In the weeks leading up to EPA’s June 2, 2014, release of its momentous proposal on controlling greenhouse gas (GHG) emissions from existing fossil-fuel power plants, the Agency issued two major reports on the impacts of climate change.  

Publication of the National Climate Assessment was followed quickly by the appearance of Climate Change Indicators in the United States.  The newer report summarizes data on 30 indications that support the argument that the climate is changing and changing at an accelerated rate in recent decades. 

While the report draws a link between the indicators and GHGs emitted into the atmosphere by human activity, the EPA states those links are explored in more detail in the scientific literature.

35 percent global increase

Total U.S. GHG emissions have decreased by 10 percent since 2005.  But, since climate change is a global phenomenon, the more significant observation is that worldwide net emissions went up 35 percent from 1990 to 2010.  Also, from 1990 to 2013, the total warming effect from GHGs added by humans to the earth’s atmosphere increased by 34 percent, says the EPA.

Lyme disease and pollen season

The list of indicators is topped by GHG emissions and atmospheric concentrations of GHGs, which the report states are “higher than any levels recorded for hundreds of thousands of years, even after accounting for natural fluctuations.”

The second tier of indicators comprises weather and climate specifically.  Some of the data are familiar.  For example, 7 of the 10 warmest years on record have occurred since 1998; since 1901, precipitation has increased at an average rate of 0.5 percent per decade in the contiguous 48 states and 0.2 percent per decade over land areas worldwide; and nationwide, 9 of the 10 years for extreme 1-day precipitation events occurred since 1990. 

Other, less common indicators include the rate of reported cases of Lyme disease, which is caused by ticks and has reportedly doubled since 1991.  Tick habitat and populations are influenced by many factors, including climate, states the report.  The ragweed pollen season, along with associated effects on people with allergies, has lengthened in 10 of the 11 locations studied in the central U.S. and Canada since 1995.  Warming temperatures have also caused birds to shift their wintering ranges north by an average of 40 miles in North America. 

New indicators

Lyme disease is one of the four new indicators the EPA has added since the previous edition of the report was issued in 2012.  The three others are:

• Heating and cooling degree days.  These measure the difference between outdoor temperatures and the temperatures people find comfortable indoors.  In recent years, heating degree days have decreased and cooling degree days have increased overall, suggesting that Americans need to use less energy for heating and more energy for air conditioning.
• Wildfires.  Between 1983 and 2013, 9 of the 10 years with the largest acreage burned occurred since 2000.
• Great Lakes water levels and temperatures.  Water levels in most of the Great Lakes have declined in the last few decades, and average surface temperatures have increased a few degrees for Lakes Superior Michigan, Huron, and Ontario. 

Peer reviewed

“This report consists of peer-reviewed, publicly available data from a number of government agencies, academic institutions, and other organizations,” says the EPA. 

“EPA also received feedback from scientists, researchers, and communications experts in nongovernmental and private sectors.  The entire report, including its technical support document, was peer-reviewed by independent technical experts.”

Climate Change Indicators in the United States