Climate Change 2001:
Synthesis Report
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Observed changes in regional climate over the past 50 years have affected biological and hydrological systems in many parts of the world (see Table 2-1).

2.21 There has been a discernible impact of regional climate change, particularly increases in temperature, on biological systems in the 20th century. In many parts of the world the observed changes in these systems3, either anthropogenic or natural, are coherent across diverse localities and are consistent in direction with the expected effects of regional changes in temperature. The probability that the observed changes in the expected direction (with no reference to magnitude) could occur by chance alone is negligible. Such systems include, for example, species distributions, population sizes, and the timing of reproduction or migration events. These observations implicate regional climate change as a prominent contributing causal factor. There have been observed changes in the types (e.g., fires, droughts, blowdowns), intensity, and frequency of disturbances that are affected by regional climatic change (either anthropogenic or natural) and land-use practices, and they in turn affect the productivity of and species composition within an ecosystem, particularly at high latitudes and high altitudes. Frequency of pests and disease outbreaks have also changed, especially in forested systems, and can be linked to changes in climate. In some regions of Africa, the combination of regional climate changes (Sahelian drought) and anthropogenic stresses has led to decreased cereal crop production since the year 1970. There are some positive aspects of warming: For example, the growing season across Europe has lengthened by about 11 days from the years 1959 to 1993, and energy consumption for heating in winter has decreased.

WGII TAR Sections 5.4, 5.6.2,, 11.2,, &, & WGII TAR Figure SPM-1
2.22 Coral reefs are adversely affected by rising sea surface temperatures. Increasing sea surface temperatures have been recorded in much of the tropical oceans over the past several decades. Many corals have undergone major, although often partially reversible, bleaching episodes when sea surface temperatures rise by 1°C in any one season, and extensive mortality occurs for a 3°C rise. This typically occurs during El Niño events and is exacerbated by rising sea surface temperatures. These bleaching events are often associated with other stresses such as pollution.

WGI TAR Section & WGII TAR Sections 6.4.5 &
2.23 Changes in marine systems, particularly fish populations, have been linked to large-scale climate oscillations. The El Niño affects fisheries off the coasts of South America and Africa and the decadal oscillations in the Pacific are linked to decline of fisheries off the west coast of North America.

WGI TAR Section 2.6.3 & WGII TAR Sections, 14.1.3, &
2.24 Changes in stream flow, floods, and droughts have been observed. Evidence of regional climate change impacts on elements of the hydrological cycle suggest that warmer temperatures lead to intensification of the hydrological cycle. Peak stream flow has shifted back from spring to late winter in large parts of eastern Europe, European Russia, and North America in the last decades. The increasing frequency of droughts and floods in some areas is related to variations in climate -- for example, droughts in Sahel and in northeast and southern Brazil, and floods in Colombia and northwest Peru. WGI TAR Section, WGII TAR SPM, WGII TAR Sections 4.3.6,, 14.3, &, & WGII TAR Table 4-1

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