Below is a chart that some may find useful. It combines various global temperature estimates:
- HadCRU3v: measurements from land stations + SST, starts in 1850, the reference period is 1961-1990. data link.
- NASA GISS: measurements from land stations + SST, starts in 1880, the reference period is 1951-1980. data link.
- NCDC: measurements from land stations + SST starts in 1880, the reference period is 1951-1980. data link.
- UAH versions 5.2: satellite based measurements of the lower troposphere, starts in 1979, the reference period is 1979-2000. data available here.
Each dataset has a different reference period. A temperature offset is added to CRU, NCDC and UAH temperatures in order to represent the temperatures in a common reference period (1951-1980). The offset values are the following (in deg. C):
- CRU: 0.0855
- NCDC: -0.0330
- UAH: 0.2425
Figure 1. Adjusted global temperature estimates. Click on the image to get a svg image.
Over the period 1979-2009, we can compute the median temperature value from the four estimates. The August median temperature measurement is +0.62 deg. C (98.2% of observed values are below).
Figure 2. (Red) median temperature estimate from 1979 to August 2009. (light yellow) range of temperature values; (yellow) 99% probability interval. The blue curve is the empirical CDF curve derived from all the datasets combined. Click on the image to get a svg image.