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This week is Earth Day and we may have found Earth 2:
The artist's concept depicts Kepler-186f , the first validated Earth-size planet to orbit a distant star in the habitable zone. Image: NASA Ames/SETI Institute/JPL-Caltech
The diagram compares the planets of our inner solar system to Kepler-186, a five-planet star system about 500 light-years from Earth in the constellation Cygnus. The five planets of Kepler-186 orbit an M dwarf, a star that is half the size and mass of the sun. Image: NASA Ames/SETI Institute/JPL-Caltech
"The discovery of Kepler-186f is a significant step toward finding worlds like our planet Earth," said Paul Hertz, NASA's Astrophysics Division director at the agency's headquarters. Kepler-186f resides in the Kepler-186 system, about 500 light-years from Earth in the constellation Cygnus. The system is also home to four companion planets, which orbit a star half the size and mass of our sun.Kepler-186f orbits its star once every 130-days and receives one-third the energy from its star that Earth gets from the sun, placing it nearer the outer edge of the habitable zone. On the surface of Kepler-186f, the brightness of its star at high noon is only as bright as our sun appears to us about an hour before sunset.
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The U.S. Environmental Protection Agency (EPA) released its 19th annual report of overall U.S. greenhouse gas (GHG) emissions, showing a 3.4 percent decrease in 2012 from 2011. The Inventory of U.S. Greenhouse Gas Emissions and Sinks, which is submitted annually to the Secretariat of the United Nations Framework Convention on Climate Change, presents a national-level overview of annual greenhouse gas emissions since 1990.
The major contributors to the decrease in emissions from 2011-2012 were the decrease in energy consumption across all sectors in the U.S. economy, and the decrease in carbon intensity for electricity generation due to fuel switching from coal to natural gas. Other factors included a decrease in transportation sector emissions attributed to an increase in fuel efficiency across different transportation modes and limited new demand for passenger transportation.
Greenhouse gases are the primary driver of climate change, leading to increased heat-related illnesses and deaths; worsening the air pollution that can cause asthma attacks and other respiratory problems; and expanding the ranges of disease-spreading insects. Climate change is also affecting the frequency and intensity of heat waves, droughts, and other extreme weather events.
Under the Climate Action Plan, EPA is taking steps to address carbon pollution from the power and transportation sectors, and to improve energy efficiency in homes, businesses and factories. This includes increasing fuel efficiency for cars and light trucks for model years 2012-2025 that, over the lifetime of these vehicles, will save Americans more than $1.7 trillion. In addition, we are increasing energy efficiency through the Energy Star program that saved Americans more than $26 billion in utility bills in 2012.
According to the report, GHG emissions in 2012 showed a 10 percent drop below 2005 levels. Total emissions of the six main greenhouse gases in 2012 were equivalent to 6,526 million metric tons of carbon dioxide. These gases include carbon dioxide, methane, nitrous oxide, hydrofluorocarbons, perfluorocarbons and sulfur hexafluoride.
EPA develops an annual report called the Inventory of U.S. Greenhouse Gas Emissions and Sinks (Inventory). This report tracks total annual U.S. emissions and removals by source, economic sector, and greenhouse gas going back to 1990. EPA uses national energy data, data on national agricultural activities, and other national statistics to provide a comprehensive accounting of total greenhouse gas emissions for all man-made sources in the United States. EPA also collects greenhouse gas emissions data from individual facilities and suppliers of certain fossil fuels and industrial gases through the Greenhouse Gas Reporting Program. The most recent Inventory report is available for download at the bottom of this page.
The national greenhouse gas inventory is submitted to the United Nations in accordance with the Framework Convention on Climate Change. In preparing the annual emissions inventory report, EPA collaborates with hundreds of experts representing more than a dozen U.S. government agencies, academic institutions, industry associations, consultants and environmental organizations.
Overview of Greenhouse Gases
Sources of Greenhouse Gas Emissions
Greenhouse Gas Emission Trend
Greenhouse Gas Emissions by Gas
As the largest source of U.S. greenhouse gas emissions, CO2 from fossil fuel combustion has accounted for approximately 78 percent of GWP-weighted emissions since 1990, and is approximately 78 percent of total GWP-weighted emissions in 2012. Emissions of CO2 from fossil fuel combustion increased at an average annual rate of 0.3 percent from 1990 to 2012. The fundamental factors influencing this trend include (1) a generally growing domestic economy over the last 23 years, (2) an overall growth in emissions from electricity generation and transportation activities, along with (3) a general decline in the carbon intensity of fuels combusted for energy in recent years by most sectors of the economy.
Between 1990 and 2012, CO2 emissions from fossil fuel combustion increased from 4,745.1 Tg CO2 Eq. to 5,072.3 Tg CO2 Eq.—a 6.9 percent total increase over the twenty-three-year period. From 2011 to 2012, these emissions decreased by 198.8 Tg CO2 Eq. (3.8 percent).
Transportation End-Use Sector
When electricity-related emissions are distributed to economic end-use sectors, transportation activities accounted for 34.4 percent of U.S. CO2 emissions from fossil fuel combustion in 2012. The largest sources of transportation greenhouse gases in 2012 were passenger cars (43.1 percent); light duty trucks, which include sport utility vehicles, pickup trucks, and minivans (18.4 percent), freight trucks (21.9 percent), commercial aircraft (6.2 percent), rail (2.5 percent), and ships and boats (2.2 percent). These figures include direct emissions from fossil fuel combustion used in transportation and emissions from non-energy use (i.e. lubricants) used in transportation, as well as HFC emissions from mobile air conditioners and refrigerated transport allocated to these vehicle types.
In terms of the overall trend, from 1990 to 2012, total transportation emissions rose by 18 percent due, in large part, to increased demand for travel with limited gains in fuel efficiency over the same time period. The number of vehicle miles traveled by light-duty motor vehicles (passenger cars and light-duty trucks) increased 35 percent from 1990 to 2012, as a result of a confluence of factors including population growth, economic growth, urban sprawl, and low fuel prices during the beginning of this period. Almost all of the energy consumed for transportation was supplied by petroleum-based products, with more than half being related to gasoline consumption in automobiles and other highway vehicles. Other fuel uses, especially diesel fuel for freight trucks and jet fuel for aircraft, accounted for the remainder. The primary driver of transportation-related emissions was CO2 from fossil fuel combustion, which increased by 16 percent from 1990 to 2012. This rise in CO2 emissions, combined with an increase in HFCs from close to zero emissions in 1990 to 72.9 Tg CO2 Eq. in 2012, led to an increase in overall emissions from transportation activities of 18 percent.
Industrial End-Use Sector
Industrial CO2 emissions, resulting both directly from the combustion of fossil fuels and indirectly from the generation of electricity that is consumed by industry, accounted for 27 percent of CO2 from fossil fuel combustion in 2012. Approximately 57 percent of these emissions resulted from direct fossil fuel combustion to produce steam and/or heat for industrial processes. The remaining emissions resulted from consuming electricity for motors, electric furnaces, ovens, lighting, and other applications. In contrast to the other end-use sectors, emissions from industry have steadily declined since 1990. This decline is due to structural changes in the U.S. economy (i.e., shifts from a manufacturing-based to a service-based economy), fuel switching, and efficiency improvements.
Residential and Commercial End-Use Sectors
The residential and commercial end-use sectors accounted for 20 and 18 percent, respectively, of CO2 emissions from fossil fuel combustion in 2012. Both sectors relied heavily on electricity for meeting energy demands, with 72 and 78 percent, respectively, of their emissions attributable to electricity consumption for lighting, heating, cooling, and operating appliances. The remaining emissions were due to the consumption of natural gas and petroleum for heating and cooking. Emissions from the residential and commercial end-use sectors have increased by 9 percent and 19 percent since 1990, respectively, due to increasing electricity consumption for lighting, heating, air conditioning, and operating appliances.
The United States relies on electricity to meet a significant portion of its energy demands. Electricity generators consumed 35 percent of total U.S. energy uses from fossil fuels and emitted 40 percent of the CO2 from fossil fuel combustion in 2012. The type of fuel combusted by electricity generators has a significant effect on their emissions. For example, some electricity is generated through non-fossil fuel options such as nuclear, hydroelectric, or geothermal energy. Including all electricity generation modes, generators relied on coal for approximately 39 percent their total energy requirements in 2012. In addition, the coal used by electricity generators accounted for 93 percent of all coal consumed for energy in the United States in 2012. Recently a decrease in the carbon intensity of fuels consumed to generate electricity has occurred due to a decrease in coal consumption, and increased natural gas consumption and other generation sources. Including all electricity generation modes, electricity generators used natural gas for approximately 29 percent of their total energy requirements in 2012. Across the time series, changes in electricity demand and the carbon intensity of fuels used for electricity generation have a significant impact on CO2 emissions.
Other significant CO2 trends included the following:
Methane (CH4) is more than 20 times as effective as CO2 at trapping heat in the atmosphere (IPCC 1996). Over the last two hundred and fifty years, the concentration of CH4 in the atmosphere increased by 151 percent (IPCC 2007). Anthropogenic sources of CH4 include natural gas and petroleum systems, agricultural activities, landfills, coal mining, wastewater treatment, stationary and mobile combustion, and certain industrial processes.
Some significant trends in U.S. emissions of CH4 include the following:
2012 U.S. Energy Consumption by Energy Source
Recent Trends in Various U.S. Data (Index 1990 = 100)
API welcomes EPA report on falling U.S. emissions: The Environmental Protection Agency’s (EPA) latest report shows that natural gas continues to help shrink America’s carbon footprint, said API Spokesman Zachary Cikanek.
“America is leading the world in reducing greenhouse gasses thanks, in part, to the revolution in natural gas production,” said Cikanek. “This latest report shows that emissions dropped an additional 3.4 percent from 2011 to 2012, and emissions are down 10 percent since 2005. Innovations in hydraulic fracturing and horizontal drilling have helped make the U.S. the largest producer of natural gas in the world, and these technologies are a great example of how we can grow the economy, create jobs, and protect the environment.”
The American Gas Association (AGA) today applauded the announcement by the U.S. Environmental Protection Agency (EPA) that estimates of emissions from our nation’s natural gas delivery system continue their declining trend. The 19th Annual Inventory of U.S. Greenhouse Gas Emissions and Sinks affirms that “the major contributors to the decrease in emissions from 2011-2012 were the decrease in energy consumption across all sectors in the U.S. economy, and the decrease in carbon intensity for electricity generation due to fuel switching from coal to natural gas.”
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