Changes in Earthâ€™s Average Temperature
The temperature increase has been widespread over the globe and is greater at higher northern latitudes.
- Changes in the earthâ€™s average temperature from 1850 to 1915 were rare, besides the fluctuations associated with the natural variability.
- An increase in the warming occurred from 1919 to 1940s, followed by a slight cooling which was again followed by a rapid warming up to the end of 2006. Notable increases were reported from 1950 onwards.
- The changes in the temperature extremes have been found to be consistent with warming. While the number of frost days has declined significantly, there has been an increase in the number of warm extreme days and a reduction in the number of daily cold extreme days.
- The most marked changes have been observed in the case of cold nights, which were observed to have declined during 1951â€“2003 in all regions. Correspondingly, heat waves have increased in duration.
The following graph shows how global temperature has changed over time from 1850.
Changes in the earthâ€™s average temperature from 1850 onwards â€“ for recent periods, the slope is greater, indicating accelerated warming. The shaded areas are the uncertainty intervals estimated from a comprehensive analysis of known uncertainties.
Source: IPCC 2007
You can view an animation depicting projected temperature rise at Hadley Centre.
Average Northern Hemisphere temperatures during the second half of the 20th century were very likely higher than during any other 50-year period in the last 500 years, and likely the highest in at least the past 1300 years (IPCC 2007).
Warming has been more significant over land areas than in oceans. In the last two decades, while warming over the land has occurred at the rate of 0.27 Â°C per decade, oceans have warmed by 0.13 Â°C per decade.
The average temperature of the earth's surface has risen by 0.74 Â°C since the late 1800s. It is expected to increase by another 1.8 Â°C to 4 Â°C by the year 2100, which is very alarming and would result in rapid and profound change if necessary action is not taken. Even if the minimum predicted increase takes place, it will be larger than any century-long trend in the last 10,000 years.