Even in the best scenario of emissions, the level of the oceans could continue to rise until 2300. According to a group of scientists, the level of the planet’s oceans is likely to continue to rise even if the objectives of the Paris Agreement are met. They also warn that the taking of half-measures and delays will have dramatic consequences.
It has been a long time since scientists sounded the alarm about sea level rise, a major consequence of anthropogenic climate change. Moreover, its effects are already visible at the moment. Increasing temperatures as a result of our greenhouse gas (GHG) emissions increase the volume of oceanic water and accelerate the melting of mountain glaciers, ice caps and ice sheets. Even more frightening, the impact of our current emissions will be fully felt in the centuries, even millennia to come.
While many studies predict sea level rise in the centuries to come and beyond, none of them have looked at the effects of the 2015 Paris Agreement targets on rising sea levels. An international team of researchers, one of whose members has received EU funding under the CD-LINKS and CRESCENDO projects, has decided to fill this gap in scientific knowledge. Their findings, published in “Europe PMC”, show the impact of the constraints of the Paris Agreement on rising sea levels up to the 2300 horizon.
The Paris Agreement calls on countries to cap their GHG emissions as soon as possible, in order to limit the increase in global temperature well below 2 ° C, or better still, to 1.5 ° C above pre-industrial levels. After reaching the ceiling, emissions must be reduced in such a way that anthropogenic GHGs are offset by the natural sequestration of trees, soil and oceans. The goal is to achieve this balance, called “net zero emissions” of GHGs, between 2050 and 2100.
The project team studied various scenarios. They compared the effects of zero net GHG emissions to zero net carbon emissions (with the exception of other GHGs such as methane or nitrous oxide) on future sea level rise. The estimate of sea level rise is based on emission reduction rates of 0.3, 0.5 and 0.7 gigatonnes of carbon per year after reaching the emission ceiling.
According to the scientists, depending on the speed with which we begin to reduce emissions during the 21st century, the rise in sea level should be between 0.7 and 1.2 m by 2300, as long as we maintain zero net emissions of GHGs until then. Even more disastrous, if only CO2 emissions are neutralized during this period, the rise in sea level will be between 1.1 and 1.6 m. This creates a urgent need, as every five years delay before reaching the emission cap will result in an additional 20 cm increase in sea level by 2300.
Other estimates also suggest that if only CO2 emissions are taken into account, the stabilization of global temperature below 2 ° C above pre-industrial levels will not be sufficient to contain the rising sea level below 1.5 m. In fact, once temperatures exceed 1.5 ° C, no scenario involving zero net CO2 emissions indicates a sea level rise of less than 1.2 m by 2300. More optimistically, after reaching zero net GHG emissions, for each decade when temperatures exceed 1.5 ° C, the average sea level will rise only 4 cm.
It is therefore clear that early emission caps, accompanied by drastic reductions in emissions, are the sine qua non for containing as much as possible the rise in ocean levels. Any delay in taking action will jeopardize the legacy of future generations.