|
Scope of the Assessment
This report has been prepared at the request of the Conference of the Parties
to the United Nations Framework Convention on Climate Change (UNFCCC) and its
subsidiary bodies (specifically, the Subsidiary Body for Scientific and Technological
Advice-SBSTA). The special report provides, on a regional basis, a review of
state-of-the-art information on the vulnerability to potential changes in climate
of ecological systems, socioeconomic sectors (including agriculture, fisheries,
water resources, and human settlements), and human health. The report reviews
the sensitivity of these systems as well as options for adaptation. Though this
report draws heavily upon the sectoral impact assessments of the Second Assessment
Report (SAR), it also draws upon more recent peer-reviewed literature (inter
alia, country studies programs).
Nature of the Issue
Human activities (primarily the burning of fossil fuels and changes in land
use and land cover) are increasing the atmospheric concentrations of greenhouse
gases, which alter radiative balances and tend to warm the atmosphere, and,
in some regions, aerosols-which have an opposite effect on radiative balances
and tend to cool the atmosphere. At present, in some locations primarily in
the Northern Hemisphere, the cooling effects of aerosols can be large enough
to more than offset the warming due to greenhouse gases. Since aerosols do not
remain in the atmosphere for long periods and global emissions of their precursors
are not projected to increase substantially, aerosols will not offset the global
long-term effects of greenhouse gases, which are long-lived. Aerosols can have
important consequences for continental-scale patterns of climate change.
These changes in greenhouse gases and aerosols, taken together, are projected
to lead to regional and global changes in temperature, precipitation, and other
climate variables-resulting in global changes in soil moisture, an increase
in global mean sea level, and prospects for more severe extreme high-temperature
events, floods, and droughts in some places. Based on the range of sensitivities
of climate to changes in the atmospheric concentrations of greenhouse gases
(IPCC 1996, WG I) and plausible changes in emissions of greenhouse gases and
aerosols (IS92a-f, scenarios that assume no climate policies), climate models
project that the mean annual global surface temperature will increase by 1-3.5°C
by 2100, that global mean sea level will rise by 15-95 cm, and that changes
in the spatial and temporal patterns of precipitation would occur. The average
rate of warming probably would be greater than any seen in the past 10,000 years,
although the actual annual to decadal rate would include considerable natural
variability, and regional changes could differ substantially from the global
mean value. These long-term, large-scale, human-induced changes will interact
with natural variability on time scales of days to decades [e.g., the El Niņo-Southern
Oscillation (ENSO) phenomenon] and thus influence social and economic well-being.
Possible local climate effects which are due to unexpected events like a climate
change-induced change of flow pattern of marine water streams like the Gulf
Stream have not been considered, because such changes cannot be predicted with
confidence at present.
Scientific studies show that human health, ecological systems, and socioeconomic
sectors (e.g., hydrology and water resources, food and fiber production, coastal
systems, and human settlements), all of which are vital to sustainable development,
are sensitive to changes in climate-including both the magnitude and rate of
climate change-as well as to changes in climate variability. Whereas many regions
are likely to experience adverse effects of climate change-some of which are
potentially irreversible-some effects of climate change are likely to be beneficial.
Climate change represents an important additional stress on those systems already
affected by increasing resource demands, unsustainable management practices,
and pollution, which in many cases may be equal to or greater than those of
climate change. These stresses will interact in different ways across regions
but can be expected to reduce the ability of some environmental systems to provide,
on a sustained basis, key goods and services needed for successful economic
and social development, including adequate food, clean air and water, energy,
safe shelter, low levels of disease, and employment opportunities. Climate change
also will take place in the context of economic development, which may make
some groups or countries less vulnerable to climate change-for example, by increasing
the resources available for adaptation; those that experience low rates of growth,
rapid increases in population, and ecological degradation may become increasingly
vulnerable to potential changes.
|