The Intergovernmental Panel for Climate Change (IPCC) – The 4th Report

In 2007 The IPCC released its fourth Assessment Report that claimed that based on contemporary computer model simulations the temperature rises in the last half century is very likely due to human activity, particularly CO2 emissions. This claim was made despite a limited correlation between CO2 and temperature rises in that century. In the period between the world wars there was economic stagnation and therefore a limited growth in CO2 yet there was a significant rise in temperature during this period. In the period after world war two when there was significant economic activity and CO2 production (compared to other times) the temperature actually fell. It didn’t start to rise again until 1976 and the ended in 1998, and then started falling again post 2002, despite increasing CO2 levels.

The IPCC rationale was that these early emissions in fact reflected solar radiation and therefore constrained global temperatures against any rise in CO2 or enhanced greenhouse effect.
Accordingly the IPCC contended that only their models with aerosol and CO2 forcing were able to reproduce the warming record of the twentieth century with any accuracy. (Any emphasis added is mine.)

“The “evidence” is no more than model tuning with plausible parameters” - William Kininmonth (Oct 2008)

In stark contrast to the often repeated assertion that the science of climate change is “settled,” significant new peer-reviewed research has cast even more doubt on the hypothesis of dangerous human-caused global warming. But because IPCC working groups were generally instructed to consider work published only through May, 2005, these important findings are not included in their reports; i.e., the IPCC assessment reports are already materially outdated.- Excerpt from an Open Letter to the IPCC by distinguished academics and researchers.