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As discussed yesterday, climate change is directly attributable to emissions of greenhouse gases (GHGs) that trap infrared heat in the Earth’s atmosphere. That simple phenomenon has extremely complex repercussions, many of which are just beginning to be understood and documented in scientific literature.
To begin, average temperatures have been rising across the 48 contiguous states since 1901. Since 1998, we have experienced 7 of the top 10 warmest years on record in the United States, and the 10 warmest years on record worldwide. In the United States, the greatest temperature increases have been in the North, West, and Alaska. Although the country has yet to exceed the records set during the 1930s, from 2000 to 2009, twice as many daily high-temperature records were set compared to records for daily low temperature.
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Precipitation is also increasing at an average rate of 0.5 percent per decade since 1901 in the 48 contiguous states. Globally, precipitation has increased 0.2 percent per decade over the same period. Heavy precipitation single-day events are also increasing with 9 of the top 10 years for extreme events occurring since 1990, and data show an increase in abnormally high annual precipitation totals as well. Despite these increases, shifts in weather patterns are bringing less rain to the Southwest and Hawaii, and while drought trends vary by region, new information shows that between 2000 and 2013, approximately 20 percent to 70 percent of the country experienced drought at any given time.
Other important indicators are snow and ice, especially ice cover in the Arctic Ocean, which was at the lowest amount ever recorded in 2012. The average age of Arctic Sea ice is also dropping, making it thinner and more vulnerable to melting. Similarly, glaciers here and around the world have been shrinking since the 1960s, and the melting rate has increased over the past decade contributing to rising sea levels. Lakes in the northern United States are also experiencing freeze dates about a day later and thaw dates up to 2 days earlier compared to the 1800s and early 1900s.
Snowfall is also on a downward trend since the 1930s, with three-quarters of locations studied seeing more rain replacing snow in winter. Although there is much year-to-year variability, recorded average snow cover also decreased at a rate of about 3,500 square miles per year (based on weekly measurements) between 1972 and 2013. The depth of snow, or the snowpack, has varied, with some regions increasing and others decreasing. However, the average change in spring snowpack across all states from 1955 to 2013 showed an approximate decline of 14 percent.
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As a result of these climatic changes, a number of human health impacts are emerging. As temperatures go up, those without access to air-conditioning can experience extreme health problems and death. Although establishing long-term trends in heat-related deaths is difficult, the EPA reported almost 8,000 deaths directly related to heat in the United States over the past 30 years, a number that increases when adding deaths related indirectly to heat.
Another health issue is Lyme disease, a bacterial illness spread through deer tick bites. Studies have shown evidence that increased temperatures may help expand the range of ticks carrying Lyme disease and also extend the period of time people are exposed to them. Since 1991, reported cases of Lyme disease have almost doubled.
Allergy season is also being impacted as warmer temperatures and later frost dates allow for ragweed to produce pollen longer. Since 1995, studies show the ragweed pollen season is longer at 10 of 11 locations studied in the Central United States and Canada, with an increase of 27 days in Saskatchewan, Canada, compared to a 1-day increase in Oklahoma and a 1-day decrease in Texas.
These are just a few of the many climate change indicators revealed. The full report is available at http://www.epa.gov/climatechange/science/indicators/index.html.