Climate Change Impacts – UNIPCC and the Skeptics

Climate feedbacks are crucial to climate change forecasts. As Richard Lindzen1 said in his congressional testimony last year

  1. A doubling of CO2, by itself, contributes only about 1C to greenhouse warming. All models project more warming, because, within models, there are positive feedbacks from water vapor and clouds, and these feedbacks are considered by the IPCC to be uncertain.
  2. If one assumes all warming over the past century is due to anthropogenic greenhouse forcing, then the derived sensitivity of the climate to a doubling of CO2 is less than 1C. The higher sensitivity of existing models is made consistent with observed warming by invoking unknown additional negative forcings from aerosols and solar variability as arbitrary adjustments.

As Roy Spencer has recently claimed2,

In fact, NO ONE HAS YET FOUND A WAY WITH OBSERVATIONAL DATA TO TEST CLIMATE MODEL SENSITIVITY. This means we have no idea which of the climate models projections are more likely to come true.

Warren Meyer3 comments that

70-80% or more of the warming in catastrophic warming forecasts comes from feedback, not CO2 acting.

The impact is worse than that. It is not predicted temperature rise that is important. It is the catastrophic consequences that follow. These rise exponentially with temperature, so without the feedbacks more than 95% of the catastrophe does not happen. This is illustrated by the Climate Impacts table on page 10 of the UNIPCC Summary for policy makers4, where most of the impacts dramatically – almost exponentially – increase with temperature.

To illustrate this simply, the consequences of global warming will create costs. The reduced water availability, or crop failures will lead to increased hunger and in the extreme lead to deaths. The costs could also include the loss of species, both plant and animal.

To illustrate this graphically, plotting temperature increase against climate change costs, gives a Climate Change Impact curve as illustrated below.

There is no scale. There is no firm forecast of how high temperatures could go. The Stern review (Page 12) even saw fit to include a study with an upper estimate of 17.1oC maximum increase, and the UNIPCC AR4 has outlier estimates of 10oC. Neither do we know the costs. However, without the feedbacks, there is a temperature increase of around 1oC and so no hardly any noticeable costs. It is the pink line CCIS (S for skeptic) below.



  1. Quoted by Warren Meyer at

  2. Roy Spencer on 28th January 2011
  4. UNIPCC Summary for Policy Makers (SPM) reached from

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