Dr. Steven Amstrup, PBI Sr. Scientist, Dying Cub & Nature Paper

Posted Jan. 9th, 2011 by Daniel J. Cox

Dr. Amstrup pauses while documenting polar bear behavior

Dr. Steven C. Amstrup, senior scientist with Polar Bears International, addresses the question of the Dying Cub Video. He also discusses the paper he recently published in the prestigious journal, Nature, which offers hope for polar bears if we significantly reduce carbon emissions.

There are many unknowns about the dying cub, but the behavior is consistent with starvation. The mother bear is obviously very, very thin and probably had not been lactating for some time. And, greater nutritional stress is something that we already have observed quantitatively (as opposed to qualitatively, as in this video) in the long-term data on the Western Hudson Bay bears.

It is important to emphasize, that when biologists report findings—as they have with the Western Hudson Bay population—that survival rate of young is reduced, what that means is that mortality has increased.  And starvation is a principal mechanism of increased mortality in polar bears.  With ever-longer ice-free periods, we will see ever-increasing rates of starvation.  I think that most in the media and public, and policy makers, don’t really understand that when we speak of lowered survival in scientific papers, what we really are referring to is starvation. This video is a painful reminder of what declining survival means, and of what our greenhouse gas emissions are doing to polar bears and other wildlife dependent upon cold conditions.

Greenhouse Gas Emissions

Our paper in Nature offers hope for polar bears if we can significantly reduce greenhouse gas emissions and not let them rise beyond 450 ppm. It disproves the idea of an irreversible tipping beyond which arctic sea ice can’t recover.

Some have questioned whether the 450ppm scenario on which we focused is not really possible to achieve.

It surely is an aggressive scenario and would take considerable political will and leadership.  The criticism has been stated in the context of the lack of progress, in the Cancun climate change, etc., toward even more modest changes.

When such comments come up, it is important not to confuse physical possibility with political plausibility.  There has been an incredible amount of material written on this and other reduction scenarios.  Those documents describe in great detail how we would have to change our economy and society, but they do not describe anything that is not physically possible.

Cover of Nature. Click photo for larger view

One of my co-authors, Eric DeWeaver of the National Science Foundation, spoke with Leon Clark, lead author on the main Climate Change Science Program document, regarding this scenario. Clark stated that he felt it still was physically possible to achieve, although certainly challenging politically.

We chose this scenario, which allows CO2 to rise to 450ppm by the end of the century, for a variety of reasons. One of those was the fact that it is very well documented and that the pathways for achieving it have been discussed extensively in the literature.  Also, it is consistent with the goal of keeping temperature rise below 2 C, which is a target many have suggested is necessary to prevent significant anthropogenic interference with the climate.

James Hansen, in fact has argued that 450ppm is too high and we need to get back town to 350ppm.  There is debate about Hansen’s concept. But perhaps the biggest limitation in discussions about achieving 350 is that we already are beyond that. So, focusing too much on 350 risks people feeling there is nothing they can do.  The message of our paper is HOPE—that there is something we can do.  So, I am not inclined to deal much with 350 until we have made it well along the way to achieve 450.  Once we have demonstrated we can do that, then we can work our way down to 350.  But that is a bit beside my current point: that point is not to confuse physical achievability with political plausibility.

Even more important, is that this criticism loses sight of one of the main results of our paper.  We did not see evidence of irreversible thresholds in our model outcomes—sea-ice habitat features smoothly declined as temperatures rose.  And even after modeled rapid ice-loss events, we showed recovery could occur if GHG concentrations were lowered.  Therefore, the biggest news is the simple message that conserving polar bears is a matter of minimizing temperature rise.  This is important because the smooth relationship between temperature and sea ice habitat decline means that if we strive for really aggressive mitigation but don’t quite make it, or if we overshoot before getting down to our target, we still will have preserved more sea ice and more bears.   The message is that to save polar bears we need to lower temperature rise and that by doing so we will have gone a long way toward saving the climate in which humans, and the rest of life currently residing on earth, have flourished.

We should not allow ourselves, therefore, to become embroiled in an argument about taking significant steps versus taking no steps at all.  Rather we need to keep the focus on the need to act strongly and quickly and focus on reducing temperature rise as much as is humanly possible.

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