2009年-世界发展银行全球_Climate_Change_and_Sea_Level_Rise___A_Review_of_the_Scientific_Evidence_36页_2mb

Summary of "Climate Change and Sea Level Rise: A Review of the Scientific Evidence"

Core Content

This document provides a comprehensive review of the scientific evidence and projections related to climate change and sea level rise (SLR), focusing on the contributions of various factors such as ocean thermal expansion, glaciers, ice sheets, snow on land, and permafrost.

Main Points

• Sea Level Rise as a Global Threat:
  Sea-level rise due to climate change is a serious global threat. The rate of global sea level rise has increased significantly, especially from 1993 to 2003, with an average of 3.1 mm/year, compared to 1.8 mm/year from 1961 to 2003. This is much higher than the average rate of 0.1–0.2 mm/year recorded over the last 3,000 years.

• Long-Term Warming and Delayed Response:
  Even if greenhouse gas concentrations are stabilized, anthropogenic warming and SLR will continue for centuries due to the slow response of the climate system and feedback mechanisms.

• Contributors to SLR:
  The main contributors to SLR include:

  • Ocean thermal expansion
  • Glacial melt from glaciers and ice caps
  • Melting of the Greenland and Antarctic Ice Sheets
  • Changes in snow on land
  • Permafrost thawing

• Observed Contributions (1961–2003):

  • Ocean thermal expansion contributed 0.42 ± 0.12 mm/year (about 25% of total SLR).
  • Glaciers and ice caps contributed 0.50 ± 0.18 mm/year.
  • Greenland Ice Sheet contributed 0.05 ± 0.12 mm/year.
  • Antarctic Ice Sheet contributed 0.14 ± 0.41 mm/year.
  • The total observed SLR was 1.8 ± 0.5 mm/year, with the sum of these contributions being 1.1 ± 0.5 mm/year, suggesting a missing component.

• Recent Evidence (1993–2003):

  • Thermal expansion contributed 1.6 ± 0.5 mm/year.
  • Glaciers and ice caps contributed 0.77 ± 0.22 mm/year.
  • The total observed SLR was 3.1 ± 0.7 mm/year, with thermal expansion and ice melt each accounting for about half of the observed rise.

• IPCC AR4 Projections (21st Century):

  • SLR is projected to increase beyond the 1961–2003 rate.
  • Projections range from 0.18 to 0.59 meters, depending on emission scenarios.
  • The IPCC models did not fully account for dynamic ice flow changes, leading to criticisms that they are too conservative.
  • Thermal expansion is expected to continue as a major contributor, even if GHG concentrations are stabilized.
  • Glacial retreat will continue, with their contribution to SLR expected to decline in the long term.
  • Greenland's ice sheet is projected to contribute more to SLR than Antarctica, due to higher surface melting.

• Dynamic Processes and Uncertainties:

  • There is significant uncertainty regarding the dynamic processes of ice sheets, especially the potential for abrupt changes.
  • The Greenland and Antarctic ice sheets may experience rapid mass loss if warming continues, with the Greenland Ice Sheet potentially contributing 1–2 meters of SLR by the end of the 21st century.
  • The collapse of the West Antarctic Ice Sheet (WAIS) is a concern due to increased ice flow and the destabilizing effect of ice shelf loss.

• Impacts of SLR:

  • SLR can lead to storm surges, wetland loss, erosion, saltwater intrusion, coral bleaching, and changes in ocean productivity and species migration.
  • These impacts are socio-economically significant, particularly for developing countries.
  • A one-meter rise in sea level could submerge 194,000 km² and displace 56 million people in coastal developing regions.

Key Information

• Thermal Expansion:

  • The upper 700 m of the ocean has warmed faster than the deeper layers.
  • The rate of thermal expansion from 1993 to 2003 was 1.6 ± 0.5 mm/year, higher than the 0.42 ± 0.12 mm/year from 1961 to 2003.
  • Projections for 2080–2100 suggest thermal expansion could reach 1.9–3.8 mm/year, depending on the emission scenario.

• Glaciers and Ice Caps:

  • These have contributed significantly to SLR, with estimates ranging from 0.50 ± 0.18 mm/year (1961–2003) to 0.77 ± 0.22 mm/year (1993–2003).
  • Their contribution is expected to decrease in the long term as freshwater stores diminish.

• Greenland and Antarctic Ice Sheets:

  • Greenland's ice sheet is losing mass due to increased melting and ice flow, with projections of 0.21 ± 0.07 mm/year (1993–2003).
  • Antarctica's ice sheet is less certain, with a range of mass balance estimates from 0.14 ± 0.41 mm/year (1961–2003) to 0.21 ± 0.35 mm/year (1993–2003).
  • The Greenland and Antarctic ice sheets together contain enough water to raise global sea levels by up to 70 meters.

• Projections and Uncertainties:

  • The IPCC AR4 projections are considered too conservative due to the exclusion of rapid ice flow changes.
  • New evidence suggests that the Greenland Ice Sheet could trigger a large SLR if warming exceeds 1.9–4.6°C.
  • The WAIS may collapse due to ice shelf weakening, potentially leading to significant SLR.

• Adaptation and Socio-Economic Impacts:

  • The actual impacts of SLR will depend on a country's ability to adapt.
  • Developing countries are particularly vulnerable to the socio-economic consequences of SLR, including displacement, property loss, and damage to infrastructure.

Conclusion

The document concludes that while the IPCC AR4 projections are useful, they may underestimate the true rate of SLR due to the exclusion of dynamic ice flow processes. Recent evidence suggests that the Greenland and Antarctic ice sheets are more vulnerable to warming than previously thought, with the potential for significant and possibly abrupt SLR in the 21st century. The socio-economic consequences of SLR, especially for coastal developing countries, are profound and require urgent attention.