January 31, 2011

Arctic Ice “Tipping Point” Rejected

Filed under: Arctic, Polar

A common rhetorical device to make potential future climate sounds even scarier, is to invoke the concept of “tipping points”—events that no one is sure when or even if they will happen, but suggest that when and if they do come to pass, they will lead to some sort of catastrophe that can’t be recovered from. Of course, global warming will push us closer to reaching these “tipping points.”

President Obama’s advisor on Science and Technology and Director of the Office of Science and Technology Policy, John Holdren, is a fond user of such scare tactics.

Here is a portion of Holdren’s testimony before the (now-disbanded) House Select Committee on Energy Independence and Global Warming back on December 2, 2009:

But these more or less steadily increasing impacts are not the only possible outcome. Climate scientists worry about “tipping points” in the climate system, including ecosystems, meaning thresholds beyond which a small additional increase in average temperature or some associated climate variable results in major changes to the affected system. Examples of tipping points of potential concern include the complete disappearance of Arctic sea ice in summer, leading to drastic changes in ocean circulation and climate patterns across the whole Northern Hemisphere; drastic acceleration of the rate of ice loss from the Greenland and Antarctic ice sheets, driving rates of sea-level increase that could reach 6 feet per century or more; ocean acidification from CO2 absorption reaching a level that causes massive disruption in ocean food webs; and a flood of carbon dioxide and methane from warming tundra and thawing permafrost, accelerating the onset of all of the other impacts of concern.

While our understanding of the global climate system and our ability to project its future behavior have grown enormously over the past couple of decades, we cannot yet predict with confidence exactly where on a rising temperature trajectory these or other thresholds would be crossed. It seems clear, however, that the probability of crossing one or more of them goes up sharply as the global-average surface temperature increase compared to 1900 goes above 3.6°F (2°C). That is a major reason for the growing global consensus that worldwide efforts should limit heat-trapping emissions sufficiently to hold the average temperature increase to 3.6°F (2°C) or less.

Ok then.

The latest science indicates that perhaps Holdren ought to rethink this whole line of argument. It is grossly outdated and misinformed.

First off, a flood of new research has hit the library shelves concerning the rates of ice flow of Greenland’s glaciers indicating that many of the proposed mechanisms for large and rapid ice loss there do not work the way they have been postulated to. And, new findings into how they do work indicate a much less drastic response to a warming climate. For examples and summaries of these new findings, see here, here, and here, among other places.

But, there’s more!

Now, a team of scientists from the Max Planck Institute for Meteorology, in Hamburg, Germany, led by Steffen Tietsche, examine whether or not there is indeed a “tipping point” when it comes to Arctic sea ice coverage.

To do this, they used the Max Plank Institute climate model, and “prescribed” ice-free conditions during one Arctic summer. They then watched the model output to see how the conditions evolved during the coming months and years. If the Arctic remained locked into an ice-free summer state, then this was a good indication that a tipping point existed in this system.

But, what they found was virtually the opposite.

It turns out, that in the model at least, the extra heat that was absorbed by the ice-free ocean during the summer was largely lost to space during the following winter which itself was marked by an ice cover than was anomalously thin and thus less insulating. While the surface temperature anomalies were quite large (and positive) during the fall and early winter immediately following the ice-free summer, by late winter the temperature anomalies were back within the range of normal variability. And the ice coverage the following summer had nearly completely recovered to its average state.

In other words, ice-free conditions in the Arctic are not a condition from which nature does not readily recover—in fact, nature apparently can recover within a very few number of years.

This really shouldn’t come as any surprise as the Arctic was likely characterized by much reduced, if not ice-free summers for an extended period (i.e. several thousand years) during the early-to-mid Holocene (about 6-8 thousand years ago, see here for example).

Here is how Tietsche et al. describe their results:

[W]e find that even dramatic perturbations of summer sea-ice cover in the Arctic are reversible on very short time scales of typically two years. This suggests that a so-called tipping point, which would describe the sudden irreversible loss of Arctic summer sea ice during warming conditions, is unlikely to exist.

This is not to say that the general outlook for Arctic sea ice is not for a continued decline (and concomitant impacts) as the climate warms, but just that the specter of a “tipping point” is not one that haunts the process.

So, the results of the Tietsche et al. research, along with new findings about glaciers in Greenland (linked above), mean it is high time to remove “tipping point” scare scenarios from the telling of the story of what the future climate likely holds in store.

The earth’s climate is much more resilient that climate alarmists want you to believe.

Reference:

Tietsche, S., et al., 2011. Recovery mechanisms of Arctic summer sea ice. Geophysical Research Letters, 38, doi:10.1029/2010GL045698.




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