1. Global Change: Greenhouse Gases
Environmental Sustainability Educational Resources
prepared by
Gregory A. Keoleian
Associate Research Scientist,
School of Natural Resources and Environment
Co-Director, Center for Sustainable Systems
University of Michigan
Greenhouse gases
Those gases, such as water vapor, carbon dioxide, nitrous oxide, methane, hydrofluorocarbons (HFCs), perfluorocarbons (PFCs) and sulfur hexafluoride, that are transparent to solar (short-wave) radiation but opaque to long-wave radiation, thus preventing long-wave radiant energy from leaving the atmosphere. The net effect is a trapping of absorbed radiation and a tendency to warm the planet's surface.
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2. Contents Human Impact on Global Climate [slide 4]
Greenhouse Effect [slide 5]
Global Warming Potentials [slide 6]
1998 GHG Emissions in U.S. [slide 7]
Trends in U.S. GHG Emissions, 1990–1998 [slide 8]
Carbon Dioxide (non-energy related) Emissions [slide 9]
Methane Emissions [slide 10]
Nitrous Oxide (N2O) Emissions [slide 11]
Perfluorocarbons (PFC’s) Emissions [slide 12]
Sulfur Hexafluoride (SF6) Emissions [slide 13]

3. Total Energy Related Carbon Emissions for Selected Manufacturing Industries, 1994 [slide 14]
CO2 Emissions per Capita for Selected Countries [slide 15]
Global Atmospheric Concentration of CO2 [slides ]
CO2 & Temperature Relationships (Historical) [slides ]
GHG Emissions (Projected) [slide 20]
Carbon Emissions by Region [slide 20]
Carbon Emissions by Region [slide 21]
Potential Climate Change Impacts [slide 22]
Temperature [slides 23-25]
Sea level [slides 26-27]
Policy: Kyoto Protocol [slides ]
Additional Resources [slide 30]

4. Human Impact on Global Climate
“The balance of evidence suggests a discernable human influence on global climate” IPCC 1995
Intergovernmental Panel on Climate Change (IPCC)
The IPCC was created jointly by the World Meteorological Organisation and the United Nations Environment Programme in The IPCC is responsible for compiling and synthesizing the growing body of scientific literature on climate change. The comprehensive assessments of IPCC form the scientific basis for climate change policies.
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5. Greenhouse Effect
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.
Without this natural “greenhouse effect,” temperatures would be much lower than they are now, and life as known today would not be possible. Instead, thanks to greenhouse gases, the earth’s average temperature is a more hospitable 60°F. However, problems may arise when the atmospheric concentration of greenhouse gases increases.
Since the beginning of the industrial revolution, atmospheric concentrations of carbon dioxide have increased nearly 30%, methane concentrations have more than doubled, and nitrous oxide concentrations have risen by about 15%. These increases have enhanced the heat-trapping capability of the earth’s atmosphere.
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6. Global Warming Potentials (100 year time horizon)
Numerical Estimates of Global Warming Potentials Compared With Carbon Dioxide (Kilogram of Gas per Kilogram of Carbon Dioxide).
Note: The typical uncertainty for global warming potentials is estimated by the Intergovernmental Panel on Climate Change at ±35 percent.
Source: Intergovernmental Panel on Climate Change, Climate Change 1995: The Science of Climate Change (Cambridge, UK: Cambridge University Press, 1996), p. 121.
Global Warming Potential (GWP)
GWPs are calculated as the ratio of the radiative forcing that would result from the emissions of one kilogram of a greenhouse gas to that from emission of one kilogram of carbon dioxide over a period of time (usually 100 years).
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.
Additional resources

7. The total U.S. GHG emissions in 1998 were 1803 Million Metric Tons of Carbon Equivalents (MMTCE) (EIA 1999). Energy-related GHG emissions from the combustion of fossil fuels account for 81% of this total. These emissions are divided between residential (19%), commercial (16%), industrial (32%) and transportation (33%) sectors.
Other U.S. GHG emissions include carbon dioxide from non-combustion sources, methane, nitrous oxide, and other potent gases such as hydrofulorocarbons (HFCs), perfluorocarbons (PFCs) and sulfur hexafluoride (SF6). Agriculture; petroleum, coal, and natural gas industries; transportation; cement manufacture; and utilities are responsible for a majority of these releases. While the global warming potentials of HFCs, PFCs, and SF6 are large, they accounted for only 2% of the U.S. total in Total emissions from these gases were estimated at 37.2 MMTCE, including semiconductor manufacture (1.3), electrical transmission and distribution (7.0), magnesium production and processing (3.0), HCFC-22-production (8.2), and aluminum smelting (2.9).
Source: Energy Information Administration Report DOE/EIA 0573(98)

8. Trends in U.S. GHG Emissions, 1990–1998
Abbreviations
GHG = Greenhouse Gases
MMTCE = Million Metric Tons of Carbon or Carbon Equivalents
Trends in U.S. GHG emissions indicated in this figure are also alarming. Between 1990 and 1998 emissions have risen 10% with an average annual increase of 1.2%, which is slightly higher than the growth rate in U.S. population (1.1%) but more slowly than gross domestic product (2.6%) (EIA 1999).
Source: Energy Information Administration Report DOE/EIA 0573(98)

9. Carbon Dioxide (non-energy related) Emissions
Cement manufacture
calcium carbonate is heated to produce lime
In 1998, the United States manufactured an estimated 85.5 million metric tons of cement, resulting in the direct release of carbon dioxide containing about 10.6 million metric tons of carbon into the atmosphere.
In addition to CO2 emissions from combustion, CO2 can be generated from chemical processes such as the calcining of limestone (CaCO3) to produce lime (CaO) for cement.
Source: Energy Information Administration Report DOE/EIA 0573(98)

10. Methane Emissions Energy production and consumption Waste management
coal mining
natural gas systems
Waste management
landfill gas
Agriculture
manure management
cattle (enteric fermentation)
rice cultivation
Methane contributes 9% of the total greenhouse gas emissions in the US and has a GWP = 21.
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.
There are three principal sources of U.S. methane emissions: energy production and consumption, waste management, and agriculture. A fourth source, industrial processes, adds about 0.5 percent to estimated methane emission totals. Emissions from energy sources, representing 35 percent of all U.S. methane emissions (Figure 5), declined by more than 6 percent between 1990 and 1998, largely due to the 1.1 million metric ton drop in emissions from coal mining. Methane emissions from waste management, which account for about one-third of total methane emissions, decreased by more than 11 percent between 1990 and 1998 due to the drop in emissions from landfills. Emissions from agriculture represent about 30 percent of all U.S. methane emissions. Emissions from agriculture have grown by 6.9 percent since 1990, with approximately half the growth associated with increased swine populations and the resultant waste output. The majority of the remaining increase is associated with larger sized cattle, generating more methane emissions from enteric fermentation.
Source: Energy Information Administration Report DOE/EIA 0573(98)

11. Nitrous Oxide (N2O) Emissions
Agricultural soil management
nitrogen fertilization
Mobile sources
Adipic acid production
used to make nylon
Nitrous oxide is emitted during agricultural and industrial activities, as well as during combustion of solid waste and fossil fuels.
Nitrous oxide accounts for 6 percent of U.S. GWP-weighted greenhouse gas emissions. Emissions estimates for nitrous oxide are more uncertain than those for either carbon dioxide or methane.
Agricultural sources account for about 71 percent of nitrous oxide emissions. Emissions associated with nitrogen fertilization of soils account for about three-quarters of agricultural emissions. Emissions associated with fossil fuel use account for another 22 percent of nitrous oxide emissions, of which about 82 percent comes from mobile sources, principally motor vehicles equipped with catalytic converters. The balance of nitrous oxide emissions are caused by certain chemical manufacturing and wastewater treatment processes.
Source: Energy Information Administration Report DOE/EIA 0573(98)

12. Perfluorocarbons (PFC’s)
Aluminum production
perfloromethane (CF4)
GWP = 6500
perfloroethane (C2F6)
GWP = 9200
Perfluorocarbons are compounds composed of carbon and fluorine. PFC emissions are not regulated or reported, although their high GWPs (6,500 for perfluoromethane and 9,200 for perfluoroethane). PFCs are also characterized by long atmospheric lifetimes (up to 50,000 years); hence, unlike HFCs, they are essentially permanent additions to the atmosphere. As byproducts of aluminum production, they arise during discrete periods of process inefficiency. Emissions can be reduced by improving process efficiency. A Voluntary Aluminum Industrial Partnership is aimed at reducing PFC emissions from the aluminum industry.
The principal quantifiable source of PFCs is as a byproduct of aluminum smelting. The EPA estimates U.S. emissions at 1,430 metric tons of perfluoromethane and 140 metric tons of perfluoroethane in U.S. primary aluminum production has been increasing since 1994, and the trend is expected to continue as the automobile industry expands its use of aluminum.
Another source of PFC emissions is semiconductor manufacturing. Perfluoromethane and perfluoroethane are used as etchants and cleaning agents in semiconductor manufacturing. Although anywhere from 5 to 95 percent of the CF4 and C2F6 is destroyed, the process produces fugitive emissions of perfluoroethane, perfluoromethane, and sulfur hexafluoride. The United States consumed an estimated 800 tons of perfluoroethane and perfluoromethane in 1995.(63) The EPA's Climate Protection Division estimates that emissions of PFCs, HFC-23, and sulfur hexafluoride from the semiconductor industry totaled about 1 million metric tons carbon equivalent in 1994, with about 60 to 70 percent of GWP-weighted emissions consisting of perfluoroethane. For 1996, the EPA estimates total emissions of all greenhouse gases from semiconductor manufacturing at 1.3 million metric tons carbon equivalent.
Source: Energy Information Administration Report DOE/EIA 0573(98)

13. Sulfur Hexafluoride (SF6) Emissions
Insulator for electrical equipment
Fugitive emission from semiconductor manufacture
Cover gas for magnesium production
prevents the oxidation of molten magnesium in presence of air
Sulfur hexafluoride (SF6) is used as an insulator for circuit breakers, switch gear, and other electrical equipment. In addition, its extremely low atmospheric concentration makes it a useful atmospheric tracer gas for a variety of experimental purposes. It is also a fugitive emission from certain semiconductor manufacturing processes, and it is used as a cover gas during magnesium production and processing, to prevent the violent oxidation of molten magnesium in the presence of air.
Sulfur hexafluoride has a high GWP of 23,900, but it is not produced or used in large quantities. In 1989, global production and emissions were estimated at 5,000 metric tons. The EPA's estimates indicate a gradual increase in U.S. emissions between 1990 and 1995, from 1,120 metric tons to 1,530 metric tons and holding steady thereafter.
Source: Energy Information Administration Report DOE/EIA 0573(98)

14. Total Energy Related Carbon Emissions for Selected Manufacturing Industries, 1994
Source: Energy Information Administration Report DOE/EIA 0573(98)

15. Carbon Emissions per Capita for Selected Countries
The U.S. accounts for 24 % of the 6,175 MMTCE of total global carbon emissions based on 1997 estimates with a population that is only 4.6 % of the world total. Several methods can be used to refine an assessment of the U.S. GHG emitting intensity relative to other countries. GHG normalization by population, as shown in this figure, indicates the U.S. is the leading emitter on a per capita basis. The relatively large U.S. GHG contribution is due to both its high industrial productivity but more significantly to the high level of consumption in residential and transportation sectors. Comparison of U.S. emissions with other countries is further complicated by differences in the carbon intensity of goods imported and exported. While the U.S. has a significant trade deficit it is not clear how carbon intensity would alter our GHG national profile.
The U.S. has the second highest emissions per GDP among developed countries.
Source: Energy Information Agency, Report #DOE/EIA-0484(2000)

16. Atmospheric CO2 has increased from a pre-industrial concentration of about 280 ppmv to about 367 ppmv at present (ppmv= parts per million by volume). CO2 concentration data from before 1958 are from ice core measurements taken in Antarctica and from 1958 onwards are from the Mauna Loa measurement site. The smooth curve is based on a hundred year running mean. It is evident that the rapid increase in CO2 concentrations has been occurring since the onset of industrialization. The increase has closely followed the increase in CO2 emissions from fossil fuels.
Source: United Nations Environment Programme / GRID-Arendal; Vital Climate Graphics : Introduction to climate change

17. CO2 concentrations in the atmosphere have been measured at an altitude of about 4,000 meters on the peak of Mauna Loa mountain in Hawaii since The measurements at this location, remote from local sources of pollution, have clearly shown that atmospheric concentrations of CO2 are increasing. The mean concentration of approximately 316 parts per million by volume (ppmv) in 1958 rose to approximately 369 ppmv in The annual variation is due to CO2 uptake by growing plants. The uptake is highest in the northern hemisphere springtime.
Source: United Nations Environment Programme / GRID-Arendal; Vital Climate Graphics : Introduction to climate change

18. Expected Consequences of GHG Concentration Increases
Temperature: 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.
Trends: Data on a wide variety of environmental indicators are consistent with the consequences that scientists generally expect to result from increasing concentrations of greenhouse gases.

19. Over the last 400,000 years the Earth's climate has been unstable, with very significant temperature changes, going from a warm climate to an ice age in as rapidly as a few decades. These rapid changes suggest that climate may be quite sensitive to internal or external climate forcings and feedbacks. As can be seen from the blue curve, temperatures have been less variable during the last years. Based on the incomplete evidence available, it is unlikely that global mean temperatures have varied by more than 1°C in a century during this period. The information presented on this graph indicates a strong correlation between carbon dioxide content in the atmosphere and temperature. A possible scenario: anthropogenic emissions of GHGs could bring the climate to a state where it reverts to the highly unstable climate of the pre-ice age period. Rather than a linear evolution, the climate follows a non-linear path with sudden and dramatic surprises when GHG levels reach an as-yet unknown trigger point.
Source: United Nations Environment Programme / GRID-Arendal; Vital Climate Graphics : Introduction to climate change

20. Carbon Emissions by Region 1997 (6175 Million Metric Tons Carbon)
Original data sources: International Energy Outlook DOE/EIA-0484(2000) History: Energy Information Administration (EIA), International Energy Annual 1997, DOE/EIA-0219(97) (Washington, DC, April 1999). Projections: EIA, World Energy Projection System (2000).
Energy demand in developing Asia and Central and South America is projected to more than double between 1997 and Both regions are expected to sustain energy demand growth of more than 3 percent annually throughout the forecast, accounting for more than one-half of the total projected increment in world energy consumption and 83 percent of the increment for the developing world alone.
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21. Carbon Emissions by Region 2020 (10,009 Million Metric Tons Carbon)
Original data sources: International Energy Outlook DOE/EIA-0484(2000) History: Energy Information Administration (EIA), International Energy Annual 1997, DOE/EIA-0219(97) (Washington, DC, April 1999). Projections: EIA, World Energy Projection System (2000).
Energy demand in developing Asia and Central and South America is projected to more than double between 1997 and Both regions are expected to sustain energy demand growth of more than 3 percent annually throughout the forecast, accounting for more than one-half of the total projected increment in world energy consumption and 83 percent of the increment for the developing world alone.
Source: International Energy Outlook 2000 DOE/EIA-0484(2000)

22. Humanity’s greenhouse gas emissions are expected to lead to climatic changes in the 21st century and beyond. These changes will potentially have wide-ranging effects on the natural environment as well as on human societies and economies. Scientists have made estimates of the potential direct impacts on various socio-economic sectors, but in reality the full consequences would be more complicated because impacts on one sector can also affect other sectors indirectly. To assess potential impacts, it is necessary to estimate the extent and magnitude of climate change, especially at the national and local levels. Although much progress has been made in understanding the climate system and climate change, projections of climate change and its impacts still contain many uncertainties, particularly at the regional and local levels.
Source: United Nations Environment Programme / GRID-Arendal; Vital Climate Graphics : Introduction to climate change

23. Predictions of future temperature
Since 1979, scientists have generally agreed that a doubling of atmospheric carbon dioxide increases the earth’s average surface temperature by °C (3-8°F).
Since 1979, scientists have generally agreed that a doubling of atmospheric carbon dioxide increases the earth’s average surface temperature by °C (3-8°F). More recent studies have suggested that the warming is likely to occur more rapidly over land than the open seas. Moreover, the warming in temperatures tends to lag behind the increase in greenhouse gases. At first, the cooler oceans will tend to absorb much of the additional heat and thereby decrease the warming of the atmosphere. Only when the ocean comes into equilibrium with the higher level of CO2 will the full warming occur. As a result of the delay induced by the oceans, climate scientists do not expect the earth to warm by the full °C (3-8°F), even though the level of CO2 is expected to more than double and other greenhouse gases would add to the warming. Currently, the Intergovernmental Panel on Climate Change
projects a warming of °C ( °F) by the year 2100.
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24. Using the IS92 emission scenarios, projected global mean temperature changes relative to 1990 were calculated up to Climate models calculate that the global mean surface temperature could rise by about 1 to 4.5 centigrade by The topmost curve is for IS92e, assuming constant aerosol concentrations beyond 1990 and high climate sensitivity of 4.5 °C. The lowest curve is for IS92c and assumes constant aerosol concentrations beyond 1990 and a low climate sensitivity of 1.5 °C. The two middle curves show the results for IS92a with "best estimate" of climate sensitivity of 2.5 °C: the upper curve assumes a constant aerosol concentration beyond 1990, and the lower one includes changes in aerosol concentration beyond (It is assumed that the Greenhouse effect is reduced with increased aerosols.)
Note: In IPCC reports, climate sensitivity usually refers to the long- term or equilibrium, change in global mean surface temperature following a doubling of CO2-equivalent atmospheric concentrations. More generally, it refers to the equilibrium change in surface air temperature following a unit change in radiative forcing (°C/Wm-2)
Source: United Nations Environment Programme / GRID-Arendal; Vital Climate Graphics : Vital Climate Graphics : Potential Impacts of Climate Change

25. New Temperature Projections
The globally averaged surface temperature is projected to increase by 1.4 to 5.8ºC over the period 1990 to 2100.
Source: Shanghai Draft IPCC WGI THIRD ASSESSMENT REPORT
Source: Shanghai Draft IPCC WGI THIRD ASSESSMENT REPORT
· Temperature increases are projected to be greater than those in the IPCC Second Assessment Report (SAR), which were about 1.0 to 3.5ºC based on the six IS92 scenarios. The higher projected temperatures and the wider range are due primarily to the lower projected sulphur dioxide emissions in the IPCC Special Report on Emission Scenarios (SRES) scenarios relative to the IS92 scenarios.
· The projected rate of warming is much larger than the observed changes during the 20th century and is very likely to be without precedent during at least the last 10,000 years, based on palaeoclimate data.
Footnote (10): Complex physically based climate models are the main tool for projecting future climate change. In order to explore the full range of scenarios, these are complemented by simple climate models calibrated to yield an equivalent response in temperature and sea level to complex climate models. These projections are obtained using a simple climate model whose climate sensitivity and ocean heat uptake are calibrated to each of 7 complex climate models. The climate sensitivity used in the simple model ranges from 1.7 to 4.2ºC which is comparable to the commonly accepted range of 1.5 to 4.5ºC.
Footnote (11): This range does not include uncertainties in the modeling of radiative forcing, e.g. aerosol forcing uncertainties. A small carbon-cycle climate feedback is included.

26. Sea Level
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.
Warmer temperatures are expected to raise sea level by expanding ocean water, melting mountain glaciers, and melting parts of the Greenland Ice Sheet. Warmer temperatures also increase precipitation, as described below. Snowfall over Greenland and Antarctica is expected to increase by about 5 percent for every 1°F warming in temperatures. Increased snowfall tends to cause sea level to drop if the snow does not melt during the following summer, because the only other place for the water to be is the ocean. (The amount of water in the atmosphere is less than the water it takes to raise the oceans one millimeter). Considering all of these factors, the IPCC estimates that sea level will rise 20 to 86 cm by the year A recent EPA study estimated that global sea level has a 50 percent chance of rising 45 cm (1-1/2 ft) by the year 2100, but a 1-in-100 chance of a rise of about 110 cm (over 3-1/2 ft). Over the longer run, more substantial changes in sea level are possible. Some scientists believe that the West Antarctic Ice Sheet could slide into the oceans after a sustained warming, or if other factors raised sea level. The vulnerability of this ice sheet is poorly understood. It contains enough ice to raise sea level 6 meters (20 feet), and coastal scientists generally agree that sea level was 20 feet higher than today during the last interglacial period, which was only slightly warmer than today. While some scientists have suggested that there is fossil evidence on the polar ocean floor that this ice sheet collapsed during the last interglacial period, there is no scientific consensus on this question. An EPA study solicited the opinions of 8 US glaciologists on the vulnerability of this ice sheet. All but one concluded that Antarctica is most likely to have a negligible contribution to sea level over the next century. Nevertheless, they all agreed that there is some risk that a catastrophic collapse of the ice sheet could occur over a couple of centuries if polar water temperatures warm by a few degrees. Most of the scientists estimated that such a risk had a probability of between 1 and 5 percent. Because of this risk, as well as the possibility of a larger than expected melting of the Greenland Ice Sheet, the EPA study estimated that there is a 1 percent chance that global sea level could rise by more than 4 meters (almost 14 feet) in the next two centuries.Sea level rise along the US coast is likely to be somewhat greater than the global average. The EPA study includes a set of projections that coastal residents can use to calculate how much sea level will rise in specific communities. Along the coast of New York, which typifies the US Coast, sea level is likely to rise 26 cm (10 inches) by 2050 and 55 cm (almost 2 feet) by There is also a 1 percent chance of a 55 cm rise by 2050, a 120 cm rise (4 ft) by 2100, and a 450 cm rise (15 feet) by the year 2200.
Source:

27. Using the IS92 emission scenarios, projected global mean sea level increases relative to 1990 were calculated up to Taking into account the ranges in the estimate of climate sensitivity and ice melt parameters, and the full set of IS92 emission scenarios, the models project an increase in global mean sea level of between 13 and 94 cm. During the fist half of the next century, the choice of emission scenario has relatively little effect on the projected sea level rise due to the large thermal inertia of the ocean-ice-atmosphere climate system, but has increasingly larger effects in the later part of the next century. In addition, because of the thermal inertia of the oceans, sea level would continue to rise for many centuries beyond 2100 even if concentrations of greenhouse gases were stabilized at that time.
Source: United Nations Environment Programme / GRID-Arendal; Vital Climate Graphics : Vital Climate Graphics : Potential Impacts of Climate Change

28. Kyoto Protocol Framework
stabilize greenhouse gas emissions to prevent anthropogenic interference with the climate system
emission targets for industrialized countries between are collectively about 5% lower than 1990 emissions
US target is 7% reduction
developing countries do not have quantified targets
six gases
CO2, CH4, N2O, HFCs, PFCs, SF6
The Kyoto Protocol to the United Nations Framework Convention on Climate Change strengthens the international response to climate change.Adopted by consensus at the third session of the Conference of the Parties (COP-3) in December 1997, it contains legally binding emissions targets for Annex I (developed) countries for the post-2000 period. By arresting and reversing the upward trend in greenhouse gas emissions that started in these countries 150 years ago, the Protocol promises to move the international community one step closer to achieving the Convention’s ultimate objective of preventing “dangerous anthropogenic [man-made] interference with the climate system”.
The developed countries commit themselves to reducing their collective emissions of six key greenhouse gases by at least 5%.This group target will be achieved through cuts of 8% by Switzerland, most Central and East European states, and the European Union (the EU will meet its target by distributing different rates to its member states); 7% by the US; and 6% by Canada, Hungary, Japan, and Poland. Russia, New Zealand, and Ukraine are to stabilize their emissions, while Norway may increase emissions by up to 1%, Australia by up to 8%, and Iceland 10%. The six gases are to be combined in a “basket”, with reductions in individual gases translated into “CO2 equivalents” that are then added up to produce a single figure.
Source: The Kyoto Protocol Sheet 21, Climate Change Information Kit, United Nations Development Programme,

29. The Protocol is subject to ratification, acceptance, approval or accession by Parties to the Convention.
It shall enter into force on the ninetieth day after the date on which not less than 55 Parties to the Convention, incorporating Annex I Parties which accounted in total for at least 55 % of the total carbon dioxide emissions for 1990 from that group, have deposited their instruments of ratification, acceptance, approval or accession.
Each country’s emissions target must be achieved by the period It will be calculated as an average over the five years. “Demonstrable progress” must be made by Cuts in the three most important gases – carbon dioxide (CO2), methane (CH4), and nitrous oxide (N20) - will be measured against a base year of 1990 (with exceptions for some countries with economies in transition). Cuts in three long-lived industrial gases – hydrofluorocarbons (HFCs), perfluorocarbons (PFCs), and sulphur hexafluoride (SF6) - can be measured against either a 1990 or 1995 baseline. (A major group of industrial gases, chlorofluorocarbons, or CFCs, are dealt with under the 1987 Montreal Protocol on Substances that Deplete the Ozone Layer.)
Source: The Kyoto Protocol Sheet 21, Climate Change Information Kit, United Nations Development Programme,

30. Additional Resources
Global Change Courses at the University of Michigan
Introduction to Global Change (AOSS 171/172)
In addition to the resources and web sites listed here the Global Change Course web site provides other useful materials.
From course web site:
“The University of Michigan's Global Change Project is a novel approach in undergraduate science and social science education. In three interdisciplinary, team-taught courses the topic of Global Change from physical and human perspectives are examined, and case studies are used to explore conditions for sustainability.
The courses are aimed at first and second year students who want to understand the historical and modern aspects of Global Change. These 4-credit courses include hands-on sections and carry NS and SS distribution credit.”