IPCC draw firm conclusions unjustified by the science, especially given the acknowledged weakness of cloud physics in the climate models. For example, even those who accept that there is a warming trend point out that there is a big difference between correlation and causality. In other words, just because temperatures have generally been rising since the beginning of the Industrial Revolution, that doesn't necessarily mean that the Industrial Revolution has caused the change in temperature (see post hoc, ergo propter hoc argument). On the other hand, the period since the beginning of the Industrial Revolution has indeed produced ever-growing "urban heat islands" that could be skewing temperature measurements that indicate the recent warming.