Introduction:One of the major challenges facing humankind is to provide an equitable standard of living for this and future generations: adequate food, water and energy, safe shelter and a healthy environment (e.g., clean air and water).
Unfortunately, human-induced climate change, as well as other global environmental issues such as land degradation, loss of biological diversity and stratospheric ozone depletion, threatens our ability to meet these basic human needs.
The overwhelming majority of scientific experts, whilst recognizing that scientific uncertainties exist, nonetheless believe that human-induced climate change is inevitable.
Indeed, during the last few years, many parts of the world have suffered major heat waves, floods, droughts, fires and extreme weather events leading to significant economic losses and loss of life.
While individual events cannot be directly linked to human-induced climate change, the frequency and magnitude of these types of events are predicted to increase in a warmer world.
The question is not whether climate will change in response to human activities, but rather how much (magnitude), how fast (the rate of change) and where (regional patterns).
It is also clear that climate change will, in many parts of the world, adversely affect socio-economic sectors, including water resources, agriculture, forestry, fisheries and human settlements, ecological systems (particularly forests and coral reefs), and human health (particularly diseases spread by insects), with developing countries being the most vulnerable.
The good news is, however, that the majority of experts believe that significant reductions in net greenhouse gas emissions are technically feasible due to an extensive array of technologies and policy measures in the energy supply, energy demand and agricultural and forestry sectors.
In addition, the projected adverse effects of climate change on socio-economic and ecological systems can, to some degree, be reduced through proactive adaptation measures.
These are the fundamental conclusions, taken from already approved/accepted IPCC assessments, of a careful and objective analysis of all relevant scientific, technical and economic information by thousands of experts from the appropriate fields of science from academia, governments, industry and environmental organizations from around the world.
Decision-makers should realize that once carbon dioxide, the major anthropogenic greenhouse gas, is emitted into the atmosphere, it stays in the atmosphere for more than a century.
This means that if policy formulation waits until all scientific uncertainties are resolved, and carbon dioxide and other greenhouse gases are responsible for changing the Earth’s climate as projected by all climate models, the time to reverse the human-induced changes in climate and the resulting environmental damages, would not be years or decades, but centuries to millennia, even if all emissions of greenhouse gases were terminated, which is clearly not practical.
This presentation, which briefly describes the current state of understanding of the Earth's climate system and the influence of human activities; the vulnerability of human health, ecological systems, and socio-economic sectors to climate change; and approaches to mitigate climate change by reducing emissions and enhancing sinks, is based on accepted and approved conclusions from the IPCC Second Assessment Report (SAR) and a series of Technical Papers and Special Reports (e.g., the Special Reports on Emissions Scenarios; Land-Use, Land-Use Change and Forestry; and Methodological and Technological Issues in Technology Transfer) and, supplemented by recent information that is being assessed in the draft IPCC Third Assessment Report (TAR).
The Working Group I and II reports of the TAR have already been distributed to governments for final review, while the Working Group III report will be distributed to governments for final review within a couple of weeks.
The Working Group Reports will be approved/accepted at a series of plenary meetings between January and March, 2001. The Synthesis Report of the TAR, which addresses a series of policy-relevant questions, will be approved/adopted in September 2001.
None of the conclusions presented in this report are taken from the TAR, but are consistent with the draft conclusions, which are subject to change until final government approval and acceptance early next year.
Part I: The Earth's Climate System: The Influence of Human -Activities:
The Earth’s climate is changing: The Earth's climate has been relatively stable since the last ice age (global temperature changes of less than 1 degree Centigrade over a century during the past 10,000 years).
During this time modern society has evolved, and, in many cases, successfully adapted to the prevailing local climate and its natural variability. However, the Earth's climate is now changing.
The Earth's surface temperature this century is clearly warmer than any other century during the last thousand years, i.e., the climate of the 20th century is clearly atypical .
The Earth has warmed by between 0.4 and 0.8 degree centigrade over the last century, with land areas warming more than the oceans , and with the last two decades being the hottest this century .
Indeed, the three warmest years during the last one hundred years have all occurred in the 1990s and the twelve warmest years during the last one hundred years have all occurred since 1983.
In addition, there is evidence that precipitation patterns are changing, that sea level is increasing, that glaciers are retreating world-wide, that Arctic sea ice is thinning, and that the incidence of extreme weather events is increasing in some parts of the world.
The atmospheric concentrations of greenhouse gases are changing due to human activities: The atmospheric concentrations of greenhouse gases have increased because of human activities, primarily due to the combustion of fossil fuels (coal, oil and gas), deforestation and agricultural practices, since the beginning of the pre-industrial era around 1750: carbon dioxide by nearly 30 percent methane by more than a factor of two (figure 5), and nitrous oxide by about 15 percent.
Their concentrations are higher now than at any time during the last 420,000 years, the period for which there are reliable ice-core data, and probably significantly longer.
In addition, the combustion of fossil fuels has also caused the atmospheric concentrations of sulfate aerosols to have increased.
Greenhouse gases tend to warm the atmosphere and, in some regions, primarily in the Northern Hemisphere, aerosols tend to cool the atmosphere.
The weight of scientific evidence suggests that the observed changes in the Earth’s climate are, at least in part, due to human activities: Climate models that take into account the observed increases in the atmospheric concentrations of greenhouse gases, sulfate aerosols and the observed decrease in ozone in the lower stratosphere, in conjunction with natural changes in volcanic activity and in solar activity, simulate the observed changes in annual mean global surface temperature quite well.
This, and our basic scientific understanding of the greenhouse effect, suggests that human activities are implicated in the observed changes in the Earth's climate. In fact, the observed changes in climate, especially the increased temperatures since the around 1970, cannot be explained by changes in solar activity and volcanic emissions alone as shown in figure 6a.
Where-as figure 6b shows that the observed changes in temperature, especially those since around 1970, can be simulated quite well by a climate model that takes into account human-induced changes in greenhouse gases and aerosols.
Not only is there evidence of a change in climate at the global level consistent with climate models, but there is observational evidence of regional changes in climate that are consistent with those predicted by climate models.
For example, climate models predict an increase in intense rainfall events over the United States of America consistent with the observations.
Emissions of greenhouse gases are projected to increase in the future due to human activities: Future emissions of greenhouse gases and the sulfate aerosol precursor, sulfur dioxide, are sensitive to the evolution of governance structures world-wide, changes in population and economic growth, the rate of diffusion of new technologies into the market place, energy production and consumption patterns, land-use practices, energy intensity, and the price and availability of energy.
While different development paths can result in quite different greenhouse gas emissions, most projections suggest that greenhouse gas concentrations will increase significantly during the next century in the absence of policies specifically designed to address the issue of climate change (IPCC Special Report on Emission Scenarios - SRES).
Some projections suggest that an initial increase in emissions could be followed by a decrease after several decades if there was a major transition in the worlds energy system due to the pursuit of a range of sustainable development goals.
The SRES reported, for example, carbon dioxide emissions from the combustion of fossil fuels are projected to range from about 5 to 35 GtC per year in the year 2100: compared to current emissions of about 6.3 GtC per year.
Such a range of emissions would mean that the atmospheric concentration of carbon dioxide would increase from today’s level of about 365 ppmv (parts per million by volume) to between about 550 and 1000 ppmv by 2100.
Latest projections of carbon dioxide emissions are consistent with earlier projections, but projected sulfur dioxide emissions are much lower: While the SRES reported similar projected energy emissions for carbon dioxide to the 1992 projections, it differed in one important aspect from the 1992 projections, in-so-far-as the projected emissions of sulfur dioxide are much lower, because of structural changes in the energy system and because of concerns about local and regional air pollution (i.e., acid deposition).
This has important implications for future projections of temperature changes, because sulfur dioxide emissions lead to the formation of sulfate aerosols in the atmosphere, which as stated earlier can partially offset the warming effect of the greenhouse gases.
Global mean surface temperatures are projected to increase by about 1.5 to 6.0oC by 2100.
Based on the range of climate sensitivities and the plausible ranges of greenhouse gas and sulfur dioxide emissions reported in the SRES, a number of climate models project that the global mean surface temperature could increase by about 1.5 to 6.0oC by 2100.
This range compares to that reported in the IPCC SAR of 1.0 – 3.5 oC. The revised higher estimates of projected warming arise because the lower projected emissions of sulfur dioxide result in less offset of the warming effect of the greenhouse gases.
These projected global-average temperature changes would be greater than recent natural fluctuations and would also occur at a rate significantly faster than observed changes over the last 10,000 years.
Temperature changes are expected to differ by region with high latitudes projected to warm more than the global average, and during the next century land areas are projected to warm more than the oceans, and the northern hemisphere is projected to warm more than the southern hemisphere .
However, the reliability of regional scale predictions is still low.
Seasonal and latitudinal shifts in precipitation with arid and semi-arid areas becoming drier: Model calculations show that evaporation will be enhanced as the climate warms, and that there will be an increase in global mean precipitation and an increase in the frequency of intense rainfall.
However, not all land regions will experience an increase in precipitation, and even those land regions with increased precipitation may experience decreases in run-off and soil moisture, because of enhanced evaporation.
Seasonal shifts in precipitation are also projected. In general, precipitation is projected to increase at high latitudes in winter, while run-off and soil moisture is projected to decrease in some mid-latitude continental regions during summer.
The arid and semi-arid areas in Southern and Northern Africa, Southern Europe, the Middle East, parts of Latin America and Australia are expected to become drier.
Sea level projected to rise about 15-95 cms by 2100: Associated with changes in temperature, sea level is projected to increase by about 15 - 95 cm by 2100 (IPCC SAR), caused primarily by thermal expansion of the oceans and the melting of glaciers.
The revised temperature projections are not likely to result in significantly different projections of changes in sea level over the next century because of the large thermal inertia of the oceans, i.e., the temperature of the oceans responds very slowly to a change in greenhouse gas concentrations.
However, recent more advanced models are tending to project somewhat lower values of sea level rise.
It should be noted that even when the atmospheric concentrations of greenhouse gases are stabilized, temperatures will continue to increase by another 30-50 percent over several decades, sea level will continue to rise over hundreds of years and ice sheets will continue to adjust for thousands of years.
Sea level increases by more than a factor of 5 over hundreds of years after the atmospheric concentration of carbon dioxide is stabilized.
The frequency and magnitude of ENSO events may increase: Long-term, large-scale, human-induced changes in climate are likely to interact with natural climate variability on time-scales of days to decades (e.g., the El Nino-Southern Oscillation (ENSO) phenomena).
Recent trends in the increased frequency and magnitude of ENSO events (figure 14), which lead to severe floods and droughts in regions of the tropics and sub-tropics, are projected to continue in many climate models.
Incidence of some extreme events projected to increase: While the incidence of extreme temperature events, floods, droughts, soil moisture deficits, fires and pest outbreaks is expected to increase in some regions, it is unclear whether there will be changes in the frequency and intensity of extreme weather events such as tropical storms, cyclones, and tornadoes.
However, even if there is no increase in the frequency and intensity of extreme weather events there may be shifts in their geographic location to places less prepared and more vulnerable to such events.
Part II: The Vulnerability of Water Resources, Agriculture, Natural Ecosystems, and Human Health to Climate Change and Sea Level Rise:
The IPCC has assessed (IPCC SAR and the IPCC Special Report on the Regional Impacts of Climate Change: An Assessment of Vulnerability) and is continuing to assess (IPCC TAR) the potential consequences of changes in climate for socio-economic sectors, ecological systems and human health for different regions of the world at the regional and global scale.
Because of uncertainties associated with regional projections of climate change, the IPCC assesses the vulnerability of these natural and social systems to changes in climate, rather than attempting to provide quantitative predictions of the impacts of climate change at the regional level.
Vulnerability is defined as the extent to which a natural or social system is susceptible to sustaining damage from climate change, and is a function of the magnitude of climate change, the sensitivity of the system to changes in climate and the ability to adapt the system to changes in climate. Hence, a highly vulnerable system is one that is highly sensitive to modest changes in climate and one for which the ability to adapt is severely constrained.
Most impact studies have assessed how systems would respond to a climate change resulting from an arbitrary doubling of atmospheric carbon dioxide concentrations.
Very few studies have considered the dynamic responses to steadily increasing greenhouse gas concentrations; fewer yet have been able to examine the consequences of increases beyond a doubling of greenhouse gas concentrations or to assess the implications of multiple stress factors.
Thus there is a need for the increased development and use of time-dependent integrated assessment models.
The IPCC SAR concluded that human health, terrestrial and aquatic ecological systems, and socioeconomic systems (e.g., agriculture, forestry, fisheries, water resources, and human settlements), which are all vital to human development and well-being, are all vulnerable to changes in climate, including the magnitude and rate of climate change, as well as to changes in climate variability.
Whereas many regions are likely to experience the adverse effects of climate change—some of which are potentially irreversible—some effects of climate change are likely to be beneficial. Hence, different segments of society can expect to confront a variety of changes and the need to adapt to them.
By: Robert T. Watson
Sixth Conference of Parties - to the United Nations Framework Convention on Climate Change November 13, 2000
Source: www.ipcc.ch.
© 2001 Mena Report (www.menareport.com)
