In 2006, Americans experienced a summer heat wave that broke records from coast to
coast and killed almost 200 people. The year ended and 2007 began with the warmest
winter on record globally. This unseasonably warm weather 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 second
half of the 19th century. Earlier this year, the United Nations’ Intergovernmental Panel on
Climate Change (IPCC) concluded that the evidence of global warming is “unequivocal”
and that human activities are responsible for most of the rise in temperatures.
To examine recent temperature patterns in the United States, we compared temperature
data for the years 2000-2006 from 255 weather stations located in all 50 states and
Washington, DC with temperatures averaged over the 30 years spanning 1971-2000.
Overall, we found that temperatures were above the 30-year average across the country,
indicating pervasive warming.
SUMMER 2006: RECORD-BREAKING HEAT
A long-lasting summer heat wave hit most of the country in 2006, making it the second
warmest summer on record for the contiguous United States. Heat waves have serious
implications for human health, causing heat stroke, heat exhaustion, and even death. Our
analysis of climate data for June-August 2006 showed:
• During the summer of 2006, the average temperature was at least 0.5°F above the
30-year average at 82% of the locations studied. In Rapid City, South Dakota and
Helena, Montana, average summertime temperatures were 5°F above normal.
• The average maximum temperature — the peak temperature on any given day — was
at least 0.5°F above the 30-year average at two-thirds (67%) of the locations studied.
The Great Plains and Mountain West suffered some of the most above-normal summer temperatures in 2006.
• The summer heat wave produced a high number of dangerously hot days at or
above 90°F across the country. Almost three-fourths (71%) of the locations
examined recorded more frequent (compared with the historical average)
days with peak temperatures of at least 90°F. Tupelo, Mississippi experienced 40
more 90°F or warmer days than normal in 2006.
• The 2006 summer heat wave was marked by above-average minimum temperatures
— the lowest temperatures recorded on a given day, usually at night. The average
minimum temperature was at least 0.5°F above the 30-year average at 81% of the
locations studied and 9.7°F above normal in Reno, Nevada, the highest in the
country. Warmer nighttime temperatures exacerbate the public health effects of heat
waves, since people need cooler nighttime temperatures to recover from excessive
heat exposure during the day.
In April 2007, the IPCC warned that North American cities that currently experience heat
waves are expected to face “an increased number, intensity, and duration of heat
waves,” threatening public health, particularly that of elderly Americans and infants.
2006: SECOND WARMEST YEAR ON RECORD
With a scorching summer and mild start to winter, the 2006 average temperature for the
contiguous United States was the second warmest on record, according to the National
Climatic Data Center. Every state in the Lower 48 experienced above normal
temperatures in 2006. Our analysis of 2006 climate data showed:
• In 2006, the average temperature was at least 0.5°F above the 30-year average at
87% of the locations examined. The Upper Midwest and Mountain West in
particular experienced warmer-than normal average temperatures in 2006.
• The average maximum temperature was at least 0.5°F above the 30-year average at
81% of the stations examined. Warmer than- average days hit Texas and the Great
Plains the hardest in 2006, with average peak temperatures soaring more than 5°F
above normal in Oklahoma City, Oklahoma.
• The average minimum temperature was at least 0.5°F above the 30-year average at
80% of the stations examined. Minimum temperatures were particularly mild in the
Upper Midwest, where temperatures soared almost 5°F above the 30-year
average in Minneapolis-St. Paul, Duluth, and Rochester, Minnesota.
2000-2006: TEMPERATURES RISING
The above-average temperatures of 2006 are part of a broader warming trend since 2000.
Our analysis of climate data for 2000-2006 showed:
• Between 2000 and 2006, the average temperature was at least 0.5°F above the
30-year average at 87% of the locations studied. Average temperatures in Alaska
were the most anomalous, with Talkeetna near Denali National Park averaging more
than 4°F above the 30-year average.
• The average maximum temperature was at least 0.5°F above the 30-year average at
more than two-thirds (68%) of the locations studied. Average maximum
temperatures in Pueblo and Alamosa, Colorado were 2.6°F above normal.
• Overall, temperatures are not dropping at night as much now as they did in the past.
Between 2000 and 2006, the average minimum temperature was at least 0.5°F
above the 30-year average at 80% of the locations studied. Albuquerque, New
Mexico and Sault Ste. Marie, Michigan reported average minimum temperatures
of more than 3°F above normal.
Even though the IPCC identified significant risks with continued global warming, the
panel also concluded that “many impacts can be avoided, reduced, or delayed” by quickly
and significantly reducing global warming pollution. To protect future generations, the
United States should:
Cap global warming emissions. The United States should establish mandatory, sciencebased
limits on carbon dioxide and other global warming pollutants that reduce total
emissions from today’s levels by the end of the decade, by at least 15-20% by 2020, and by at
least 80% by 2050.
Adopt complementary clean energy policies to reduce global warming emissions. To
achieve these reductions, the United States should adopt strong policies and financial
incentives to improve energy efficiency and increase the use of clean, renewable energy.
