Global Warming: Beware The Greenland Effect Downplayed By IPCC

Last week, the Intergovernmental Panel on Climate Change issued a widely publicized updated policy summary (the detailed scientific reports won't come out until later this year) of the latest scientific consensus on global warming. (See IPCC, Climate Change 2007: The Physical Science Basis, Summary for Policymakers.)

The headlines largely focused on the conclusion that scientists are now more confident than ever that (1) there has been warming of the planet over the past century, and (2) that such warming is caused, at least in large part, by human activities that include burning of fossil fuels.

Most articles also highlighted conclusions from the summary that, left unchecked, continued carbon emissions from fossil fuels will contribute to significant additional global warming over the next century, and that such warming is highly likely to raise sea levels by 7-23 inches.

The new IPCC report is good because it shines a spotlight on global warming and intensifies the debate over what we should do about it. It is unfortunate, however, that the summary was written so conservatively that it has, unwittingly, provided fodder to the climate change skeptics who say we needn't do anything other than bask in the warmer winter days.

Those skeptics typically argue that taking steps to reduce carbon emissions will be far more expensive and counterproductive than simply living with a modest rise in sea levels of 7-23 inches over the next century.

If that were all there was to it, we'd probably agree. While a sea level rise of 23 inches--nearly two feet--would have major implications for many coastal cities, we think most would be able to adapt over the long period of time being contemplated. Just think how much cities have changed in the past century.

Unfortunately, that's not all there is to it. Put aside conclusions about growing desertification and major changes in weather systems. The elephant in the room, cryptically acknowledged by the IPCC report and all but ignored by most news articles and commentators, is the vast Greenland ice sheet.

The problem is that, at present, there is not enough information known about the Greenland ice sheet and how it may be affected by global warming to form a scientific consensus, so for the time being it is being shoved aside.

[Note: the Antarctic ice sheet is a different story. Warming in the southern hemisphere has been much less than in the northern hemisphere and is expected to be less going forward. The consensus is that even under the more dire scenarios, the Antarctic ice sheet will show little shrinkage over the next century--it may even get larger due to increased precipation.]

But there's certainly enough to worry about Greenland if you look for it, and we think the report's authors wanted us to be aware of the risk even as scientists take a closer look and acquire more data.

Here's the biggie: about 125,000 years ago, average polar temperatures were 3-5 degrees centigrade higher than today due to differences in the Earth's orbit. Sea levels during that period were likely 4 to 6 meters (i.e. 12-18 feet!) higher than today at that time, mostly because of the retreat of the Greenland ice sheet and Arctic ice fields. (See p. 10 of the IPCC report.)

The likelihood of average temperatures in Greenland and other Arctic areas increasing by 3-5 degrees C over the next century are not small. Indeed, the IPCC report has computer modelled scenarios that could result in significantly higher temperatures in the Arctic region (to as much as 6-7 degrees C) by the end of the century.

Here's the dry scientific language that is most alarming (p. 14 of the IPCC summary):

Models used to date do not include uncertainties in climate-carbon cycle feedback nor do they include the full effects of changes in ice sheet flow, because a basis in published literature is lacking. The projections include a contribution due to increased ice flow from Greenland and Antarctica at the rates observed for 1993-2003, but these flow rates could increase or decrease in the future. For example, if this contribution were to grow linearly with global average temperature change, the upper ranges of sea level rise for SRES scenarios shown in Table SPM-3 would increase by 0.1 m to 0.2 m. Larger values cannot be excluded, but understanding of these effects is too limited to assess their likelihood or provide a best estimate or an upper bound for sea level rise.

In other words, right now scientists don't have adequate data to forecast what will happen to the Greenland ice sheet and how it will affect sea levels, so they haven't factored in any contribution more than what has been observed over the past decade. BUT, we know that 125,000 years ago, the Greenland effect was huge. So, don't be surprised if in our next report, after more data is in, we raise our estimate considerably.

For now, scientists think it would take thousands of years for the Greenland sheet to retreat to the point seen 125,000 years ago. But, they really don't know., especially if temps go even higher than before.

The question is, are we willing to take that risk for our great grandchildren? We shouldn't. Our great grandchildren will have no choice but to live in a world without significant oil because by then their forebears will have depleted most of it, regardless whether they do anything about carbon emissions. We owe it to them to develop the new technologies now and not bet their future on the gamble that sea level rises and other climate changes will be "manageable".