Читать книгу Sociology - Anthony Giddens - Страница 230

Global warming is regarded by many people as the most serious environmental challenge. If scientific forecasts are correct, then it has the potential to alter irreversibly the functioning of the Earth’s climate, producing a series of devastating environmental consequences. Global warming refers to the gradual rise in the Earth’s average surface temperature resulting from changes in the chemical composition of the atmosphere. The current scientific consensus is that this is caused in large measure by industrial processes which produce gases, notably CO₂, that have built up in the atmosphere.

Global warming is closely related to the concept of the greenhouse effect – the buildup of heat-trapping gases within the Earth’s atmosphere. The principle is a simple one. Energy from the sun passes through the atmosphere and heats the Earth’s surface. Although most of the solar radiation is absorbed directly, some of it is reflected back. The greenhouse gases act as a barrier to this outgoing energy, trapping heat within the atmosphere much like the glass panels of a greenhouse. A natural greenhouse effect keeps the Earth at a reasonably comfortable surface temperature – about 15.5°C. If it were not for the role of greenhouse gases in retaining heat, the Earth would be a very different place, with an average temperature of −17°C.

When concentrations of atmospheric greenhouse gases rise, the greenhouse effect is intensified and much warmer temperatures are produced. Since the start of industrialization, the concentration of greenhouse gases has risen significantly. Concentrations of carbon dioxide (CO₂, the main greenhouse gas) have increased by around 40 per cent since 1750 – the onset of modern industrialization; methane has increased by 150 per cent and nitrous oxide by 20 per cent (IPCC 2015: 44) (see ‘Global society’ 5.1).

Most climate scientists agree that the increase in carbon dioxide in the atmosphere can be attributed to the burning of fossil fuels and other human activities, such as industrial production, large-scale agriculture, deforestation, mining and landfill, and vehicle emissions. The overall impact of these industrial processes is referred to as anthropogenic (human-created) climate change. The Industrial Revolution of the eighteenth and nineteenth centuries and the spread of industrialization around the globe have produced major, world-historical change.

The Fifth Assessment of the Intergovernmental Panel on Climate Change (IPCC 2015) reports that, on the basis of analyses comparing actual observations with a model forecast based only on natural climate changes and a second model based on natural changes plus anthropogenic climate change, it is extremely likely that the increase in observed temperatures since the mid-twentieth century is due to human activity. In the cautious scientific language of the IPCC, this means a probability of over 95 per cent. This is a much stronger conclusion than that arrived at in the Third and Fourth Assessment Reports of 2001 and 2007 respectively. Figure 5.1 shows the rising trend in surface temperature between 1910 and 2010 compared to the IPCC models.