A report "A Sensitive Matter: How the IPCC Buried Evidence Showing Good News About Global Warming" by climate scientist Nicholas Lewis and science writer Marcel Crok shows that the IPCC suppressed evidence that the climate is much less sensitive to greenhouse gas emissions than was previously thought.
The executive summary says,
"The best observational evidence indicates our climate is considerably less sensitive to greenhouse gases than climate scientists had previously thought. The clues and the relevant scientific papers are all mentioned in the full IPCC report. However, this important conclusion is not drawn in the full report – it is only mentioned as a possibility – and is ignored in the Summary for Policymakers
The average estimate of equilibrium climate sensitivity from climate models is 3.2 C, "However, several recent studies give best estimates of between 1.5 C and 2 C, substantially lower than most earlier studies indicated."
Many studies used in AR5 used inappropriate statistical methods "that biased them towards higher values, thus making the global warming problem appear ‘worse’.... However, there is now a body of empirical estimates of climate sensitivity, prepared using sound methodology and appropriate data, that give substantially lower values – both of long-term warming and of transient warming towards the end of this century – than climate model simulations."
"Since the last IPCC report was prepared greenhouse gas concentrations have continued to increase, yet global temperatures have not risen; more importantly, estimates of the cooling efficacy of aerosol pollution have been cut. This combination of factors is indicative of the climate system being less sensitive to greenhouse gases than previously appeared to be the case. But the new evidence about aerosol cooling is not reflected in the computer climate
The authors give a best estimate equilibrium climate sensitivity of 1.75 ºC, which is 55% of the mean climate model result. This result assumes that virtually all the warming over the last 150 years was due to human causes.
Large parts of the AR5 report are out of line with the latest scientific evidence as climate models are used to make most of the climate projections.
A news release announcing the report by the Global Warming Policy Foundation is here.
Climate scientists Pat Michaels and Paul "Chip" Knappenberger provide relevant commentary in an article "Climate Insensitivity: What the IPCC Knew But Didn’t Tell Us" here.