AskPablo: Is the IPCC wrong on sea level rise?

sea-level.jpgDespite its name, Greenland is anything but green (which I can appreciate since my name is also a bit misleading because I am not even remotely Hispanic — I was born in Germany…And no, you may not AskPablo about this, ask my mom). In another bit of irony you will also find that Iceland is more green than icy (which makes me think that perhaps there is a Spaniard out there with a really good German name like Fritz, Dieter, or Wolfgang…). This week the decidedly French Jacques asked me about sea-level rise. Is it really possible for the oceans to rise by 20 feet if the entire Greenland ice sheet were to go away?

Greenland’s ice sheet currently covers 1.71 million km2 and, at an average depth of 1.66 km, it has a volume of 2.85 million km^3. Since we know that ice has a density of 0.9167 g/cm^3 we can figure out that the mass of Greenland’s ice sheet is 2.61×10^18 g. Since water has a density of 0.9998 g/cm^3 we also know that the melted volume of the Greenland Ice Sheet is around 2.61×10^15 m^3. That’s a lot of water!
The world has a surface area of 510,065,600 km2, 70.8% of which is water, or around 361,126,445 km^2. If we divide the volume of melt-water by the surface area of the oceans we should get a rough idea of the sea level rise. 2.61 x10^15 m^3 divided by 3.61×10^14 m^2 comes out to 7.23 m, or 23.6 ft, which is close to what the IPCC estimates.
But there seems to be something missing… As sea levels rise and low-lying land is taken over, the planet’s liquid surface area is going to grow significantly. So, as coastal areas are inundated the oceans grow but the relative increase in sea level will be less. But how much less?
With the help of a GIS (geographic information system) specialist at work, I took global elevation data and figured out what the elevation profile of global coastlines looks like. For the first 600 m of elevation, the surface area of the oceans would grow rapidly, at about 143,000 square km for every meter of sea level rise. So every meter rise in sea levels provides room for an additional 1.43 x 10^11 m^3 (143,000 km^2 x 1,000,000 m^2/km^2 x 1 m) of melt-water.
Using my GIS data I was able to find that the true sea-level rise from a complete melting of the Greenland ice sheet would be closer to 7.19 meters. Despite this more accurate approach, the sea level rise is only 4 cm lower than the number I calculated earlier. The actual number used by the IPCC is 7.2 meters, which is within rounding convention of both of my results. I guess the IPCC did earn that Nobel prize after all…

Pablo Päster

Sustainability Engineer
For more information on sea-level rise see: