Judith Curry: Special Report on Sea Level Rise

I have now completed my assessment of sea level rise and climate change.

The complete report can be downloaded here [Special Report- Sea Level Rise].

My preliminary compilation of information was provided in the 7 part Climate Etc. series Sea level rise acceleration (or not). […]

The alarm over sea level rise

The public discourse on the threat of sea level rise is typified by these dire statements from climate scientists:

“That’s the big thing – sea-level rise – the planet could become ungovernable.” – Dr. James Hansen, former Director, NASA GISS “We’re talking about literally giving up on our coastal cities of the world and moving inland.” – Dr. Michael Mann, Penn State

The alarm over sea level rise is not so much about the 7-8 inches or so that global sea level has risen since 1900. Rather, it is about projections of 21stcentury sea level rise from human-caused global warming.

This Report refers extensively to the Assessment Reports prepared by the Intergovernmental Panel on Climate Change (IPCC), since these Reports are used to guide policies developed by the UN Framework Convention on Climate Change, including the 2015 Paris Agreement.

According to the IPCC, the projected 21st century sea level rise depends on the amount of greenhouse gas emissions. The likely range of projected sea level rise by the end of the 21st century is from 0.26 to 0.82 m [10 to 32 inches], depending on the emissions scenario.

The primary concern over future sea level rise is related to the potential collapse of the West Antarctic Ice Sheet, which could cause global mean sea level to rise substantially above the IPCC’s likely range in the 21st century. The IPCC AR5 has medium confidence that this additional contribution from the West Antarctic ice sheet would not exceed several tenths of a meter [less than a foot] of sea level rise during the 21st century.

Subsequent to the 2013 IPCC AR5, there has been a focus on the possible worst-case scenario for global sea level rise. Estimates of the maximum possible global sea level rise by the end of the 21st century range from 1.6 to 3 meters [5-10 feet], and even higher. These extreme values of possible sea level rise are regarded as extremely unlikely or so unlikely that we cannot even assign a probability. Nevertheless, these extreme, barely possible values of sea level rise are now becoming anchored as outcomes that are driving local adaptation plans [link].

Is the alarm over sea level rise a ‘false alarm,’ or not? The following four issues frame this report: Whether recent global sea level rise is unusual in context of the historical and geological record. The extent to which recent global sea level rise is caused by human-caused global warming, relative to natural causes of global sea level rise. The extent to which local sea level rise is influenced by the global sea level rise, relative to local vertical land motion and land use practices. Projections of sea level rise (global and local) for the 21st century, from all causes.

This Report critically evaluates the assessment and conclusions from the IPCC and other recent assessment reports regarding sea level rise, and includes an assessment of recent research and the knowledge frontiers. The IPCC and other assessment reports have been framed around assessing support for the hypothesis of human-caused climate change. As a result, natural processes of climate variability have been relatively neglected in these assessments. Arguments are presented here supporting the important and even dominant role that natural processes play in global and regional sea level variations and change.

Understanding and predicting sea level rise is a vibrant and active area of research. The challenges and uncertainties are well recognized by international scientific community, as formulated by the World Climate Research Programme (WCRP) Grand Challenge on Regional Sea Level Change and Coastal Impacts.

Conclusions

Here are my conclusions:

Mean global sea level has risen at a slow creep for more than 150 years; since 1900, global mean sea level has risen about 7-8 inches. The implications of the highest values of projected sea-level rise under future climate change scenarios are profound, with far reaching socioeconomic and environmental implications. However, these projections are regarded as deeply uncertain and the highest of these projections strain credulity.

The IPCC and other assessment reports are framed around providing support for the hypothesis of human-caused climate change. As a result, natural processes of climate variability have been relatively neglected in these assessments. Arguments have been presented here supporting the important and even dominant role that natural processes play in global and regional sea level variations and change.