Key words Global warming
1. Global warming is an increase in the temperature of the land, seas and atmosphere of the earth. The sun provides most of the heat for the earth, but gases such as carbon dioxide and methane in the atmosphere absorb some reflected heat from the sun and stop it escaping back into space. This is known as the greenhouse effect. Carbon dioxide and methane are produced by animals when they breathe and by plants when they decompose, so there is a natural greenhouse effect which traps enough heat to warm the earth sufficiently for humans to live there. However, global temperatures have risen steadily over the past 150 years, with an increase in average surface temperature of about 0.74o
C between 1905 and 2005. During this period,
humans have burned much larger quantities of coal and oil, which released large amounts of carbon dioxide into the atmosphere. They have also cut down many forests, destroying plants which could absorb carbon dioxide as they grow. Thus, the main increase in greenhouse gas concentrations, which is thought to be responsible for the increase in temperature, is due to human activities.
2. Global warming disturbs the interaction between the oceans and the atmosphere, which regulates the climate and weather of the earth. It gives rise to long-term changes in climate. Scientists have studied this phenomenon with computer models of the climate. These models have to be simplified because of limitations in computer power and the complexity of the climate system. The models predict that the earth could be between 1.1 and 6.4°C hotter by the end of the 21st
century, compared with 2000. Researchers test the accuracy
of these models by running them from points in the past and comparing their predictions to actual past measurements of surface temperature. The models represent the past climate reasonably accurately. This gives confidence in their ability to predict the future climate.
3. A small group of scientists deny that global warming is a problem. These global warming sceptics claim that the main reason for global warming is not increased carbon dioxide in the atmosphere due to human activities, but increased heat from the sun. In addition, they suggest that computer models of the climate are inaccurate because they do not take into account the raised temperatures in urban areas due to human activity (known as the Urban Heat Island effect), which would increase the overall amount of warming that is observed. They also point to measurements of carbon dioxide and temperature from Antarctic ice cores which seem to show that, in the past, increases in carbon dioxide concentrations followed increases in temperature and were thus a result of warming and not the cause of it. The majority of scientists do not agree with these claims. However, many ordinary people find them attractive because if global warming is not a problem, they do not have to change their lifestyles.
Roadhouse encyclopaedia of environmental science. (2007) London: Roadhouse Publishers.
controversial methane absorb reflected escaping space decompose steadily average released have cut down forests destroying concentrations thought to be disturbs interaction regulates gives rise to long term phenomenon computer models simplified limitations computer power complexity predict could reasonably confidence deny sceptics take into account raised urban point to Antarctic ice cores
to change their lifestyles
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ACCESS EAP: Foundations • Unit 9
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