Here is a link to a paper that questions the validity of the climate data used to fit the climate models.
To the extent that the data is not accurate, the models are not realistic, and the statistical analysis is based on assumptions that do not hold, a fair conclusion is that climate change forecasts are not reliable.
I do not think there is any reason to be sure of the impact of human activity on climate change or how much and how fast the climate is changing or to believe that anyone knows.
Here is the abstract.
The objective of this research was to test the hypothesis that Global Average Surface Temperature (GAST) data, produced by NOAA, NASA, and HADLEY, are sufficiently credible estimates of global average temperatures such that they can be relied upon for climate modeling and policy analysis purposes. The relevance of this research is that the validity of all three of the so- called Lines of Evidence in EPA’s GHG/CO2 Endangerment Finding require GAST data to be a valid representation of reality.
In this research report, the most important surface data adjustment issues are identified and past changes in the previously reported historical data are quantified. It was found that each new version of GAST has nearly always exhibited a steeper warming linear trend over its entire history. And, it was nearly always accomplished by systematically removing the previously existing cyclical temperature pattern. This was true for all three entities providing GAST data measurement, NOAA, NASA and Hadley CRU.
As a result, this research sought to validate the current estimates of GAST using the best available relevant data. This included the best documented and understood data sets from the U.S. and elsewhere as well as global data from satellites that provide far more extensive global coverage and are not contaminated by bad siting and urbanization impacts. Satellite data integrity also benefits from having cross checks with Balloon data.
The conclusive findings of this research are that the three GAST data sets are not a valid representation of reality. In fact, the magnitude of their historical data adjustments, that removed their cyclical temperature patterns, are totally inconsistent with published and credible U.S. and other temperature data. Thus, it is impossible to conclude from the three published GAST data sets that recent years have been the warmest ever –despite current claims of record setting warming.
Finally, since GAST data set validity is a necessary condition for EPA’s GHG/CO2 Endangerment Finding, it too is invalidated by these research findings.