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Climate scientists drive through the heart of skeptics' argument



Global warming skeptics sometimes say rising temperatures are just another naturally occurring shift in Earth's climate, like the Medieval Warm Period of the years 800 to 1200 or the Little Ice Age, a period of cooling that spanned from roughly 1300 to 1850. [19659002] But a pair of studies published Wednesday provides stark evidence that the rise in global temperatures over the past 150 years has been far more rapid and widespread than any warming period in the past 2,000 years – a finding that undercuts claims today's global warming isn

"The familiar maxim that the climate is always changing is surely true," Scott St. George, a physical geographer at the University of Minnesota in Minneapolis, said in a written commentary on the studies. "But even when we push our perspective to the earliest days of the Roman Empire, we can not discern any event that is remotely equivalent ̵

1; either in degree or extent – to warming over the last few decades."

Since the beginning of the 20th century, the global average temperature on Earth has risen by about 2 degrees Fahrenheit. A consensus of climate scientists pins the increase primarily on the burning of fossil fuels, which spews carbon dioxide and other heat-trapping greenhouse gases into the air. In the absence of concerted efforts to reduce greenhouse gas emissions, the United Nations says that global average temperature could rise by an additional 5.4 to 9 degrees Fahrenheit by 2100.

One of the studies, published in the journal Nature, Little Ice Age and other natural fluctuations affected only limited regions of the planet at a time, making modern warming the first and only planetwide warm period in the past two millennia. The other study, published in Nature Geoscience, shows that the rate of modern warming has far outpaced changes that occurred before the rise of the industrial age.

For the research, a team led by Raphael Neukom, and a postdoctoral researcher at the University of Bern's Institute of Geography in Switzerland, analyzed 2,000 years of climate data. In the absence of direct temperature information – the thermometer measurements were scarce before mid-19th century – scientists looked at the data on the old trees' growth rings, the layers of glacier ice and the remnants of corals, whose layers have different chemical compositions depending on the temperature of the seawater

The Nature study mapped the temperature fluctuations across the planet, finding, for example, that Little Ice Age did not affect the whole world at once. Temperatures bottomed out in the Pacific Ocean around 1500, the scientists found; Europe and North America did not fully chill out for another two centuries.

The same pattern was observed for the higher temperatures seen during the Medieval Warm Period.


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