Reading the dossier that the Flemish Green party prepared as a proof that our government is wrong about its climate goals: “Climate disruption: long winter, bad spring – The link between climate disruption, long winters and more precipitation” was an educational experience. Already the title caught my attention. Longer winters, that is a new thing. Previous, shorter winters were predicted. Also wet winters (more rain, less snow) and dry summers. According to the dossier the prediction of more precipitation in winter still stands, but there are seemingly no changes in precipitation in other seasons (although a small increase in summer precipitation since the 1970s…).
There are three sections in the dossier: first there were the statements of scientists and a weatherman, second part is about precipitation and last part about climate politics in Belgium and more specifically Flanders. I will first look into the first statement.
It is from an article from De Morgen (Flemish newspaper) of March 26, 2013 in which Jean-Pascal Van Ypersele (vice president IPCC) explained that by changes in the jet stream there are more North-South winds than West-East winds. This means more extreme temperatures (if there is a North-South wind → colder, if there is a West-East wind → warmer). It seems plausible. In fact, the explained phenomenon sounds rather familiar to me.
First, it is a real phenomenon, but no mention of its name: the “Arctic Oscillation” (AO). Yes, OSCILLATION. As in possibly having phase shifts. Indeed, the AO index went in a negative trend a couple years ago (but also other oscillations went negative), so it would be no surprise that the temperatures went down.
The degree to which Arctic air penetrates into middle latitudes is related to the AO index, which is defined by surface atmospheric pressure patterns. When the AO index is positive, surface pressure is low in the polar region. This helps the middle latitude jet stream to blow strongly and consistently from west to east, thus keeping cold Arctic air locked in the polar region. When the AO index is negative, there tends to be high pressure in the polar region, weaker zonal winds, and greater movement of frigid polar air into middle latitudes.
Second, it reminded me of the ice age scare of the 1970s, in which the same phenomenon (upper atmospheric wind patterns that favors North-South circulation i.s.o. West-East circulation) was brought in to explain a return to an ice age (this scare was probably a Northern Hemisphere thing, probably more about this in a later post).
The statement he starts early with is: “the science is rather clear on this”. When I hear such a statement, my BS meter is going into overdrive. I heard this many times before and afterwards it was wrong anyway. Sure, the science is clear, but what exactly is the science clear about? Is it about the phenomenon (which I think is real) or about human attribution (which I think will be hard to proof)? When it is the last thing, he could have a point there (he tries to connect the vertical winds to human emissions, via the melting icecap), but I think it is the first thing he means. Not all scientists are sure about the attribution. They consider it, ahem, a natural cycle.
A question I ask myself: when in the positive phase the signal is in the same direction as global warming, how to differentiate between the two?
In the end, we really can be comforted that, although in the past something completely different was predicted/projected (by the same people), global warming is still on track and the science is still clear as ever. 😉