Read here. The U.S. government climate scientists and agencies, plus the UN's IPCC, have allowed the once globe-spanning climate station network to shrink to a fraction of its previous size. In addition, as has been well documented, the majority of the remaining stations have serious maintenance and siting problems that result in reported temperatures having a significant upward bias. Despite spending billions on global warming climate research, the responsible climate scientists and agencies have managed to squander an immense resource built by the previous generation of scientists. The result has been the growing disbelief of both global temperatures being reported and the wildly wrong climate model predictions that these same climate scientists produce.
Note of interest: The U.S. mainland area has, by many multiples, the most complete station coverage of any large land area on the globe. Over the last 11 years, surface temperatures are declining at a -7.3°F per century rate. If other large land masses had the same proper station coverage, it might well show that significant global cooling is worldwide.
(click image to enlarge - click on embedded video to see animation from here)