GLOBAL CLIMATE CHANGE

Transcription

1 1 GLOBAL CLIMATE CHANGE From About Transportation and Climate Change (Source; Volpe center for Climate Change and Environmental forecasting, Greenhouse effect has occurred from increased CO in atmosphere, from 280 ppm to 380 ppm in later 20 th century. This is expected to reach 550 to 960 ppm by Substantial physical evidence exists that climate changes are occurring. The Science of Climate Change An Introduction The earth's climate is predicted to change, in part because human activities are altering the chemical composition of the atmosphere through the buildup of greenhouse gases - primarily carbon dioxide, methane, and nitrous oxide. The heat-trapping property of these gases is undisputed. Although uncertainty exists about exactly how earth's climate responds to these gases, global temperatures are rising. Percentage of U.S. Greenhouse Gas Emissions, 2000

2 2 What Are Greenhouse Gases? Some greenhouse gases occur naturally in the atmosphere, while others result from human activities. Naturally occurring greenhouse gases include water vapor, carbon dioxide, methane, nitrous oxide, and ozone. Certain human activities, however, add to the levels of most of these naturally occurring gases: Carbon dioxide is released to the atmosphere when solid waste, fossil fuels (oil, natural gas, and coal), and wood and wood products are burned. Methane is emitted during the production and transport of coal, natural gas, and oil. Methane emissions also result from the decomposition of organic wastes in municipal solid waste landfills, and the raising of livestock. Nitrous oxide is emitted during agricultural and industrial activities, as well as during combustion of solid waste and fossil fuels. Greenhouse gases that are not naturally occurring include byproducts of foam production, refrigeration, and air conditioning called chlorofluorocarbons (CFCs), as well as hydro fluorocarbons (HFCs) and perfluorocarbons (PFCs) generated by industrial processes. Each greenhouse gas differs in its ability to absorb heat in the atmosphere. HFCs and PFCs are the most heat-absorbent. Methane traps over 21 times more heat than carbon dioxide, and nitrous oxide absorbs 270 times more heat than carbon dioxide. Often, estimates of greenhouse gas emissions are presented in units of millions of metric tons of carbon equivalents (MMTCE), which weights each gas by its GWP value, or Global Warming Potential. Our Changing Atmosphere Energy from the sun drives the earth's weather and climate, and heats the earth's surface; in turn, the earth radiates energy back into space. Atmospheric greenhouse gases (water vapor, carbon dioxide, and other gases) trap some of the outgoing energy, retaining heat somewhat like the glass panels of a greenhouse. Warming Global temperatures are rising. Observations collected over the last century suggest that the average land surface temperature has risen C ( F) in the last century. The surface of the ocean has also been warming at a similar rate. Studies that combine land and sea measurements have generally estimated that global temperatures have warmed C ( F) in the last century. About two-

3 3 thirds of this warming took place between 1900 and Global temperatures declined slightly from the 1940s through the 1970s; but have risen more rapidly during the last 25 years than in the period before Surface temperatures are not rising uniformly. Night-time low temperatures are rising on average about twice as rapidly as daytime highs. The winters in areas between 50 and 70 North Latitude (the latitude of Canada and Alaska) are warming relatively fast, while summer temperatures show little trend. Urban areas are warming somewhat more rapidly than rural areas, because of both the changes in land cover and the consumption of energy that take place in densely developed areas (a feature known as the "urban heat island" effect). Red circles reflect warming/blue circles reflect cooling. Note: cooling in Southeast U.S. may be due to sulfate aerosol influence. In the United States, temperatures in the last 50 years have cooled in the East while warming in the West. Over the last 100 years, the pattern is similar, except that New England is warmer than 100 years ago because it warmed more in the first half of the 20th century by more than it cooled in the second half. This pattern of warming and cooling may be part of a worldwide pattern: while most of the earth has warmed, the regions that are downwind from major sources of sulfur dioxide emissions have generally cooled (see the discussion on sulfates in the Atmospheric Change section). This pattern is evident when one compares the two world maps below.

4 4 Trends of Surface Temperature ( ) Global Historical Climate Network (GHCN) The first map of the world shows the areas that have warmed and cooled from The second map of the world shows the amount of incoming solar radiation blocked by the cloud of atmospheric sulfates downwind from industrial emissions of sulfur dioxide. Solar Energy Blocked by Atmospheric Sulfates (Radiative Forcing in Watts per Square Meter)

5 5 Source: based on IPCC (1994) Although scientists have incontrovertible evidence that the surfaces of the land and oceans have been warming, some scientists are not yet convinced that the atmosphere is also warming. The satellite data do not show a warming trend; however, the data series may be too short to show a trend in atmospheric temperature. Part of the reason that satellites do not show a warming trend may be a coincidence regarding the year that NASA began to collect this data. Balloon data, which shows the same absence of warming over the period, shows a significant warming trend from 1958 to Measurement errors associated with the new technology, and cyclical variations in temperature due to El Ninos, may also be responsible for the lack of a warming trend. Nevertheless, to many scientists, the absence of a warming trend in the satellite data provides an important caution that there is still much to learn about the global climate.

6 6 *Note: measurements are relative to the average of (surface) and (satellite) temperatures. Data Sources: Phil Jones, University of East Anglia (UK) and David Parker, United Kingdom Meteorological Office (surface data); John Christy, University of Alabama and Roy Spencer, National Aeronautics and Space Administration (satellite data).

7 7 Some Examples Mt. Hood Oregon, Same day Glacier, Chile, 1928, 2004 Ocean Temperatures Sept 18, 2005 Hurricane Rita

8 8 Precipitation Precipitation has increased by about 1 percent over the world's continents in the last century. High latitude areas are tending to see more significant increases in rainfall, while precipitation has actually declined in many tropical areas. In North America, precipitation has increased significantly. Precipitation in the United States has increased by an average of about 5 percent in the last century. Along the northern tier states and in Southern Canada, rainfall has increased percent. Much of the increase in rainfall has been taking place between September and November. Rainfall is also tending to be more concentrated in heavy downpours, according to studies by the National Oceanic and Atmospheric Administration NOAA. At the beginning of the 20th century, only 9 percent of the nation experienced a storm each year in which more than two inches of precipitation fell in a 24-hour period. In recent decades, such a severe storm has occurred each year over close to 11 percent of the nation. Precipitation Trends, 1900 to Present Red circles reflect increasing precipitation; Blue circles reflect decreasing precipitation

9 9 Precipitation of the USA Affected by Much Above Normal Portion of Annual Precipitation From Extreme Events The change in the area of the USA affected by increases in the proportion of total annual precipitation derived from extreme daily precipitation events (more than 2 inches) Sea Levels Sea level has risen worldwide approximately cm (6-8 inches) in the last century. Approximately 2-5 cm (1-2 inches) of the rise has resulted from the melting of mountain glaciers. Another 2-7 cm has resulted from the expansion of ocean water that resulted from warmer ocean temperatures. The pumping of ground water and melting of the polar ice sheets may have also added water to the oceans. Along most of the U.S. coast, sea level has been rising mm/yr (10-12 inches per century). Nevertheless, the rate varies from about 1 cm per year (three feet per century) along the Louisiana Coast, to a drop of several millimeters per year (a few inches per decade) in parts of Alaska. The rapid rate in Louisiana resulted from the settling of newly created land formed by the sediments that washed down the Mississippi River. In Galveston, the removal of groundwater led the land above the water table to sink. In areas that were covered by glaciers during the last Ice Age, by contrast, the land is rising because of the removal of the weight of the ice, which had previously compressed the land downward. As a result, the sea is dropping relative to these coasts.

10 10 Impacts Rising global temperatures are expected to raise sea level, and change precipitation and other local climate conditions. Changing regional climate could alter forests, crop yields, and water supplies. It could also threaten human health, and harm birds, fish, and many types of ecosystems. Deserts may expand into existing rangelands, and the character of some of our National Parks may be permanently altered. Most of the United States is expected to warm, although sulfates may limit warming in some areas. Scientists currently are unable to determine which parts of the United States will become wetter or drier, but there is likely to be an overall trend toward increased precipitation and evaporation, more intense rainstorms, and drier soils.

11 11 Unfortunately, many of the potentially most important impacts depend upon whether rainfall increases or decreases, which can not be reliably projected for specific areas. More information about the impacts of global climate change is available through the EPA Global Warming Site ( )and the U.S. Global Change Research Program's U.S. National Assessment. (

12 GLOBAL CLIMATE CHANGE Table 2. Projected impacts of climate change on the United States, adapted from Climate Change Impacts on the United States: The Potential Consequences of Climate Variability and Change, by the National Assessment Synthesis Team. 1. Increased warming and more intense precipitation will characterize the 21 st century. 2. Differing regional impacts will occur, with greater warming in the western US, but a greater rise in heat index in the east and south. 3. Vulnerable ecosystems, particularly alpine areas, barrier islands, forests in the Southeast, and other vulnerable ecosystems will be significantly impacted. 4. Water will be a concern across the country, with increased competition for available resources, and the potential for more droughts and floods and reduced winter snowpack in some areas. 5. Food availability will increase because of increased crop productivity, although lowered commodity prices will stress farmers in marginal areas. 6. Forest growth will increase in the near-term, but some forests will be threatened over the long-term by increased susceptibility to fire, pests, and other disturbances. 7. Increased damage is very likely in coastal regions due to sea-level rise and more intense storms, while damage in other areas will result from increased melting of permafrost. 8. Adaptation will determine the importance of health outcomes, so that strengthening of the nation s community and health infrastructure will become increasingly important. 9. The impacts of other stresses will be magnified by climate change, with multiple factors causing adverse impacts on coral reefs, wildlife habitats, and air and water quality. 10. Uncertainties remain in current understanding and there is a significant potential for unanticipated changes.

13 GLOBAL CLIMATE CHANGE Comparison between modeled and observations of temperature rise since 1960 Source: