Forecasting “Tipping Points” in the Climate System

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 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.

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