Is sea level rise in line with climate projections?

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Researchers recently compared the actual sea level rise observed to that anticipated by climate models over the most recent period. And this, both on a global and regional scale. The results were published on February 12 in the scientific journal Nature communications.

One of the many consequences of global warming is the widespread rise in sea levels. A phenomenon that is mainly explained by the melting of land ice and the fact that warmer water occupies a slightly larger volume. Since the beginning of the industrial era, the average level of the oceans increased by about twenty centimeters. This may sound quite small, but you have to realize that the pace of the rise is accelerating.

Evolution of the average sea level between 1993 and 2020. Credits: OPINION / CNES.

Since the mid-1990s, the rate at which water has risen has been around 3.4 millimeters per year. A value twice as high as the 1900-2000 average established at 1.7 millimeters per year. Previous work has shown that climate models accurately reproduced the evolution observed over the past century, whether on a global or regional scale. However, until now, such an analysis had not been carried out for the more recent period.

A very good agreement between observations and models

It is now done. In a new study, researchers from China and Australia compared the most recent projections of the IPCC (AR5, 2013 & SROCC, 2018) to the observations made over the period 2007-2018. They include several satellite datasets combined with 177 tidal series. Finally, to make a relevant comparison, the scientists considered three scenarios of greenhouse gas emissions among those studied by the IPCC. An optimistic (RCP 2.6), intermediate (RCP 4.5) and pessimistic (RCP 8.5) case.

As in the past century, the authors found a very good agreement between climate projections and the changes actually observed. If the result was expected on a global scale, the degree of precision at the more regional level is a very encouraging observation. ” Our analysis implies that the models are close to observations and strengthens confidence in the current projections for the next decades. ”Notes John Church, expert on the subject and co-author of the study.

sea ​​level
Comparison between models (blue and green) and observations (yellow, orange, red and purple). The vignette (a) represents the temporal evolutions with the study area indicated by a light blue band. (b) and (c) indicate the averages over the period 2007-2018 for trend and acceleration, respectively. Credits: Jinping Wang et al. 2021.

Sea level: towards a rise of several meters at the current rate

Nevertheless, it must be recognized that the period worked by scientists is relatively short. Also, the study does not exclude the appearance of notable differences in the longer term. “There remains a potential for greater sea level rise. In particular, beyond 2100 for high emission scenarios. Therefore, it is urgent that we always try to meet the commitments of the Paris Agreement by drastically reducing emissions ”, adds John Church.

The initiative also asked to filter the variations in the level of the oceans due to phenomena of natural variability in order to capture only the climatic signal. “We have carefully eliminated the impacts of natural variability, eg El Niño, and corrected the vertical movement of land, which has led to a better understanding”, explains Xuebin Zhang, co-author of the paper. John Church adds that“Analysis of recent data indicates that the world follows a trajectory between RCP 4.5 and the worst case scenario RCP 8.5. If we continue with large continuous emissions as we are now, we will initiate a sea level rise of several meters over the centuries to come ”.

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