Feeling the Heat: Global Warming and Rising Temperatures in the United States
To examine recent temperature patterns in the United States, we compared temperature data for the years 2000 to 2007 with the historical average, or "normal," temperature for the preceding 30 years, 1971 to 2000. Our data were collected at 255 weather stations ”those with the highest quality data” in all 50 states and Washington, D.C. Overall, we found that temperatures were above the 30-year average across the country, indicating pervasive warming.
Globally, the year 2007 tied for the second warmest year on record, behind the record warmth of 2005. This warmth is part of a long-term trend toward rising temperatures and extreme weather events resulting from global warming.
Global average surface temperatures have increased by more than 1.4°F since the mid-19th century. In 2007, the United Nations’ Intergovernmental Panel on Climate Change concluded that the evidence of global warming is “unequivocal” and that human activities are responsible for most of this rise in temperature.
To examine recent temperature patterns in the United States, we compared temperature data for the years 2000–2007 with the historical average, or “normal,” temperature for the preceding 30 years, 1971–2000. Our data were collected at 255 weather stations—those with the highest quality data—in all 50 states and Washington, DC. Overall, we found that temperatures were above the 30-year average across the country, indicating pervasive warming.
2007: 10th Warmest Year on Record for the United States
The 2007 average temperature for the continental United States was the 10th warmest on record, according to the National Climatic Data Center. Nearly every state in the Lower 48 experienced above normal temperatures in 2007. Our analysis of 2007 temperature data at the local level showed:
In 2007, the average temperature was at least 0.5°F above the 30-year average at 84 percent of the weather stations. The Mountain West and Southeast in particular experienced warmer-than-normal average temperatures in 2007. In Helena, Montana, the average temperature during 2007 was 4.6°F above the 30-year average. Average temperatures soared 4.0°F above the 30-year average in Reno, Nevada and 3.0°F or more above normal in six cities in Tennessee.
The average maximum temperature—the peak temperature on any given day—was at least 0.5°F above the 30-year average at 71 percent of the weather stations. Warmer-than-average days hit the Southeast and parts of the West the hardest in 2007, with average peak temperatures soaring 4°F or more above normal in Greenville-Spartanburg, South Carolina; Chattanooga, Knoxville, and Nashville, Tennessee; Rapid City, South Dakota; Helena, Montana; and Louisville, Kentucky.
Rising temperatures resulted in extremely hot days in 2007 where temperatures peaked at or above 90°F at locations across the country. Nearly three-fourths (71 percent) of the locations examined recorded more frequent days with peak temperatures of at least 90°F compared with the historical average. Raleigh, North Carolina experienced 45 more 90°F or warmer days than normal in 2007.
The average minimum temperature—the lowest temperature recorded on a given day, usually at night—was at least 0.5°F above the 30-year average in 2007 at 79 percent of the stations examined. Minimum temperatures were particularly mild in the Mountain West, Midwest, and parts of the East. The average minimum temperature soared 5.5°F above the 30-year average in Reno, Nevada.
2000–2007: Temperatures Rising
The above-average temperatures of 2007 are part of a warming trend across the United States. Our analysis of local temperature data for 2000–2007 showed:
The average temperature from 2000–2007 was at least 0.5°F above the 30-year average at 89 percent of the locations studied. Average temperatures in Alaska were the most anomalous, with Talkeetna near Denali National Park averaging nearly 4°F above the 30-year average.
The average maximum temperature from 2000–2007 was at least 0.5°F above the 30-year average at nearly three-fourths (74 percent) of the locations studied. Talkeetna, Alaska also experienced the most above-normal maximum temperature (2.9°F) over the eight-year period.
Between 2000 and 2007, the average minimum temperature was at least 0.5°F above the 30-year average at 82 percent of the locations studied. In Reno, Nevada, the average minimum temperature was 5.3°F above normal.
The latest climate science tells us that the United States and the world must break its dependence on fossil fuels and transition rapidly to 100 percent clean, renewable energy if we hope to avoid the most catastrophic effects of global warming. The United States should immediately take the following first steps:
Adopt mandatory, science-based caps on global warming pollution. At minimum, those caps should reduce total U.S. emissions by 20 percent below today’s levels by 2020 and by 80 percent below today’s levels by 2050. Revenues from any program that puts a price on global warming pollution should be used to aid in the transition to a clean energy economy and to reduce the cost of emission reductions to consumers.
Make energy efficiency improvements and accelerated development of renewable energy the centerpiece of our environmental and economic development policies. Advanced building energy codes; strong energy efficiency standards for buildings, appliances, and vehicles; and mandatory targets for renewable power generation and energy efficiency savings are among the policies that can reduce global warming pollution and put the nation on a clean energy path.
Make global warming and fossil fuel dependence central considerations in land-use planning and public sector investment decisions. America should increase its investment in public transportation and rail transportation to reduce emissions from transportation. All new public buildings should meet rigorous standards for energy efficiency and the use of clean energy.