Special COP21: sea level has risen

Unless you avoid reading the news, you probably know that right now world leaders are meeting in Paris to try and find a compromise to limit our destruction of the environment. Economic growth and industry preservation are a regular excuse to avoid too strict such compromises. But one of the main reasons for our unwillingness to act on climate change lies in our brains: we have survived and evolved by caring much more about immediate dangers than distant ones, even if the distant ones are worse (other reasons are listed in this excellent post by Karin van der Wiel). We can’t really care about deathly droughts in 50 years if we have a deadline next week. Except that in fact, climate change is already happening and can already be seen. So, before the end of COP21, I will write a series of post about these current calamities, starting today with my favourite topic: sea level rise!

1) How much has sea level risen to date?

Sea level rise has two causes:
– the addition of extra water from land into the ocean (melting of land-based glaciers),
– the warming or freshening (decrease in salinity) of the water that is already in the ocean.
Both things have been happening for decades now, so it is not surprising that sea level rise is occurring already.

Global sea level rise rate is currently of 3 mm per year. Sea level has increased by just under 7 cm over the last twenty years, and about 25 cm since 1870 (see precise numbers and graphs on climate.nasa.gov). That sounds quite small, no?

2) How is sea level affecting our everyday life?

The main problem is not sea level rise per se; it is sea level rise on stormy days. First, these stormy days seem to be coming back more often and with an increased strength (but that would be the topic of another post). But also, these extra centimetres of sea level are enough to render our coastal defences useless. They have been designed to withstand “the storm of the century”, not “the storm of the century” + 25 cm. So we have been seeing more and more of these:


Houses collapsed after the 5 December 2013 storm surge on the Norfolk coast, UK (credit: Reuters)

Houses collapsed after the 5 December 2013 storm surge on the Norfolk coast, UK (credit: Reuters)

Storm surges. Coastal flooding, usually due to a storm. And its associated destruction:
– of habitation and transport , directly or after coastal erosion (like in Norfolk)
– of specific environments (salty water on agricultural land or in fresh marsh)
– of water supply and sewage
and even death, the most recent that I am aware of being in the south of France less than two months ago.

3) Who are the victims of sea level rise?

Basically, anyone who lives by the coast is a potential victim. That is 44% of the world population according to the UN. In recent years, deadly storm surges have occurred in Mexico, Bangladesh, Sweden, the US… And flooding causes expensive damages, tens of billions of dollars!

More drastically, in the Pacific Ocean, some countries are actually at risk of disappearing soon. The tropical paradise atolls have hardly any elevation, and some islands now get entirely underwater during strong storms! And I will leave you with this TED talk discussion with Anote Tong, president of Kiribati, and charismatic voice of these directly threatened Pacific island nations:


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