REPORTS - ASSESSMENT REPORTS
Synthesis Report - Question 2

Climate Change 2001: Synthesis Report


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2.16

Changes have also occurred in other important aspects of climate (see Table 2-1).

 
2.17 Over the 20th century there has been a consistent, large-scale warming of both the land and ocean surface, with largest increases in temperature over the mid- and high latitudes of northern continents. The warming of land surface faster than ocean surface from the years 1976 to 2000 (see Figure 2-6b) is consistent both with the observed changes in natural climate variations, such as the North Atlantic and Arctic Oscillations, and with the modeled pattern of greenhouse gas warming. As described below, statistically significant associations between regional warming and observed changes in biological systems have been documented in freshwater, terrestrial, and marine environments on all continents.

WGI TAR Sections 2.2.2, 2.6.3, & 2.6.5, & WGII TAR Section 6.3
2.18 Warm episodes of the El Niño Southern Oscillation (ENSO) phenomenon have been more frequent, persistent, and intense since the mid-1970s, compared with the previous 100 years. ENSO consistently affects regional variations of precipitation and temperature over much of the tropics, subtropics, and some mid-latitude areas. It is not obvious from models, however, that a warmer world would have a greater frequency of occurrence of El Niño events.

WGI TAR Section 2.6.2
2.19 Some important aspects of climate appear not to have changed. A few areas of the globe have not warmed in recent decades, mainly over some parts of the Southern Hemisphere oceans and parts of Antarctica (see Figure 2-6b). Antarctic sea-ice extent has stayed almost stable or even increased since 1978, the period of reliable satellite measurements. Current analyses are unable to draw conclusions about the likelihood of changes in the frequency of tornadoes, thunder days, or hail events for the limited regions that have been studied. In addition, insufficient data and conflicting analyses prevent an assessment of changes in intensities of tropical and extra-tropical cyclones and severe local storm activity in the mid-latitudes.

WGI TAR Sections 2.2.2, 2.2.5, & 2.7.3
Figure 2-5: A limited number of sites in Europe have nearly continuous records of sea level spanning 300 years and show the greatest rise in sea level over the 20th century. Records shown from Amsterdam, The Netherlands, Brest, France, and Swinoujscie, Poland, as well as other sites, confirm the accelerated rise in sea level over the 20th century as compared to the 19th.

WGI TAR Figure 11-7
Figure 2-6a: Precipitation during the 20th century has on average increased over continents outside the tropics but decreased in the desert regions of Africa and South America. While the record shows an overall increase consistent with warmer temperatures and more atmospheric moisture, trends in precipitation vary greatly from region to region and are only available over the 20th century for some continental regions. Over this period, there were relatively small long-term trends in land areas experiencing severe drought or severe wetness, but in many regions these changes are dominated by inter-decadal and multi-decadal climate variability that has no trends evident over the 20th century.

WGI TAR Figure 2-25
Figure 2-6b: A consistent, large-scale warming of both the land and ocean surface occurred over the last quarter of the 20th century, with largest temperature increases over the mid- and high latitudes of North America, Europe, and Asia. Large regions of cooling occurred only in parts of the Pacific and Southern Oceans and Antarctica. The warming of land faster than ocean surface is consistent both with the observed changes in natural climate variations such as the North Atlantic and Arctic Oscillations and with the modeled pattern of greenhouse-gas warming. As described in the text, warming in some regions is linked with observed changes in biological systems on all continents.
WGI TAR Figure 2-9d

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