Instrumental temperature record
The instrumental temperature record shows the fluctuations of the temperature of the atmosphere and the oceans as measured by temperature sensors. A quasi-global record exists since about 1850. See also temperature record.
Global records databases
Currently, the Hadley Centre maintains the HADCRUT3, a global surface temperature dataset [2], NASA maintains GISTEMP, which provides a measure of the changing global surface temperature with monthly resolution for the period since 1880[3], and the NOAA maintains the Global Historical Climatology Network (GHCN-Monthly) data base contains historical temperature, precipitation, and pressure data for thousands of land stations worldwide [4].
The global record 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 standardization are less. The instrumental temperature record is viewed with considerable skepticism for the early years.
The temperature data for the record come from measurements from land stations and ships. On land, temperature sensors are kept in a Stevenson screen or a MMTS. The sea record consists of surface ships taking sea temperature measurements from engine inlets or buckets. The land and marine records can be compared. [5] Land and sea measurement and instrument calibration is the responsibility of the National Meteorological Services. Standardization of methods is organized through the World Meteorological Organization and its predecessor, the International Meteorological Organization.[1]
In the present day most meteorological observations are taken for use in weather forecasts. Centers 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.
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. The ocean temperature record too suffers from changing practices (such as the switch from collecting water in canvas buckets to measuring the temperature from engine intakes) but they are immune to the urban heat island effect or to changes in local land use/land cover (LULC) at the land surface station.
Warming in the instrumental temperature record
Most of the observed warming occurred during two periods: 1910 to 1945 and 1976 to 2000; the cooling/plateau from 1945 to 1976 is attributed to sulphate aerosol [6]. Attribution of the temperature change to natural or anthropogenic factors is an important question: see global warming and attribution of recent climate change.
Land and sea measurements independently show much the same warming since 1860 [7]. 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] per decade according to AR4.
The U.S. National Academy of Sciences, both in its 2002 report to President George W. Bush, and in later publications, has strongly endorsed evidence of an average global temperature increase in the 20th century [8].
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
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 [9]. The Antarctic peninsula has warmed by 2.5 °C (4.5 °F) in the past five decades in certain places [10]; meanwhile East Antarctic has not significantly warmed [11].
Uncertainties in the temperature record
One component of the scientific method is to discuss and quantify uncertainties. The National Institute of Standards and Technology has issued guidelines on establishing and expressing the uncertainty of measurement results. [12] Roger A. Pielke published a paper calling for the NOAA to make “available an evaluation of the statistical uncertainty of each step in their adjustment process from the raw data to the processed values.“ [13] Unfortunately, the NOAA has not made this available for researchers to better understand the steps and uncertainties of the temperature record. [14] See Comment #131
In August 2007, Stephen McIntyre investigated a sudden jump in temperature around the year 2000. He discovered "a programming error" and detailed its distribution alongside the problems in the USHCN temperature data on his website. [15] He emailed GISS advising them of the problem and it promply issued corrected data. [16] The corrected data show the 10 hottest years to be 1934, 1998, 1921, 2006, 1931, 1999, 1953, 1990, 1938, and 1939 (1st to 10th).
Uncertainty also enters if the weather stations are poor quality. A number of scientists and scientific organizations have expressed concern about the possible deterioration of the land surface observing network. [17] [18][19] [20] The metadata needed to quantify the uncertainty from poorly sited stations does not currently exist. Anthony Watts (see below) is leading the effort to document station quality in the U.S. Roger A. Pielke has called for a similar documentation effort for the rest of the world, which will also be led by Watts. [21]
Uncertainty is also introduced when a weather station network is sparsely populated. Station densities are highest in the northern hemisphere, providing more confidence in climate trends in this region. Station densities are far lower in other regions, including the tropics, northern Asia and the former Soviet Union. This results in much less confidence in the robustness of climate trends in these areas. If a sparsely populated grid has a poor quality station with an artificial warming bias, the impact on global temperature is greater than if it occurred in a grid with many weather stations. [22] Pielke has identified a number of such sites. [23]
Criticism of the United States land surface temperature record
The surface temperature stations are expected to meet certain minimum standards regarding instrumentation, siting, and reporting.[24] The observing systems available are able to detect year-to-year temperature variations such as those caused by El Niño or volcanic eruptions.[25] These stations can undergo undocumented changes such as relocation, changes in instrumentation and exposure (including changes in nearby thermally emitting structures), changes in land use (e.g., urbanization), and changes in observation practices. All of these changes can introduce biases into the stations' long term records. In the past, these local biases were generally considered to be random and therefore would cancel each other out using many stations and the ocean record. [26] A 2006 paper analyzed a subset of U.S. surface stations found that 95% displayed a warming trend after land use/land cover (LULC) changes, though the authors stated "this does not necessarily imply that the LULC changes are the causative factor."[27]
Various studies [28]) have documented examples of well and poorly sited monitoring stations in the United States, including ones near buildings, roadways, and air conditioning exhausts. Brooks investigated Historical Climate Network (USHCN) sites in Indiana, and assigned 16% of the sites an ‘excellent’ rating, 59% a ‘good’ rating, 12.5% a ‘fair’ rating, and 12.5% ‘poor’ rating.[29] Davey and Pielke visited 10 HCN sites in Eastern Colorado, but did not provide percentages of good or badly sited stations. They stated that some of the sites "are not at all representative of their surrounding region" and should be replaced in the instrumental temperature records with other sites from the U.S. cooperative observer network.[30]
Peterson has argued that existing empirical techniques for validating the local and regional consistency of temperature data are adequate to identify and remove biases from station records, and that such corrections allow information about long-term trends to be preserved. [31]. Pielke and co-authors disagree [32].
In 2007, television weatherman Anthony Watts [33] began an all-volunteer effort to document the quality of each U.S. Historical Climatology Network (USHCN) weather station in the United States.[34] The SurfaceStations.org website was launched on June 4, 2007. The project has received support from Roger A. Pielke who identified it as "a very important need for the climate science community".[35] The surfacestations.org project has not yet published any papers in peer reviewed journals.
External links
References
- IPCC Fourth Assessment Report (AR4) WGI Summary for Policy Makers (SPM)[36]
- Global average temperature for the last 150 years and discussion of trends
- Preliminary data from the last 2000 years
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