An irreducibly simple climate-sensitivity model is designed to empower even non-specialists to research the question how much global warming we may cause. In 1990, the First Assessment Report of the Inter- governmenta...An irreducibly simple climate-sensitivity model is designed to empower even non-specialists to research the question how much global warming we may cause. In 1990, the First Assessment Report of the Inter- governmental Panel on Climate Change （IPCC） expressed ＂substantial confidence＂ that near-term global warming would occur twice as fast as subsequent observation. Given rising CO2 concentration, few models predicted no wann- ing since 2001. Between the pre-final and published drafts of the Fifth Assessment Report, IPCC cut its near-term warming projection substantially, substituting ＂expert assessment＂ for models＇ near-term predictions. Yet its long-range predictions remain unaltered. The model indi- cates that IPCC＇s reduction of the feedback sum from 1.9 to 1.5 W m^-2 K^-1 mandates a reduction from 3.2 to 2.2 K in its central climate-sensitivity estimate; that, since feed- backs are likely to be net-negative, a better estimate is 1.0 K; that there is no unrealized global warming in the pipeline; that global warming this century will be 〈1 K;and that combustion of all recoverable fossil fuels will cause 〈2.2 K global warming to equilibrium. Resolving the discrepancies between the methodology adopted by IPCC in its Fourth and Fifth Assessment Reports that are highlighted in the present paper is vital. Once those dis- crepancies are taken into account, the impact of anthro- pogenic global warming over the next century, and even as far as equilibrium many millennia hence, may be no more than one-third to one-half of IPCC＇s current projections.展开更多
文摘An irreducibly simple climate-sensitivity model is designed to empower even non-specialists to research the question how much global warming we may cause. In 1990, the First Assessment Report of the Inter- governmental Panel on Climate Change （IPCC） expressed ＂substantial confidence＂ that near-term global warming would occur twice as fast as subsequent observation. Given rising CO2 concentration, few models predicted no wann- ing since 2001. Between the pre-final and published drafts of the Fifth Assessment Report, IPCC cut its near-term warming projection substantially, substituting ＂expert assessment＂ for models＇ near-term predictions. Yet its long-range predictions remain unaltered. The model indi- cates that IPCC＇s reduction of the feedback sum from 1.9 to 1.5 W m^-2 K^-1 mandates a reduction from 3.2 to 2.2 K in its central climate-sensitivity estimate; that, since feed- backs are likely to be net-negative, a better estimate is 1.0 K; that there is no unrealized global warming in the pipeline; that global warming this century will be 〈1 K;and that combustion of all recoverable fossil fuels will cause 〈2.2 K global warming to equilibrium. Resolving the discrepancies between the methodology adopted by IPCC in its Fourth and Fifth Assessment Reports that are highlighted in the present paper is vital. Once those dis- crepancies are taken into account, the impact of anthro- pogenic global warming over the next century, and even as far as equilibrium many millennia hence, may be no more than one-third to one-half of IPCC＇s current projections.
