Seasonal Peturbations

A low ceiling of grey cloud and screaming 40 knot northerlies means that Spring has arrived in Wellington today. Not that this would be cause for excitement, since the Winter was so mild I hardly even noticed it, apart from a couple of really cold weeks at the end of June.

During Winters when I was a kid, we had these things called frosts. Y'know? Like, when the dew freezes over the ground and stuff. I don't remember a single frost this year.

We've gone from the warmest May on record to utter chaos in the space of a few weeks. People might mutter under their breath about global warming, but there is a reasonable explanation for at least some of the climactic mood swings we have been experiencing:

When the axis is aligned so it points toward the Sun during perihelion, one polar hemisphere will have a greater difference between the seasons while the other hemisphere will have milder seasons. The hemisphere which is in summer at perihelion will receive much of the corresponding increase in solar radiation, but that same hemisphere will be in winter at aphelion and have a colder winter. The other hemisphere will have a relatively warmer winter and cooler summer.

At present perihelion occurs during the Southern Hemisphere's summer, and aphelion is reached during the southern winter. Thus the Southern Hemisphere seasons are somewhat more extreme than the Northern Hemisphere seasons, when other factors are equal.