There is a new paper that presents a claim that the Earth’s climate system is dominated by positive radiative feedbacks, and that includes the heading in section of the paper “Planet Earth today: imminent peril”. This sensationalism, however, in the view of Climate Science, is unsubstantiated by examining even the most basic of measures, where if the 2007 values of the IPCC radiative forcing are accepted, and the observed ocean heat storage data is used to diagnose what has been the sum total of real world radiative forcings and feedbacks in the last few decades, the climate feedbacks have been negative (as is discussed below)! This contradicts the fundamental premise of the paper
Hansen, J., M. Sato, P. Kharecha G. Russell, D. W. Lea, M. Siddall, 2007: Climate change and trace gases; Phil. Trans. R. Soc. A (2007) 365, 1925–1954 doi:10.1098/rsta.2007.2052 Published online 18 May 2007.
The abstract reads,
“Palaeoclimate data show that the Earth’s climate is remarkably sensitive to global forcings. Positive feedbacks predominate. This allows the entire planet to be whipsawed between climate states. One feedback, the ‘albedo flip’ property of ice/water, provides a powerful trigger mechanism. A climate forcing that ‘flips’ the albedo of a sufficient portion of an ice sheet can spark a cataclysm. Inertia of ice sheet and ocean provides only moderate delay to ice sheet disintegration and a burst of added global warming. Recent
greenhouse gas (GHG) emissions place the Earth perilously close to dramatic climate change that could run out of our control, with great dangers for humans and other creatures. Carbon dioxide (CO2) is the largest human-made climate forcing, but other trace constituents are also important. Only intense simultaneous efforts to slow CO2 emissions and reduce non-CO2 forcings can keep climate within or near the range of the past million years. The most important of the non-CO2 forcings is methane (CH4), as it causes the second largest human-made GHG climate forcing and is the principal cause of increased tropospheric ozone (O3), which is the third largest GHG forcing. Nitrous oxide (N2O) should also be a focus of climate mitigation efforts. Black carbon (‘black soot’) has a high global warming potential (approx. 2000, 500 and 200 for 20, 100 and 500 years, respectively) and deserves greater attention. Some forcings are especially effective at high latitudes, so concerted efforts to reduce their emissions could preserve Arctic ice,
while also having major benefits for human health, agricultural productivity and the global environment.”
One statement in the conclusion reads,
“Earth’s climate is remarkably sensitive to forcings, i.e. imposed changes of the planet’s energy balance. Both fast and slow feedbacks turn out to be predominately positive. As a result, our climate has the potential for large rapid fluctuations. Indeed, the Earth, and the creatures struggling to exist on the planet, have been repeatedly whipsawed between climate states.”
This is obviously an erroneous statement! If all of the feedbacks were predominately positive, the climate would long ago evolved to a a very extreme state. This clearly has not occurred, and such statements in this article are unsubstantiated scientifically in the paper, and, even more importantly, fail to represented the dynamics of the current climate system, where, as has been summarized on Climate Science, the net effect of all of the feedbacks, assuming the 2007 IPCC estimate of climate forcings is correct, is negative!
That the feedbacks must be negative in recent years (or the 2007 IPCC net forcing is in error) is discussed in
The Net Climate Feedbacks Must Be A Negative Effect On The Global Average Radiative Imbalance If The IPCC Conclusion Of Net Anthropogenic Radiative Forcings Is Correct.
Just two excerpts from the paper are needed to recognize what the Hansen et al paper is all about, i.e.
“The Arctic epitomizes the global climate situation. The most rapid feasible slowdown of CO2 emissions, coupled with focused reductions of other forcings, may just have a chance of avoiding disastrous climate change.”
“The potential of these ‘amber waves of grain’ and coastal facilities for permanent underground storage ‘from sea to shining sea’ to help restore America’s technical prowess, moral authority and prestige, for the sake of our children and grandchildren, in the course of helping to solve the climate problem, has not escaped our attention.”
This paper is clearly an advocacy article using the guise of cherrypicked science to promote a particular political and policy agenda. It very much fits into the definition of “stealth issue advocacy” as discussed in
Pielke, R. A. Jr., 2007: The Honest Broker: Making Sense of Science in Policy and Politics
Roger A., Jr. University of Colorado, Boulder
The Hansen et al paper is clearly not an example of serving as an honest broker of climate science.
Hansen et al, of course, are correct that the climate system is nonlinear and sudden transitions on a variety of space and time scales do occur, as we discussed in
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.
The Hansen et al article, however oversimplifies the climate system as being dominated by the radiative effect of human added CO2. Such a perturbation, of course, just as easily could move us away from undesirable climate transitions, instead of toward such transitions. Prudence suggests that we work to minimize our disturbance of the climate system since we do not understand the climate system well enough.
However, to focus on just a small subset of forcings is seriously misleading policymakers on the most effective way to deal with our social and environmental vulnerability from the entire spectrum of the actual environmental risks and other threats that we face.