Global Environmental Outlook
Climate change

Global carbon dioxide emissions   (Click image to enlarge) Source: CDIAC 1999

Global carbon dioxide emissions continue to mount. Average annual increase over the past decade has been 1.3 per cent or nearly 300 million tonnes a year

Annual global emissions of carbon dioxide from the burning of fossil fuels, cement manufacture and gas flaring reached a new high of nearly 23 900 million tonnes in 1996 (CDIAC 1999). This was some 400 million tonnes more than in 1995 and nearly four times the 1950 total. Only in some countries in Europe and Central Asia has there been a significant drop in emissions during the past decade, mainly as a result of the economic crises in Eastern and Central Europe. Atmospheric concentrations of CO2 in 1997 reached more than 360 parts per million (ppm), the highest level in 160 000 years (Keeling and Whorf 1998).

In assessing the possible impact of rising atmospheric concentrations of CO2 and other greenhouse gases (GHGs), the WMO/UNEP Intergovernmental Panel on Climate Change (IPCC) concluded in its 1995 report that 'the balance of evidence suggests that there is a discernible human influence on global climate' (IPCC 1996a). Recent research suggests that climate change would have complex impacts on the global environment. The IPCC mid-range scenario projects an increase in global mean temperature of 2.0 °C, within a range of 1.0 to 3.5 °C, by the year 2100, the largest warming in the past 10 000 years. Average sea level is projected to rise by about 50 cm, within a range of 15 to 95 cm, by the year 2100. A 50-cm rise in sea level would lead to the displacement of millions of people in low-lying delta areas and a number of small island states could be wiped out (IPCC 1996b).

Carbon dioxide emissions per capita   (Click image to enlarge) Source: compiled by UNEP GRID Geneva from CDIAC 1998 and WRI, UNEP, UNDP and WB 1998

In a warmer world there would be higher agricultural production in the high latitudes of the northern and southern hemispheres but reduced production in the tropics and sub-tropics where there is already food deficiency. The species composition of forests and other terrestrial ecosystems is likely to change - entire forest types may disappear. Although forest productivity could increase, the standing biomass of forests may not increase because of more frequent outbreaks and extended ranges of pests and pathogens, and increasing frequency and intensity of fires. Climate change could influence lakes, streams and wetlands through altered water temperatures, flow regimes and water levels. Increases in the variability of water flow, particularly the frequency and duration of large floods and droughts, would tend to reduce water quality and biological productivity and habitat in freshwater ecosystems (IPCC 1998).

In addition to these environmental effects, climate change may have direct and indirect health impacts. Greater frequency and severity of heat waves, and changes in agriculture and food production, could affect nutritional status and vector distributions (Lindsey and Birley 1996). The expansion of warmer areas may increase and extend the ranges of mosquito and other vector populations, affecting the incidence of vector-borne diseases and re-introducing malaria to Europe (Bradley 1996).

Despite the improved ability of climate models to simulate observed trends, there are still considerable uncertainties in key factors, including the magnitude and patterns of natural variability, the effects of human influence, and the rates of carbon sequestration. There are also new questions to be resolved. For example, is the observed increasing magnitude of El Niño events during recent decades related to human-induced climate change? To what extent do reductions in sulphur emissions, required to reduce the acid rain problem, offset warming by greenhouse gases by reducing sulphate aerosols in the atmosphere?

At what level should greenhouse gas concentrations be stabilized?   According to the IPCC (1996a), stabilization of CO2 at 450 ppm and other GHGs at levels somewhat above the present concentrations will lead to an increase of the global mean temperature by 1.5-4.0 °C, and stabilization at 550 ppm CO2 will lead to an increase of 2.0-5.5 °C. Carbon cycle models show that immediate stabilization of the atmospheric CO2 concentration at its present level of about 360 ppm could be achieved only if emissions are immediately reduced by 50-70 per cent and further reduced thereafter. If stabilization at below 550 ppm were to be aimed for, the annual mean per capita CO2 emission for the whole world would need to be approximately 5 tonnes during the next century and below 3 tonnes by 2100. Current levels are about 4 tonnes/capita as a world average, with a maximum emission of nearly 20 tonnes/capita in North America and a minimum of less than 1 tonne/capita in many parts of Africa.

A key factor in assessing the consequences of climate change is the inertia of the climate system: climate change occurs slowly and once a significant change has occurred it will not disappear quickly. Hence, even if a stabilization of greenhouse gas concentrations is achieved (see box), warming could continue for several decades, and sea levels could continue to rise for centuries.

Future GHG emissions will be a function of global energy demand, and the rate of development and introduction of carbon-free and low carbon energy technologies. Several variables make predictions of future emissions uncertain: economic growth rates, energy prices, the adoption of effective energy policies and the development of efficient industrial technologies. Meeting the targets for emission reductions agreed at Kyoto, itself a formidable challenge for some countries, is only a first step in bringing under control what is generally agreed to be the most critical environmental problem that the world faces. But even meeting all the targets agreed at Kyoto will have an insignificant effect on the stabilization levels of carbon dioxide in the atmosphere.