Climate Change: Global Temperature
Temperatures measured on land and at sea for more than a century show that Earth's globally averaged surface temperature is rising. For the last 45 years, global surface temperature rose at an average rate of about 0.17°C (around 0.3° Fahrenheit) per decade—more than twice as fast as the 0.07°C per decade increase observed for the entire period of recorded observations (1880-2015).
Explore this interactive graph: Click and drag to display different parts of the graph. To squeeze or stretch the graph in either direction, hold your Shift key down, then click and drag. The graph shows average annual global temperatures since 1880 (source data) compared to the long-term average (1901-2000). The zero line represents the long-term average temperature for the whole planet; blue and red bars show the difference above or below average for each year.
About surface temperature
The concept of an average temperature for the entire globe may seem odd. After all, at this very moment, the highest and lowest temperatures on Earth are likely more than 100°F (55°C) apart. Temperatures vary from night to day and between seasonal extremes in the Northern and Southern Hemispheres. This means that some parts of Earth are quite cold while other parts are downright hot. To speak of the "average" temperature, then, may seem like nonsense. However, the concept of a global average temperature is convenient for detecting and tracking changes in Earth's condition over time.
To calculate a global average temperature, scientists begin with temperature measurements taken at locations around the globe. Because their goal is to track changes in temperature, measurements are converted from direct temperature readings to temperature anomalies—values that represent the difference between the observed temperature and the long-term average temperature for each location and date.
Across inaccessible areas that have few measurements, scientists use surrounding temperatures and other information to fill in the missing values. Each value is then used to calculate a global temperature average. This process provides a consistent, reliable method for monitoring changes in Earth's surface temperature over time. Read more about how the global surface temperature record is built in our Climate Data Primer.
Change over time
Though warming has not been uniform across the planet, the upward trend in the globally averaged temperature shows that more areas are warming than cooling. Since 1976, every year including 2015 has had an average global temperature warmer than the long-term average. Over this 38-year period, temperature warmed at an average of 0.50 °F (0.28 °C) per decade over land and 0.22 °F (0.12 °C) per decade over the ocean.
By 2020, models project that global surface temperature will be more than 0.5°C (0.9°F) warmer than the 1986-2005 average, regardless of which carbon dioxide emissions pathway the world follows. By 2030, however, the projected temperature pathways begin to diverge, with unchecked carbon dioxide emissions likely leading to several additional degrees of warming by the end of the century.
References and Further Reading
NOAA National Centers for Environmental Information, State of the Climate: Global Analysis for Annual 2015, published online January 2016, retrieved on June 13, 2016 from http://www.ncdc.noaa.gov/sotc/global/201513.
IPCC, 2013: Summary for Policymakers. In: Climate Change 2013: The Physical Science Basis. Contribution of Working Group 1 to the 5th Assessment Report of the Intergovernmental Panel on Climate Change [Stocker, T.F., D. Qin, G.-K. Plattner, M. Tignor, S.K. Allen, J. Boschung, A. Nauels, Y. Xia, V. Bex and P.M. Midgley (eds.)]. Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA.
Hansen, James, The Elusive Absolute Surface Air Temperature, GISS Surface Temperature Analysis, Updated July 12, 2005.
Herring, David, Earth's Temperature Tracker, NASA Earth Observatory. Published November 5, 2007.
Annual global temperature anomalies for land and ocean combined, expressed as departures from the 1901-2000 average. National Climatic Data Center.