All too often, global warming is discussed as something that will affect future generations of people, penguins and polar bears. That it will. But a mounting body of evidence demonstrates that climate change is neither distant nor theoretical. It is here and now:
• The latest report from the Intergovernmental Panel on Climate Change, the internationally accepted authority on the subject, concludes that the climate system has warmed dramatically since the 1950s, and that scientists are 95% to 100% sure human influence has been the dominant cause. In the Northern Hemisphere, 1983 to 2012 was likely the warmest 30-year period of the past 1,400 years, the IPCC found. Atmospheric concentrations of greenhouse gases -- carbon dioxide, methane and nitrous oxide -- have jumped to levels unprecedented in at least the past 800,000 years.
• A year-long USA TODAY special report, "Weathering the Change," documents how climate change is already affecting Americans. Risk and intensity of heat waves, downpours, drought and wildfires are increasing. Sea levels are rising. The oceans are becoming more acidic. In Alaska, glaciers and permafrost are melting.
• A report released in September by the Bulletin of the American Meteorological Society analyzed 12 extreme weather events last year and found compelling evidence that human-caused climate change contributed to half of them. For example, the report concluded, about 35% of the extreme warmth experienced in the eastern U.S. in March-May 2012 can be attributed to man-made factors.
All this ought to be enough to shift the political debate, once and for all, from whether global warming is real to how to respond. Instead, the skeptics have seized on one piece of the 2,216-page IPCC report to renew their contention that concern is overblown.
The report found that the rate of surface warming over the past 15 years (1998-2012) was smaller than the rate calculated since 1951. This "pause" suggests some of the climate models that predicted faster warming are flawed, and natural climate variability is powerful. But it doesn't prove that warming has stopped or is inconsequential.
For one thing, much of the excess warmth being put into the climate system by greenhouse gases is sinking into the world's oceans. For another, 1998 was an extreme outlier of a warm year, thanks to El Niño, a warming of tropical Pacific water that can affect temperatures and weather around the world. Using 1998 as a starting point for a temperature trend is a bit like using Babe Ruth's 60 home runs in 1927 as a benchmark for power hitting.
Perhaps the most sobering part of the IPCC report is its conclusion that "most aspects of climate change will persist for many centuries even if emissions of carbon dioxide are stopped." This doesn't mean it's pointless to put a price on carbon pollution, or to negotiate cuts with China and other big emitters. But it shows that the response will also have to include adaptation, geoengineering research and investments in green alternatives to fossil fuels.
The latest findings ensure one other thing: In 50 years, Americans are far less likely to be talking about this month's budget follies in Washington than they are to be asking why this generation was warned about the risks of man-made climate change and didn't do more about them.
Copyright 2013 USA TODAY
Original headline: Mounting evidence proves that climate change is here and now
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