Excerpt 1 The climate of Earth is changing.Climatologists are confident that over the past century, the global average surface temperature has increased by about half a degree Celsius.This warming is thought to be at least partly the result of human activities, such as the burning of fossil fuels and the clearing of forests for agriculture. As the global population grows and national economies expand, the global average temperature is expected to continue increasing by an additional 1.0°C to 3.5°C by the year 2100. Excerpt 2 Global warming may or not be the great environmental crisis of the 21st century, but—regardless of weather it is or isnt—we wont do much about it.We will argue over it and may even, as a nation,make some fairly solemn-sounding commitments to avoid it.But the more dramatic and meaningful these commitments seem,the less likely they are to be observed. Excerpt 3 Since the early eighties we have been only too aware of the devastating effects of large-scale environmental pollution.Such pollution is generally the result of poor government planning in many developing nations or the short-sighted, selfish policies of the already industrialized countries which encourage a minority of the worlds population to squander the majority of its natural resources. Excerpt 4 Even if we were to magically stop all greenhouse-gas emissions tomorrow the impact on global climate would continue for decades.Delay will simply make the problem worse.The fact is that some of us are doing quite well the way things are.In the developed world prosperity has been built on 150 years of cheap fossil fuels. Material progress has been linked to energy consumption.Today 75 percent of all the worlds energy is consumed by a quarter of the worlds population.The average rich world resident adds about 3.2 tons of CO2 yearly to the atmosphere, more than four times the level added by each Third World citizen.The US, with just 7 percent of the global population, is responsible for 22 percent of global warming. Excerpt 5 One group, led by Gerald Meel at NCAR, used two state-of-the-art climate models to explore what could happen if the world had held atmospheric concentrations of greenhouse gases steady since 2000.The results:Even if the world had slammed on the brakes five years ago, global average temperatures would rise by about 1 degree Fahrenheit by the end of the 21st century.Sea levels would rise by another 4 inches over 20th-century increases. Excerpt 6 We must, however, find a solution to the threat of global warming early in the 21st century.Such a commitment would require a degree of shared vision and common responsibilities new to humanity.Success lies in the force of imagination, in imagining what would happen if we fail to act.Although many living in cold regions would welcome the global-warming effect of a warmer summer, few would cheer the arrival of the subsequent tropical diseases, especially where there had been none. Which of the following is NOT mentioned as a reason for the global warming?