The climate of the globe is changing in ways that may have profound impact on physical and biological systems of aquatic, terrestrial, and marine environments. Ironically, climate change is principally caused by human activities, particularly emissions of carbon dioxide from fossil-fuel burning, land use changes, and pollution, while the impacts of climate change constitute hazards to human population health, especially in the tropics and subtropics. The Intergovernmental Panel on Climate Change (IPCC) projects that climate change could affect human health through increases in heat-stress mortality, tropical vector-borne diseases, urban air pollution problems, and decreases in cold-related diseases. Human conditions will no doubtedly also be impacted by projected climate extremes, in terms of loss of human life and capital due to floods, storms, and droughts. These and other impacts, and the underlying causes and conditions, are discussed below.

Global Climate

Based on the time series from 1880 to 1998 for global temperature anomalies, the National Oceanic and Atmospheric Administration (NOAA), National Climatic Data Center reported that the calendar year 1998 was the warmest year since widespread instrument records began in the late 19^th century. While anomolously warm temperatures were found throughout the tropics, the warmest anomalies occurred over North America and northern Asia. The second warmest year was 1997, and seven of the ten warmest years occurred in the 1990s.

Data from a global network of 63 radiosonde stations operated by the NOAA Air Resources Laboratory show similar trends (Figure 11.1). These estimates have been calculated relative to a 1958-1977 reference period mean. For the globe as a whole, the data show that temperatures have been consistently and substantially above the reference period in the 1980s and 1990s.

On an absolute scale, global surface air temperature data from the Global Historical Climatology analyzed by NASA Goddard Institute for Space Studies (GISS) show that the average surface temperature of the Earth has increased by about 0.6 degrees Centigrade (1.0 degrees Fahrenheit) during the 20^th century (Figure 11.2). The higher latitudes have warmed more than the equatorial regions.

According to the IPCC Special Report on Emission Scenarios, the globally averaged surface air temperature is projected by models to warm 1.4 to 5.8 degrees Centigrade (2.5 to 10.4 degrees Fahrenheit) by 2100 relative to 1990, and globally averaged sea level is projected by models to rise 0.09 to 0.88 meters by 2100. These projections indicate that warming will vary by region, and be accompanied by increases and decreases in precipitation. In addition, there will be changes in the variability of climate and changes in the frequency and intensity of some extreme climate phenomena. See the section on Regional Impacts of Climate Change below.

Greenhouse Gas Emissions

Increasing atmospheric concentrations of greenhouse gases -- mainly carbon dioxide, but also methane, nitrous oxide, CFCs, sulfur hexafluoride, hydrofluorocarbons, and perfluorocarbons -- are implicated in the global warming trends discussed above. Human activities (primarily the burning of fossil fuels and changes in land use and land cover ) are increasing the atmospheric concentrations of these gases, which alter radiative balances and tend to warm the atmosphere.

Since 1751 over 270 billion tons of carbon have been released to the atmosphere from the consumption of fossil fuels and cement production. Half of these emissions have occurred since the mid 1970s. The 1997 estimate for global CO₂ emissions, 6.601 billion metric tons of carbon, is the highest fossil-fuel emission estimate ever. The 1997 estimate represents a 1.3 percent increase over 1996, continuing a trend of modest growth since a 1991-1993 decline in CO₂ emissions.

Globally, liquid and solid fuels accounted for 77.5 percent of the emissions from fossil-fuel burning in 1997. Combustion of gas fuels (e.g., natural gas) accounted for 18.3 percent (1211 million metric tons of carbon) of the total emissions from fossil fuels in 1997 and reflects a gradually increasing global utilization of natural gas (Figure 11.3). Emissions from cement production rose to 206 million metric tons of carbon, a twenty-fold increase since the 1920s. Emissions from gas flaring for 1997 were estimated to be 66 million metric tons of carbon, well below the levels of the 1970s. Collectively, emissions from cement production and gas flaring contributed less than 5 percent to the total emissions for 1997.

CO₂ emissions trends are quite uneven among regions (Figure 11.4).

• Centrally Planned Asia (CPA). Growth in CO2 emissions in CPA, which includes Vietnam, North Korea (officially Democratic People's Republic of Korea), Mongolia, and the Peoples Republic of China, has been virtually continuous since l950 as the CPA contribution rose from 1.4 percent of the world total in 1950 to 16.1 percent in 1996. Fossil-fuel CO2 emissions have more than tripled since l973, when growth in many western nations essentially ceased.
• Far East. Fossil-fuel emissions of CO₂ from the Far East were approximately 22 times greater in 1996 than in 1950, the culmination of 46 years of growth averaging 7.0 percent per year. This reflects the growth that has taken place not only in countries like India and South Korea (officially the Republic of Korea), but also in Indonesia, Taiwan, Thailand, Pakistan, Malaysia, the Philippines, and other less populous nations. India and South Korea are responsible for 61.6 percent of the region's 1996 fossil-fuel CO₂ emissions, with the above mentioned six countries contributing another 34.8 percent.
• Africa. Population is growing rapidly, but industrialization is occurring slowly, so energy consumption is stable and CO₂ emissions are rising only slightly. Total emissions for Africa have increased by a factor of 8 since 1950 reaching 205 million metric tons of carbon in 1996, still less than the emissions for some single nations including the United States, China, Russia, Japan, India, and Germany.
• Central and South America. This region, as represented here, constitutes nearly 50 political entities, including Greenland, Bermuda, and the island nations of the Caribbean, in addition to all of Central and South America. Only two countries (Mexico and Brazil) from this region appear in the inventory of the top 20 highest fossil-fuel CO₂- emitting countries. Mexico and Brazil account for 50 percent of the 1996 regional total of 337 million metric tons of carbon but neither of these countries emits more than 100 million metric tons of carbon. Other countries emitting >10 million metric tons of carbon per year are Venezuela (39.9), Argentina (35.4), Colombia (17.8), and Chile (13.3). Liquid fuels account for 68 percent of the 1996 regional emissions.
• Centrally Planned Europe (Eastern Europe). This region, which includes Albania, Bulgaria, Czech Republic, Slovakia, Hungary, Poland, Romania, and the 15 republics of the former Soviet Union, saw linear growth in fossil-fuel CO₂ emissions for the period from the mid 1940s through 1988. From 1989-90, CO₂ emissions from Eastern Europe fell 8.3 percent to early-1980s levels, and from 1990-96, emissions dropped 30 percent due to depressed economies and mild winters. Coal has been the traditional fuel for the region and contributed 83 percent of the total fossil-fuel CO₂ emissions in 1950. Most recently, use of gas fuels has increased dramatically; in 1996 gas contributed 37 percent of CO₂ emissions while the coal contribution was down to 40 percent.
• Germany. Fossil-fuel emissions of CO₂ from unified Germany rose 3.2 percent in 1996 to 235 million metric tons of carbon. This continues a recent increasing trend that has prevailed since 1994. Although the largest fraction of emissions (41 percent) is from burning of solid fuels, the use of coal has been in general decline since 1950, at which time 96.8 percent of the total emissions were from coal burning. Natural gas burning first contributed over 1 percent in 1968 and is now 19 percent of the total.
• Middle East. This region's 15 nations contribute a large fraction of the world's oil but through their own energy consumption produce only 5.0 percent of global CO₂ emissions from fossil fuels and cement. (An exception is the dramatic singularity of CO₂ emissions for 1991 when Kuwaiti oil field fires resulted in 130 million metric tons of carbon being emitted to the atmosphere, more than the 1996 total fossil-fuel CO₂ emissions of the 8th largest national emitter, Canada.) The three major fuel consumers discharge 63 percent of the region's CO₂: Saudi Arabia, 73.1 million metric tons of carbon in 1996; Iran, 72.8 million metric tons of carbon; and Turkey, 48.7 million metric tons of carbon. Gas flaring has been a major source of regional emissions, and in a few years during the early 1970s, before infrastructure was available for gas use and reinjection, flaring accounted for almost half of the total fossil-fuel CO₂ emissions. Growth has been nearly continuous since 1950, although it started from a very low base.
• North America. North America, as defined here, consists of the United States and Canada, however about 93 percent of current fossil-fuel CO₂ emissions from the region are from the United States. Both countries and the region show slight declines in total emissions from 1989-1990 followed by recoveries leading to all-time highs in the mid 1900s-1996. In contrast with CO₂ emissions from other regions, the striking features are a relatively uniform growth rate from 1950 to 1973 (2.7 percent per year), an essentially constant rate of emissions from 1973 to 1987, growth years during 1988-1989, declines from 1989-1991, and record highs in 1994. Because of more rapid growth elsewhere, emissions from North America have shrunk from 46.4 percent of the global total in 1950 to 25.1 percent in 1996.
• Oceania. Oceania consists of nineteen countries, including Japan, Australia, New Zealand, and a number of less populous nations of the Pacific region. Only Japan and Australia are represented in the list of top 20 fossil-fuel CO₂-emitting countries, and together they contribute 97 percent of the regional sum. The pattern of fossil-fuel CO₂ emissions for Oceania bears many similarities with those in North America and Western Europe: that is, strong growth up until 1973 and a leveling off thereafter. From 1973-1987 emissions crept upward but in an irregular and halting pattern. Since 1987 emissions have risen 30 percent to 413 million metric tons of carbon. Japan's slowly decreasing reliance on liquid fuels strongly affects the regional sums.
• Western Europe. The region is constituted of 25 political entities, 3 of which (United Kingdom, Italy, and France) are among the top 20 national fossil-fuel CO₂ emitters. These three nations, along with Spain, contribute 64 percent of the region's total fossil-fuel CO₂ emissions. Per capita emissions for 1996 range from the high of 5.5 metric tons of carbon per person per year in Luxembourg to the low of 0.2 metric tons of carbon per year in Bosnia-Herzegovinia, but for most countries the value lies between 1.5 and 3.5 metric tons of carbon per year. Gas fuels have become increasingly important since about 1970 and now contribute 23 percent of total CO₂ emissions.

Greenhouse Gas Concentrations

Since 1860, it is estimated that global CO₂ concentrations have increased from about 280 parts per million to about 367 parts per million in 1998, or about 30 percent. Roughly half of that increase has occurred since 1970.

Atmospheric methane concentrations have been increasing in the atmosphere by about 0.6 percent annually and have more than doubled since 1860. Methane has both natural sources (peat bogs, termites, swamps, and other wetlands) and human sources (rice paddies, domestic animals, landfills, biomass burning, and the production and burning of fossil fuels). About 60 to 80 percent of all methane emissions are of human origin, with fossil fuels accounting for about 20 percent of the total. Methane accounts for about 20 percent of greenhouse warming from human sources.

Nitrous oxide, which accounts for about five percent of the human sources of greenhouse warming, comes from the application of nitrogen fertilizers to agricultural lands, the burning of biomass and fuels, and industrial chemical production.

Impacts of Climate Change

The IPCC reports that regional changes in climate, particularly increases in temperature and associated changes in many aquatic, terrestrial, and marine environments, are being observed already in many parts of the world. Examples cited include shrinking of glaciers, thawing of paermafrost, shorter duration of ice on rivers and lakes, lenghtneing of mid-to high-latitude grwoing seasons, shifts in plant and animal ranges towards the poles and higher altitudes, declines in some plant and animal populations, and earlier seasonal flowering of trees, emergence of insects, and egg-laying in birds.

In a 1998 report assessing regional impacts of climate change, IPCC reviews state-of-the-art information on potential impacts of climate change for ecological systems, water supply, food production, coastal infrastructure, human health, and other resources for ten global regions. Key findings of this assessment include:

• The African continent is particularly vulnerable to the impacts of climate change because of factors such as widespread poverty, recurrent droughts, inequitable land distribution, and overdependence on rain-fed agriculture.
• The Antarctic peninsula and the Arctic are very vulnerable to projected climate change and its impacts. Direct effects could include ecosystem shifts, sea- and river-ice loss, and permafrost thaw.
• In the arid western Asia (Middle East and arid Asia), where water is an important limiting factor for ecosystems, food and fiber production, human settlements, and human health, climate change is anticipated to alter the hydrologic cycle and is unlikely to relieve limitations caused by water scarcity.
• Australia's relatively low latitude makes it particularly vulnerable to climate change impacts on its scarce water resources and on crops growing near or above their optimum temperatures. New Zealand, on the other hand, with it's cooler, wetter, mid-latitude location may realize some benefit through the ready availability of suitable crops and likely increases in agricultural production.
• The major effects of climate change in Europe are likely to be changes in the frequency of extreme events and precipitation, causing more droughts in some areas and more river floods elsewhere.
• In Latin Amercia, increasing environmental destruction (chnages in water availability, losses of agricultural lands, and flooding) arising from climate variability, climate change, and land-use practices are likely to aggravate socioeconomic and health problems, encourage migration of rural and coastal populations, and deepen national and international conflicts.
• In North America, the most vulnerable sectors and regions include long-lived natural forest ecosystems in the east and interior west; water resources in the southern plains; human health in areas currently experiencing diminished urban air quality; northern ecosystems and habitats; estuarine beaches in developed areas; and low-latitude cool- and cold-water fisheries. Other sectors and regions may benefit from warmer temperatures or, potentially, from carbon dioxide fertilization -- including west coast coniferous forests; some western rangelands; reduced energy costs for heating in the northern latitudes; reduced salting and snow-removal costs; longer open-water seasons in northern channels and ports; and agriculture in the northern latitudes, the interior west, and the west coast.

Ozone Depletion

Stratospheric ozone is a naturally-occurring gas that filters the sun's ultraviolet (UV) radiation. Releases of chlorofluorocarbons (CFCs) and other ozone-depleting substances, which were used for over 50 years as refrigerants, insulating foams, and solvents, has lead to long-term ozone depletion and increased UV radiation reaching the earth's surface. Increased UV can lead to skin cancer, cataracts, and weakened immune systems in humans, reduced agricultural crop production, and disruptions in the marine food chain.

The 1998 Scientific Assessment of Ozone Depletion presents the consensus conclusions of nearly 300 atmospheric researchers worldwide on the causes and effects of ozone depletion. Several of the key scientific findings and observations include:

• The total combined abundance of ozone-depleting compounds in the lower atmosphere peaked in 1994 and is now slowly declining. Total chlorine is declining (primarily due to reduced emissions of methyl chloroform), but bromine is still increasing (likely due to halon emissions in the 1990s in developed countries and new production of halons in developing countries).
• The abundances of hydrochlorofluorocarbons (HCFCs) and hydrofluorocarbons (HFCs) are increasing as a result of a continuation of earlier uses and of their use as substitutes for chlorofluorocarbons (CFCs).
• The total combined abundance of stratospheric chlorine and bromine is expected to peak before the year 2000. The delay in this peak in the stratosphere compared to the lower atmosphere reflects the average time required for surface emissions to reach the lower stratosphere.
• The rate of decline in stratospheric ozone at midlatitudes has slowed while the springtime Antarctic ozone hole continues unabated.
• The understanding of the relationship between increasing surface UV-B radiation and decreasing column ozone has been further strengthened by ground-based observations, and newly developed satellite methods show promise for establishing global trends in UV radiation.
• Stratospheric ozone losses since 1980 may have offset about 30 percent of the positive forcing (warming) of greenhouse gases over the same period.
• Maximum ozone depletion is expected to occur in the current or the next two decades, but recovery of the ozone layer is expected to be well after the maximum stratospheric loading of ozone-depleting gases. Potential future increases or decreases in other gases important in ozone chemistry (such as nitrous oxide, methane, and water vapor) and climate change will influence this recovery.

The Montreal Protocol on Substances that Deplete the Ozone Layer, which commemorated its 10^th anniversary in September 1997, has been remarkably successful in reducing global production of chlorofluorocarbons (CFCs) and other ozone-depleting substances.

References

Angell, J.K., NOAA Air Resources Laboratory, Global, Hemispheric, and Zonal Temperature Deviations Derived from Radiosonde Records. In: Trends: A Compendium of Data on Global Change (an Internet accessible database)(Carbon Dioxide Information Analysis Center, Oak Ridge, TN, 1999).

Alternative Fluorocarbons Environmental Acceptability Study, Production, Sales and Atmospheric Release of Fluorocarbons Through 1998 (an Internet accessible dataset).

Hansen, J. et al., Goddard Institute for Space Studies, Table of Global-Mean Monthly, Annual, and Seasonal dTs Based on Met.station Data, 1866-present (an Internet accessible data file).

Intergovernmental Panel on Climate Change (IPCC), Special Report on Emission Scenarios (IPCC, Geneva, 2000).

--,The Regional Impacts of Climate Change (IPCC, Geneva, 1998).

Keeling, C.D. and T.P. Whorf, Scripps Institution of Oceanography, Atmospheric CO2 Records from Sites in the SIO Air Sampling Network. In: Trends: A Compendium of Data on Global Change (an Internet accessible numerical database) (Carbon Dioxide Information Analysis Center, Oak Ridge National Laboratory, Oak Ridge, TN, 2000).

Marland, G., T. A. Boden, and R.J. Andres, Global, Regional, and National Fossil Fuel CO2 Emissions (an Internet accessible numerical database) (Carbon Dioxide Information Analysis Center, Oak Ridge National Laboratory, Oak Ridge, TN, 2000).

Marland, G., T. A. Boden, R.J. Andres, A.L. Brenkert, and C.A. Johnston, Global CO2 Emissions From Fossil-Fuel Burning, Cement Manufacture, and Gas Flaring: 1751-1997 (an Internet accessible numerical database) (Carbon Dioxide Information Analysis Center, Oak Ridge National Laboratory, Oak Ridge, TN, 2000).

National Oceanic and Atmospheric Administration, National Aeronautics and Space Administration, world Meterological Organization, European Commission, and United Nations Environment Programme, Scientific Assessment of Ozone Depletion: 1998 ,WMO Report No. 44 (2000).

Prinn, R.G., et al., Continuous High Frequency Gas Chromatographic Measurements of CH4, N2O, CFC-11, CFC-12, CFC-113, Methyl Chloroform, and Carbon Tetrachloride From the ALE/GAGE/AGAGE Network Station at Cape Grim, Tasmania (an Internet accessible numerical database) (Carbon Dioxide Information Analysis Center, Oak Ridge National Laboratory, Oak Ridge, TN, 1998).

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