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Common Questions about Climate Change
Published in 1997 by the United Nations Environment Programme - World Meteorological Organization




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Why Should a Few Degrees of Warming Be a Cause for Concern?

The most recent IPCC scientific assessment of climate change estimated that the globally averaged surface temperature will increase by 1 to 3.5°C (about 2 to 6°F) by the year 2100, with an associated rise in sea level of 15 to 95 cm (about 6 to 37 inches). These changes may lead to a number of potentially serious consequences. For example, mid- and high-latitude regions, such as much of the United States, Europe, and Asia, could experience an increase in the incidence of heat waves, floods, and droughts as the global climate changes. The impacts of such extreme events on human welfare as well as natural ecosystems could be significant.

Climate change is likely to have wide-ranging and mostly adverse impacts on human health. The projected increase in the duration and frequency of heat waves is expected to increase mortality rates as a result of heat stress, especially where air conditioning is not available. To a lesser extent, increases in winter temperatures in high latitudes could lead to decreases in mortality rates. Climate change is also expected to lead to increases in the potential transmission of many infectious diseases, including malaria, dengue, and yellow fever, extending the range of organisms such as insects that carry these diseases into the temperate zone, including parts of the United States, Europe, and Asia. For example, projections indicate that the zone of potential malaria transmission, in response to global surface temperature increases at the top of the projected range, may enlarge from an area containing about 45% of the world population to about 60% by the end of the twenty-first century, resulting in 50-80 million additional cases of malaria per year (Figure 10.1).

Figure 10.1

The figures show model-calculated potential malaria risk areas for the most dangerous type of malaria (P. falciparum). Panel a) shows the average annual 'epidemic potential' (EP), a measure of risk of contracting malaria, for baseline climate conditions (1931-1980) and panel b) shows EP for a mean global temperature increase of about 1.2°C. This temperature increase is projected to occur somewhere in the time frame of 2040 to 2100. Both the magnitude of risk in current transmission areas and the area of potential transmission are projected to increase.









It may be possible for global agricultural production to keep pace with increasing demand over the next 50-100 years if adequate adaptations are made, but there are likely to be difficulties in some regions. This conclusion takes into account the beneficial effects of carbon dioxide fertilization, i.e., given sufficient water and nutrients, plant growth will be enhanced by an increased concentration of carbon dioxide in the atmosphere. Changes in the spread and abundance of agricultural pests and the effects of climate variability were not reflected in this assessment. Regional changes in crop yields and productivity are expected to occur in response to climate change. There is likely to be an increased risk of famine, particularly in subtropical and tropical semi-arid and arid locations.

With 50-70% of the global human population currently living in coastal areas, future sea level rises, alterations in storm patterns, and higher storm surges could have significant effects. About 46 million people are currently at risk by flooding in coastal areas as a result of storm surges. In the absence of measures to adapt, even with current populations, a 50 cm (about 20 inches) sea level rise would increase the number of people whose land will be at risk from serious flooding or permanent inundation to about 92 million, while a 100 cm (about 40 inches) rise would increase this number to 118 million. If expected population growth is incorporated into the projections, these estimates increase substantially.

Other projected changes include a disappearance of between one- third and one-half of existing mountain glacier mass by 2100. Alpine glaciers are already observed to be in rapid retreat and many cities between 30°N and 30°S depend on these natural reservoirs for their water supply. For example, in Lima, Peru, the entire water supply for 10 million people depends on the summer melt from a glacier that is now in rapid retreat, for reasons that may or may not be related to global climate change. In the future, climate change could also lead to shifts in river flow and water supply, with serious implications for human settlements and agriculture.

Climate change is also likely to affect human infrastructure, including transportation, energy demand, human settlements (especially in developing countries), the property insurance industry, and tourism.

Go to "Why Can't Ecosystems Just Adapt?"

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