The term “tipping point” has been used to describe a change in the environment such that a different environment regime results. This term has been applied most recently with respect to the Arctic sea ice coverage and climate (e.g., see http://www.physorg.com/news6558.html). A tipping point that results in serious, negative impacts on societal and environmental conditions could be catastrophic.
The paper by Peters, D.P.C., R.A. Pielke Sr., B.T. Bestelmeyer, C.D. Allen, S. Munson-McGee, and K.M. Havstad, 2004: Cross-scale interactions, nonlinearities, and forecasting catastrophic events. Proceedings of the National Academy of Sciences, 101, No. 42, 15130-15135, concludes that,
“Catastrophic events share characteristic nonlinear behaviors that are often generated by cross-scale interactions and feedbacks among system elements. These events result in surprises that cannot easily be predicted based on information obtained at a single scale…..We show that decisions that minimize the likelihood of catastrophic events must be based on cross-scale interactions, and such decisions will often be counterintuitive. Given the continuing challenges associated with global change, approaches that cross disciplinary boundaries to include interactions and feedbacks at multiple scales are needed to increase our ability to predict catastrophic events and develop strategies for minimizing their occurrence and impacts.”
The media reports present forecasts that the Arctic sea ice will melt in the coming decades (e.g., see “Arctic ice could disappear in 55 years”). This forecast, and other multi-decadal climate change forecasts, are generally based on focusing on a single scale and type of climate forcing (the radiative effect of the added well-mixed greenhouse gases) and climate assessment tool (the numerical global climate models). However, reality likely will show a much more complicated behavior (e.g., see Rial, J., R.A. Pielke Sr., M. Beniston, M. Claussen, J. Canadell, P. Cox, H. Held, N. de Noblet-Ducoudre, R. Prinn, J. Reynolds, and J.D. Salas, 2004: Nonlinearities, feedbacks and critical thresholds within the Earth’s climate system. Climatic Change, 65, 11-38).
Even with Arctic sea ice, as one example of a missing influence, the role of the deposition of black carbon on the sea ice has been ignored in these media discussions. As discussed in our August 29th blog, which is reproduced from the 2005 National Research Council report,
“Deposition of BC aerosols over snow-covered areas can result in changes to the surface albedo (Chylek et al. 1983). Further reductions in albedo occur due to the enhanced melting that accompanies the heating of absorbing soot particles in snow. Chylek et al. (1983) estimate this enhancement to be up to a factor of ten in the rate of melting. Recent model results indicate radiative forcings of +0.3 W m−2 in the Northern Hemisphere associated with albedo effects of soot on snow and ice (Hansen and Nazarenko 2004).”
Thus before the media and some scientists present what they claim are definitive climate forecasts of reaching a “tipping point”, and whether or not the climate system will have a catastrophic event, they should also present and critically assess cross-scale interactions and feedbacks among system elements which could result in a very different climate response from what they expect.
I’m not aware of any climate scientist having made a “definitive” claim about a tipping point having been reached, although maybe tour concern was about possible future statements. I think everyone recognizes that it’s hard to calculate a tipping point given the complexities you note and the fact that we haven’t been able to observe the Arctic ice fully melt before. So, even if a substantial tipping point exists it won’t be possible to say anything “definitive” about it until the process is so far along that the analysis is essentially after the fact. Given this, what can one say? That based on current trends the Arctic will be ice-free in X years, but that a tipping point may be reached at some point (or may already have been reached) that will accelerate the process considerably.
Regarding the soot issue, the NRC report you cite talks about Northern Hemisphere snow and ice as contrasted to ice cap ice (or snow on top of that ice) in particular, which is the issue here. It seems likely that the black carbon effect would be less on the ice cap than at lower latitudes (for a couple of reasons that I can think of), but is there any specific data on that? Perhaps more to the point, do we know that it’s a major factor compared to reduced albedo from open water? If it’s a sufficiently minor factor, it may be justified to not dwell on it in public pronouncements.
Also, hasn’t the amount of black carbon in the atmosphere actually been generally decreasing over the same period that the Arctic ice has been declining? If so, doesn’t that necessarily make the BC effect minor?
Finally, it’s not clear to me that anyone has been describing the summer loss of the ice cap as being catastrophic in and of itself. Are you aware of any catastrophic implications? Maybe I’m not clear on how the term is being used.
Comment by Steve Bloom — September 30, 2005 @ 11:59 am
Steve-thanks for your valuable comments and questions. On whether or not a loss of the arctic sea ice would be catastrophic or not, some media reports certainly present it that way; e.g. see http://www.nashuatelegraph.com/apps/pbcs.dll/article?AID=/20050925/NEWS03/109250083/-1/ENTERTAINMENT where an extract says,
“With warmer temperatures, some bacteria, plants and animals could disappear, while others would thrive. Polar bears and other animals that depend on sea ice to breed and forage are at risk, scientists say, and some species could face extinction in a few decades.”
If true, this would certainly be a catastrophe for these animals and plants.
The issue of black carbon is associated with the long range transport of this material. The NASA press release from earlier this year entitled “Black on white: soot on ice”(http://www.nasa.gov/vision/earth/environment/arctic_soot.html) indicates that this is very much a real human caused climate forcing in the arctic. An excerpt from that report states,
“‘This research offers additional evidence that black carbon may have a significant warming impact on the Arctic,” Koch said. Warmer temperatures in the Arctic mean melting ice and snow, among other things. These temperature and ice changes also wind up affecting climate patterns around the world.”
Comment by Roger Pielke Sr. — October 1, 2005 @ 8:01 am
[...] all GCM’s used today do not consider such changes in vegetation cover. See also the Climate Science weblog which have an interesting post on climatic tipping points.
[...]
Pingback by Resilience Science » Is the Arctic Lost? — November 8, 2005 @ 4:39 am
Regime change?
I just stumbled over another related blog during some late night surfing - Resilience Science - which seems to have started around the same time as PNT - the more the merrier! For your reading pleasure, a good post discussing…
Trackback by The Post-Normal Times - Perspectives on Environmental Science and Policy Decisions — November 10, 2005 @ 12:25 pm
Has there ever been a “tipping point” in the Earth’s climate, where a climate phenomenon has compounded on itself, leading to the effect spiraling out of control? I have heard three arguments that the positive feedback
domination that such a scenario would imply is wrong.
1) That the El Chichon volcanic eruption in the ’90s and the resulting temperature increase fell back down as soon as it shot up, proving that positive feedback mechanisms did not take control.
2) That when observing temperature trends during the 100,000 year cycle ice ages, one notices that most of the time encompasses cooler temperatures, which somehow implies that negative feedback was domninant.
3) That the annual summer heating cycle and its eventual annual retreat back in to colder temperatures would not occur, or at least not the way it does, if positive feedback elements were dominant.
Are these arguments true? And do you have any additional ideas to add to or alter what I have suggested?
Comment by Carl Wolk — January 28, 2007 @ 12:19 pm