The scare du jour on global warming is a massive inundation of our coast caused by rapid loss of ice from Antarctica. It's a core point in Al Gore's science fiction movie, and it continues to be thumped by doomsayers around the world, in the echo chamber of the alarmist media. It's also a bunch of hooey.
If you could take the boredom, you could have read hundreds of news stories on this since An Inconvenient Truth debuted on May 25. But you'll find very little mention of a paper that appeared a mere six weeks later, in the Proceedings of the National Academy of Science, which should have stopped the whole show cold. The work is by Brenda Hall from the University of Maine and several co-authors.
First, Gore's science fiction. Due to the warming of the surrounding ocean, big ice-shelves begin to crack off and float away. Because that ice is floating, it doesn't raise sea level a bit. But then the ice cracks all the way back to where it is grounded on the ocean floor. That stuff isn't floating and the ocean rises dramatically, some twenty feet in a hundred years. Much of Manhattan, the movie suggests, is under water, along with just about every other coastal city.
Now, the truth. The notion that this is going to happen soon has just been fatally harpooned by giant Elephant Seals (Mirounga leonine). They generally hang out a long distance form Antarctica. Most of their breeding rookeries are a good 2,000 miles away on islands in the open ocean, where they feed. Most of the Antarctic coast is hemmed by huge ice shelves that prevent them from finding food.
But that wasn't always the case. According to Hall's paper, a large area of the Antarctic coast was ice-free between 1,100 and 2,300 years ago. Elephant seals established multiple rookeries on the continent. Temperatures had to be much warmer than they are today, for at least 1,200 years, and yet there was no disintegration of the large ice shelves. Hall et al. then noted another similar period, almost twice as long, from 4,000 to 6,000 years ago.
The warm millennium ended as the world's temperature descended from what scientists call the "Medieval Warm Period" into the "Little Ice Age." Antarctica has yet to fully recover from this last period, as temperatures averaged across the continent actually showed a net cooling in the last three decades.
Hall studied ancient Antarctic beaches, which could only contain relics of large numbers of elephant seals if there were open water. Others have examined extinct penguin rookeries and found that those happily footed birds tended to be absent when the seals were present. That's because penguins feed along the edges of sea-ice, so if there isn't any, there aren't any birds.
Of course this also means, even as temperatures warm to degrees seen for more than half of the last six millennia, that penguins will be displaced from their current rookeries. The horror of natural climate variability! Cute little penguins driven from their homes by cruel Mother Nature!!
Hall et al. give a quantitative perspective on today's climate. Current thinking is that the Antarctic ice shelves become susceptible to rapid breakup when the January (Summer) temperature averages about -1.5 degrees Celsius But the seals only thrive, according to the paper, "when the mean January temperature exceeds 0 [degrees] C, usually by considerable margins."
So Hall and her colleagues conclude that "January temperatures...surpassed the -1.5 [degrees] C threshold during two long periods at ~1,000-2,300 and 4,000-6,000 years b.p. [before present]."
George Denton, one of Hall's University of Maine colleagues and coauthors, summed it up in the school's U Maine Today Magazine: "Through her discovery of elephant seal remains over a widespread area where they do not exist today, she [Hall] shows evidence not only that a warming occurred, but that the Ross Ice Shelf survived that event. It's important because it speaks to the staying capacity of the ice shelf in the face of global warming."
Stories about an imminent collapse of Antarctic ice shelves can go back to the science fiction shelves, where they belonged all along.
For that matter, so can this whole apocalyptic myth. If Antarctic ice remained stable for thousands of years with temperatures considerably warmer than they are today, how in the world are we going to provoke a catastrophe? Among other things, we will still have to be powering our society on fossil fuels in the year 4,100.
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