Instrumental temperature record

From Wikipedia, the free encyclopedia

The instrumental temperature record shows the fluctuations of the temperature of the atmosphere and the oceans as measured by thermometers. A quasi-global record exists since about 1850. See also temperature record.

Contents 1 The quasi-global period: from 1850 1.1 Secondary data 1.2 Spatial variability 2 See also 3 References

[edit] The quasi-global period: from 1850

The time period for which reasonably reliable near-surface temperature records exist from actual observations from thermometers with quasi-global coverage is generally considered to start in about 1850 - earlier records exist, but coverage and instrument standardisation are less.

In the present day most meteorological observations are taken for use in weather forecasts. Centres such as ECMWF show instantaneous map of their coverage; or the Hadley Centre show the coverage for the average of the year 2000. Coverage for earlier in the 20th and 19th centuries would be significantly less. While temperature changes vary both in size and direction from one location to another, the numbers from different locations are combined to produce an estimate of a global average change.

Most of the warming occurred during two periods: 1910 to 1945 and 1976 to 2000; the cooling/plateau from 1945 to 1976 is attributed to sulphate aerosol [2]. Attribution of the temperature change to natural or anthropogenic factors is an important question: see global warming and attribution of recent climate change.

The data for the record come from thermometer measurements from land stations and ships [3], which independently show much the same warming since 1860. The data from these stations show an average surface temperature increase of about 0.74 °C during the last 100 years. The Intergovernmental Panel on Climate Change (IPCC) stated in its Fourth Assessment Report (AR4) that the temperature rise over the 100 year period from 1906-2005 was 0.74 °C [0.56 to 0.92 °C] with a confidence interval of 90%.

For the last 50 years, the linear warming trend has been 0.13 °C [0.10 to 0.16 °C] according to AR4.

The US National Academy of Science, both in its 2002 report to President George W. Bush, and in its latest publications, has strongly endorsed evidence of an average global temperature increase in the 20th century.

There are concerns about possible uncertainties in the instrumental temperature record including the fraction of the globe covered, the effects of changing thermometer designs and observing practices, and the effects of changing land-use around the observing stations. These are being continually addressed in the literature to optimally characterize the accuracy of the record. The casual reader is warned that advocacy organizations considerably exaggerate how seriously these effects contaminate the record. On the other hand considerable skepticism should be exercized for the early years. Indeed, the argument has been advanced that pre-1880 climate models could be more accurate than the instrumental record. Methods standardization and instrument calibration have been the responsibilities of the World Meteorological Organization and its predecessor, the International Meteorological Organization.

There exists a parallel record of marine observations from surface ships. These too suffer from changing practices (such as the switch from collecting water in canvas buckets to measuring the temperature from engine intakes) but they are at least immune to the urban heat island effect. The land and marine records can be compared. [4]

In relation to the instrumental temperature record of the last 100 years, the IPCC Fourth Assessment Report found that:

"Urban heat island effects are real but local, and have a negligible influence (less than 0.006 °C per decade over land and zero over the oceans) on these values."

For more information about the effects or otherwise of urbanization on the temperature record, see the main article: Urban heat island effect

[edit] Secondary data

Secondary evidence for temperature changes can be obtained by observing things that are predicted to be affected by temperature changes, such as variations in the snow cover and ice extent [5], sea level rise, precipitation [6], cloud cover [7], El Niño and extreme weather events [8]. For example, satellite data shows a 10% decrease of snow cover since the late 1960s [9], and the Northern Hemisphere spring and summer sea-ice extent has decreased by about 10% to 15% since the 1950s and there has been a widespread retreat of mountain glaciers in non-polar regions throughout the 20th century.[10].

[edit] Spatial variability

The global temperature changes are not uniform over the globe, nor would they be expected to be, whether the changes were naturally or humanly forced. Certain places, such as the north shore of Alaska, show dramatic rises in temperature, far above the average for the globe as a whole [11]. The Antarctic peninsula has warmed by 2.5 °C (4.5 °F) in the past five decades in certain places [12]; meanwhile East Antarctic has not significantly warmed [13].

[edit] See also

• Temperature record
• Satellite temperature measurements
• Temperature record of the past 1000 years
• Temperature record since 1880

[edit] References

• IPCC Fourth Assessment Report (AR4) WGI Summary for Policy Makers (SPM)[14]
• Global average temperature for the last 150 years and discussion of trends
• Preliminary data from the last 2000 years