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Why the Climate is Changing

Human Emissions Boost 'Greenhouse' Warming

Melting Arctic sea ice
Arctic sea ice is melting from greenhouse
warming of the Earth. Photo courtesy of NOAA

Many independent lines of scientific evidence underlie our understanding of "greenhouse" warming of the Earth, of how warming changes Earth's climate and of what role each of us plays in intensifying the greenhouse effect.

New York bases its climate policies on scientific studies, with regional downscaling of data to project the local consequences of ever-rising GHG concentrations.

What Causes Climate Change

Studies conducted the world over have concluded:

  • Today, the Earth's atmosphere holds about 40 percent more heat-trapping greenhouse gases (GHGs) than it did only a century and a half ago; this increase is consistent with the amount of fossil fuel burned since the Industrial Revolution.
  • More GHGs mean a more intense greenhouse effect -- more heat trapped on Earth, less heat escaping into space.
  • GHGs now in the atmosphere are known to be generated by human activities, especially by deforestation and burning of fossil fuels (signaled by a slight but steady decrease in the atmospheric proportion of an isotope of carbon that is deficient in plant-based fuels).
  • Heat trapped by excess GHGs is warming the Earth -- raising sea levels by expanding sea water and melting land ice; energizing the climate system, which disrupts familiar climates and sets off extreme temperatures and precipitation.
  • The Earth is, on average, 1.4 degrees Fahrenheit warmer since reliable temperature measurements began in 1880. And warming is speeding up -- each of the last three decades was warmer than the previous decade; the ten warmest years on record all occurred since 1997.

Greenhouse Gases are Earth-changing

Diagram showing greenhouse effect
Click to view larger image

For more than a century, physicists have known that certain gases in the atmosphere absorb heat, making the planet's overall temperature higher than it would be if these gases were not present.

Greenhouse gases (GHGs) in the atmosphere allow short-wave radiation (like sunlight) to pass through and warm the Earth, but prevents long-wave radiation (heat) from escaping back out to space. Heat trapped by this greenhouse effect raises the temperature of air, land and water.

Carbon dioxide (CO2), is the GHG with the greatest heat-trapping impact. Several other air pollutants, chiefly methane, nitrous oxide, ozone and certain synthetic industrial gases, also cause greenhouse heating.

These substances are released by human activities and accumulate in the atmosphere. CO2 and other long-lived GHGs can persist for hundreds, or even thousands, of years. Since industrialization began, CO2 has built up in the atmosphere from about 280 to nearly 400 parts per million - and GHG emissions are continuing to increase at an accelerating rate.

Extra carbon upsets Earth's carbon balance

Modern humans add billions of tons of CO2 to the atmosphere every year - and remove none.

Diagram of carbon cycle
Click to view larger image

In only about a century and a half, two types of human activities have injected into our atmosphere vast stores of carbon that had remained sequestered under the Earth for millions of years:

  • Combustion of fossil fuels (coal, oil and natural gas) oxidizes carbon in long-buried ancient plants to form the greenhouse gas CO2. As our chief source of energy for generating electricity, heating buildings and operating vehicles, fossil fuels contribute most of the CO2 we emit. Some ancient carbon has been sequestered chemically, for example as calcium carbonate in limestone rock; these compounds convert to CO2 when the rock is heated to make cement.
  • Deforestation and land use change release the carbon stored more recently in trees and soils. Besides adding significant CO2 to the atmosphere's GHG load, deforestation diminishes the biosphere's present and future capacity to remove CO2 from the atmosphere.

Humans' massive infusion of CO2 has unbalanced Earth's carbon cycle by adding more carbon than natural processes can remove.

GHG emissions add up

Globally, CO2 makes up about three-fourths of all human GHG emissions. The other one-fourth -- methane, nitrogen oxides, ozone and the synthetic industrial GHGs -- are gases that trap heat even more effectively than CO2.

To evaluate the full "carbon footprint" of human emissions, scientists use a measurement unit that takes into account the different warming characteristics of individual GHGs. The carbon dioxide equivalent (CO2e) expresses each GHG's warming impact in terms of the amount of CO2 that would create the same amount of warming.

According to the World Resources Institute, in 2011 human emissions of all GHGs totaled more than 45 billion tons of CO2e (2011 is the latest year for which data have become available). For CO2 alone, worldwide emissions in 2011 were 150 times greater than in 1850. (In the U.S., however, CO2 emissions were 266 times greater in 2011 than in 1850.)

After a century and a half of ever-increasing human GHG emissions, the atmosphere holds more total GHGs than at any time in at least 800,000 years.

Greenhouse Gas Emissions in New York

New York's GHG 'footprint'

In 2011, the last year for which complete measurements are available, New York had the following GHG emissions profile:

  • Total greenhouse gases released by human activities in New York State had a CO2e of 212 million tons. This represents an average of nearly 11 tons of CO2e for every New Yorker.
  • Combustion of fossil fuels generated 86 percent of the greenhouse gases emitted in New York. Fuel combustion GHG emissions are predominantly CO2.
  • All of New York's economic sectors generate GHGs.
    • Electricity generation was responsible for about 20 percent of the state's CO2e; the Regional Greenhouse Gas Initiative (RGGI) and other State programs have helped reduce the GHG footprint of New York's electric power.
    • Transportation and industrial, residential and commercial on-site fuel combustion contributed about equally (approximately 34 percent and 32 percent respectively).
    • Processes other than fossil fuel combustion (such as agriculture, industrial processes, electricity distribution and waste management) produced approximately 14 percent of total emissions.

The most recent update of the New York State GHG Emissions Inventory (based on 2011 energy statistics; link at right) shows that, compared with other states, each New Yorker emits relatively low amounts of greenhouse gases. This is because New York gets less electric power from coal-fired plants (the biggest emitters) and more from emission-free hydroelectric generation than many other states; and also because a larger fraction of our population lives in large cities, making widespread use of efficient public transportation and multiple housing units.

To view greenhouse gas data in New York and other states, EPA provides a transparent, powerful data resource (EPA GHG reporting link at right). Users can search for data on power plants, oil refineries and other specific facilities, or on regions.

Reducing GHG emissions will help limit climate change

It is important for all New Yorkers -- homeowners, businesses, drivers, communities, electric power generators, industries and institutions -- to reduce GHG emissions of all greenhouse gases. Through greenhouse gas mitigation programs, New York State seeks to help and encourage all sectors to save energy and emit less greenhouse gas. In partnership with other states and the international community, New York works for reductions in global GHG emissions.

To help all New Yorkers adapt to impacts of climate change that cannot be avoided, New York State is initiating climate adaptation programs with a special focus on communities.

The 2014 Community Risk and Resiliency Act (CRRA) will ensure that certain New York State grant programs, facility-siting regulations and permits take into account climate risk and the effects of extreme weather events. DEC is working with the NYS Department of State and other agencies to develop CRRA guidance, including official New York State sea level rise projections.

For more information

The links at right access more detailed explanations of greenhouse gases, Earth's carbon and heat balances, and climate change. Especially valuable are the Fifth Assessment Report of the Intergovernmental Panel on Climate Change (IPCC - published in 2014), and links to US National Oceanic and Atmospheric Administration (NOAA) and the US Environmental Protection Agency (EPA).


More about Why the Climate is Changing: