Matt Ridley: The mysterious cycles of ice ages

US winter storm 2018 [image credit: NASA]

A sort of review of leading ice age theories. A paper by Ralph Ellis that was featured at the Talkshop gets a mention. A point not mentioned: the carbon cycle dictates that cooling leads to the oceans absorbing more CO2, while warming leads to more outgassing of it to the atmosphere.

Record cold in America has brought temperatures as low as minus 44C in North Dakota, frozen sharks in Massachusetts and iguanas falling from trees in Florida, writes Matt Ridley.

Al Gore blames global warming, citing one scientist to the effect that this is “exactly what we should expect from the climate crisis”. Others beg to differ: Kevin Trenberth, of America’s National Centre for Atmospheric Research, insists that “winter storms are a manifestation of winter, not climate change”.

Forty-five years ago a run of cold winters caused a “global cooling” scare.

“A global deterioration of the climate, by order of magnitude larger than any hitherto experienced by civilised mankind, is a very real possibility and indeed may be due very soon,” read a letter to President Nixon in 1972 from two scientists reporting the views of 42 “top” colleagues. “The cooling has natural causes and falls within the rank of the processes which caused the last ice age.” The administration replied that it was “seized of the matter”.

In the years that followed, newspapers, magazines and television documentaries rushed to sensationalise the coming ice age. The CIA reported a “growing consensus among leading climatologists that the world is undergoing a cooling trend”. The broadcaster Magnus Magnusson pronounced on a BBC Horizon episode that “unless we learn otherwise, it will be prudent to suppose that the next ice age could begin to bite at any time”.

Newsweek ran a cover story that read, in part: “The central fact is that, after three quarters of a century of extraordinarily mild conditions, the Earth seems to be cooling down. Meteorologists disagree about the cause and extent of the cooling trend, as well as over its specific impact on local weather conditions. But they are almost unanimous in the view that the trend will reduce agricultural productivity for the rest of the century.”

This alarm about global cooling has largely been forgotten in the age of global warming, but it has not entirely gone away. Valentina Zharkova of Northumbria University has suggested that a quiescent sun presages another Little Ice Age like that of 1300-1850. I’m not persuaded. Yet the argument that the world is slowly slipping back into a proper ice age after 10,000 years of balmy warmth is in essence true. Most interglacial periods, or times without large ice sheets, last about that long, and ice cores from Greenland show that each of the past three millennia was cooler than the one before.

However, those ice cores, and others from Antarctica, can now put our minds to rest. They reveal that interglacials start abruptly with sudden and rapid warming but end gradually with many thousands of years of slow and erratic cooling. They have also begun to clarify the cause. It is a story that reminds us how vulnerable our civilisation is. If we aspire to keep the show on the road for another 10,000 years, we will have to understand ice ages.

The oldest explanation for the coming and going of ice was based on carbon dioxide. In 1895 the Swede Svante Arrhenius, one of the scientists who first championed the greenhouse theory, suggested that the ice retreated because carbon dioxide levels rose, and advanced because they fell. If this were true, he thought, then industrial emissions could head off the next ice age.

Continued here.