Why does the IPCC report show increased warming at higher latitudes, particularly in the northern hemisphere?



One the the pictures from the IPCC report shows substantial increased warming in the northern latitudes. I was wondering why they are predicted to be so much higher than everywhere else on Earth.

In: Earth Science

I believe a big part of it is sea ice reflects the sunlight and help keep the pools cool, as the ice melts and is replaced by land/ocean it absorbs more and gets hotter.

I’m assuming you mean compared to the southern hemisphere.

Climate is really fucking complicated (the term “butterfly effect” comes from climate science) so the answer to this includes many influencing factors. I shall outline a couple of those here.

First is that the Northern Hemisphere has most of the land. The equator is much lower down than you might think it is – the Sahara, India and China are all fully above the equator, as is much of south-east Asia and sub-Saharan Africa. Even the top part of South America is above the equator. 78% of land and around 90% of human population is above the equator. This is important because the air above land flows a bit differently to the air over ocean, in such a way that means that land is better at trapping greenhouse gases above it than ocean. More land means more ability to trap greenhouse gases. It also means more people and industry generating that greenhouse gas, and it does not get distributed evenly across the globe – air currents mean that a significant chunk of northern hemisphere air stays in the northern hemisphere, and even eventually finds itself channeled towards the north pole.

Second is that there are several strong ocean currents, particularly the gulf stream, that bring hot water up from the southern hemisphere into the northern, so the northern hemisphere is generally warmer than you would expect based on latitude alone. And, climate change is a feedback loop – the warmer it gets, the faster it gets warmer, even without increased human output, for various reasons (including, as a fun one, the melting of giant methane deposits in permafrost and deep sea methane traps, an effect thought to be responsible for the largest mass extinction event in Earth’s history and that seems to have begun happening again. Yay).

The chart in question shows “relative warming”.

It’s not saying it will be hotter in the north that at the equator. It’s saying the temperature will go up more in the north (where it is currently not hot) that it will at the equator (where it is already quite hot).

1900 climate (the baseline for that graphic) showed high difference in temperature by latitude and strong ocean currents moving heat around. Future climate will show less effective heat movement, leading to hotter everywhere but also more hotter (probably not good English) in northern areas where heat transfer made more of an effect in 1900.