The Truth About Global Warming

Claudia Cornwall

A

Eleven of the hottest years since 1850 occurred between 1995 and 2006. Last year, the United Nations Intergovernmental Panel on Climate Change (IPCC) reported that the earth was about 0.75°C warmer than it was in 1850. While this doesn't sound like a lot, a small difference in average temperature can make a big difference in climate. During the last ice age, for example, the planet was only about 5°C colder than now.

B

The IPCC has concluded that human activity is very likely responsible, by increasing the concentrations of greenhouse gases and thus the greenhouse effect. More than 25 scientific societies, including the national science academies of the G8 nations, have endorsed the conclusion. Some scientists, however, still disagree, arguing that human contribution is minimal.

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C

The effect, explains Robert Charlson, a professor at the University of Washington, 'has been on the scientific books for over a century. It has been tested very thoroughly.' Certain gases cause the atmosphere to trap heat energy at the earth's surface. Without the greenhouse effect, the earth's average global temperature would be -18°C, rather than the present comfortable 14.6°C. The concern is with the enhanced greenhouse effect that humans cause - specifically, that it will heat the planet too much.

D

The main greenhouse gases (GHGs) are carbon dioxide (CO₂), methane, nitrous oxide, chlorofluorocarbons (CFCs) and water vapour. Except for CFCs, which are for commercial purposes, these gases are found in nature. Burning fossil fuels, trees and agricultural waste adds to the CO₂ , methane and nitrous oxide, as do landfills, oil refineries and coalmines. And we affect water vapour indirectly, too. As the earth warms because other GHG levels increase, evaporation ramps up, creating more water vapour.

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E

'CO₂ has increased 35 per cent since the beginning of the industrial era,' says Gavin Schmidt, a climatologist with NASA's Goddard Institute for Space Studies in New York. 'Methane has more than doubled. Nitrous oxide has gone up 17 per cent.'

F

Scientists are particularly concerned about CO₂ because it is the most abundant of the gases that we affect directly. While we have stabilised our CFC and methane emissions, we have not done the same with CO₂ so far. The carbon dioxide in the atmosphere continues to rise by about 0.4 per cent a year - because the fossil fuels that produce it fill 85 per cent of our energy requirements.

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G

According.to NASA's Schmidt, 'CO₂ stays around for centuries.' Worldwide, we produce some 23.5 gigatonnes of CO₂ annually. (A gigatonne is a trillion kilograms.) Fortunately, only half of this amount stays in the atmosphere; natural systems absorb the rest. For instance, oceans, our largest repository of carbon dioxide, take in more than a quarter of our CO₂ emissions every year. They already hold about 50 times the amount in the atmosphere and ten times that in the land biosphere. But just how much more they can safely store is still not clear. In addition, forests and plants soak up less than a quarter of CO₂ emissions. Through photosynthesis, plants separate CO₂ into oxygen, which they emit, and carbon, which becomes part of their cells.

H

Climate change may also result from regular shifts in the orbit of the earth and the tilt of its axis changing how sunlight is distributed around the globe, and may explain why the ice ages came and went. These shifts take place slowly over hundreds of thousands of years.

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I

Tiny particles pumped into the atmosphere by erupting volcanoes and industrial pollution reflect some solar energy back to space, with the effect of making things cooler. In 1991, Mount Pinatubo in the Philippines blew so much dust into the stratosphere that the temperature dropped by half a degree for two years.

J

Water in the form of vapour and clouds plays a role, but their impact is hard to predict. Water evaporating from warmer oceans creates clouds that can both trap heat and.reflect it into space. 'Low clouds tend to cool the planet,' Professor Charlson says. 'High clouds warm it.'

K

Many researchers have concluded that natural forces alone do not explain the temperature increases over the past 30 or 40 years. Bruce Bauer, who studies ancient weather systems at the World Data Centre for Paleoclimatology in the US, says, 'When you try to do the maths, the only way you can calculate what's happening is to include the effects of artificial CO₂ .'

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L

The theory of heat-trapping gases projects that as CO₂ emissions go up, temperatures will rise in the lower atmosphere and at the surface of the earth. Thomas Karl, director of the National Oceanic and Atmospheric Administration's National Climatic Data Centre in the US, says, 'The evidence continues to support human impact on global temperature.'

M

According to the IPCC, by 2100 the average temperature might rise by as much as 5.8°C. But its report also says we could hold temperature increases to a more bearable two degrees above pre-industrial levels. Getting that result means halving current CO₂ emissions by 2050, which is achievable if we lower them by slightly over 1 per cent of current levels every year until then.

QUESTIONS 1-5

Reading Passage 1 has 13 paragraphs, A-M.
Which paragraph contains the following information?
Write the correct letter A-M in boxes 1-5 on your answer sheet.

1. Of all GHGs, methane has had the highest increase in the age of industrialisation.
2. The greenhouse effect prevents the earth's atmosphere from becoming too cold.
3. Nearly 50 per cent of CO₂ produced is dissipated in our natural environment.
4. There are contradictory opinions about the role of human beings in enhancing global warming.
5. The atmosphere surrounding us has all but one of the greenhouse gases present in it.

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QUESTIONS 6-9

Answer the following questions using NO MORE THAN THREE WORDS from the text.
Write your answers in boxes 6-9 on your answer sheet.

6. How did scientific societies and science academies respond to the result reached by the IPCC?
7. What are chlorofluorocarbons used for?
8. What environmental effect did the eruption of Mount Pinatubo have that lasted until about 1993?
9. What forms of water cause the earth's temperature to rise or to fall?

QUESTIONS 10-13

Complete each sentence with the correct ending A-F from the box below.
Write the correct letter A-Fin boxes 10-13 on your answer sheet.

10. According to Professor Robert Charlson
11. According to Bruce Bauer
12. According to Thomas Karl
13. According to the Intergovernmental Panel on Climate Change

1. carbon dioxide remains for hundreds of years.
2. one must take into account the effects of unnatural carbon dioxide.
3. our planet is warmer than it was hundreds of years ago.
4. the rise in the earth's temperature could be controlled.
5. there is proof that global temperature has been affected by humans.
6. science has known of the greenhouse effect for more than a hundred years.