Sea ice is frozen seawater that floats on the ocean surface. It forms in both the Arctic and the Antarctic regions, during their respective winters. In summer it largely melts away, but does not completely disappear. Sea ice has an incredible influence on the life and weather in the polar regions, but also affects ocean circulations and our global climate.
Sea ice is a key component in system Earth – its highly reflective nature keeps the global climate relatively cool. Yet, the polar regions belong to the most rapidly warming regions on Earth: in some parts, temperature rise is four times higher than the global average. This has resulted in the dreadful decline of Arctic sea ice, as recorded by satellites since 1979.
In fact, every ton of emitted CO2 melts the equivalent of 3m2 of sea ice. This means that you, as an average citizen of our beautiful planet, are accountable for the loss of around 30m2 of sea ice per year. However, melting ice is not just a consequence of our emissions – it acts as a major amplifier of global warming!
Here’s why: wherever sea ice disappears, a dark ocean surface emerges. This low-reflective open ocean surface is known to typically absorb 6 times more solar radiation than a surface covered with bright sea ice and snow, which has a much higher reflectivity. In other words, energy from the sun that was once reflected back into space by the ice and snow is now being absorbed into the ocean. This causes a vicious cycle of warming, which amplifies the warming effect of greenhouse gasses by 25 to 40 percent.
Complete disappearance of Arctic sea ice throughout the summer months would have the same heating effect as the emission of a staggering 1 trillion tons of additional CO2 emitted into our atmosphere. This is almost twice the amount that we are allowed to emit in order to keep global warming below the dangerous threshold of 1.5°C!
When will those ice-free Arctic summers become reality? Simplistically, one can calculate that for an ice-free Arctic Ocean to happen, we need to emit about a trillion ton of CO2. At the current annual rate of 40 billion ton, this would take us 25 years. The newest computer models, that include complex factors like ocean currents into their calculation, project a seasonally ice-free Arctic around mid-century (2044–2067). A series of exceptionally warm summers like we have seen over recent years, could mean it happens earlier.
It’s important to emphasise the irony of numbers here: it requires 1 trillion ton of CO2 to make the Arctic Ocean ice-free. The resulting change in reflectivity will add an amount of solar energy to the climate system that is equivalent to the effect of, indeed, an additional 1 trillion ton of CO2. The disappearance of sea ice therefor doubles the effect of its culprit!
The Antarctic sea ice is shown to be in decline as well. Many questions remain about the relation between the sea ice and the capacity of the Southern Oceans to absorb CO2. This highlights the necessity for extensive research in the polar regions.
And how about the vast areas with permanently frozen ground? An estimated 1.4 trillion tons of carbon is currently embedded in the world’s permafrost. For every degree of global warming, this thawing permafrost may release the equivalent of 4-6 years-worth of fossil fuel emissions. This means that if we continue business as usual, permafrost could soon be as big a source of greenhouse gas emissions as China.
There are other environmental and economic implications to the loss of ice and permafrost. Sea ice is critical to the polar ecosystems, and to the fishing industry and indigenous peoples who depend on that ecosystem. And as ice is lost, more regions will be used for commercial shipping and oil and gas exploration, which presents economic opportunity for some nations, but which also contributes to further greenhouse gas emissions.