Climate Change
Climate Change Indicators in the United States
This figure shows how average temperatures in the lower 48 states have changed since 1901. Surface data come from land-based weather stations, while satellite measurements cover the lower troposphere, which is the lowest level of the Earth's atmosphere. "UAH" and "RSS" represent two different methods of analyzing the original satellite measurements. This graph uses the 1901 to 2000 average as a baseline for depicting change. Choosing a different baseline period would not change the shape of the trend.
Data source: NOAA, 2010 1
This figure shows how average temperatures worldwide have changed since 1901. Surface data come from a combined set of land-based weather stations and sea surface temperature measurements, while satellite measurements cover the lower troposphere, which is the lowest level of the Earth's atmosphere. "UAH" and "RSS" represent two different methods of analyzing the original satellite measurements. This graph uses the 1901 to 2000 average as a baseline for depicting change. Choosing a different baseline period would not change the shape of the trend.
Data source: NOAA, 2010 2
This figure shows how average air temperatures have changed in different parts of the United States since the early 20th century (since 1901 for the lower 48 states, 1905 for Hawaii, and 1918 for Alaska).
Data source: NOAA, 2009 3
Key Points
- Since 1901, temperatures have risen across the lower 48 states at an average rate of 0.13°F per decade (1.3°F per century) (see Figure 1). Average temperatures have risen more quickly since the late 1970s (0.35 to 0.51°F per decade). Seven of the top 10 warmest years on record for the lower 48 states have occurred since 1990, and the last 10 five-year periods have been the 10 warmest five-year periods on record.
- Global average surface temperatures have risen at an average rate of 0.13°F per decade since 1901 (see Figure 2), similar to the rate of warming within the lower 48 states. Since the late 1970s, however, the United States has warmed at nearly twice the global rate. Worldwide, 2000–2009 was the warmest decade on record.
- Some parts of the United States have experienced more warming than others (see Figure 3). The North, the West, and Alaska have seen temperatures increase the most, while some parts of the South have experienced little change. However, not all of these regional trends are statistically meaningful.
Background
Temperature is a fundamental component of climate, and it can have wide-ranging effects on human life and ecosystems, as many of the other indicators in this report demonstrate. For example, increases in air temperature can lead to more intense heat waves, which can cause illness and death in vulnerable populations. Temperature patterns also determine what types of animals and plants can survive in a particular place. Changes in temperature can disrupt a wide range of natural processes, particularly if these changes occur abruptly and plant and animal species do not have time to adapt.
As greenhouse gases trap more energy in the Earth's atmosphere, average temperatures at the Earth's surface are expected to rise. However, because climate change (both natural and human-driven) can shift the wind patterns and ocean currents that drive the world's climate system, some areas might experience more warming than others, and some might experience cooling. Changes in air temperature can, in turn, cause changes in sea surface temperature, precipitation patterns, and other aspects of climate.
About the Indicator
This indicator examines U.S. and global temperature patterns from 1901 to the present. Data were provided by the National Oceanic and Atmospheric Administration, which keeps historical records from weather stations around the world. U.S. surface measurements come from stations on land, while global surface trends also incorporate observations from buoys and ships on the ocean, thereby providing data from sites spanning the entire surface of the Earth. For comparison, this indicator also displays data from satellites that have measured the temperature of the Earth's lower atmosphere since 1979.
This indicator shows annual anomalies, or differences, compared with the average temperature from 1901 to 2000. Anomalies are calculated in degrees for each location, then averaged together.
Indicator Confidence
Data from the early 20th century are somewhat less precise because there were fewer stations collecting measurements at the time. However, the overall trends are still reliable. Measurement instruments and methods (for example, the time of day measurements are taken) have also changed over time, and some stations have moved. Where possible, the data have been adjusted to account for these kinds of changes.
Data Sources
The data for this indicator were provided by the National Oceanic and Atmospheric Administration's National Climatic Data Center, which maintains a large collection of climate data online at: www.ncdc.noaa.gov/oa/ncdc.html. Surface temperature anomalies were calculated based on monthly values from a network of long-term monitoring stations. Satellite data were analyzed by two independent groups, resulting in the slightly different "UAH" and "RSS" trend lines.
Indicator Documentation
- Download related technical information PDF (10 pp, 64K, About PDF)