Here’s another climate model study that challenges the Arctic tipping point idea. Arctic melting is still sensitive to temperature rise though and any further increase in atmospheric CO2 will keep translating to further ice loss.
According to the new NASA study within decades during summer the Arctic Ocean will be ice free.
The big difference compared to a tipping point scenario is the prolonged presence of winter sea ice. Average global temperatures would have to rise by 6 degrees [meaning a lot more around the poles] for all that to disappear, the NASA scientists state in their upcoming publication in Geophysical Research Letters. [That same journal had another interesting publication on (the linearity of) the Arctic melting trend last week.]
Seasonal albedo break
One of the reasons an ice-free summer may occur before 2050, whereas an ice-free winter could still be centuries away, is that the albedo effect, according to many the positive climate feedback responsible for self-accelerating Arctic ice melting, takes a seasonal break each year:
During the polar winters there is no sun, thus no solar absorption or reflection, so during these months the climate really doesn’t care whether we painted the Arctic coal-black or brilliant white – it only cares about temperature of the water and the air.
How to regrow lost ice?
Some may derive optimism from the absence of an Arctic tipping point. NASA even states that when they lowered the CO2 concentration again, their model reproduced a nice ice cap over the Arctic Ocean, which implies Arctic ice loss is not irreversible – although that conclusion is highly theoretical:
Emissions reductions are intrinsically incapable of lowering atmospheric CO2 concentrations. Thus far, we can only slow down the increase.
Perhaps the model results do open a door for Arctic geoengineering approaches though, for instance by influencing Arctic Ocean salinity and heat transport or through Arctic solar radiation management.
Arctic tipping point #2
Of course succesful [and continued for as long as CO2 remains elevated] implementation of such geoengineering schemes is almost equally theoretical as switching your CO2 climate model to reverse.
But the planet could still do with the good news of having a small chance – because the Arctic is not just air and water. If a climate model can’t find an Arctic tipping point, perhaps an Earth model could. On all accounts we don’t want to see The Methane Bomb go off again.
© Rolf Schuttenhelm | www.bitsofscience.org