last warm period, around the end of the first millennium, was some degrees cooler than recent average temperatures.
Spring snow cover, which can have a marked effect on water conservation, had decreased in northern latitudes. The sea absorbs much of the additional heat, leading to natural expansion and rising levels. There have been marked reductions in permafrost and the melting of sea ice in Greenland and the Antarctic. Currently, there is insufficient data to judge whether the rate of rise is accelerating. Again, the graphs covering the last 100 years show a steady, threatening trend.
Water vapour in the atmosphere is largely controlled by temperature, and so this has been increasing. Various areas across the world have become wetter, while others have become drier. Disaster has often been the result.
Forecasting the future is a different problem. The principal method is the use of complex models which attempt to take account of perceived relevant values and their interplay. Educated assumptions often have to be inserted, and necessarily the room for error increases with the length of the period predicted. However, many different scientists applying their own models independently give a useful, if not infallible check. Indeed, the predictions made in the previous IPCC assessment in 2001 needed considerable updating in 2007. Some leading climatologists have recently argued that cyclical changes in atmosphere and ocean currents will actually cool the earth over the next 20 years; this may mask the underlying trend.
Many of the future outcomes are unavoidable because we have yet to undergo the full results of past atmospheric changes. Over the next 20 years various scenarios show that an increase similar to our recent experience will continue. Beyond that, the most likely scenarios suggest increasingly higher temperatures by the end of the century (compared to year 2000), in the order of 2°to 4° C, but could be half as much again. It was estimated that sea levels would rise by 30 to 40 centimetres. And accelerated loss of ice from Greenland and the Antarctic would increase this by up to 20 centimetres. Some more recent studies, which look closely at the possible effects of melting ice, suggest an overall sea level rise of a metre and over. A recent report by the Met Office suggests that these changes could occur within 50 years from now. But many factors, and their interaction, within these projections are not yet well understood, and doubtless they will become more accurate as these aspects are more closely studied.
Naturally, different regions of the earth will be affected in different ways and different levels of severity. In a future column on climate change I will look at how different regions of the world may be affected.
How long will the effects of climate change last? We are certainly talking hundreds of years. Hold on to your seat belts for a long and bumpy ride.
Readers who are familiar with the IPCC assessment, will be aware of the sparseness of my description. But I think it better for us to grasp the overall picture which the assessment paints than to get lost in detail. Many interesting and knowledgeable comments have been made to Climate Change – 1. I hope you will continue your critique and suggestions with this second instalment.