TOKYO -- The average global temperature is likely to increase by up to 4.8 degrees Celsius, and sea levels could rise a maximum of about 32 inches by the end of the century if greenhouse gas emissions continue to rise, according to a draft of a U.N. report on climate change.
The latest draft of the Intergovernmental Panel on Climate Change (IPCC) task force said heat waves caused by human activities have very likely been increasing in some parts of the world.
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The IPCC's fifth assessment report will serve as the foundation for international negotiations to create a framework to combat global warming from 2020 onward. A summary of the report for policymakers will be discussed at an IPCC meeting scheduled for late September in Sweden. The IPCC is to announce the report after making necessary revisions to the draft.
A Japanese Environment Ministry committee met Friday to study measures to use the report to set Japan's greenhouse gas emission target and produce countermeasures.
According to the draft, the global average temperature has risen by 0.89 C in the 112 years since the beginning of the 20th century. The average global temperature has risen 0.79 C in the last 100 years, up from the 0.74 C that was announced in the IPCC's fourth report in 2007.
The draft said there is a "more than 95 percent" possibility that human activities have contributed to more than 50 percent of the rise in the global average temperature since the mid-20th century, which is up from "more than 90 percent" in the previous report.
The average temperature in the future varies, depending on how much CO2 emissions increase.
In experiments using large computers, the IPCC predicted future temperatures for the 20-year period from 2081 through 2100 based on four scenarios, comparing them with the average of the 20 years through 2005.
In the scenario with the lowest CO2 concentration level, the temperature rose by a maximum of 1.7 C. If no measures were taken to reduce emissions and the concentration level continued to rise, the temperature was expected to increase by a maximum of 4.8 C.
The sea level has risen more than 19 centimeters since the beginning of this century due to global warming.
In the scenario with a low carbon dioxide concentration level, the IPCC predicted that the sea level would likely rise by up to 54 centimeters (21 inches) at the end of this century, and by up to 81 centimeters in the scenario with a high concentration level. Taking into account the effect of melting ice sheets in Greenland and the Antarctic due to global warming, the IPCC revised the higher projection from up to 59 centimeters in the last report.
According to the Environment Ministry, 80 percent of Japan's sand beaches would be lost if the sea level rose by 65 centimeters.
The draft report said the length and frequency of heat waves have highly likely been increasing in Asia, Europe and Australia since 1950, and human activities are most likely the main cause of global warming. It also said heat waves and severe downpours are extremely likely to increase in most areas of the world by the end of this century.
The ice coverage in the Arctic Ocean has been shrinking since 1979, reaching a record low last summer.
The IPCC draft report said there is a high possibility that the summer Arctic sea ice may disappear by the middle of this century if measures to reduce CO2 are not taken.