The last 25 years of temperature variation]]

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

The uncertainty in annual measurements of the global average temperature (95% range) is estimated to be ~0.05°C since 1950 and as much as ~0.15°C in the earliest portions of the instrumental record. The error in recent years is dominated by the incomplete coverage of existing temperature records. Early records also have a substantial uncertainty driven by systematic concerns over the accuracy of sea surface temperature measurements.^[12][13] 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 such as the tropics, northern Asia and the former Soviet Union. This results in less confidence in the robustness of climate trends in these areas. If a sparsely populated grid has a poor quality station, the impact on global temperature would be greater than if it occurred in a grid with many weather stations^[14].

Uncertainty can also be based on poorer quality weather stations. A number of scientists and scientific organizations have expressed concern about the possible deterioration of the land surface observing network.^{[15][16][17][18]} Roger A. Pielke has also claimed to have identified a number of sites where poorly sited stations in sparse regions "will introduce spatially unrepresentative data into the analyses." ^[19] The metadata needed to quantify the uncertainty from poorly sited stations does not currently exist. Anthony Watts is currently documenting station quality in the U.S. Pielke has called for a similar documentation effort for the rest of the world ^[20]. This is an effort Watts is planning to undertake. ^[21]

Criticism of the United States land surface temperature record

The U.S. National Weather Service Cooperative Observer Program has established minimum standards regarding the instrumentation, siting, and reporting of surface temperature stations.^[22] The observing systems available are able to detect year-to-year temperature variations such as those caused by El Niño or volcanic eruptions.^[23] 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.^[23]

In 2007, broadcast meteorologist Anthony Watts^[24] delivered a presentation^[25] based on preliminary results of his all-volunteer effort to document the quality of each U.S. Historical Climatology Network (USHCN) weather station in the United States at a Cooperative Institute for Research in Environmental Sciences workshop in Boulder, Colorado.^[26]. Using a 5-point rating scale based on government guidelines, Watts labeled 5% of the stations the best quality or "Class 1", 10% a "Class 2", 16% a "Class 3", 52% a "Class 4", and 17% the worst or "Class 5".^[27] Watts founded SurfaceStations.org, which was launched on June 4, 2007. The project has not yet published any papers in peer reviewed journals. The results as of September 12, 2007 of their 33% completed survey, with 404 stations surveyed, of the USHCN network are posted on their website.^[28]

A 2006 paper analyzed a subset of U.S. surface stations, 366 stations, and found that 95% displayed a warming trend after land use/land cover (LULC) changes. The authors stated "this does not necessarily imply that the LULC changes are the causative factor."^[29] Another study ^[30] has 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.^[31] 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.^[32]

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.^[33] Pielke and co-authors disagree.^[34]

External links

• The EdGCM project has provided Google Earth

References

• IPCC Fourth Assessment Report (AR4) WGI Summary for Policy Makers (SPM)http://www.ipcc.ch/SPM2feb07.pdf
• Global average temperature for the last 150 years and discussion of trends
• Preliminary data from the last 2000 years

See also 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.

Global records databases

Currently, the Hadley Centre maintains the HADCRUT3, a global surface temperature dataset^[1], NASA maintains GISTEMP, which provides a measure of the changing global surface temperature with monthly resolution for the period since 1880^[2], 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^[3].

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^[4]. Land and sea measurement and instrument calibration is the responsibility of National Meteorological Services. Standardization of methods is organized through the World Meteorological Organization and its predecessor, the International Meteorological Organization.^[5]

Currently, 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

The uncertainty in annual measurements of the global average temperature (95% range) is estimated to be ~0.05°C since 1950 and as much as ~0.15°C in the earliest portions of the instrumental record. The error in recent years is dominated by the incomplete coverage of existing temperature records. Early records also have a substantial uncertainty driven by systematic concerns over the accuracy of sea surface temperature measurements.^[12][13] 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 such as the tropics, northern Asia and the former Soviet Union. This results in less confidence in the robustness of climate trends in these areas. If a sparsely populated grid has a poor quality station, the impact on global temperature would be greater than if it occurred in a grid with many weather stations^[14].

Uncertainty can also be based on poorer quality weather stations. A number of scientists and scientific organizations have expressed concern about the possible deterioration of the land surface observing network.^{[15][16][17][18]}Roger A. Pielke has also claimed to have identified a number of sites where poorly sited stations in sparse regions "will introduce spatially unrepresentative data into the analyses." ^[19] The metadata needed to quantify the uncertainty from poorly sited stations does not currently exist. Anthony Watts is currently documenting station quality in the U.S. Pielke has called for a similar documentation effort for the rest of the world ^[20]. This is an effort Watts is planning to undertake. ^[21]

Criticism of the United States land surface temperature record

The U.S. National Weather Service Cooperative Observer Program has established minimum standards regarding the instrumentation, siting, and reporting of surface temperature stations.^[22] The observing systems available are able to detect year-to-year temperature variations such as those caused by El Niño or volcanic eruptions.^[23] 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.^[23]

In 2007, broadcast meteorologist Anthony Watts^[24] delivered a presentation^[25] based on preliminary results of his all-volunteer effort to document the quality of each U.S. Historical Climatology Network (USHCN) weather station in the United States at a Cooperative Institute for Research in Environmental Sciences workshop in Boulder, Colorado.^[26]. Using a 5-point rating scale based on government guidelines, Watts labeled 5% of the stations the best quality or "Class 1", 10% a "Class 2", 16% a "Class 3", 52% a "Class 4", and 17% the worst or "Class 5".^[27] Watts founded SurfaceStations.org, which was launched on June 4, 2007. The project has not yet published any papers in peer reviewed journals. The results as of September 12, 2007 of their 33% completed survey, with 404 stations surveyed, of the USHCN network are posted on their website.^[28]

A 2006 paper analyzed a subset of U.S. surface stations, 366 stations, and found that 95% displayed a warming trend after land use/land cover (LULC) changes. The authors stated "this does not necessarily imply that the LULC changes are the causative factor."^[29] Another study ^[30] has 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.^[31] 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.^[32]

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.^[33] Pielke and co-authors disagree.^[34]

External links

• The EdGCM project has provided Google Earth

References

• IPCC Fourth Assessment Report (AR4) WGI Summary for Policy Makers (SPM)http://www.ipcc.ch/SPM2feb07.pdf
• Global average temperature for the last 150 years and discussion of trends
• Preliminary data from the last 2000 years

•  • [ e] Global warming and Climate change
Temperatures	Instrumental record Satellite record Past 1000 years Since 1880 Geologic record
Causes	Scientific opinion on climate change Anthropogenic: Carbon dioxide Climate sensitivity Deforestation Global dimming Global warming potential Greenhouse effect Greenhouse gases Keeling Curve Urban heat island Natural: Cloud forcing Glaciation Global cooling Ocean variability Orbital variations Plate tectonics Radiative forcing Solar variation Volcanism
Models	Global climate model
Issues	Ozone depletion Ocean acidification
Politics	Global warming controversy Intergovernmental Panel on Climate Change Scientists opposing the mainstream assessment
Effects	Sea level rise Glacier retreat Climate change and agriculture National Assessment on Climate Change Economics of global warming Shutdown of thermohaline circulation
Mitigation	Individual and political action on climate change Kyoto Protocol: Clean Development Mechanism Schemes: Emissions trading Personal carbon trading Carbon tax Carbon offsets Carbon dioxide sink (Carbon sequestration) Energy conservation: Efficient energy use Renewable energy Renewable energy commercializationRenewable energy development Soft energy path
Adaptation	United Kingdom Climate Change Programme European Climate Change Programme

•  • [ e] Global warming and Climate change
Temperatures	Instrumental record Satellite record Past 1000 years Since 1880 Geologic record
Causes	Scientific opinion on climate change Anthropogenic: Carbon dioxide Climate sensitivity Deforestation Global dimming Global warming potential Greenhouse effect Greenhouse gases Keeling Curve Urban heat island Natural: Cloud forcing Glaciation Global cooling Ocean variability Orbital variations Plate tectonics Radiative forcing Solar variation Volcanism
Models	Global climate model
Issues	Ozone depletion Ocean acidification
Politics	Global warming controversy Intergovernmental Panel on Climate Change Scientists opposing the mainstream assessment
Effects	Sea level rise Glacier retreat Climate change and agriculture National Assessment on Climate Change Economics of global warming Shutdown of thermohaline circulation
Mitigation	Individual and political action on climate change Kyoto Protocol: Clean Development Mechanism Schemes: Emissions trading Personal carbon trading Carbon tax Carbon offsets Carbon dioxide sink (Carbon sequestration) Energy conservation: Efficient energy use Renewable energy Renewable energy commercializationRenewable energy development Soft energy path
Adaptation	United Kingdom Climate Change Programme European Climate Change Programme