Future Sea Level Rise

I've spent the last couple of months looking into the various reasons for sea level rise, so I think it's high time (or high tide?) I put all this together and consider how the sea level could change in the future.

This looks like a worst case scenario for King Canute (Credit: Henry Tapper)

Scientists have varying degrees of confidence in each component of sea level rise, and for a long time all the different causes could not explain the extent of sea level rise we were observing - until groundwater was included that its. Even as it is, the melting of ice sheets have the highest potential to increase sea level - perhaps global mean sea level rise of up to 70 metres, but ice sheet dynamics aren't fully understood yet (Rahmstorf, 2007), so as you can imagine it is very very difficult to predict how sea level is going to change in the future. So let's start with the IPCC AR5. They state:

"It is very likely that the rate of global mean sea level rise during the 21st century will exceed the rate observed during 1971-2010 for all Representative Concentration Pathway (RCP) scenarios due to increases in ocean warming and loss of mass from glaciers and ice sheets."

 

This is very important because even the RCP2.6 scenario, in which emissions stabilise and then start to decrease before 2100 (van Vuuren et al. 2011), involves increased sea level rise. You can see this more clearly on the graph below. So even if we do everything we can in terms of reducing our emissions, models agree that we will experience continued sea level rise of at least 30 cm by 2100.

Projected sea level from the RCP2.6 and RCP8.5 scenarios relative to 1986-2005 from the CMIP ensemble (IPCC)

I think in terms on the way a warming climate will impact on our lives, increasing sea level is arguably the biggest problem that we are going to have to deal with. You can start to get an idea of the extent small sea level rises will effect us here. Just taking a look at some of the countries I've already looked at and a 1 metre global sea level rise, it's really quite scary the extent of the problem. So forward planning, mitigation, and adaption are essential. But how reliable can any projection of sea level rise be?


Rahmstorf et al. (2007) compared model projections from the 2001 IPCC report with subsequent observations of sea level. The models, which began in 1990 and didn't incorporate any sea level observations after this date, consistently underestimated global mean sea level rise between 1990 and 2006, despite accurately predicting other aspects of the climate system such as carbon dioxide. Church et al. (2013) suggests that this could be natural variabilty, such as the 60-year sea level oscillation proposed by Chambers et al (2012), not recreated by process based models, rather than a systematic misrepresentation of the climate system. Models have advanced considerably since, alongside out understanding of the climate system, and computer power allowing inclusion of more processes, but it's still worth remembering that all models are wrong - they can only be an indication of future change. With any projection we should always bear their limitations in mind.


So we are pretty sure global mean sea level is going to rise, but it's a bit hard to comprehend the effect this will have on us. I think it's really important to look at the impacts on a more personal regional level. We don't expect sea level to rise uniformly all over the world - things like salt content, ocean dynamics, and post glacial isostatic rebound mean that sea level changes differently all over the world. Some countries will experience accelerating sea level rise, while others will experience falling sea level despite the trend in global sea level. It's all about being prepared, if this is something you are interested in, definitely check out Yuchao's blog on the future economic impacts of sea level rise.