根据对气候专家的一项调查，如果而二氧化碳排放继续增加，人类导致的全球变暖可能让地球的气候在200年内达到一个倾覆点的几率大约50%。科学家最近开始把倾覆点定义为影响地球至少一半并且持续数十年的根本性的气候变化。M. Granger Morgan及其同事对14位气候科学家进行了一场面对面的访谈，据该研究说，这些科学家代表了一系列的主流观点。
在访谈期间，向这些专家提供了到2200年CO2增加的低、中、高轨迹——所有这些轨迹都在IPCC的最新预测中，然后让他们提出每一种情景迫使气候系统越过倾覆点的概率。这组作者报告说，对于高轨迹，14位专家中的13位回答说可能性大约50%，而10位专家说可能性大于等于75%。这组作者说，这种可能改变气候的CO2情景尽管是高的，但是它仍然位于IPCC提供的情景范围之内。(生物谷www.bioon.net)
生物谷推荐原文出处：
PNAS doi: 10.1073/pnas.0908906107
Expert judgments about transient climate response to alternative future trajectories of radiative forcing
Kirsten Zickfelda,2, M. Granger Morganb,1, David J. Framec, and David W. Keithd
aSchool of Earth and Ocean Sciences, University of Victoria, Victoria, BC V8P 5C2, Canada;
bDepartment of Engineering and Public Policy, Carnegie Mellon University, Pittsburgh, PA 15213;
cSmith School of Enterprise and the Environment and Department of Physics, University of Oxford, Oxford OX1 2BQ, UK; and
dDepartment of Chemical and Petroleum Engineering, University of Calgary, Calgary, AB T2N 1N4, Canada
There is uncertainty about the response of the climate system to future trajectories of radiative forcing. To quantify this uncertainty we conducted face-to-face interviews with 14 leading climate scientists, using formal methods of expert elicitation. We structured the interviews around three scenarios of radiative forcing stabilizing at different levels. All experts ranked “cloud radiative feedbacks” as contributing most to their uncertainty about future global mean temperature change, irrespective of the specified level of radiative forcing. The experts disagreed about the relative contribution of other physical processes to their uncertainty about future temperature change. For a forcing trajectory that stabilized at 7 Wm-2 in 2200, 13 of the 14 experts judged the probability that the climate system would undergo, or be irrevocably committed to, a “basic state change” as ≥0.5. The width and median values of the probability distributions elicited from the different experts for future global mean temperature change under the specified forcing trajectories vary considerably. Even for a moderate increase in forcing by the year 2050, the medians of the elicited distributions of temperature change relative to 2000 range from 0.8–1.8?°C, and some of the interquartile ranges do not overlap. Ten of the 14 experts estimated that the probability that equilibrium climate sensitivity exceeds 4.5?°C is > 0.17, our interpretation of the upper limit of the “likely” range given by the Intergovernmental Panel on Climate Change. Finally, most experts anticipated that over the next 20 years research will be able to achieve only modest reductions in their degree of uncertainty.
