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BIOMES OF THE EARTH - OCEANS Phần 5

Tham khảo tài liệu 'biomes of the earth - oceans phần 5', ngoại ngữ, anh ngữ phổ thông phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 92 OCEANS Among IPCC scientists the consensus is that human activities are releasing high levels of greenhouse gases into the atmosphere and this is causing an enhanced greenhouse effect that is overheating the planet. What is the greenhouse effect Some of the gases that occur naturally in the atmosphere carbon dioxide and methane for example absorb infrared radiation emitted from Earth s surface. They are called greenhouse gases because like the glass in a greenhouse they absorb outgoing infrared radiation and trap heat energy as they do so. On a sunny day in winter for example the air in a greenhouse becomes much warmer than the air outside partly because of this effect. On a global scale greenhouse gases trap heat in the atmosphere and warm Earth s surface. The greenhouse effect is a natural process that has been happening through much of the planet s life. Without it the Earth today would probably be at least 54 F 30 C cooler. The problem lies in human activities enhancing the greenhouse effect. When people burn large quantities of fossil fuels oil products natural gas coal and so on the activity releases extra carbon dioxide into the atmosphere. This increases the greenhouse effect trapping more heat energy in the atmosphere and thus slightly warming the planet. By analyzing the record of carbon dioxide trapped in polar ice over the last few hundred years scientists have discovered that atmospheric carbon dioxide levels have risen by one-quarter in the last 150 years. Recent temperature measurements across the globe reveal that the 1990s were the hottest decade since records began. Global warming appears to be happening. Since the late 1990s for example the thickness and coverage of Arctic sea ice has declined perhaps an early warning sign of global warming. In 1998 many coral reefs across the Indian Ocean turned white. This coral bleaching comes about when coral polyps eject their partner algae see Coral grief pages 213-215 . The bleaching event can be enough