- The Earth's global mean surface temperature has warmed by about half a degree Centigrade over the last 100 years.
- The six warmest years this century have occurred since 1990, and eight of the next ten warmest have occurred since 1980.
- The amount and spatial and temporal patterns of precipitation are changing.
- Average sea level has increased by I 5-25 centimeters during the last 100 years.
- Glaciers are retreating worldwide.
Underlying causes of change
- Human activities, primarily energy-use and land-use practices, are increasing the atmospheric concentrations of greenhouse gases
and, in same regions, aerosols.
- Greenhouse gases warm the atmosphere, while aerosols tend to cool the atmosphere.
- The balance of scientific evidence suggests a discernible human influence on the Earth's climate.
Projected impact of human activities on the climate system
- Without globally coordinated policies to specifically address human-Induced climate change, the concentrations of greenhouse
gases in the atmosphere are projected to increase significantly. The atmospheric concentration of carbon dioxide is projected to
increase from 360 parts per million by volume (ppmv) today to between 500 and 900 ppmv in 2100, depending on population and
economic growth rates, energy prices, and the development and deployment of new technologies.
- Global mean surface temperatures are projected to increase by between I.0 and 3.5 degrees Centigrade by 2 I 00, a rate faster
than anything observed during the last I 0,000 years.
- Sea levels are projected to rise by l5-95 centimeters by 2100.
- Global warming caused by increases in the atmospheric concentrations of greenhouse gases can only be reversed very slowly
because of the century-scale atmospheric residence times of the gases and the large thermal inertia of the oceans.
Social and economic consequences of projected changes
- Projected changes in climate may result in: adverse effects on human health, in particular an increase in heat-stress mortality and
vector-borne diseases, with potentially tens of millions of additional cases of malaria per year; changes in the boundaries, structure,
and functioning of ecological systems, especially forests where there could be a near-term die back and a shift in boundaries of
between I 50 and 650 kilometers polewards; a decrease in agricultural production in the tropics and subtropics, even if total global
food production does not drop; less predictable availability of freshwater; and the displacement of tens of millions of people from
small island states and low lying deltaic areas, if sea levels increase by one meter
- Developing countries will be particularly vulnerable to the impacts of climate change because of their limited institutional and
- The cost of damage associated with a climate change caused by a doubling of atmospheric carbon dioxide has been estimated to lie
between 1.5 and 2.0 percent of world GDP, with damages in developing countries in the range of 2-9 percent of GDP.
Technologies, policies, and measures to mitigate the projected changes in climate
- A range of cost-effective technologies and policies can be used now in both developed and developing countries to markedly
reduce the emissions of greenhouse gases from the energy supply (more efficient production; fuel switching, e.g., coal to gas;
nuclear power; renewable energies, e.g., solar, wind, modern biomass, hydroelectric; and carbon sequestration) and energy de-
mand sectors (more efficient buildings, transportation, and industry sectors), as well as changes in land management, including
forestry and agricultural practices.
- Policy measures to accelerate technology development, diffusion, and transfer are available, but need wider application if emis-
sions reductions are to be achieved.
- By the year 2100, the world's commercial energy system will be replaced at least twice, providing opportunities to use new,
heter-performing technologies over coming years without the premature retirement of capital stock.
Status of international agreements
- The Framework Convention on Climate Change (FCCC) was signed at the l 992 Earth Summit in Rio, and has since been ratified
by 164 countries. The aim of Annex I countries (OECD and the FSU) was to limit their emissions of greenhouse gases to their
1990 level in the year 2000.
- In December 1997 industrialized countries agreed to reduce their emissions of greenheuse gases by an average of 5.2 percent
during the period 2008-20 I 2 relative to l990 (Kyoto Protocol).
"Protecting Our Planet, Securing Our Future" UNEP / U.S. NASA / World Bank, 1997