Our understanding of sea level change has greatly improved even just since the AR4.  New paleo data gives us high confidence that sea levels were substantially higher when greenhouse gas concentrations were higher and surface temperatures were higher than pre-industrial.  Instrumental tide-gauge records also show that current rates of sea level rise are an order of magnitude greater than those during the Holocene. 

 

An improved understanding of the contributors to sea level rise and the processes and mechanisms controlling them have allowed scientists to project future sea level change with more certainty.  Thus, it is virtually certain that sea level will continue to rise through the 21st century and beyond (Figure 13.27).  Initially the rise will be dominated by climate variability before the climate signal emerges more coherently.  In all scenarios, the rate of 21st century rise will outstrip that of the 20th century and by 2100 the rate of increase will approach that similar to that following the last deglaciation (~20m/thousand years). 

 

This projected sea level rise will also lead to an increase in the frequency and magnitude of extreme sea level events (storm surges).  It is also likely wave height will increase in the Southern Ocean.

 

Remaining Uncertainties

Despite recent advances and improvements, significant uncertainties still plague these projections.  In particular the dynamics of ice sheet contribution, specifically the rate and magnitude, are still uncertain.  The potential collapse of large ice masses also adds another factor of uncertainty to future predictions.  Additionally, uncertainty in the physics of modeling regional sea level change remains an issue.  This is especially important for short- and long-term plans regarding coastal infrastructure and hazard mitigation. 

 

Even if we were to stabilize greenhouse gases immediately, global sea level would continue to rise for centuries so continued research and understanding of GMSLR is necessary moving into the future.