The purpose of Chapter 13 of the Intergovernmental Panel on Climate Change (IPCC) Fifth Assessment Report (AR5) Working Group One (WG1) is to fully assess the current state of scientific knowledge with regards to sea level change due to a changing climate.  In the Chapter Summary, each section of chapter 13 is summarized to its main points and conclusion.  

 

For an even more abbreviated summary, below are the conclusions from the Executive summary for Chapter 13:

 

 

Past Sea Level Change

 

• Paleo sea level records from warm periods during the last 3 million years indicate that global mean sea level has exceeded 5 m above present (very high confidence) when global mean temperature was up to 2°C warmer than pre-industrial (medium confidence).

 

• Proxy and instrumental sea level data indicate a transition in the late 19th century to the early 20th century from relatively low mean rates of rise over the previous two millennia to higher rates of rise (high confidence). It is likely that the rate of global mean sea level rise has continued to increase since the early 20th century, with estimates that range from 0.000 [–0.002 to 0.002] mm/yr to 0.013 [0.007 to 0.019] mm/yr.

 

Understanding of Sea Level Change

 

• Ocean thermal expansion and glacier melting have been the dominant contributors to 20th century global mean sea level rise.

 

• There is high confidence in projections of thermal expansion and Greenland surface mass balance, and medium confidence in projections of glacier mass loss and Antarctic surface mass balance.

 

• The sum of thermal expansion simulated by Coupled Model Intercomparison Project phase 5 (CMIP5) Atmosphere–Ocean General Circulation Models (AOGCMs), glacier mass loss computed by global glacier models using CMIP5 climate change simulations, and estimates of land water storage explain 65% of the observed global mean sea level rise for 1901–1990 and 90% for 1971–2010 and 1993–2010 (high confidence).

 

The Earth’s Energy Budget

 

• Independent estimates of effective RF of the climate system, the observed heat storage, and surface-warming combine to give an energy budget for the Earth that is closed within uncertainties (high confidence), and is consistent with the likely range of climate sensitivity.

 

Global Mean Sea Level Rise Projections

 

• It is very likely that the rate of global mean sea level rise during the 21st century will exceed the rate observed during 1971– 2010 for all Representative Concentration Pathway (RCP) scenarios due to increases in ocean warming and loss of mass from glaciers and ice sheets. Projections of sea level rise are larger than in the AR4, primarily because of improved modeling of land-ice contributions. For the period 2081–2100, compared to 1986–2005, global mean sea level rise is likely (medium confidence) to be in the 5 to 95% range of projections from process- based models, which give 0.26 to 0.55 m for RCP2.6, 0.32 to 0.63 m for RCP4.5, 0.33 to 0.63 m for RCP6.0, and 0.45 to 0.82 m for RCP8.5. For RCP8.5, the rise by 2100 is 0.52 to 0.98 m with a rate during 2081–2100 of 8 to 16 mm/yr.

 

• Some semi-empirical models project a range that overlaps the process-based likely range while others project a median and 95th percentile that are about twice as large as the process- based models. In nearly every case, the semi-empirical model 95th percentile is higher than the process-based likely range.

 

• It is virtually certain that global mean sea level rise will continue beyond 2100, with sea level rise due to thermal expansion to continue for many centuries. The amount of longer-term sea level rise depends on future emissions.

 

• The available evidence indicates that sustained global warming greater than a certain threshold above pre-industrial would lead to the near-complete loss of the Greenland ice sheet over a millennium or more, causing a global mean sea level rise of about 7 m.

 

Regional Sea Level Change Projections

 

• It is very likely that in the 21st century and beyond, sea level change will have a strong regional pattern, with some places experiencing significant deviations of local and regional sea level change from the global mean change.

 

Projections of 21st Century Sea Level Extremes and Surface Waves

 

• It is very likely that there will be a significant increase in the occurrence of future sea level extremes in some regions by 2100, with a likely increase in the early 21st century.

 

• It is likely (medium confidence) that annual mean significant wave heights will increase in the Southern Ocean as a result of enhanced wind speeds.