Basic points
- Since 1901, the average surface temperature in the contiguous 48 states has increased at an average rate of 0.17°F per decade (Figure 1). Average temperatures have risen most rapidly since the late 1970s (0.32 to 0.51°F per decade since 1979). For the contiguous United States, nine of the 10 warmest years on record have occurred since 1998, and 2012 and 2016 were the two warmest years on record.
- Globally, 2023 was the warmest year on record, 2016 was the second warmest year, and 2014–2023 was the warmest decade on record since thermometer-based observations began. The average global surface temperature has increased at an average rate of 0.17°F per decade since 1901 (Figure 2), similar to the rate of warming in the contiguous United States. Since the late 1970s, however, the United States has warmed faster than the global rate.
- Some regions of the United States have experienced more warming than others (Figure 3). The North, West and Alaska have seen temperatures rise the most, while some parts of the Southeast saw little change. However, not all of these regional trends are statistically significant.
Record
Temperature is a fundamental metric for describing climate, and the temperature in specific places can have wide-ranging effects on human life and ecosystems. For example, increases in air temperature can lead to more intense heat waves (see Heat Waves), which can cause illness and death, especially in vulnerable populations. Annual and seasonal temperature patterns also determine the types of animals and plants that can survive in particular locations. Changes in temperature can disrupt a wide range of natural processes, particularly if these changes occur faster than plant and animal species can adapt.
Concentrations of heat-trapping greenhouse gases are increasing in the Earth's atmosphere (see Atmospheric Greenhouse Gas Concentrations index). In response, Earth's average surface temperatures are rising and are expected to continue to rise.1 Because climate change can shift the wind patterns and ocean currents that drive the global climate system, some regions have warmed more than others and some have cooled.
About the Index
This index looks at surface temperature patterns in the US and global surface over time. US surface measurements come from land-based weather stations, while global surface measurements also incorporate observations from buoys and ships in the ocean, thus providing data from locations spanning much of the Earth's surface. This index goes back to 1901 in addition to the detailed map of Alaska, where there are reliable statewide records available since 1925. For comparison, this index also shows satellite measurements that can be used to estimate the temperature of of Earth's lower atmosphere since 1979.
This index shows annual anomalies, or differences, compared to the average temperature from 1901 to 2000. For example, an anomaly of +2.0 degrees means that the average temperature was 2 degrees higher than the long-term average. Anomalies have been calculated for each weather station. Daily temperature readings at each location were used to calculate monthly anomalies, which were then averaged to find an annual temperature anomaly for each year. Anomalies for the contiguous 48 states and Alaska have been determined by calculating average anomalies for areas in each state based on station density, interference, and topography. These regional anomalies are then averaged together in proportion to their area to develop national results. Similarly, global anomalies have been determined by dividing the world into a grid, averaging the data for each grid cell, and then averaging the grid cells together.
About Data
Indicator notes
Evidence from the early 20th centuryu century is somewhat less accurate than more recent data because there were fewer stations collecting measurements at that time, especially in the southern hemisphere. However, the general trends are still reliable. Where possible, the data have been adjusted to account for any biases that may be caused by factors such as station moves, urbanization near the station, changes in measuring instruments and changes in the exact times at which measurements are taken.
Hawaii and US territories are not included, due to limitations in available data.
Data sources
Data for this index are provided by the National Oceanic and Atmospheric Administration's National Centers for Environmental Information, which maintains a large collection of climate data online at: www.ncei.noaa.gov. The surface temperature anomalies shown here were calculated based on monthly values from a network of long-term monitoring stations. The satellite data were analyzed by two independent groups—the Global Hydrology and Climate Center at the University of Alabama at Huntsville (UAH) and Remote Sensing Systems (RSS)—resulting in slightly different trend lines.
Manual
bibliographical references
1 Marvel, K., Su, W., Delgado, R., Aarons, S., Chatterjee, A., Garcia, ME, Hausfather, Z., Hayhoe, K., Hence, DA, Jewett, EB, Robel, A. ., Singh, D., Tripathi, A., & Vose, RS (2023). Chapter 2: Climate trends. At the USGCRP (US Global Change Research Program), Fifth National Climate Assessment.
2 NOAA (National Oceanic and Atmospheric Administration). (2024). The climate at a glance. Retrieved March 25, 2024, from www.ncei.noaa.gov/access/monitoring/climate-at-a-glance