Coyote Blog

Over at Climate Skeptic, I dissect climate models to show that the future warming in the models from CO2 alone is not much more than 0.5C.  All the catastrophe comes from positive feedbacks that modelers assume dominate the climate, an odd assumption for such a long-term stable system.  I summarize as follows:

• Climate sensitivity is the temperature increase we might expect with a doubling of CO2 to 560 ppm from a pre-industrial 280ppm
• Nearly every forecast you have ever seen assumes the
  effect of CO2 alone is about a 1C warming from this doubling.  Clearly,
  though, you have seen higher forecasts.  All of the "extra" warming in
  these forecasts come from positive feedback.  So a sensitivity of 3C
  would be made up of 1C from CO2 directly that is tripled by positive
  feedbacks.  A sensitivity of 6 or 8 still starts with the same 1C but
  has even higher feedbacks
• Most thoughtful climate scientists will admit that
  we don't know what these feedbacks are -- in so many words, modelers
  are essentially guessing.  Climate scientists don't even know the sign
  (positive or negative) much less the magnitude.  In most physical
  sciences, upon meeting such an unknown system that has been long-term
  stable, scientists will assume neutral to negative feedback.  Climate
  scientists are the exception -- almost all their models assume strong
  positive feedback.
• Climate scientists point to studies of ice cores and
  such that serve as proxies for climate hundreds of thousands of years
  ago to justify positive feedbacks.  But for the period of history we
  have the best data, ie the last 120 years, actual CO2 and measured
  temperature changes imply a sensitivity net of feedbacks closer to 1C,
  about what a reasonable person would assume from a stable process not
  dominated by positive feedbacks.