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There's already a mountain of evidence for the reality and seriousness of global warming. But a recent article in the journal Science, "Regional and global sea-surface temperatures during the last interglaciation," by Jeremy S. Hoffman and others is the best evidence yet.

During the past 2 million years, there have been about 20 "ice ages" of greater cold and ice, each lasting some 100,000 years, interspersed with shorter warmer "interglacial" periods. These temperature ups and downs are caused by predictable long-term changes in Earth's orbit around the sun. Earth has been in an interglacial period for the past 12,000 years. The previous interglacial ran from 129,000 to 116,000 years ago, and is known to be the warmest interglacial in 800,000 years.

Hoffman's team studied more than 100 previously published records of ocean surface temperatures compiled by different groups of scientists based on analyses of deeply buried deposits of ocean sediments. Hoffman's goal was to determine how temperatures during the previous interglacial compared with temperatures today. Previous studies were too inaccurate to enable such a comparison, but by combining data from 100 such studies, Hoffman's team achieved the needed accuracy.

The result: Global warming has now pushed temperatures up sufficiently that they are "indistinguishable" from temperatures during the previous interglacial.

This is bad news, because it's known that sea levels during the previous interglacial were 20 to 30 feet higher than today. Such levels are likely to occur again. Even if temperatures were to miraculously stop rising today, Hoffman's conclusion implies present temperatures will eventually melt enough ice to raise sea levels by 20 to 30 feet, swamping coastlines and coastal cities worldwide. For example, according to the research organization "Climate Central," a 20-foot rise would make refugees of some 50 million Chinese, 30 million Indians and 20 million Americans.

But temperatures are not going to miraculously stop rising. Temperatures are already 2 Fahrenheit degrees above preindustrial levels. The 2015 Paris Climate Change Agreement aims to restrain the rise to well below 3.6 Fahrenheit degrees because this is considered a dangerous tipping point. It's hard to see how we can achieve this aim, because the present rapid temperature rise isn't slowing down: 2014 was the hottest year since record-keeping began in 1880. So was 2015. So was 2016. According to Environmental Protection Agency estimates, there is no plausible scenario for greenhouse-gas reductions that can prevent another 2.7 degree rise by 2100, for a total rise of 4.7 degrees.

It's hard to say how long it will take for this nearly certain sea-level rise to occur, but the Greenland and West Antarctic ice sheets are in rapid decline and the scientifically conservative Intergovernmental Panel on Climate Change predicts another three feet of sea-level rise by 2100 in addition to the 8 inches that have already occurred, while the National Oceanic and Atmospheric Administration predicts a rise of up to 8 feet by 2100.

Because the present high level of greenhouse gases (mainly carbon dioxide) in the atmosphere is completely unprecedented during the entire ice-age period, scientists are unable to estimate how long it will take before the full 20- to 30-foot rise occurs. The greenhouse gas level is now above 400 "parts per million," meaning that there are 400 carbon dioxide molecules in the atmosphere for every million air molecules. By studying bubbles of air in deeply buried (and thus very old) ice in Antarctica, scientists know that greenhouse gas levels have remained below 300 parts per million for at least 800,000 years.

It's been 3 million years, long before the ice ages began, since greenhouse gas levels were as high as 400 parts per million. At that time, average temperatures were 6 degrees warmer than today, but 18 degrees warmer at the poles, and sea levels were 80 feet higher! This suggests we could see such sea levels soon.

If we lack the will to really change our habits, this disaster will soon become irrevocable. Those who deny global warming are selling the planet down the river.

The good news is a national solution is surprisingly easy: Enact a fee on carbon production that rises predictably every year and distribute the proceeds to households. This would boost the economy by putting cash for alternate energy sources in people's pockets. For details, see

The local chapter of Citizen's Climate Lobby, which promotes this policy, is holding a benefit supper and concert from 5:30 to 8 p.m. April 7 at St. Paul's Episcopal Church in Fayetteville. Join us! There is no reason to continue our suicidal path.

Commentary on 02/21/2017

Print Headline: On course to crash

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