Instrumental temperature record

Instrumental temperature record

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The instrumental temperature record shows fluctuations of the temperature
Temperature
Temperature is a physical property of matter that quantitatively expresses the common notions of hot and cold. Objects of low temperature are cold, while various degrees of higher temperatures are referred to as warm or hot...

 of the global land surface and oceans. This data is collected from several thousand meteorological stations, Antarctic research stations and satellite observations of sea-surface temperature. Currently, the longest-running temperature record is the Central England temperature
Central England temperature
The Central England Temperature record was originally published by Professor Gordon Manley in 1953 and subsequently extended and updated in 1974, following many decades of painstaking work...

 data series, that starts in 1659. The longest-running quasi-global record starts in 1850.

Global records databases


Currently, the Hadley Centre maintains the HADCRUT3, a monthly-mean global surface temperature analysis, and NASA
NASA
The National Aeronautics and Space Administration is the agency of the United States government that is responsible for the nation's civilian space program and for aeronautics and aerospace research...

 maintains GISTEMP, another monthly-mean global surface temperature analysis, for the period since 1880. The two analyses differ in the details of how they obtain temperature values on a regular grid from the network of irregularly spaced observation sites; thus, their results for global and regional temperature differ slightly. The United States
United States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...

 National Oceanic and Atmospheric Administration
National Oceanic and Atmospheric Administration
The National Oceanic and Atmospheric Administration , pronounced , like "noah", is a scientific agency within the United States Department of Commerce focused on the conditions of the oceans and the atmosphere...

 (NOAA) maintains the Global Historical Climatology Network
Global Historical Climatology Network
The Global Historical Climatology Network is a database of temperature, precipitation and pressure records managed by the National Climatic Data Center, Arizona State University and the Carbon Dioxide Information Analysis Center....

 (GHCN-Monthly) data base contains historical temperature, precipitation, and pressure data for thousands of land stations worldwide. Also, NOAA's National Climatic Data Center
National Climatic Data Center
The United States National Climatic Data Center in Asheville, North Carolina is the world's largest active archive of weather data. The center became established in late 1951, with the move into the new facility occurring in early 1952....

 (NCDC), which has "the world's largest active archive" of surface temperature measurements, maintains a global temperature record since 1880.

The global record from 1850


The period for which reasonably reliable instrumental records of near-surface temperature exist with quasi-global coverage is generally considered to begin around 1850. Earlier records exist, but with sparser coverage and less standardized instrumentation.

The temperature data for the record come from measurements from land stations and ships. On land, temperature sensors are kept in a Stevenson screen
Stevenson screen
A Stevenson screen or instrument shelter is an enclosure to shield meteorological instruments against precipitation and direct heat radiation from outside sources, while still allowing air to circulate freely around them. It forms part of a standard weather station...

 or a maximum minimum temperature system
MMTS (meteorology)
A Maximum Minimum Temperature System or MMTS is a temperature recording system that keeps track of the maximum and minimum temperatures that have occurred over some given time period....

 (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. Land and sea measurement and instrument calibration is the responsibility of national meteorological services. Standardization of methods is organized through the World Meteorological Organization
World Meteorological Organization
The World Meteorological Organization is an intergovernmental organization with a membership of 189 Member States and Territories. It originated from the International Meteorological Organization , which was founded in 1873...

 and its predecessor, the International Meteorological Organization
International Meteorological Organization
The International Meteorological Organization was the first organization formed with the purpose of exchanging weather information among the countries of the world. It was born from the realization that weather systems move across country boundaries and knowledge of pressure, temperature,...

.

Currently, most meteorological observations are taken for use in weather forecasts. Centers such as ECMWF
European Centre for Medium-Range Weather Forecasts
The European Centre for Medium-Range Weather Forecasts is an independent intergovernmental organisation supported by 19 European Member States and 15 Co-operating States...

 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
Urban heat island
An urban heat island is a metropolitan area which is significantly warmer than its surrounding rural areas. The phenomenon was first investigated and described by Luke Howard in the 1810s, although he was not the one to name the phenomenon. The temperature difference usually is larger at night...

 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 has been mostly attributed to sulphate aerosol. However, a study in 2008 suggests that the temperature drop of about 0.3°C in 1945 could be the apparent result of uncorrected instrumental biases in the sea surface temperature record. Attribution of the temperature change to natural or anthropogenic factors is an important question: see global warming
Global warming
Global warming refers to the rising average temperature of Earth's atmosphere and oceans and its projected continuation. In the last 100 years, Earth's average surface temperature increased by about with about two thirds of the increase occurring over just the last three decades...

 and attribution of recent climate change
Attribution of recent climate change
Attribution of recent climate change is the effort to scientifically ascertain mechanisms responsible for recent changes observed in the Earth's climate...

.

Land and sea measurements 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
Intergovernmental Panel on Climate Change
The Intergovernmental Panel on Climate Change is a scientific intergovernmental body which provides comprehensive assessments of current scientific, technical and socio-economic information worldwide about the risk of climate change caused by human activity, its potential environmental and...

) stated in its Fourth Assessment Report
IPCC Fourth Assessment Report
Climate Change 2007, the Fourth Assessment Report of the United Nations Intergovernmental Panel on Climate Change , is the fourth in a series of reports intended to assess scientific, technical and socio-economic information concerning climate change, its potential effects, and options for...

 (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
United States National Academy of Sciences
The National Academy of Sciences is a corporation in the United States whose members serve pro bono as "advisers to the nation on science, engineering, and medicine." As a national academy, new members of the organization are elected annually by current members, based on their distinguished and...

, 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.

The IPCC Fourth Assessment Report found that the instrumental temperature record for the past century included urban heat island effects but that these were primarily local, having a negligible influence on global temperature trends (less than 0.006 °C per decade over land and zero over the oceans).

The preliminary results of an independent assessment, carried out by the Berkeley Earth Surface Temperature
Berkeley Earth Surface Temperature
The Berkeley Earth Surface Temperature project is an effort to resolve criticism of the current records of the Earth's surface temperatures by preparing an open database and analysis of these temperatures and temperature trends, to be available online, with all calculations, methods and results...

 group and made public in October 2011, found that over the past 50 years the land surface warmed by 0.911°C, and their results mirrors those obtained from earlier studies carried out by the NOAA, the Hadley Centre and NASA
NASA
The National Aeronautics and Space Administration is the agency of the United States government that is responsible for the nation's civilian space program and for aeronautics and aerospace research...

's GISS. The study addressed scientific concerns raised by skeptics including urban heat island effect, poor station quality, and the risk of data selection bias and found that these effects did not bias the results obtained from these earlier studies.

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.

Temperature trends from 1901 are positive over most of the world's surface except for Atlantic Ocean south of Greenland, the south-eastern USA and parts of Bolivia. Warming is strongest over interior land area in Asia and North America as well as south-eastern Brazil and some area in the South Atlantic and Indian Oceans.

Since 1979 temperatures increase is considerably stronger over land while cooling has been observed over some oceanic regions in the Pacific Ocean and Southern Hemisphere, the spatial pattern of ocean temperature trend in those regions is possibly related to the Pacific Decadal Oscillation
Pacific decadal oscillation
The Pacific Decadal Oscillation is a pattern of Pacific climate variability that shifts phases on at least inter-decadal time scale, usually about 20 to 30 years. The PDO is detected as warm or cool surface waters in the Pacific Ocean, north of 20° N...

 and Southern Anular Mode
Antarctic oscillation
The Antarctic oscillation is a low-frequency mode of atmospheric variability of the southern hemisphere...

.

Seasonal temperature trends are positive over most of the globe but weak cooling is observed over the mid latitudes of the southern ocean but also over eastern Canada in spring due to strengthening of the North Atlantic Oscillation
North Atlantic oscillation
The North Atlantic oscillation is a climatic phenomenon in the North Atlantic Ocean of fluctuations in the difference of atmospheric pressure at sea level between the Icelandic low and the Azores high. Through east-west oscillation motions of the Icelandic low and the Azores high, it controls the...

, warming is stronger over northern Europe, China and North America in winter, Europe and Asia interior in spring, Europe and north Africa in summer and northern North America, Greenland and Eastern Asia in autumn.
Enhanced warming over north Eurasia is partly linked to the Northern Anular Mode
Arctic oscillation
The Arctic oscillation or Northern Annular Mode/Northern Hemisphere Annular Mode is an index of the dominant pattern of non-seasonal sea-level pressure variations north of 20N latitude, and it is characterized by pressure anomalies of one sign in the Arctic with the opposite anomalies centered...

, while in the southern hemisphere the trend toward stronger westerlies over the southern ocean favoured a cooling over much of Antarctica with the exception of the Antarctic Peninsula where strong westerlies decrease cold air outbreak from the south.
The Antarctic Peninsula
Antarctic Peninsula
The Antarctic Peninsula is the northernmost part of the mainland of Antarctica. It extends from a line between Cape Adams and a point on the mainland south of Eklund Islands....

 has warmed by 2.5 °C (4.5 °F) in the past five decades at Bellingshausen Station.

Calculating the global temperature


Deriving a reliable global temperature from the instrument data is not easy because the instruments are not evenly distributed across the planet, the hardware and observing locations have changed over the years, and there has been extensive land use change (such as urbanization) around some of the sites.

The calculation needs to filter out the changes that have occurred over time that are not climate related (e.g. urban heat islands), then interpolate across regions where instrument data has historically been sparse (e.g. in the southern hemisphere and at sea), before an average can be taken.

There are three main datasets showing analyses of global temperatures, all developed since the late 1970s: the HadCRUT
HadCRUT
HadCRUT is the dataset of monthly temperature records formed by combining the sea surface temperature records compiled by the Hadley Centre of the UK Met Office and the land surface temperature records compiled by the Climatic Research Unit of the University of East Anglia.The data is variance...

 analysis is compiled in a collaboration between the University of East Anglia
University of East Anglia
The University of East Anglia is a public research university based in Norwich, United Kingdom. It was established in 1963, and is a founder-member of the 1994 Group of research-intensive universities.-History:...

's Climatic Research Unit
Climatic Research Unit
The Climatic Research Unit is a component of the University of East Anglia and is one of the leading institutions concerned with the study of natural and anthropogenic climate change....

 and the Hadley Centre for Climate Prediction and Research
Hadley Centre for Climate Prediction and Research
The Met Office Hadley Centre for Climate Change — named in honour of George Hadley — is part of, and based at the headquarters of the Met Office in Exeter...

,http://www.cru.uea.ac.uk/cru/about/history/http://www.metoffice.gov.uk/hadobs/hadcrut3/, independent analyses largely based on the same raw data are produced using different levels of interpolation by the Goddard Institute for Space Studies
Goddard Institute for Space Studies
The NASA Goddard Institute for Space Studies , at Columbia University in New York City, is a component laboratory of NASA's Goddard Space Flight Center Earth-Sun Exploration Division and a unit of The Earth Institute at Columbia University...

 and by the National Climatic Data Center
National Climatic Data Center
The United States National Climatic Data Center in Asheville, North Carolina is the world's largest active archive of weather data. The center became established in late 1951, with the move into the new facility occurring in early 1952....

. These datasets are updated on a monthly basis and are generally in close agreement.

In the late 1990s, the Goddard team used the same data to produce a global map of temperature anomalies to illustrate the difference between the current temperature and average temperatures prior to 1950 across every part of the globe.

Temperature processing software


In September 2007, the GISTEMP software which is used to process the GISS version of the historical instrument data was made public. The software that was released has been developed over more than 20 years by numerous staff and is mostly in FORTRAN
Fortran
Fortran is a general-purpose, procedural, imperative programming language that is especially suited to numeric computation and scientific computing...

; large parts of it were developed in the 1980s before massive amounts of computer memory was available as well as modern programming languages and techniques.

Two recent open source
Open source
The term open source describes practices in production and development that promote access to the end product's source materials. Some consider open source a philosophy, others consider it a pragmatic methodology...

 projects have been developed by individuals to re-write the processing software in modern open code. One, http://www.opentemp.org/, was by John van Vliet.
More recently, a project which began in April 2008 (Clear Climate Code) by staff of Ravenbrook Ltd to update the code to Python
Python (programming language)
Python is a general-purpose, high-level programming language whose design philosophy emphasizes code readability. Python claims to "[combine] remarkable power with very clear syntax", and its standard library is large and comprehensive...

 has so far detected two minor bugs in the original software which did not significantly change any results.

Uncertainties in the temperature record


A number of scientists and scientific organizations have expressed concern about the possible deterioration of the land surface observing network. Climate scientist Roger A. Pielke
Roger A. Pielke
Roger A. Pielke, Sr. is an American meteorologist with interests in climate variability and climate change, environmental vulnerability, numerical modeling, atmospheric dynamics, land/ocean - atmosphere interactions, and large eddy/turbulent boundary layer modeling...

 has stated that he has identified a number of sites where poorly sited stations in sparse regions "will introduce spatially unrepresentative data into the analyses." University of Alabama-Huntsville professor of atmospheric science and former IPCC lead author John Christy has stated that "[t]he temperature records cannot be relied on as indicators of global change."
The metadata needed to quantify the uncertainty from poorly sited stations does not currently exist. Pielke has called for a similar documentation effort for the rest of the world.

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. 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 region with few stations includes a poor quality station, the impact on global temperature would be greater than in a grid with many weather stations.

Evaluation of the United States land surface temperature record



In 1999 a panel of the U.S. National Research Council studied the state of US climate observing systems. The panel evaluated many climate measurement aspects, 4 of which had to do with temperature, against ten climate monitoring principles proposed by Karl et al. 1995. Land surface temperature had "known serious deficiencies" in 5 principles, vertical distribution and sea surface in 9 and subsurface ocean in 7.

The U.S. National Weather Service
National Weather Service
The National Weather Service , once known as the Weather Bureau, is one of the six scientific agencies that make up the National Oceanic and Atmospheric Administration of the United States government...

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

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." Another study 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. 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.

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. Pielke and co-authors disagree.

Warmest years


The list of warmest years on record is dominated by years from this millennium; each of the last 10 years (2001–2010) features as one of the 11 warmest on record. Although the NCDC
National Climatic Data Center
The United States National Climatic Data Center in Asheville, North Carolina is the world's largest active archive of weather data. The center became established in late 1951, with the move into the new facility occurring in early 1952....

 temperature record begins in 1880, less accurate reconstructions of earlier temperatures suggest these years may be the warmest for several centuries to millennia.
20 warmest years on record (°C
Celsius
Celsius is a scale and unit of measurement for temperature. It is named after the Swedish astronomer Anders Celsius , who developed a similar temperature scale two years before his death...

 anomaly from 1901–2000 mean)
Year Global Land Ocean
2005 0.6183 0.9593 0.4896
2010 0.6171 0.9642 0.4885
1998 0.5984 0.8320 0.5090
2003 0.5832 0.7735 0.5108
2002 0.5762 0.8318 0.4798
2006 0.5623 0.8158 0.4669
2009 0.5591 0.7595 0.4848
2007 0.5509 0.9852 0.3900
2004 0.5441 0.7115 0.4819
2001 0.5188 0.7207 0.4419
2008 0.4842 0.7801 0.3745
1997 0.4799 0.5583 0.4502
1999 0.4210 0.6759 0.3240
1995 0.4097 0.6533 0.3196
2000 0.3899 0.5174 0.3409
1990 0.3879 0.5479 0.3283
1991 0.3380 0.4087 0.3110
1988 0.3028 0.4192 0.2595
1987 0.2991 0.2959 0.3005
1994 0.2954 0.3604 0.2704
1983 0.2839 0.3715 0.2513


The values in the table above are anomalies from the 1901–2000 global mean of 13.9°C. For instance, the +0.55°C anomaly in 2007 added to the 1901–2000 mean of 13.9°C gives a global average temperature of 14.45 °C (58.00 °F
Fahrenheit
Fahrenheit is the temperature scale proposed in 1724 by, and named after, the German physicist Daniel Gabriel Fahrenheit . Within this scale, the freezing of water into ice is defined at 32 degrees, while the boiling point of water is defined to be 212 degrees...

) for 2007.

The coolest year in the record was 1911.

Warmest Decades



Numerous cycles have been found to influence annual global mean temperatures. The tropical El Niño-La Niña cycle
El Niño-Southern Oscillation
El Niño/La Niña-Southern Oscillation, or ENSO, is a quasiperiodic climate pattern that occurs across the tropical Pacific Ocean roughly every five years...

 and the Pacific Decadal Oscillation
Pacific decadal oscillation
The Pacific Decadal Oscillation is a pattern of Pacific climate variability that shifts phases on at least inter-decadal time scale, usually about 20 to 30 years. The PDO is detected as warm or cool surface waters in the Pacific Ocean, north of 20° N...

 are the most well-known of these cycles. An examination of the average global temperature changes by decades reveals continuing climate change. Following chart is from NASA data of combined land-surface air and sea-surface water temperature anomalies.
Years Temp. anomaly
(°C
Celsius
Celsius is a scale and unit of measurement for temperature. It is named after the Swedish astronomer Anders Celsius , who developed a similar temperature scale two years before his death...

 anomaly (°F
Fahrenheit
Fahrenheit is the temperature scale proposed in 1724 by, and named after, the German physicist Daniel Gabriel Fahrenheit . Within this scale, the freezing of water into ice is defined at 32 degrees, while the boiling point of water is defined to be 212 degrees...

 anomaly) from 1951–1980 mean)
1880–1889 -0.274 C-change
1890–1899 -0.254 C-change
1900–1909 -0.259 C-change
1910–1919 -0.276 C-change
1920–1929 -0.175 C-change
1930–1939 -0.043 C-change
1940–1949 0.035 C-change
1950–1959 -0.02 C-change
1960–1969 -0.014 C-change
1970–1979 -0.001 C-change
1980–1989 0.176 C-change
1990–1999 0.313 C-change
2000–2009 0.513 C-change

External links

  • The EdGCM
    EdGCM
    The Educational Global Climate Model or ' is a fully functional global climate model that has been ported for use on desktop computers...

     project has provided GISTEMP stations in Google Earth
    Google Earth
    Google Earth is a virtual globe, map and geographical information program that was originally called EarthViewer 3D, and was created by Keyhole, Inc, a Central Intelligence Agency funded company acquired by Google in 2004 . It maps the Earth by the superimposition of images obtained from satellite...

  • GISTemp – A Human View, introduction & overview, how it's made.
  • Met.office Global-average temperature records, condensed explanation