The Greenland ice sheet is the second largest ice mass on earth. The melting of the Greenland ice sheet is accelerating and is currently raising global sea levels by about 0.7 mm per year. About half of the melting of the Greenland ice sheet occurs at the surface. The rest is caused by melting at the base of the ice sheet and by the breaking off or “calving” of icebergs at its edge. (Source)
Why is the Greenland ice sheet a tipping point?
The Greenland ice sheet is only there because it is already there — if there were no ice sheet in Greenland, we could not rebuild it under today’s climate. So once it’s gone, it’s gone at least until the next glacial period.
The most important tipping point is the elevation of the ice sheet. As the ice sheet melts, it becomes thinner, which means the surface is at a lower and warmer elevation, leading to further melting. After the tipping point, this is a self-reinforcing loop that continues even if we stop emitting greenhouse gases.
Another important factor is the snow line (the height at which the ice cover is covered with snow). Bright white snow has a higher albedo than dark, bare ice, meaning it reflects back much more solar energy. Thus, as the snowline moves to higher elevations as the ice sheet warms, more bare ice is exposed. This bare ice will absorb more of the incoming solar radiation, leading to further melting.
Where is the tipping point of the Greenland ice sheet?
Studies suggest that the tipping point sits between 0.8°C and 3.2°C, with the best estimate being 1.6°C. After this tipping point, the melting will not be abrupt, but it is clear that it will increase and that the collapse of the Greenland ice sheet is irreversible. The rate of collapse is highly dependent on future climate and varies from a loss of about 80% after 10,000 years to a complete loss after only 2000 years.
What would happen if we crossed the tipping point?
The Greenland ice sheet holds enough water to raise global sea levels by 7.2 meters, and its disintegration would change the shape of the world’s coastlines. Additionally, Earth’s albedo would decrease, meaning it would reflect less solar energy, resulting in higher temperatures.