|
|
HOW THE GREEHOUSE EFFECT WORKS
|
|
|
|
1. Most of the sun's energy reaches the Earth.
(The ozone layer shields the Earth from the sun's harmful ultraviolet radiation.)
2. About 30 percent of the energy is reflected back into space.
3.
Burning of fossil fuels and deforestation increase carbon dioxide in the atmosphere. Added to this are chlorofluorocarbons (human-made gases used in spray cans,
refrigerants and insulations) and methane (from landfills, farming and swamps).
4. Together, these gases form a "blanket" which traps energy, thus
warming the Earth.
|
|
Source: World Resources Institute, Changing Climate: A Guide
to the Greenhouse Effect (1989).
|
|
One reason the Earth is warm enough to support life is that carbon dioxide and other gases in the upper
atmosphere act as a kind of transparent umbrella, allowing sunlight to pass through and then trapping the heat below. This intricate but natural process is known
as the greenhouse effect. With increased burning of coal, oil, and natural gas over the past century and with the destruction of much of the Earth's forest cover, the
greenhouse effect may be intensifying. The burning of fossil fuels releases carbon dioxide, some of which is used by trees and other vegetation during
photosynthesis and some of which is absorbed by the oceans. When vast amounts of carbon dioxide are being produced and less is being used by plants, however, the
concentration of carbon dioxide in the atmosphere increases. This accumulation of carbon dioxide and other greenhouse gases (methane, ozone, nitrous
oxides, and chlorofluorocarbons) in Earth's atmosphere may be causing the average temperature around the globe to rise, a phenomenon referred to as "global warming."
With only 5 percent of the world's population, the United States produces 23.4 percent of the carbon dioxide
released from burning fossil fuels.* In all, the Energy Information Adminstration estimated that there were
1,883 million metric tons of human-induced carbon equivalents into the atmosphere in 2001, an increase of about 200 million metric tons (11 %) compared to 1990*.
Nearly 85 percent of these gases are in the form of carbon dioxide, while methane (9.3 percent), nitrous oxide (5.2
percent), and HFCs, PCFs and SF make up the remaining one percent. The electric utility industry is responsible for an
estimated 39 percent of all carbon dioxide emissions in the United States, while transportation accounts for another 33 percent .* Texas alone produces more carbon dioxide than either the United Kingdom or Canada.* Texas produces and
uses more electricity than any other state in the country.* Texas utilities, depending heavily on fossil fuels, for example,
contributed an estimated 248 million metric tons of carbon dioxide in 2002, or about 30 percent of all greenhouses
gases emitted in Texas and about 11 percent of all carbon dioxide emissions from all power plants in the U.S. *.
Without major changes in how Texas produces its energy, these levels are expected to continue. In fact, given rising
natural gas prices, Texas is expected to rely heavily on coal and lignite to produce its power in the coming years.
The environmental implications of global warming are serious. Higher average temperatures could hasten melting of
the polar ice caps, raising sea levels and distorting rainfall patterns. Coastal cities and plant and animal habitat could be
destroyed. An alteration of climate could also reduce crop production. While certain areas of the Earth might actually benefit from global warming, others would suffer disastrous effects.
In Texas, climatic changes predicted as a result of global warming could profoundly alter how Texans live and work. In
Dallas, for example, if the predictions of the Panel on Climate Change are true, the number of days when the
temperature reaches 100 degrees F could increase from 19 to 78 per year by 2050. In Central Texas, average temperatures could go up 5 degrees during the same period.* Water availability might also be affected. Rainfall would
decline in most areas of, and the hotter temperatures would increase the rate of evaporation, resulting in a reduced
water supply. Coastal areas, however, would likely face more intense rainfall, as clouds forming from increased
evaporation of ocean waters give rise to more violent storms. Low-level areas along the coast could be subject to more
flooding from increased rainfall and rising sea levels. Texas may, however, also derive some positive benefits from
warmer annual temperatures. One of these effects is that milder winters may reduce the risk of freezes that cripple citrus crops.*
|
GREENHOUSE GASES EMISSIONS AND THEIR SOURCES
|
|
GAS
|
SOURCE
|
% TOTAL EMISSIONS, 2001
|
LIFE SPAN
|
|
Carbon dioxide (CO2)
|
Fossil fuels, deforestation, soil destruction
|
83.8 %
|
500 years
|
|
Methane (CH4)
|
Cattle, biomass, rice paddies, gas leaks, mining, termites
|
9.3%
|
7-10 years
|
|
Nitrous oxide (N2O)
|
Fossil fuels, soil cultivation, deforestation
|
5.2%
|
140-190 years
|
|
Chlorofluorocarbons (CFCs 11 and 12), HFCs, PFCs and Sulfur Hexaflouride
|
Refrigeration, air conditioning, aerosols, foam blowing, solvents
|
1.7%
|
65-110 years
|
|
Ozone and other trace gases
|
Photochemical processes, cars, power plants, solvents
|
Less than 0.5%
|
Hours to days in upper troposphere
|
|
Source: World Resources Institute, The 1994 Information Please
Environmental Almanac (Boston: Houghton Mifflin Co., 1994), 344 and U.S. Energy Information Administration, Emissions of Greenhouse Gases in the U.S., 2001 (2003),
Table ES-2.
|
|
There is some debate about the phenomenon of global warming. Scientists like James Hansen, of NASA's
Goddard Institute, believe that the Earth is already experiencing an enhanced greenhouse effect. For example, seven of the ten hottest years in recorded history occurred between 1990 and 2000.* And studies have shown a correlation between the concentration of carbon dioxide in the atmosphere and a rise in global temperature.* Critics like Richard Lindzen of the Massachusetts Institute of Technology believe that, while carbon dioxide accumulation may lead
to warming climates, the actual impacts of warming will be mitigated by other factors. For instance, the increase in soot, sulfuric acid, and particulate matter in the atmosphere,
which help scatter light away from the Earth, may be counteracting temperature increases that would otherwise occur from the accumulation of greenhouse gases. Still other
scientists believe that temperature fluctuations are a normal occurrence, attributable to such events as sun spots, and
that techniques for measuring temperature are not accurate enough to permit scientists to design proper models of global temperature.
Nonetheless, overall, global temperatures have increased about 1 degree F in the past 130 years, half of that in the
past 40 years. A body of 2,000 scientists around the globe known as the United Nation's Intergovernmental Panel on
Climate Change (IPCC) has projected that by the year 2100, the average surface temperature will increase an additional 3.5 degrees F from 1990 levels.* The effects of these increases would be felt unevenly around the globe,
with temperature changing less at the equator than at higher latitudes. The IPCC has continued to refine these
numbers, but has continued to conclude that global warming is a very real phenomena.
To delay or prevent global warming, world and national leaders have called for a reduction in carbon dioxide emissions,
to be accomplished through a shift away from the use of oil, gas, and coal and toward the use of more renewable
energy sources like solar power. The 1992 Rio treaty on climate change committed signatory nations to begin negotiations toward cutting greenhouse gas emissions.
In December 1997 most of the world's nations hammered out a world agreement in Kyoto, Japan, that established
limits and phased in reductions on the release of several greenhouse gases.* The agreement commits the developed
nations -- including the United States -- to an 11 percent reduction in greenhouse gases over 1990 levels by 2010, but it
does not determine what, if any, reductions developing nations must make, nor does it spell out exactly how the
developed nations will make reductions. In addition, in 2001, the new Bush administration announced to the
consternation of most nations that it would not seek ratification of the agreement or begin cutting carbon dioxide
emissions as many had hoped. Many of the developed countries -- including Mexico, Texas' neighbor to the south --
which signed the agreement are developing emission reduction plans. While legislation was introduced in the U.S.
Senate to force utilities and other major greenhouse gas sources to address carbon dioxide emissions -- largely
through an emissions cap and trading program -- the legislation is stalled and is not supported by the current
administration. Both the Environmental Protection Agency -- through programs like Energy Star -- and the Department
of Energy have developed successful programs to reduce emissions voluntarily from both power plants and from
energy reduction by commercial businesses and even residents. Several large utilities such as Texas Utilities have
reported reduced millions of tons of carbon dioxide through the DOE voluntary program*. Some states, like California,
have begun to work on reductions of global greenhouse gases by passing laws to address carbon dioxide emissions
from cars. In Texas, however, no major state-led regulatory efforts have occured.
|
