Instrumental temperature record

For other uses, see Temperature record.

Instrumental global surface temperature record since widespread reliable measurements began in the late 19th century; see also [1] The X axis represents time, and the Y axis represents the temperature anomaly (departure from 1961-1990 baseline of 14.0°C, Jones et al. 1999).

Map of the land-based long-term monitoring stations included in the Global Historical Climatology Network. Colors indicate the length of the temperature record available at each site.

Watch how summer temperatures in the Northern Hemisphere change from 1955 to 2011. "Hot" (orange), "very hot" (red) "extremely hot" (brown) "average" (white), unusually "cold" (light blue), "very cold" (dark blue) and "extremely cold" (purple).

The instrumental temperature record shows fluctuations of the temperature of earth's climate system. Initially the instrumental temperature record only documented land and sea surface temperature, but in recent decades instruments have also begun recording ocean temperature. Data is collected from thousands of meteorological stations around the globe and through satellite observations. The longest-running temperature record is the Central England temperature data series, that starts in 1659. The longest-running quasi-global record starts in 1850.

Warmest years

The global average and combined land and ocean surface temperature, show a warming of 0.85 [0.65 to 1.06] °C, in the period 1880 to 2012, based on multiple independently produced datasets. The Earth's average surface temperature rose by 0.74±0.18 °C over the period 1906–2005. The rate of warming almost doubled for the last half of that period (0.13±0.03 °C per decade, versus 0.07±0.02 °C per decade).

Surface record

NOAA graph of Global Annual Temperature Anomalies 1950–2012

NASA stated in their press release January 2015: The year 2014 ranks as Earth’s warmest since 1880, according to two separate analyses by NASA and National Oceanic and Atmospheric Administration (NOAA) scientists. The 10 warmest years in the instrumental record, with the exception of 1998, have now occurred since 2000. This trend continues a long-term warming of the planet, according to an analysis of surface temperature measurements by scientists at NASA’s Goddard Institute of Space Studies (GISS) in New York.

Surface and ocean record

Based on the NOAA dataset, the following table lists the global combined land and ocean annually-averaged temperature rank and anomaly for each of the 10 warmest years on record.

Top 10 Warmest Years (NOAA)

(1880–2014)

Rank	Year	Anomaly °C
1	2014	0.69
2 (tie)	2010	0.65
2 (tie)	2005	0.65
4	1998	0.63
5 (tie)	2013	0.62
5 (tie)	2003	0.62
7	2002	0.61
8	2006	0.60
9 (tie)	2009	0.59
9 (tie)	2007	0.59

Although the NCDC temperature record begins in 1880, reconstructions of earlier temperatures based on climate proxies, suggest these years may be the warmest for several centuries to millennia, or longer.

El Niño and La Niña years

El Niño generally tends to increase global temperatures around the globe. La Niña, on the other hand, usually causes years which are cooler than the short-term average. El Niño is the warm phase of the El Niño Southern Oscillation (ENSO) and La Niña the cold phase.

Warmest decades

Global temperature change — decadal averages, 1880s-2000s (NOAA).

1880–2011 Global annual and decadal mean surface temperature change. Data Source: NOAA

Numerous cycles have been found to influence annual global mean temperatures. The tropical El Niño-La Niña cycle and the Pacific Decadal Oscillation 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 anomaly (°F anomaly) from 1951–1980 mean)
1880–1889
1890–1899
1900–1909
1910–1919
1920–1929
1930–1939
1940–1949
1950–1959
1960–1969
1970–1979
1980–1989
1990–1999
2000–2009
2010–2014 (note: incomplete)

Absolute temperatures v. anomalies

Records of global average surface temperature are usually presented as anomalies rather than as absolute temperatures. A temperature anomaly is measured against a reference value or long-term average. For example, if the reference value is 15 °C, and the measured temperature is 17 °C, then the temperature anomaly is +2 °C (i.e., 17 °C -15 °C).

Temperature anomalies are useful for deriving average surface temperatures because they tend to be highly correlated over large distances (of the order of 1000 km). In other words, anomalies are representative of temperatures over large areas and distances. By comparison, absolute temperatures vary markedly over even short distances.

The Earth's average surface absolute temperature for the 1961-1990 period has been derived by spatial interpolation of average observed near-surface air temperatures from over the land, oceans and sea ice regions, with a best estimate of 14 °C (57.2 °F). The estimate is uncertain, but probably lies within 0.5 °C of the true value.

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 or a maximum minimum temperature system (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 and its predecessor, the International Meteorological Organization.

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.

Warming in the instrumental temperature record

Comparison of ground based (blue) and satellite based (red: University of Alabama in Huntsville; green: RSS) records of global surface temperature change from 1979-2009. Linear trends plotted since 1982.

Global surface temperature change for the period 1980-2004. The blue line is the monthly average, the black line is the annual average and the red line is the 5-year running average. Data source: http://www.cru.uea.ac.uk/

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. Some of the temperature variations over this time period may also be due to ocean circulation patterns.

Attribution of the temperature change to natural or anthropogenic (i.e., human-induced) 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. 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 90% confidence interval.

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 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).

Uncertainties in the temperature record, e.g., the urban heat island effect, are discussed further in a later section.

Robustness of evidence

There is a scientific consensus that climate change is occurring and that greenhouse gases emitted by human activities are the primary driver. The scientific consensus is reflected in example, by the Intergovernmental Panel on Climate Change (IPCC) an international body which summarizes existing science, and the U.S. Global Change Research Program.

The methods used to derive the principal estimates of global surface temperature trends — HadCRUT3, NOAA and NASA/GISS — are largely independent.

Other reports and assessments

This graph shows how short-term variations occur in the global temperature record. However, the graph still shows a long-term trend of global warming. Image source: NCADAC.

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.

The preliminary results of an assessment carried out by the Berkeley Earth Surface Temperature 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's GISS. The study addressed concerns raised by "skeptics" including urban heat island effect, "poor" station quality, and the "issue of data selection bias" and found that these effects did not bias the results obtained from these earlier studies.

Internal climate variability and global warming

Further information: Attribution of recent climate change § Internal climate variability and global warming

One of the issues that has been raised in the media is the view that global warming "stopped in 1998". This view ignores the presence of internal climate variability. Internal climate variability is a result of complex interactions between components of the climate system, such as the coupling between the atmosphere and ocean. An example of internal climate variability is the El Niño Southern Oscillation (ENSO). The El Niño in 1998 was particularly strong, possibly one of the strongest of the 20th century.

Cooling between 2006 and 2008, for instance, has likely been driven by La Niña, the opposite of El Niño conditions. The area of cooler-than-average sea surface temperatures that defines La Niña conditions can push global temperatures downward, if the phenomenon is strong enough. Even accounting for the presence of internal climate variability, recent years rank among the warmest on record. For example, every year of the 2000s was warmer than the 1990 average.

Regional temperature

1901–2011 global temperature trend

Global Land temperature anomaly 1880-2012

Global Ocean temperature anomaly 1880-2012

Temperature trends from 1901 are positive over most of the world's surface except for Atlantic Ocean south of Greenland, the southeastern United States, 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 and Southern Annular Mode.

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

Evaluation

The U.S. National Weather Service 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.

The urban heat island effect is very small, estimated to account for less than 0.002 °C of warming per decade since 1900.

Brooks investigated Historical Climate Network (USHCN) sites in Indiana in 2005, and assigned 16% of the sites an ‘excellent’ rating, 59% a ‘good’ rating, 12.5% a ‘fair’ rating, and 12.5% ‘poor’ rating. A 2006 study analyzed 366 U.S. surface stations, results indicate relatively few significant temperature trends, and these are generally evenly divided between warming and cooling trends. 95% of the stations displayed a warming trend after land use/land cover changes took place, and the authors noted "this does not necessarily imply that the changes are the causative factor." Another study that same year, documented examples of well and poorly sited monitoring stations in the United States, including ones near buildings, roadways, and air conditioning exhausts.

Another study concluded in 2006, 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. A study in 2013, also found that urban bias can be accounted for, and when all available station data is divided into rural and urban, that both temperature sets are broadly consistent.

Global surface and ocean datasets

See also: Temperature measurement

National Oceanic and Atmospheric Administration (NOAA) maintains the Global Historical Climatology Network (GHCN-Monthly) data base contains historical temperature, precipitation, and pressure data for thousands of land stations worldwide. Also, NOAA's National Climatic Data Center (NCDC). of surface temperature measurements, maintains a global temperature record since 1880.

HadCRUT, a collaboration between the University of East Anglia's Climatic Research Unit and the Hadley Centre for Climate Prediction and Research

NASA's Goddard Institute for Space Studies maintains GISTEMP.

More recently the Berkeley Earth Surface Temperature dataset. These datasets are updated frequently, and are generally in close agreement.

See also

• Temperature record of the past 1000 years
• List of large-scale temperature reconstructions of the last 2,000 years
• Satellite temperature measurements
• Sea surface temperature

External links

• GISS Surface Temperature Analysis (GISTEMP)
• Google Earth interface for CRUTEM4 land temperature data
• International Surface Temperature Initiative