Climate Change
Climate Change Indicators in the United States
This graph shows how the average surface temperature of the world's oceans has changed since 1880. This graph uses the 1971 to 2000 average as a baseline for depicting change. Choosing a different baseline period would not change the shape of the trend. The shaded band shows the likely range of values, based on the number of measurements collected and the precision of the methods used.
Data source: NOAA, 2010 5
This image is an example of a sea surface temperature map based on satellite measurements and computer models. "Warm" colors such as red and orange indicate warmer water temperatures.
Source: NASA, 2008 1
Key Points
- Sea surface temperature increased over the 20th century. From 1901 through 2009, temperatures rose at an average rate of 0.12 degrees per decade. Over the last 30 years, sea surface temperatures have risen more quickly at a rate of 0.21 degrees per decade (see Figure 1).
- Sea surface temperatures have been higher during the past three decades than at any other time since 1880 (see Figure 1).
- The largest increases in sea surface temperature occurred in two key periods: between 1910 and 1940, and from 1970 to the present. Sea surface temperatures appear to have cooled between 1880 and 1910 (see Figure 1).
Background
Sea surface temperature—the temperature of the water at the ocean surface—is an important physical attribute of the world's oceans. The surface temperature of the world's oceans varies mainly with latitude, with the warmest waters at the equator and the coldest waters in the Arctic and Antarctic regions. As air temperatures change, so can sea surface temperatures, as well as the ocean circulation patterns that transport warm and cold water around the globe.
Changes in sea surface temperature can alter marine ecosystems in several ways. For example, variations in ocean temperature can affect what species of plants and animals are present in a location, alter migration and breeding patterns, threaten fragile ocean life such as corals, and change the frequency and intensity of harmful algal blooms. 2 Over the long term, increases in sea surface temperature also can reduce the amount of nutrients supplied to surface waters from the deep sea, leading to declines in fish populations. 3
Because the oceans constantly interact with the atmosphere, sea surface temperature also can have profound effects on global climate. Based on changes in sea surface temperature, the amount of atmospheric water vapor over the oceans is estimated to have increased by about 5 percent during the 20th century. 4 This water vapor feeds weather systems that produce precipitation, and the increase in water vapor increases the risk of heavy rain and snow (see the Heavy Precipitation and Tropical Cyclone Intensity indicators). Changes in sea surface temperature can also shift precipitation patterns, potentially leading to droughts in some areas.
About the Indicator
This indicator tracks average global sea surface temperature from 1880 through 2009 using data compiled by the National Oceanic and Atmospheric Administration. Techniques for measuring sea surface temperature have evolved since the 1800s. For instance, the earliest data were collected by inserting a thermometer into a water sample collected by lowering a bucket from a ship. Today, temperature measurements are collected more systematically from ships, as well as at stationary buoys.
The data for this indicator have been carefully reconstructed and filtered to correct for biases in the different collection techniques and to minimize the effects of sampling changes over various locations and times. The data are shown as anomalies, or differences, compared with the average sea surface temperature from 1971 to 2000.
Indicator Confidence
Because this indicator tracks sea surface temperature at a global scale, the data cannot be used to analyze local or regional trends.
Due to denser sampling and improvements in sample design and measurement techniques, newer data have more certainty than older data. The earlier trends shown by this indicator are less precise because of lower sampling frequency and less precise sampling methods.
Data Sources
Data for this indicator were provided by the National Oceanic and Atmospheric Administration's National Climatic Data Center and are available online at: www.ncdc.noaa.gov/oa/climate/ research/sst/ersstv3.php. These data were reconstructed from actual measurements of water temperature, which are available from the National Oceanic and Atmospheric Administration at: http://icoads.noaa.gov/ products.html.
Indicator Documentation
- Download related technical information PDF (5 pp, 36K)