View source for Global surface temperature

[[Category:Done 2015-10-15]] 
<onlyinclude>The '''global surface temperature''' is an estimate of the overall average [[temperature]] of the surface of the Earth across the globe. The value is obtained by measuring the average [[water]] temperature of the first few [[meter]]s below the surface of the ocean and the temperature between the land surface and 1.5 meters above.</onlyinclude><ref>Dictionary of the Climate Debate. (October 17, 2015). ''Global Surface Temperature'' [Online]. Available: http://www.odlt.org/dcd/ballast/global_surface_temperature.html</ref> This concept is closely linked to [[land surface air temperature]], which looks only at temperatures above land. Generally speaking, we are more concerned with average temperature changes over time. Because of this, global surface temperature is measured using '''anomalies''' - expressed in degrees off of average temperatures.<ref name=IPCC_SREX>IPCC, 2012: Glossary of terms. In: Managing the Risks of Extreme Events and Disasters to Advance Climate Change Adaptation [Field, C.B., V. Barros, T.F. Stocker, D. Qin, D.J. Dokken, K.L. Ebi, M.D. Mastrandrea, K.J. Mach, G.-K. Plattner, S.K. Allen, M. Tignor, and P.M. Midgley (eds.)]. A Special Report of Working Groups I and II of the Intergovernmental Panel on Climate Change (IPCC). Cambridge University Press, Cambridge, UK, and New York, NY, USA, pp. 555-564.</ref> A positive anomaly means temperatures were warmer than a reference value, while negative anomalies are cooler than that reference value.<ref name="RE1"/>

[[File:tempanom.png|400px|framed|center|Figure 1. A map showing surface temperature anomalies worldwide in 2014.<ref>Global Climate Change NASA. (November 11, 2015). ''Data Visualizations'' [Online]. Available: http://climate.nasa.gov/vital-signs/global-temperature/</ref>]]
 
==Why Use Anomalies?==
There are several reasons that anomalies are used to measure global surface temperature instead of absolute temperature. First, absolute estimates of average surface temperature are very challenging to obtain. Uneven distribution of temperature measurement stations worldwide and large amounts of interpolation for data-sparse regions leads to a large degree of uncertainty in these absolute measurements. As well, measurements in mountainous regions are impacted drastically by elevation and the time of year measurements are taken.<ref name="RE1">NOAA. (October 18, 2015). ''Global Surface Temperature Anomalies'' [Online]. Available: https://www.ncdc.noaa.gov/monitoring-references/faq/anomalies.php</ref> To avoid these uncertainties, anomalies are  calculated using reference values computed on more local scales to show whether temperatures in a certain small region were above or below average. 

Additionally, anomalies show how temperature is changing over time. By showing whether or not temperatures are below or above normal, anomalies describe how [[climate]] is changing over larger areas more clearly than absolute temperatures. As well, while a certain absolute temperature may be normal in one region of the globe, it could be above average in another. Anomalies remove this uncertainty in what is "normal" and present data that shows how temperature is deviating locally.<ref name="RE1"/>

==Trends==
To establish a baseline, between 1961 and 1990 the average temperature around the globe was approximately [[celsius|14.0°C]] according to the World Meteorological Organization.<ref>University Corporation for Atmospheric Research. (October 18, 2015). ''What is the Average Global Temperature Now?'' [Online]. Available: https://www2.ucar.edu/climate/faq/what-average-global-temperature-now</ref> In 2014, the temperature anomaly was measured to be 0.68°C warmer than the historical average, making it the hottest year on record - with the data going back to 1880.<ref name="RE2">NASA Global Climate Change. (October 18, 2015). ''Global Temperature'' [Online]. Available: http://climate.nasa.gov/vital-signs/global-temperature/</ref> ( For some interesting visualizations of time series global surface temperature data, click [http://climate.nasa.gov/vital-signs/global-temperature/ here]).

[[File:climate-change-33.gif|900px|thumb|center|Figure 2. A time-lapse video showing sixty years of global warming. Note how as the years progress the average temperature all over the globe increases and the image becomes more red.<ref>While these data are from NASA, this image was downloaded from http://bgr.com/2014/01/29/global-warming-gif-video/ on September 4th, 2015.</ref>]]

Additionally, it is important to note that 2014, while the hottest year on record, was well within what [[climate change model]]s predict. The 15 warmest years on record have all occurred since 1998, a clear indication of a trend.<ref name="RE2"/> Additionally, the average surface temperature is projected to rise continually over the next hundred years.<ref name="RE3">US EPA. (October 18, 2015). ''Global Warming Basics'' [Online]. Available: http://www3.epa.gov/climatechange/basics/</ref> Trends worldwide show an overall increase in global surface temperatures - a change that can be attributed to the [[global warming]] occurring as a result of [[fossil fuel]] [[combustion]] and the release of [[greenhouse gas]]es into the [[atmosphere]].<ref name="RE3"/>

For a great deal of details on temperature anomalies, by region, by month or by year please see [https://www.ncdc.noaa.gov/cag/time-series/global/globe/land_ocean/ytd/12/1880-2014 NOAA's website].
==References==
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