Have we accidentally prevented another ice age?


Sometimes you learn the darnedest things if you read a news story all the way to the end.

Take the story in the March 16 issue of New Scientist, the British science weekly. The story is headlined, “New climate record shows pace of today’s warming.”

The story is about a study done by a research team at Oregon State University’s College of Earth, Ocean, and Atmospheric Sciences led by Dr. Shaun A. Marcott. Marcott’s team did a study of global temperatures over the ll,300 years since the end of the last ice age, aka the Holocene epoch.

(Since records of measured temperatures go back only to about 1860, Marcott’s team used “proxies” to determine temperatures for the years before that. Proxies include tree rings, which are thicker during warm years when trees can grow faster. Tree ring data can provide a pretty good temperature reconstruction for the last 2,000 years. For the years prior to that, Marcott’s team looked at shells from marine organisms that had been preserved in sediments. The ratios of isotopes in the shells vary with the temperature at the time they were created.)

Remember the fabled (or infamous, depending on your perspective) “Hockey Stick Graph” that showed global temperatures spiking in the 20th century? What Marcott’s study did in effect was extend the hockey stick’s handle from about 2,000 years to 11,300 years.

What Marcott’s team reported was that the world has been warming faster since the late 19th century than during any time during the previous 11,300 years. No surprises there. It also concluded that average global temperatures for the last 10 years still haven’t exceeded the peak temperatures reached during the Holocene but are nonetheless “warmer than during approximately 75% of the Holocene temperature history,” and will probably exceed the highest readings and the range of natural variation by the end of the century. Again, not particularly surprising.

What was surprising, at least to me, was this:

It turns out that the warmest temperatures in the Holocene occurred during the first half of it. During the early Holocene temperatures rose quickly (i.e. over the first 1,000 years) to a level somewhat above the average temperature for the whole period — and stayed there for the next 5,000 years or so.

Those temperatures were slightly higher than today’s.

Then, about 5,000 years ago, a cooling trend set in — resulting in the lowest average temperatures of the Holocene epoch during the “‘Little Ice Age’, about 200 years ago,” according to Marcott’s paper. (NASA defines the Little Ice Age as beginning in 1550 and lasting until 1850. Some climatologists think it started as early as 1350. It saw glaciation increase, ice on Lake Superior in July, rivers freeze in Northern Europe, and recurrent crop failures throughout the world. New York Harbor froze solid enough in the winter of 1780 for people to walk from Manhattan to Staten Island.)

Then, beginning in the late 19th century, temperatures spiked from the Holocene’s near-low to today’s nearhigh.

Like most (but not all) climatologists, Marcott ascribes the spike to human-caused increases in CO2.

But what caused the long cooling that preceded the quick warming?

That’s where the juicy details in the final paragraphs of the New Scientist story come in.

The gradual downward drift of global temperatures before the 19th century was driven by changes in the Earth’s axis of rotation, Marcott told the magazine. The planet’s tilt increased early in the Holocene, before decreasing again. “It sort of wobbles,” he said. A greater tilt leads to more sunlight at the poles in the summer, and this keeps the Earth warmer.

And then there’s this second-from-last paragraph from the article:

“If humans had not begun warming the planet by releasing greenhouse gases, Earth would eventually return to an ice age. ‘If we were following the orbital trend we’d still be cooling,’ Marcott says.”

Which raises some inconvenient questions:

Did our carbon-loving lifestyle accidentally prevent a new ice age? Did Big Coal, Big Oil, Dick Cheney (and his six billion fellow CO2 spewers) turn around five millenia of global chilling in the space of two human lifetimes — faster than you can say “frack you, Mac,” geologically speaking.

Would a return to pre-industrial revolution levels of CO2 bring back, not some temperate idyll, but the Little Ice Age, which just might be a prelude to a big ice age? If so, do we really want to stop and reverse our collective carbonization of the atmosphere and thus get back on the toboggan of death sliding down the slippery slope of global chilling?

Under the circumstances, what’s not to like about global warming?

Among other things, droughts, desertification, stronger hurricanes and more extreme climate events, I hear you say.

Well, yes, but when it comes to extreme climate events, it’s hard to beat 3,000 feet of ice in your yard.

Droughts and deserts? You can get them in cold venues as well as warm ones. For instance, average annual precipitation for Antarctica is about 6.5 inches a year, and for about half the continent it is 4 inches or less. Areas that receive less than 10 inches of precipitation a year are classified as deserts.

Temperature extremes? Granted, 120 F temperatures suck, but they’re a lot easier to take than minus 75 F temperatures, which helps explain why there are 7.2 million people living in Baghdad and 300 people living at McMurdo station.

So which is the better future? Mangos in Montana or polar bears in Portland?

Respond: letters@boulderweekly.com

This opinion column does not necessarily reflect the views of Boulder Weekly.