Climate Change Indicators in the United States

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Combined bar and line graph showing changes in average temperatures for the contiguous 48 states from 1901 to 2012. Image, Courtesy US EPA

Since 1901, the average surface temperature across the contiguous 48 states has risen at an average rate of 0.14 ??F per decade (1.4 ??F per century). The figure above shows how annual average temperatures in the contiguous 48 states have changed since 1901.

Surface data come from land-based weather stations. 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 data over time. Average temperatures have risen more quickly since the late 1970s (0.36 to 0.55 ??F per decade).

Seven of the top 10 warmest years on record for the contiguous 48 states have occurred since 1998, and 2012 was the warmest year on record.

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Combined bar and line graph showing changes in average temperatures worldwide from 1901 to 2012. Image courtesy US EPA

Worldwide, 2001-2010 was the warmest decade on record since thermometer-based observations began. Global average surface temperature has risen at an average rate of 0.15 ??F per decade since 1901 (see Figure 2), similar to the rate of warming within the contiguous 48 states.

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Color-coded map showing how average air temperatures changed across the United States from 1901 to 2012. Image courtesy US EPA

Since the late 1970s, however, the United States has warmed faster than the global rate. 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 Southeast have experienced little change. However, not all of these regional trends are statistically significant.

Data source: NOAA, 2013?? and EPA webpage: “Climate Change Indicators in the United States”.

More details including background information, data source details, indicator notes, technical documentation may be found on that referenced EPA webpage at: www.epa.gov/climatechange/science/indicators/weather-climate/temperature.html