Introduction

Surface temperature measurements recorded daily at hundreds of locations for more than 100 years indicate that the Earth's surface has warmed by about 0.6ºC in the past century. This warming has been particularly strong during the last 20 years, and accompanied by retreating glaciers, thinning arctic ice, rising sea levels, lengthened growing seasons for some areas, and an earlier arrival of migratory birds. As a recent report from the US National Research Council states, "the warming trend in the global mean surface temperature observations during the past 20 years is undoubtedly real and is substantially greater than the average rate of warming in the 20th century." The majority of scientists around the world agree that global warming in the last 50 years is likely the result of increases in greenhouse gases. But how much of the temperature rise to date is the result of human activities is uncertain, since models do not adequately represent all the processes contributing to variability of the climate system. Nonetheless, projections of future warming suggest a global increase of 1.4ºC to 5.8ºC by 2100, which could mean further increases in sea level and changes in precipitation, including more frequent floods and droughts. Such change could have far-reaching and/or unpredictable environmental, social and economic consequences.

The Greenhouse Effect

The sun's radiation interacts with the surface of the earth in several ways. Some portion of this energy is reflected back into space by the earth's atmosphere, while another is dispersed and scattered in the atmosphere. Another portion penetrates through the earth's atmosphere to reach the surface of the earth. The radiation reaching the earth's surface is mostly absorbed, which results in surface warming. Much of this absorbed energy is eventually re-radiated in longer infrared wavelengths. As it leaves the earth, it once again interacts with the atmosphere. Some of this re-radiated energy escapes to space, but much of this re-radiated energy is reflected back to the earth's surface by the earth's atmosphere. This reflected energy results in a warming of the earth's surface.

The greenhouse gases responsible for this phenomenon, i.e. water (H₂O), nitrous oxide (N₂O), methane (CH₄), and carbon dioxide (CO₂) act like a greenhouse, trapping re-radiated energy. Without these gases, life on earth would not be possible, as the surface temperature of the earth would likely be about 60°F colder. Increasing the concentration of these gases in the atmosphere increases the atmosphere's ability to block the escape of infrared radiation. In other words, the earth's insulator gets thicker. If the concentration of greenhouse gases becomes too thick, it could have dramatic effects on the earth's climate. Climates suitable for human existence do not exist simply above some minimum threshold level of greenhouse gas concentration, but within a limited range of greenhouse gas concentrations that makes life as we know it possible.

While the concentrations of almost all greenhouse gases have increased since the industrial revolution, CO₂ has had the greatest effect. During the 1980s, humans released 5.5 billion tons of CO₂ into the atmosphere annually by burning fossil fuels (coal, oil, natural gas) for heat, transportation, and electricity. An additional 1.6 billion tons was released from human-induced changes in land-use, such as clearing land for agriculture, pastures, etc. Scientists are not certain where all of the 7.2 billion tons of atmospheric carbon goes. Ocean modelers find that the ocean takes up approximately 2 billion tons a year. Around 2 billion tons are taken up by a presently unidentified "sink" or reservoir of carbon. This leaves a remainder of 3.2 billion tons of CO₂, and global atmospheric measurements indicate that this amount is simply being added to existing concentrations already present in the atmosphere. This results in an increase of the atmospheric concentration of CO₂ at a rate of approximately 1.5 ppm (parts per million) per year and an overall increase of 30% since the beginning of the industrial revolution.

Human beings are causing the release of CO₂ and other greenhouse gases into the atmosphere at rates much faster than the earth can cycle them. Fossil fuels such as oil, coal, and natural gas, are formed through the compression of organic material for millions of years, and humans are burning billions of tons of these fuels annually. However, the CO₂ expelled into the atmosphere does not disappear immediately, but remains in the atmosphere for decades or centuries. This means that the CO₂ emitted into the atmosphere today will affect the earth's climate for several generations to come.

Despite the widespread recognition of this fact, worldwide emissions of fossil fuels continue to increase at a rate of about 1% per year (IPCC, 1995). Emissions will increase even further as the developing world moves towards greater industrialization. As of 1995 the industrialized world (the United States, Western Europe, Eastern Europe, and the Former Soviet Union) contributed more than 70% of the total world emissions. If use of fossil fuels continues to increase at present rates, by 2035 humans will annually be contributing 12 billion tons of CO₂ to the atmosphere, about 50% of which will be due to developed nations and about 50% of which will be due to developing nations. Almost all of the major greenhouse gases -- with the exception of chlorofluorocarbons (CFCs) -- have both natural and human-induced sources. For example, CO₂ is not only formed by the decay in plant matter, but also by the burning of coal, oil, natural gas, and wood. And atmospheric methane can be formed by growing rice, raising cattle, coal mining, using land-fills, and handling natural gas. Both CO₂ and methane are more abundant in the Earth's atmosphere now than at any time during the past 400,000 years. CO₂ is probably the single most important agent contributing to climate changes, while the other gases combined contribute to climate changes approximately equal to that of CO₂.

Intergovernmental Panel on Climate Change (IPCC) and the Third Assessment Report (TAR)

A leading scientific authority on climate change is the Intergovernmental Panel on Climate Change (IPCC), a joint project of the United Nations Environment Programme and the World Meteorological Organization established in 1988 to assess the scientific, technical and socio-economic information for understanding climate change. It does not carry out new research nor does it monitor climate-related data. It bases its assessment mainly on published and peer reviewed scientific technical literature. The IPCC has three working groups and a Task Force:

• Working Group I assesses the scientific aspects of the climate system and climate change.
• Working Group II addresses the vulnerability of socio-economic and natural systems to climate change, negative and positive consequences of climate change, and options for adapting to it.
• Working Group III assesses options for limiting greenhouse gas emissions and otherwise mitigating climate change.

The Task Force on National Greenhouse Gas Inventories oversees the National Greenhouse Gas Inventories Programme.

In 1990, the IPCC completed its First Assessment Report, which played an important role in establishing the Intergovernmental Negotiating Committee for a UN Framework Convention on Climate Change (UNFCCC) by the UN General Assembly. Its Second Assessment Report, Climate Change 1995, provided a key input to the negotiations, which led to the adoption of the Kyoto Protocol to the UNFCCC in 1997. The IPCC also prepares Special Reports and Technical Papers on topics where independent scientific information and advice are needed and it supports the UNFCCC through its work on methodologies for National Greenhouse Gas Inventories.

The Third Assessment Report (TAR), released in May 2001, confirmed the findings of the Second Assessment Report, providing new and stronger evidence of a warming world. A Fourth Assessment Report is currently being planned. The IPCC also produces shorter Technical Papers and Special Reports on specific issues at the request of the COP or the SBSTA. In addition, the IPCC carries out important work on improving methodologies for estimating and reporting greenhouse gas emissions.

COP 7

At COP-7 in November 2001, Parties considered the TAR entitled "Climate Change 2001" and adopted a decision expressing appreciation to the IPCC for its excellent work and encouraging Parties to make full use of the TAR. Parties were also invited to provide their views on the TAR and possible IPCC activities in support of the needs of the Convention and its Kyoto Protocol. It also requested the secretariat to organize a workshop to explore how the TAR can facilitate the work of the SBSTA and other convention bodies and prepare a report for SBSTA-16. The report of the workshop, held from April 4-6, 2002, in Bonn, Germany, presents the summary of the discussion, and identifies some action in relation to possible future work of the SBSTA.

SB-16

One of the most difficult discussions at SB-16 focused on the IPCC's TAR and the role it would play in deliberations under the UNFCCC. Many Parties emphasized the importance of disseminating the TAR’s findings and supported additional work on the historical responsibility for climate change. Others said the TAR justified further action on climate change and supported discussions on stronger emissions reductions. However, other countries said a dangerous level of greenhouse gases could not be determined given scientific uncertainties.

The conclusions adopted on the TAR note the three broad areas--scientific basis; impacts, adaptation and vulnerability; and mitigation--covered by the TAR, and agree that “in general it should be used routinely” for informing the deliberations of the COP and its subsidiary bodies. The conclusions also note significant progress in the TAR compared to the Second Assessment Report in addressing scientific, technical and socioeconomic aspects related to the UNFCCC’s “ultimate objective, principles, and general provisions.” They add, however, that many uncertainties exist and that further research is required, observing that there is “a wide range of opinions” on issues pertaining to the UNFCCC’s objective and provisions.

At COP-8, The SBSTA will consider the issue of research and systematic observation and a substantive discussion of research issues will likely take place under this agenda item. Future sessions of the SBSTA will consider impacts, vulnerability and adaptation to climate change and scientific, technical and socio-economic aspects of mitigation. For more information, see the UNFCCC Secretariat’s Issue Brief on Third Assessment Report of the Intergovernmental Panel on Climate Change.

Potential Impacts

Climate change will likely have significant impacts around the world. For instance, sea-level rise will compound pressures that coastal communities already face, including erosion, storms, and pressures from development. In arid and semi-arid regions, relatively modest changes in precipitation can have large impacts on already limited water supplies. Most projections of future impacts do not address what could happen if warming continues beyond 2100, which is inevitable if steps to reduce emissions are not taken, or if the rate of change accelerates. Even if greenhouse gas emissions are reduced, some further warming is unavoidable, in that the amount of CO₂ released into the atmosphere in the next 30 years is expected to double or triple. Global surface temperatures in 1999 set a new record for the period of instrumental measurements, according to the NASA Goddard Institute for Space Studies. The global temperature exceeded that of the previous record year, 1995, by about 0.2°C (0.4°F). In the near term, agriculture and forestry may benefit, but hotter and drier conditions increase the potential for crop distributions to change. Areas around the world already having water shortages or water quality problems will see these problems worsen.

In the latest report of IPCC's Working Group II, which addresses the vulnerability of socio-economic and natural systems to climate change, scientists predict glaciers and polar icecaps melting, countless species of animals, birds and plant life dying out, farmland turning to desert, coral reefs destroyed, and small island states submerged by the sea. The final report of Working Group II addresses, among others issues:

• Water Resources - the effects of climate change on water supplies, water demands, and flood and drought hazards;
• Agriculture and Food Supply - the effects of climate change on crop yields and food supply;
• Terrestrial Ecosystems - the effects of climate change on forest, grassland, desert, aquatic, and alpine ecosystems and their wildlife;
• Coastal Zones and Marine Ecosystems - the effects of climate change and sea level rise on coastal zones and marine ecosystems;
• Human Settlements, Energy and Industry - vulnerabilities of human settlements, energy and industry to climate change, including potential changes in extreme weather hazards;
• Insurance and Other Financial Services - trends in economic and insured losses from extreme climate events and vulnerabilities of the financial sector to climate change; and
• Human Health - the effects of climate change on human health, including changes in exposure to infectious diseases (e.g. malaria, Dengue) and death rates and illness associated with heat stress and cold weather.

The report addresses adaptation options for each of these areas, and includes reports on regional concerns, vulnerabilities and adaptive capacities in: Africa, Asia, Australia and New Zealand, Europe, Latin America, North America, Polar Regions (Arctic and Antarctic) and Small Island States. According to the report, ``projected climate changes during the 21st century have the potential to lead to future large-scale and possibly irreversible changes in Earth systems, resulting in impacts on continental and global scales.'' The Summary for Policymakers adds that "climate change in polar regions is expected to be among the greatest of any region on the Earth." Already, the extent and thickness of Arctic sea ice has decreased, permafrost has thawed and the distribution and abundance of species has been affected. The trends may continue even long after greenhouse gas emissions are stabilized, causing irreversible impact on ice sheets, global ocean circulation and sea levels.