How warm can it get?
How warm it gets depends upon climate sensitivity of CO2 to warming. Values for CO2 climate sensitivity vary from about 0.6 °C (Spencer & Braswell), 0.7 °C (Lindzen & Choi), 0.85 °C (Tim Ball), 1.3 °C (Nic Lewis' review). At this time I'm inclined to go with the lower range values of 0.6 °C to 0.85 °C by Spencer, Braswell, Lindzen, Choi, & Ball. Some of these are their own measurements. Some are judgements. Due to uncertainty over what's been happening with surface temperature measurements and whether these have been adjusted from raw values, I'm disinclined to trust them. That means I must trust the satellite values more. Therefore I go with Spencer & Braswell. Climate sensitivity estimates get a lot higher than this (but we are long past the time when anyone considered 10 °C seriously. Today anyone estimating over 2 °C is clearly an alarmist. Not to be taken seriously. In addition to apparent political climate science there are tendencies to overstate positive feedbacks due to the nature of the system, and discount negative feedbacks. Dr Roy Spencer explains this here. e.g.:
For some reason, the main “feedback” which stabilizes the climate system, the so-called “Planck effect” (increasing infrared output as temperature increases) is NOT called a “feedback” in climate research. I don’t know why this is the case. When the Planck effect is included with all of the other feedbacks, the total feedback (even in climate models which produce huge warming) is still negative.
Any climate sensitivity value below about 1.4 °C is fine by me. It does not scare me. This will not lead to any catastrophic climate change. The big reason for panicking over climate and caving into the greens has been the threat of catastrophic change. It is just not there. Climate disaster is not happening. Without catastrophic warming, nearly all the effects of climate change are currently good, apart from sea level rise.
“As a result, the climate sensitivity for a doubling of CO2 is estimated to be 0.7 K (with the confidence interval 0.5K – 1.3 K at 99% levels). This observational result shows that model sensitivities indicated by the IPCC AR4 are likely greater than than the possibilities estimated from the observations” This value of 0.7 C somewhat lower than the 1.0 C value that you highlighted, and is consistent with their previous result (0.5 C) and also Dr Spencer & Dr Braswell’s measurement (0.6 C).--Anthony Watts discussion
- Another Potential Reason Why Climate Sensitivity is Over-Estimated, 2 Jun 2016, by Dr Roy Spencer
- On the diagnosis of radiative feedback in the presence of unknown radiative forcing, (pdf) 2010, by Roy Spencer & William Braswell
- Estimating climate sensitivity using two-zone energy balance models, by J. Ray Bates. Finds EqCS = 1.0 °C. estimates of climate sensitivity reflect publication bias. e.g. by overestimating climate sensitivity by a factor of 2, (pdf). Accounting for this effect they estimate it at 1.6 °C.
- global climate sensitivity to increased carbon dioxide, and the potential feedback mechanism of increased water vapor in Earth’s atmosphere, is actually far less than postulated by the IPCC, by Willis Eschenbach and Anthony Watts.
- All IPCC models vastly overrate climate sensitivity, by Dr David Evans: former climate modeller for the Government’s Australian Greenhouse Office, with six degrees in applied mathematics. The major cause of global warming is likely “albedo modulation”, the waxing and waning of reflected radiation from the Sun
- Climate Scientists Misapplied Basic Physics, by Dr David Evans.