Climate change trends in average temperature in the United States
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Average Temperature Trends in the United States
Average annual temperatures across the contiguous United States have increased significantly over the past century. From 1986 to 2016, the average temperature rose by 1.2°F (0.7°C) compared to 1901–1960, and by 1.8°F (1.0°C) when considering the period from 1895 to 2016. Both surface and satellite data confirm rapid warming since 1979, and recent decades are the warmest in at least the past 1,500 years. Projections indicate that average annual temperatures will continue to rise, with increases of about 2.5°F (1.4°C) expected in the next few decades under all emission scenarios. By the late 21st century, temperature increases could range from 2.8–7.3°F (1.6–4.1°C) under lower emissions and 5.8–11.9°F (3.2–6.6°C) under higher emissions scenarios .
Regional and Seasonal Variations in Temperature Change
Temperature trends in the United States show strong regional and seasonal differences. The northern United States has experienced the most pronounced warming, especially in spring. In contrast, some regions, particularly the central United States, have seen modest cooling trends in late summer and fall. These patterns are influenced by factors such as sea surface temperature variability and the hydrologic cycle, with increased precipitation often linked to reduced warming in certain regions and seasons 24.
Trends in Temperature Extremes and Volatility
There have been marked changes in temperature extremes. The frequency of cold waves has decreased since the early 1900s, while heat waves have become more common since the mid-1960s. The number of high temperature records set in recent decades far exceeds the number of low temperature records. Projections suggest that extreme temperatures will increase even more than average temperatures, with more intense heat waves and less intense cold waves expected. The number of days above 90°F will rise, while days below freezing will decline . Additionally, the volatility of daily maximum temperatures—how much temperatures change from day to day—has increased significantly in the Central United States, with trends of about 0.2–0.3°C per decade .
Urban and Rural Differences in Temperature Trends
Urban areas, especially in the Southwest deserts, have shown larger increases in minimum temperatures compared to rural areas, indicating the influence of urban heat island effects. Urban stations in cities like Las Vegas, Phoenix, Tucson, and Yuma have experienced significant warming, particularly in nighttime temperatures, while rural sites show smaller trends . Studies also highlight that some global temperature datasets may have an urban bias, which can exaggerate warming trends in urbanized regions .
Diurnal Temperature Range and Minimum/Maximum Temperatures
The diurnal temperature range (DTR)—the difference between daily maximum and minimum temperatures—has generally decreased across the United States over the past century. This decrease is most significant in summer and fall, and is linked to rising minimum temperatures, especially in urban areas. Maximum temperatures have also increased, but at a slower rate than minimum temperatures in many regions 59.
Regional Case Studies: Northeast and Southwest United States
In the Northeastern United States, nearly all states have experienced statistically significant increases in annual temperatures over the past century, with rates ranging from 0.00006 to 0.02°F per year. The Southwest United States has also seen significant warming, with annual maximum temperatures increasing at rates of 0.6 to 3.1°C per century and minimum temperatures rising at 0.1 to 8°C over the last century 69.
Conclusion
In summary, the United States has experienced clear and significant warming trends in average temperature over the past century, with notable regional, seasonal, and urban-rural differences. Temperature extremes and volatility are increasing, and projections indicate that these trends will continue and intensify in the coming decades.
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