Here is a statement taken from the IPCC official website...


The global average surface temperature has increased over the 20th century by about 0.6°C.

The global average surface temperature (the average of near surface air temperature over land, and sea surface temperature) has increased since 1861. Over the 20th century the increase has been 0.6 ± 0.2°C5, 6 (Figure 1a). This value is about 0.15°C larger than that estimated by the SAR for the period up to 1994, owing to the relatively high temperatures of the additional years (1995 to 2000) and improved methods of processing the data. These numbers take into account various adjustments, including urban heat island effects. The record shows a great deal of variability; for example, most of the warming occurred during the 20th century, during two periods, 1910 to 1945 and 1976 to 2000.

Globally, it is very likely7 that the 1990s was the warmest decade and 1998 the warmest year in the instrumental record, since 1861 (see Figure 1a).

New analyses of proxy data for the Northern Hemisphere indicate that the increase in temperature in the 20th century is likely7 to have been the largest of any century during the past 1,000 years. It is also likely7 that, in the Northern Hemisphere, the 1990s was the warmest decade and 1998 the warmest year (Figure 1b). Because less data are available, less is known about annual averages prior to 1,000 years before present and for conditions prevailing in most of the Southern Hemisphere prior to 1861.

On average, between 1950 and 1993, night-time daily minimum air temperatures over land increased by about 0.2°C per decade. This is about twice the rate of increase in daytime daily maximum air temperatures (0.1°C per decade). This has lengthened the freeze-free season in many mid- and high latitude regions. The increase in sea surface temperature over this period is about half that of the mean land surface air temperature.


Note that the maximum-minimum thermometer was not in common use until about 1800, so any temperature "data" before that time is a guess (or worse, a lie).

Also, the warmest period in the century was 1936-42, the hight of the Depression and the slowest industrial output of the period in question.

Not mentioned is that all of the increase is in the minimum temperature. No change in maximum readings at all. This is consistant with the ability of city buildings and roards to store heat and release it night. The weather stations in rural areas at the begining of the century were often in a city 100 years later.

The temperature is always changing to some extent. The 0.6 degrees C is very small compared to most other similar periods of the. It hardly deserves the term "global warming". Actually, "global normalcy" be a more correct term, but that would not put the public in a state of alarm.