The CERES team (Willie Soon, Ronan and Michael Connolly) was invited by the Heritage Foundation to contribute a Special Report on what is known about the causes of global warming since the 1850s. Although they were offered payment for this report, they did it pro bono for the reasons they outline on their website here.
The report is a fascinating read about temperature measurements, Urban Heat Island effect, solar reconstructions, all explained in easy to understand language. Here is their summary:
Despite the confidence with which the Intergovernmental Panel on Climate Change (IPCC) claims to have “settled the science” around the detection and attribution of climate change, this challenging scientific debate has not yet been satisfactorily resolved. The IPCC did not provide a strong enough argument for its choice of the available global temperature trends, and the same applies to its choice of the available Total Solar Irradiance (TSI) datasets. The IPCC was overly confident and premature in its detection and attribution statements. The scientific debate is still ongoing, and the scientific community is not yet in a position to establish whether the observed temperature changes since the 1800s are mostly natural, mostly human-caused, or a mixture of both.