Understanding Climate Change Feedbacks (2003) / Chapter Skim
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1 Introduction
1 Introduction
Pages 15-20
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From page 15... ...
Interactions among physical, chemical, and biological processes that determine the response of the climate system to human activities are not fully understood. If the carbon dioxide concentration in the atmosphere were doubled and the climate were allowed sufficient time to come into a new equilibrium, the projected uncertainty in the warming of the global mean surface temperature would still be large ~ In this document we have generally tried to follow the IPCC practice of using the word "projection" when referring to estimates of future climates that are hypothetical in the sense that they depend on an assumption of a particular scenario for emissions (and hence radiative forcing)
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From page 16... ...
find that the magnitude of global warming over the next 40 years is insensitive to the rate of greenhouse gas releases; in their study the range of possible warmings is determined by the range of estimates of the strength of climate feedbacks and not by the range of estimates of climate forcing. Therefore, study of climate feedbacks and climate sensitivity is very important for projecting climate changes over the next 40 years.
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From page 17... ...
Use of the instrumental record of global mean temperature cannot constrain climate sensitivity to a narrow range because the climate-forcing magnitude, amount of heat storage, and even the temperature record itself are not known with sufficient precision. An enhanced effort to understand and model the most important climate feedback processes is needed to improve our fundamental knowledge and will lead to better characterizations of the climate system, potentially reducing the wide ranges now seen in climate change projections.
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From page 18... ...
In addition, because climate change feedbacks often incorporate processes from different disciplines, such as sea-ice processes and ocean circulation, or land surface processes and cloud processes, climate feedbacks research will also require greater synergy between traditional subdisciplines in climate science. Many climate feedback processes operate on time scales short enough to be tested effectively by comparing numerical weather forecasts with instantaneous data.
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From page 19... ...
If a forcing of 4 Wm is applied to this system, then the expected equilibrium surface temperature change is about 1 °K. The gain factor, g, is the fraction of the equilibrium climate change associated with feedback processes in addition to basic blackbody feedback.
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From page 20... ...
, will double the temperature response to climate forcing, changing the equilibrium response to doubled carbon dioxide from 1°C to 2°C. If an additional feedback only half as strong as water vapor feedback is added to the system, with a gain factor of +0.25, then the temperature response will be 4.0°C if the weaker feedback is positive, and 1.3°C if the weaker feedback is negative.
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