Geography, why it matters

When I was a kid I was what you might call a “climate nerd.” I would be at a party my parents took me to and pour over atlases and maps, as well as descriptive books on climatology, just to pass the time. Though it was just a phase I have kept a lot of that knowledge with me, and I’ve found it really useful. Many times I’m shocked at how ignorant many of my friends are of geography. If one was to choose between learning technique or information (e.g., math vs. history) I would pick technique because my own feeling is that technique is very versatile. But in the real world we don’t choose, we mix & match. We combine a theoretical model of the world with a dense network of empirical data. A few weeks ago I was chatting with a friend of mine and it became clear that he thought China was placed “very far north.” I told him to look at a map and he was shocked. The reality is that China is to a great extent a subtropical country, with a small portion even to the south of the Tropic of Cancer.
One of the main things I recall from my childhood climate phase is the importance of physical geographical parameters in combining to produce a particular regime. Additionally, one can work with a few rules of thumb to make predictions. For example, the wider a landmass east-west is the greater the difference in mean winter temperature will be between the west coast and the east coast, with the former generally being far milder than the latter. But let’s make this concrete.

And here’s a chart:

I assume a substantial proportion of the readership of this weblog are aware of the locations of Lisbon, New York City and Beijing. Eureka is just to the south of the Oregon border, to the north of San Francisco, on the California coast. What you are seeing here is the pattern of eastern coastal cities exhibiting a more continental weather regime. To some extent this is just a function of the spin of the earth, around 40 degrees north (and south) the dominant winds come from the west. This means that the western coasts tend to be characterized by a maritime climate. In contrast, eastern locales are often subject to winds from the interior, which in winter or summer are characterized by temperature extremes because of the differential physics of heating up water and the earth’s surface. Also note the difference between Beijing and New York; the surface area of the interior of Eurasia is far larger than of North America, so the continental affect is more notable.
Of course there are many other factors, such as ocean currents and the distorting influence of mountain ranges. In any case, there’s a map of the Koppen climate classification system (click for larger image):