Transcript Document
2 A Channel 4 documentary "The Great Global Warming Swindle" claims that man-made global warming is "a lie" and "the biggest scam of modern times." The documentary says the Earth has warmed and cooled throughout history. The recent climate changes are natural, it claims. What is a theory? Theories are ideas created by scientists to explain why things happen. A theory explains evidence from observations or experiments. It predicts future observations. A theory can be tested by making observations and doing experiments. Global warming Global warming is the rise in temperature of the Earth's atmosphere. Many scientists believe that greenhouse gases cause global warming. Global warming causes climate change. Climate change The Earth's climate has always been changing. Now, climate change means changes in our climate since 1900. Greenhouse gases Greenhouse gases trap heat from the Sun. They make up about 1% of the Earth's atmosphere. Carbon dioxide (CO2) is a greenhouse gas. Without greenhouse gases, the Earth would be 30°C colder. Humans could not survive. 1 4 There is evidence that the world is getting warmer. 2 5 There is evidence that the current temperature rise is unusual. 3 6 There is a fairly strong correlation between CO2 levels and atmospheric temperatures. 4 7 There is evidence that human activity causes rising carbon dioxide levels. 5 8 There is evidence that global warming causes more extreme weather. 6 9 There is evidence that humans could prevent global warming. Theory A: Human activity causes global warming Burning fossil fuels Extra greenhouse gases make releases greenhouse global temperatures rise. gases into the atmosphere. This leads to climate change. The evidence: Global temperatures have gone up by 0.7C since 1700. Most warming was between 1910 and 1940 and after 1976. Many scientists agree that increasing amounts of greenhouse gases have made global temperatures go up. The 1990's was the warmest decade of the last thousand years. Scientists predict that increasing global temperatures will make sea levels rise. Before the industrial revolution, 0.028% of the atmosphere was CO2. Now the level is 0.037%. The increase in CO2 is linked to human activity. The concentration of CO2 in our atmosphere is higher now than it has been for 650,000 years. Scientists predict more intense hurricanes. Carbon dioxide takes 100 years to disperse. If we stop making carbon dioxide now, the effects of what we have already done will influence our weather for years. 10 Theory B: Global warming is natural The Earth has gone through many cool and warm periods. Human activity is not significant when you The causes of these climate changes are complex. consider all the factors that affect climate. The evidence: Global temperatures have gone up by 0.7C since 1700. This is not significant. Global temperatures actually decreased between 1940 and 1976. Satellites and balloons have measured atmosphere temperature since 1979. This data shows little warming up to 8 km above the Earth’s surface. Water vapour is the most important greenhouse gas. It makes up 95% of all greenhouse gases in the atmosphere. Water particles in clouds reflect heat from the Sun. “The Great Global Warming Swindle” says that human activity makes 6.5 gigatonnes of CO2 each year. Plants and other animals make 150 gigatonnes each year. Dying leaves make even more CO2. The oceans are the biggest source of CO2. CO2 levels in the atmosphere increase or decrease because of temperature change. When the climate cools, oceans absorb CO2. When the climate warms, oceans release CO2. Solar activity influences global warming and cooling more than any activity on Earth. Solar activity is now very high. This may have caused recent record temperatures. Current global warming is nothing unusual. Temperatures were even more extreme in the Medieval Warm Period. It is difficult to link weather events like hurricanes to global warming. The climate of the world is always changing. 11