Sea level rise acceleration (or not)–Part V: Detection & Attribution

In looking for causes, I have applied the ‘Sherlock Holmes procedure’ of eliminating one suspect after another. The procedure has left us without any good suspect. Thermal expansion was the candidate of choice at the time of the first IPCC review. The computed steric rise is too little, too late, and too linear.– Walter Munk

Introduction

To make credible predictions of future sea
 level rise, we must first understand the mechanisms of past and current sea level change. The issues of detecting recent acceleration in sea level rise and arguments attributing sea level rise to human-caused global warming deserve critical evaluation, in context of identifying any possible indicators of a high sea level projection pathway in the 21^st century.

The outstanding issue in the scientific debate surrounding sea level rise is whether the elevated rates during recent decades represent an acceleration in the long-term rate of change that can be attributed to human-caused warming, or a temporary increase due to natural climate variability.

Detection and attribution of anthropogenic signals in sea level change is a new and rapidly developing field. In the terminology of the IPCC, detection seeks to demonstrate a statistical change in the climate system, while attribution evaluates the contribution of multiple causes to such a change.

There are three main challenges to identifying a sea level rise signal from human-caused global warming:

• The timescales in the ocean are very long, and there is substantial lag time between external forcing and the realization of sea level change
• High amplitude natural internal variability in the ocean basins on timescales from the interannual to the millennial
• Strong regional variations in the signal.

Read the full article at Climate Etc.