Researchers at the University of Hawaii have found that global warming not only raises sea level. It also increases its variability on a global average. Significant results for the coastal areas and published on August 20 in the scientific journal PNAS.

With the warming of the climate, the level of the oceans increases. A phenomenon that is due to the melting of continental ice (glaciers and polar caps) as well as to the expansion of water when its temperature increases. This rise is not evenly distributed in space, and some regions see the ocean rising faster than others.

Increased variability in sea level

In a recent study, a team of researchers found that in warmer climates, it is also the variability of sea level that becomes more important. A result obtained after analysis of the projections made by about twenty climate models. At cause, thermal expansion and its non-linear relation to the temperature of the water. That is, if we graph the magnitude of the expansion as a function of the latter, we do not get a straight line.

“While it is understood that the rate of mean sea level rise will accelerate with future warming – in part due to the more rapid expansion of the oceans at higher temperatures – how this property Nonlinear expansion of water will affect future sea level variability was so far unexplored, ”says Matthew Widlansky, lead author of the paper. Here too, there is a strong spatial heterogeneity with areas much more affected than others.

Strong implications for coastal regions

When we talk about a higher variability, this implies seasonal and inter-annual variations (due for example to El-nino) of greater amplitude. “According to the laws of thermodynamics, the variability of sea level increases in a warmer climate because the same variations in temperature, linked for example to the seasonal cycle, lead to greater fluctuations in density – and therefore in sea level,” details Matthew Widlansky.

In their study, the authors note that with an ocean warming that is 2 °C higher, the average variability will increase by 4% to 10%. Significant values for the coastal domain. We think in particular of episodes of marine submersions or the phenomenon of erosion. In addition, it is worth remembering that a 2 °C increase by the end of the century is almost a given. Finally, although there are uncertainties about regional changes in variability, all models indicate an overall average increase. Thus, this is an effect that should be taken into account when assessing future risks associated with sea level rise.