Dennis T. Avery
March 24, 2006
Humans now control Earth’s climate, James Hansen of NASA told CBS’ “60 Minutes” last week. His evidence: the edges of the Greenland ice sheet are melting rapidly. Hansen says the speed of this melting proves that man-made greenhouse gases are responsible.
Sorry, Dr. Hansen, but the melting edges of the Greenland ice sheet don’t prove your point. Melting around the edges is exactly what the Vikings saw on Greenland 1000 years ago when they named the island—for its green coastal meadows. They moved in with their cattle, and thrived for 300 years, during what we now call the Medieval Warming.
The Vikings’ mistake was thinking that Greenland would stay warm, that the Earth’s climate was stable. Greenland was then warmer than today, and the summers were longer. There was ample grass and hay for the Vikings’ dairy cows. The Norse settlement grew to 3000 people.
Then Greenland’s climate suddenly got colder. The Little Ice Age had begun. Sea ice moved south, and the Vikings’ sailing ships could no longer get through to trade wood for seal furs. Shorter summers produced less hay to feed the Viking cows through longer, colder winters. The last written record found in the abandoned Viking colonies was dated 1408.
Our panic-prone scientists seem to have forgotten their own ice cores, drilled deep into the Greenland ice sheet in the 1980s. These ice cores document a natural, sudden-but-moderate 1500-year global warming cycle. Oxygen isotopes in the ice layers show 300 worldwide warmings over the past 500,000 years.
The ice cores tell us that variations in the sun are constantly warming and cooling our planet. The big Ice Ages come about every 100,000 years. The warm interglacial periods like our own last about 10,000 to 12,000 years.
Through it all, however, runs the moderate, natural 1500-year climate cycle that raises temperatures about 2 degrees C above the mean for 750 years or so—and then abruptly drops the temperatures 2 degrees C below the mean (at the latitude of northern Europe).
Man’s climate impacts are puny compared to the million-degree heat of the sun. There’s no evidence that human-emitted CO2 has added much to the current temperatures. Our moderate warming to date—0.8 degree C—virtually all occurred before 1940, and thus before much industrial development.
If you want to talk about sudden, ice cores from the Freemont Glacier in Wyoming show it went from Little Ice Age cold to Modern Warming warm in the ten years between 1845 and 1855. Naturally.
Greenland today has 20,000 people, 50,000 sheep and a sizeable fishing industry. But the climate cycle will turn in a few more centuries. Then Greenland’s sheep will be in serious trouble and its fishermen will need icebreakers to reach the fishing grounds. (There were no fish bones in the Norse colonies’ trash heaps).
As for melting ice from Greenland flooding London, remember that it didn’t happen during the Medieval Warming, so it’s unlikely to happen in the Modern Warming. The melting of 100 cubic kilometers of Greenland ice would raise sea levels by only 0.01 inch. Dr. Hansen should know that recent satellite research shows Greenland’s interior ice sheet has thickened 2 inches in the past 11 years, because warmer temperatures are evaporating more seawater to make more snow.
The Vikings can be forgiven for missing the 1500-year climate cycle. They didn’t have thermometers, written records or the ice core histories. NASA’s Dr. Hansen cannot be let off the hook so easily.
Dennis T. Avery is a senior fellow for Hudson Institute in Washington, DC and the Director for Global Food Issues (www.cgfi.org). He was formerly a senior analyst for the Department of State. Readers may write him at Post Office Box 202, Churchville, VA 24421.
26 mar 2005