(Part of the How to Talk to a Global Warming Skeptic guide)
Objection: Sure, sea ice is shrinking in the Arctic, but it is growing in the Antarctic. Sounds like natural fluctuations that balance out in the end.
Answer: Overall, it is true that sea ice in the Antarctic is increasing.
But the rest of the continent has not shown any clear warming or cooling and sea ice has increased over the last decade or so.
This is not actually a big surprise.
In fact, it is completely in line with model expectations that CO2-dominated forcing will have a disproportionately large effect in the north. The reasons lie in the much larger amount of land in the northern hemisphere and the fact that the ocean’s thermal inertia and ability to mix delay any temperature signal from the ongoing absorption of heat. The local geography also plays a dominating role. The circumpolar current acts as a buffer preventing warm water from the tropics from transporting heat to the South Pole, a buffer that does not exist in the north. You can read some more details about that here.
Does it “balance out” in the end? Not really. Sea ice in the Arctic is reaching dramatic record lows. There are other components of the cryosphere that we can look at as well, permafrost, the Greenland ice sheet, global glacier mass, and these all carry the Global Warming signal.
One must look at the balance of evidence, not just those bits one likes. And this balance is clearly in agreement with all other indicators that warming is real and rapid.