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With the cool end to a hot British summer, now might be a good time to go over a few things about climate change.

To begin with, the myth that global warming has stopped. As Rebecca Leber reminds us in the New Republic, the temperatures that we directly experience are a small part of the overall picture:

“…even as temperature on land is zigging and zagging, it has kept rising in the seas. Ninety-three percent of the Earth’s heat is absorbed in the ocean. And there the warming trend has actually accelerated.”

A further three per cent of the the Earth’s “heat budget” goes into melting ice and a similar amount into warming up land, this leaves just one per cent for atmospheric temperatures (which is what the self-described ‘sceptics’ are referring to when they make their claims of a global warming “hiatus”.

The warming of the biggest heat sink (the oceans) matters to us because some of the heat that goes into it can come back out again, with major implications for the smaller heat sinks, such as the atmosphere. (Imagine a street in which there’s a corner shop with a small and constant number of customers next to a massive department store with a large and growing number of customers. If even a small proportion of the big shop’s customers move over, then the small shop will know all about it.)

The interaction between heat sinks is just one reason why we can’t expect atmospheric temperatures to follow a smooth trajectory. Another driver of unpredictability is explored in a fascinating post by Geoffrey Lean for the Telegraph. He begins by noting one of things that most annoys the climate sceptics – the regularity with which all manner of extreme weather events, and not just heat waves, are attributed to global warming:

“…a new study has come up with findings as to why this may indeed be valid.

“The paper – by researchers from Germany’s blue-chip Potsdam Institute for Climate Impact Research and New Mexico’s Santa Fe Institute – says that extreme weather events, which also include floods and droughts, have almost doubled over the last two decades.”

Such events are associated with unusually persistent weather systems – such as the conveyor belt of Atlantic storms that subjected Britain to such a wet-and-windy battering last winter:

“…stationary weather systems… simultaneously pull warm air from the tropics over temperate regions and push down cold air from the poles: depending on which part of the system affects it, an area is turned unusually hot or cold for several weeks at a time until the system passes on.

“The systems, adds the paper, just published in the Proceedings of the National Academy of Science, are linked with ‘anomalous circulation patterns’ in the jet stream, the high altitude river of air that does much to determine the weather.”

What could be upsetting the jet stream in this way? The paper’s authors point to the fact that the Arctic is warming much faster than more southerly regions – thus reducing the steepness of the temperature gradient between them.

This begs a further question as to why the Arctic is warming with such comparative speed. One suggested reason is that higher temperatures reduce the area of ocean covered by highly reflective sea ice, replacing it with less reflective open water – thereby accelerating the absorption of heat.

The authors of the paper are at pains to emphasise the uncertainties in the current state of scientific knowledge, but their work highlights the complexity and interconnectedness of the planet-spanning systems we’re in the process of disturbing. While we may be able to predict the result of rising carbon dioxide levels in regard to long-term average temperature trends, the specific local impacts are wildly unpredictable.

There are those who say that adaptation is a better strategy than prevention when it comes to climate change. This rather overlooks the fact that we don’t really know what we’ll be adapting to.

56 comments for: We can expect the unexpected from global warming

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