Truth: Remember that there is no such thing as a global temperature. It is the average of all of the reporting stations all over the world. For example, several years ago Ross McKitrick using CRU data showed that the rapid rise in temperatures in the 1990s directly coincided with a decrease in the number of Siberian weather stations reporting due to the break-up of the Soviet Union.
Additionally, the “hottest year on record,” 1998, was an El Nino year so it was naturally hotter than the years just before and after. Another cause of rising average global temperatures is the urban heat island effect. Cities are hotter than rural areas.
Many of the reporting stations that were once in undeveloped rural areas have experienced either suburban or urban development, or the stations have been moved to more urban settings. It is well documented that some have been, seemingly intentionally, relocated near or at heat sources such as paved parking lots and air conditioners. One reason for relocation near buildings or other structures could be that new automatic-reporting equipment needs to be connected by cable. Rather than dig up parking lots or roads to install units in a grassy or protected area, many have opted to locate them where they can be directly connected without involving costly excavation, although such sites do not meet the stated requirements.
Instead of excluding data from stations that are poorly situated, a convoluted mathematical algorithm (scheme) is used to “correct” it to presumed pre-industrial levels. In spite of all this, it appears that there has been no net warming since the late 1990s and even a slight cooling since 2005. One other problem with the new equipment is that it has a faster response time that records brief, transient signals such as car or plane exhausts that were not picked up by the older equipment. Because the equipment is designed to report maximum and minimum temperatures, this can create a false result.