Sea level data confirm that the projections on climate models were correct

Predictions of rising sea levels in this century will earn money if tested on satellite and tidal observations, scientists find.

In the early 21st century, the projections of the climate models in the early 21st century are consistent with the sea level data recorded in the corresponding period.

And the scientists who screwed up the numbers say that the finding in the coming decades does not bode well for the effects of sea level if greenhouse gas emissions are not re-applied.

In a recent article in Nature communication, scientists from Chinese and Australian institutions, including UNSW Sydney, examined the global and local sea level projections of two reports from the Intergovernmental Panel on Climate Change: the fifth assessment report (AR5) and special report on the ocean and the cryosphere in a changing climate ( SROCC).

They compared the projections of the reports with the observed global and coastal sea level data from satellites and a network of 177 thymeters from the beginning of the projections in 2007 to 2018. The scientists found that the trends of the AR5 and SROCC projections at sea level under three different scenarios of greenhouse gas emissions “agrees well with satellite and tidal area observations during the common period 2007–2018, within the confidence level of 90 percent.”

Study co-author and leading expert at sea level, Professor John Church, says that although he thought the projections of modeling at the world level would be accurate, he was pleasantly surprised that it was so accurate at local and local level.

“Our analysis implies that the models are close to observations and that this will create confidence in the current projections for the next decades,” says prof. Church, part of UNSW’s Climate Change Research Center.

But he adds a warning that, because the available comparison period is only 11 years, he will be reluctant to extend the same degree of confidence over the longer term – from the end of this century onwards – where the ice sheet is accelerating. contribution to sea level rise is less understood and can lead to larger rises.

“There is still a potential for larger sea level rises, especially after 2100 for scenarios with high emissions. Therefore, it is urgently necessary to continue to meet the obligations of the Paris Agreement by significantly reducing emissions,” says prof. Church.

Study co-author, dr. Xuebin Zhang, of CSIRO’s Oceans and Atmosphere Division, says this is the first study to compare projections of global and regional sea level rise with observations over their overlapping periods – no average performance, given the natural variability of climate and vertical land movement from region to region. region.

“We have carefully removed the effects of natural climate change, for example El Niño – Southern Oscillation, and corrected the vertical land movement, which has led to a much better agreement.”

The analysis looked at the three different emission scenarios in the IPCC reports that correspond to three different climate futures, depending on what greenhouse gas reduction strategies have been applied – known as the Representative Concentration Pathway (RCP) scenarios.

The lowest scenario (RCP2.6) examined is for a sharp reduction in greenhouse gas emissions, roughly in line with 2 ° C of global warming by 2100, but still greater than what is needed to reach the Paris Agreement of below 2 ° C.

The middle scenario (RCP4.5) requires that the radiation force be stabilized in the last half of this century, and this results in it heating up above the Paris target.

And the highest scenario (RCP8.5) is for large greenhouse gas emissions leading to continuous rapid warming and implying a commitment to large sea level rises.

“Analysis of recent sea level data indicates that the world is being watched between RCP4.5 and the worst-case scenario of RCP8.5,” says Professor Church.

“If we continue with large continuous emissions as at present, we will commit the world to rising meters sea level over the coming centuries.”

Next, the group will try to gain a better understanding of the processes that determine local sea level rise.