One of the most controversial subjects in the 2,000-page report was how to deal with a purported slowdown in warming in the past 15 years. Climate skeptics say this “hiatus” casts doubt on the scientific consensus on climate change. Many scientists say the purported slowdown reflects random climate fluctuations and an unusually hot year, 1998, picked as a starting point for charting temperatures. Another leading hypothesis is that heat is settling temporarily in the oceans, but that wasn’t included in the summary.
As expected, the IPCC raised its projections of the rise in sea levels to 10-32 inches by the end of the century. The previous report predicted a rise of 7-23 inches.
Going well beyond its four previous analyses of the emissions problem, the Intergovernmental Panel on Climate Change endorsed a “carbon budget” for humanity — an upper limit on the amount of the primary greenhouse gas, carbon dioxide, that can be emitted from industrial activities and forest destruction.
To stand the best chance of keeping the planetary warming below an internationally agreed target of 3.6 degrees Fahrenheit above preindustrial levels and thus avoiding the most dangerous effects of climate change, the panel found, only about 1 trillion tons of carbon can be burned and the resulting gas spewed into the atmosphere.
Just over half that amount has already been emitted since the beginning of the Industrial Revolution, and at current rates of energy consumption, the trillionth ton will be released around 2040.
The United States was for many decades the world’s largest emitter of greenhouse gases, though it was surpassed a few years ago by China. It refused to agree to a treaty called the Kyoto Protocol that sought to limit global emissions, greatly weakening that effort, and efforts to pass a comprehensive climate policy for the United States failed soon after Mr. Obama took office. (Wash Post, 9/27/2013, NY Times, 9/27/2013)
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