| Table 2-1: 20th
century changes in the Earth's atmosphere, climate, and biophysical
system.a |
| Indicator |
Observed Changes |
| Concentration
indicators |
|
| Atmospheric concentration of CO2 |
280 ppm for the period 1000-1750 tO368
ppm in year 2000 (31±4% increase). [WGI
TAR Chapter 3] |
| Terrestrial biospheric CO2 exchange |
Cumulative source of about 30 Gt C between the years
1800 and 2000; but during the 1990s, a net sink of about 14±7
Gt C. [ WG1 TAR Chapter
3 & SRLULUCF] |
| Atmospheric concentration of CH4 |
700 ppb for the period 1000-1750 to 1,750 ppb in year
2000 (151±25% increase). [WGI
TAR Chapter 4] |
| Atmospheric concentration of N2O |
270 ppb for the period 1000-1750 tO316
ppb in year 2000 (17±5% increase). [WGI
TAR Chapter 4] |
| Tropospheric concentration of O3 |
Increased by 35±15% from the years 1750 to
2000, varies with region. [WGI
TAR Chapter 4] |
| Stratospheric concentration of O3 |
Decreased over the years 1970 to 2000, varies with
altitude and latitude. [ WGI
TAR Chapters 4 & 6] |
| Atmospheric concentrations of HFCs, PFCs, and SF6 |
Increased globally over the last 50 years. [WGI
TAR Chapter 4] |
| Weather indicators |
|
| Global mean surface temperature |
Increased by 0.6±0.2°C over the 20th century;
land areas warmed more than the oceans (very likely). [WGI
TAR Section 2.2.2.3] |
Northern Hemisphere surface
temperature |
Increased over the 20th century greater than during
any other century in the last 1,000 years; 1990s warmest decade of
the millennium (likely). [WGI
TAR Chapter 2 ES & Section
2.3.2.2] |
| Diurnal surface temperature range |
Decreased over the years 1950 to 2000 over land: nighttime
minimum temperatures increased at twice the rate of daytime maximum
temperatures (likely). [WGI
TAR Section 2.2.2.1] |
| Hot days / heat index |
Increased (likely). [WGI
TAR Section 2.7.2.1] |
| Cold / frost days |
Decreased for nearly all land areas during the 20th
century (very likely). [WGI
TAR Section 2.7.2.1] |
| Continental precipitation |
Increased by 5-10% over the 20th century in the Northern
Hemisphere (very likely), although decreased in some regions
(e.g., north and west Africa and parts of the Mediterranean). [ WGI
TAR Chapter 2 ES & Section
2.5.2] |
| Heavy precipitation events |
Increased at mid- and high northern latitudes (likely).
[WGI TAR Section 2.7.2.2]
|
| Frequency and severity of drought |
Increased summer drying and associated incidence of
drought in a few areas (likely). In some regions, such as
parts of Asia and Africa, the frequency and intensity of droughts
have been observed to increase in recent decades. [WGII
TAR Sections 10.1.3 & 11.1.2] |
| Biological and physical
indicators |
|
| Global mean sea level |
Increased at an average annual rate of 1 to 2 mm during
the 20th century. [WGI TAR Chapter 11] |
| Duration of ice cover of rivers and lakes |
Decreased by about 2 weeks over the 20th century in
mid- and high latitudes of the Northern Hemisphere (very likely).
[ WGI TAR Chapter 2 ES
& Section 2.2.5.5,
& WGII TAR Sections
5.7 & 16.1.3.1] |
| Arctic sea-ice extent and thickness |
Thinned by 40% in recent decades in late summer to
early autumn (likely) and decreased in extent by 10-15% since
the 1950s in spring and summer. [WGI
TAR Section 2.2.5.2 & WGII
TAR Section 16.1.3.1] |
| Non-polar glaciers |
Widespread retreat during the 20th century. [WGI
TAR Section 2.2.5.4 & WGII
TAR Section 4.3.11] |
| Snow cover |
Decreased in area by 10% since global observations
became available from satellites in the 1960s (very likely).
[WGI TAR Section 2.2.5.1] |
| Permafrost |
Thawed, warmed, and degraded in parts of the polar,
sub-polar, and mountainous regions. [ WGI
TAR Sections 2.2.5.3 & 11.2.5,
& WGII TAR Section
16.1.3.1] |
| El Niño events |
Became more frequent, persistent, and intense during
the last 20 to 30 years compared to the previous 100 years. [WGI
TAR Section 7.6.5] |
| Growing season |
Lengthened by about 1 to 4 days per decade during
the last 40 years in the Northern Hemisphere, especially at higher
latitudes. [WGII TAR Section
5.2.1] |
| Plant and animal ranges |
Shifted poleward and up in elevation for plants, insects,
birds, and fish. [WGII TAR
Sections 5.2, 5.4,
5.9, & 16.1.3.1] |
| Breeding, flowering, and migration |
Earlier plant flowering, earlier bird arrival, earlier
dates of breeding season, and earlier emergence of insects in the
Northern Hemisphere. [WGII
TAR Sections 5.2.1 & 5.4.3] |
| Coral reef bleaching |
Increased frequency, especially during El Niño
events. [WGII TAR Section 6.3.8] |
| Economic indicators |
|
| Weather-related economic losses |
Global inflation-adjusted losses rose an order of
magnitude over the last 40 years (see Q2
Figure 2-7). Part of the observed upward trend is linked to socio-economic
factors and part is linked to climatic factors. [WGII
TAR Sections 8.2.1 & 8.2.2] |
| a. This table provides
examples of key observed changes and is not an exhaustive list. It
includes both changes attributable to anthropogenic climate change
and those that may be caused by natural variations or anthropogenic
climate change. Confidence levels are reported where they are explicitly
assessed by the relevant Working Group. An identical table in the
Synthesis Report contains cross-references to the WGI and WGII reports. |
