Sea level rise :
Global warming causes progressively sea level rise.
This is a problem that mankind has become aware quite recently, we are at the beginning of the problem.
It is an immense challenge that humanity will face.
The problem :
Untill now, the increase has been fairly low. Currently, it is 3.3 mm/year. So every 3 years the level rises 1 cm.
During the 20th century, the level has already rised 20 cm.
For the moment this is not yet serious, but it will become.
There is a faster rise :
- In the 20th century the average increase was 1.7 mm/year.
- In the early 21th century the increase was 3.3 mm/year.
So a strong acceleration.
All increases cumulate and produce a significant increase.
So rather quickly, first problems will appear.
This challenge is new for humanity. Since 3000 years, sea level was stable.
So humankind has been accustomed to this stability.
Many cities are along the sea.
This coastal flooding will have an astronomical economic cost. Building seawalls has equally an astronomical cost, and from a certain height it is neither possible nor profitable.
The relationship between CO2 and CH4 in atmosphere content and sea levels is demonstrated.
In the past, on a geological scale, there were variations in the oceans level.
All were from natural origin, related to changes in Earth's orbit (and also to volcanoes), modifying the CO2 and CH4 level in the atmosphere.
What is new this time :
- The human origin of the phenomenon,
related to the burning of fossil fuels.
- The phenomenon speed.
On a geological scale climate study shows there were already many glacial and interglacial eras (from natural origin).
So we know that this is possible, we can anticipate the effects.
So we know we are going to very very big problems.
There are 18 000 years, during the last glacial era, temperature was 5 degrees lower and oceans were 120 meters lower.
With a global temperature increase higher than 3 degrees, we will see how far oceans will rise.
Sea level rise will depend on the increase of the CO2 and CH4 content, and therefore of the global temperature increase.
If this increase is +4°C the consequences will not be the same that if it's +2°C.
Moreover system inertia do that the rise will be very long, it will proceed over centuries, with at the end an increase of several meters.
Some predictions are apocalyptic.
By looking on the scale of a lifetime, children born now will see a significant increase by 2100.
So if in the short term there is only a problem beginning, on the medium/long term there will be serious consequences.
Moreover, bad surprises can come from arctic and antarctic glaciers :
- Increase of the flow velocity.
- Ice shelves melting from below, because ocean water is warmer.
Some glaciers have worrisome behaviors.
For example in Greenland, in the Antarctic Peninsula, in the Land of Mary Byrd, etc.
Glacier retreat is seen on all continents.
For example Kilimanjaro (altitude 5 895 m) the summit ice cap has almost completely disappeared.
United Nations predict an increase of 1.4 m by 2100.
This process is over very long term, it will continue for centuries, even if we stopp greenhouse gases emissions.
So, we need a real solution, not only seawalls.