E. Hansen's estimate of , and Charney's model were the only models available in 1979. According to Manabe, speaking in 2004, "Charney chose 0.5 °C as a reasonable margin of error, subtracted it from Manabe's number, and added it to Hansen's, giving rise to the range of likely climate sensitivity that has appeared in every greenhouse assessment since ...." In 2008, climatologist Stefan Rahmstorf said: "At that time [it was published], the [Charney report estimate's] range [of uncertainty] was on very shaky ground. Since then, many vastly improved models have been developed by a number of climate research centers around the world." Intergovernmental Panel on Climate Change Despite considerable progress in the understanding of Earth's climate system, assessments continued to report similar uncertainty ranges for climate sensitivity for some time after the 1979 Charney report. The 1990 IPCC First Assessment Report estimated that equilibrium climate sensitivity to a doubling of lay between , with a "best guess in the light of current knowledge" of . The report used models with simplified representations of ocean dynamics. The IPCC supplementary report, 1992, which used full-ocean circulation models, saw "no compelling reason to warrant changing" the 1990 estimate; and the IPCC Second Assessment Report stated, "No strong reasons have emerged to change [these estimates]," In the reports, much of the uncertainty around climate sensitivity was attributed to insufficient knowledge of cloud processes. The 2001 IPCC Third Assessment Report also retained this likely range. Authors of the 2007 IPCC Fourth Assessment Report stated that confidence in estimates of equilibrium climate sensitivity had increased substantially since the Third Annual Report. The IPCC authors concluded that ECS is very likely to be greater than and likely to lie in the range , with a most likely value of about . The IPCC stated that fundamental physical reasons and data limitations prevent a climate sensitivity higher than from being ruled out, but the climate sensitivity estimates in the likely range agreed better with observations and the proxy climate data. The 2013 IPCC Fifth Assessment Report reverted to the earlier range of (with high confidence), because some estimates using industrial-age data came out low. (See the next section for details.) The report also stated that ECS is extremely unlikely to be less than (high confidence), and it is very unlikely to be greater than (medium confidence). Those values were estimated by combining the available data with expert judgement.