3. The world is warming - There are three main records of global
temperature at the Earth’s surface: the UK Met Office/UEA
Climatic Research Unit (CRU) record, a record produced by NASA’s
Goddard Institute for Space Studies, and a record produced by
the US National Oceanic and Atmospheric Administration (NOAA).
The records are in close agreement, showing that global average
temperature has increased by approximately 0.75°C since 1900
(Figure 7, below). Figure 7 (above): The three main records of
global average surface temperature. Red line = NOAA record, blue
line = NASA record, black line = Met Office/ UEA CRU record,
with grey shading showing 95% confidence interval on Met
Office/UEA CRU record. Source: Met Office Hadley Centre. Before
1850, instrumental time series measurements with global coverage
are not available. [IPCC AR4 (2007) (Working Group 1; 1.3.2)].
(Larger version of Figure 7 (PNG, 402 Kb) ) - The global average
temperature is currently calculated from measurements taken at
about 5,000 land-bas