A mental map of the world

By Razib Khan | February 24, 2011 3:58 pm

One of the major issues in our world today is that we’re a people of specialties. This means that we don’t have basic interpretative frameworks in which to place novel facts. Because of the abstruse and formal nature of the discipline, this is probably starkest in the domain of science, but it is not restricted to only science. Consider geography. In many ways this is “low hanging” cognitive fruit in the shallow part of the learning curve which mostly consists of assembly of facts, but because of the shifts in emphases in American education geography has tended to get short shrift. This means that whenever there’s a foreign policy crisis middle-brow journals of record such as The New York Times have to commission pieces about nations such as Libya which read like a “first book” for six year olds on that nation (and on political weblogs commenters proudly brandish their “first book” level of knowledge).

But a bigger general issue seems to be in relation to climate. “Climate Change” is in the news constantly, but the average person on the street seems to have zero historical perspective on events such as the Medieval Warm Period, the Little Ice Age, let alone more obscure epochs such as the Younger Dryas. Fair enough, it isn’t as if Deep Time is ever going to be broadly interesting. But more disturbing to me is the total lack of perspective when it comes to current spatial patterns.

For example, a friend who has college degrees in history and philosophy, has traveled to Europe, Canada, and is planning a trip to Thailand and the Philippines, thought China was further to the north than Europe. Take a look at this map:

New York City, Madrid, and Beijing, are all at the same latitude. The average low in Beijing in January is -8.4 °C. For New York City it is -3.22. And finally, for Madrid it is 2.6. Why the difference? Barcelona, to the north and east of Madrid, on the coast, has a mean low of 4.4 °C. This tells us what’s going in the most general sense. Continentality. My friend’s ignorance was understandable; Beijing has a much more frigid clime than southern Europe. China as a whole is much further south than climate without context would suggest, while Europe is much further north than most expect. All that has to do with the rough shape of the continents (and possibly the Gulf Stream for Europe, though this might be overdone taking into account the generally mild character of western upper temperate regions of continents). But first, let’s look at another example.

The town of San Luis Obispo in California gets about 33% more rainfall in the aggregate than Medford, in Oregon. The reason for this difference in aggregate rainfall seems clear when you look at their positions on the map to the left. Medford is inland, and somewhat in a rain shadow behind the Siskiyou mountains. San Luis Obispo in contrast has a much more maritime location. All things equal, maritime locations will generally have more precipitation than inland locations. But not only are all things rarely equal, notice that Medford has a longer “rainy season” than San Luis Obispo. This can’t be explained by the coastal vs. inland position.

My immediate explanation is that this must be due to the waxing and waning of the Westerlies with the seasons. The Westerlies are powerful winds in the temperate latitudes which blow out of the west and which tend to shift toward the equator during the winter, and retreat toward the poles during the summer. The shift of the westerlies on the western coasts of continents during the cold season is also accompanied by rainfall across broad swaths of the lower temperate latitudes, ergo, “Mediterranean” climate patterns on the southern tip of Africa, southwest Australia, central Chile, California, and yes, the Mediterranean. As physical dynamics not subject to magic, the movements of these winds exhibit a regular pattern where the areas which are furthest on the margin of their zones of expansion will also be the first subject to their retreat (this same pattern occurs with subtropical monsoons, as the rains abate fastest in the regions where they came the latest).

So what you have here is a two-variable model on the western coast of the United States in terms of predicting precipitation. On the one hand there are the coarse large-scale spatial relationships on the continental and planetary level which predict the flow of winds which bring the rainfall. But, there are also more fine-grained patterns of local positioning and topography.

All of the above I constructed as a model within 5 minutes, drawing upon a period of fascination with physical geography which I had when I was 8 to 10 years old. Because of my primitive mental state I only had a descriptive “stamp collecting” understanding of the patterns, but even my cursory knowledge of those patterns has been very useful to me as an adult. If the globe does warm, for example, I’d hazard to guess that the Pacific Northwest of the United States will have a climate resembling that of California far more likely than that of the American South. Why? Because the western coasts of continents are characterized by a particular set of temperature and precipitation regimes. Nature is not flat in its possibilities.

A broad background knowledge of spatial patterns allows one to infer facts and test ludicrous assertions “quick & dirty.” Of course one is often wrong if one lacks the subtle and precise knowledge of a specialist, but it is superior to the theory and data-free speculation which is par for the course in normal conversation.

Below is a Köppen climate map, the kind of mental image which I’ve long had seared in my brain:

Here are some quick facts which many people don’t know, but are often useful:

– The eastern coasts will tend to have a more “continental” climate than the western coasts (greater temperature fluctuations)

– The extent of this difference should be proportional to the size of the temperate zone hinterland

– Because of the coriolis effect winds going toward the poles will be deflected to the west, and those going toward the equator will be deflected toward the east (ergo, Westerlies vs. Trade winds)

– Large continents have a distorting effect all around them due to their massive temperature fluctuations. The larger the continent, the bigger the distorting effect (ergo, the most famous “monsoon” generated by the hyper-heating of continental interiors is the Asian one, even though there are monsoons operative in North America and Africa)

MORE ABOUT: Climate, Geography

Comments (9)

  1. Off-topic: what do you think of the supposed refutation of the Paleolithic revolution giving rise to behavioral modernity?
    Times like these make wish John Hawks had a comment section.

  2. i need to think on it. i don’t know that stuff well anyhow, so i’m muddling along like everyone else.

  3. Paul Ó Duḃṫaiġ

    Regarding how far north Europe is I always point out to my american friends that Ireland is as far north as southern Alaska and at same latitude as southern part of Bay of Hudson in Canada. So when they are complaining about rain in winter I say “It could be worse we could have Polar bears and Icebergs!”

  4. pconroy

    I tell Americans that all of Ireland is farther North than Trois Rivieres. Of course then I have to explain where Trois Rivieres is and that it’s a cold place in Canada.

  5. Don

    A fifth point.
    Low pressure emanating from tropical heat or from cold fronts spun off the polar winters will deliver weather from the opposite direction to that from which it is delivered by the Coriolis effect. So, facing the poles, the Coriolis causes a rightward veering as the Earth rotates out from under the atmosphere , low pressure causes the opposite with inward spiraling.
    Check it out on MIMIC

  6. Don

    rather, facing the equator

  7. Anthony

    San Luis Obispo, along with most of California, has dry summers because a high-pressure system which blocks storms off the Pacific builds up offshore and stays there most of the summer. If the high-pressure system moves north of its usual location, Oregon and Washington have a summer drought, while LA might get spinoff rainfall from hurricanes off the coast of Mexico.

    Why it forms, I have no idea. I’d guess it has something to do with the edge of a continent, but why does it form off California instead of Oregon, or British Columbia?

    Speaking of world-wide visualizations, I’ve read that most of Africa is rather higher than the non-mountainous parts of other continents – that the continent is essentially one big plateau with some mountains along the East African Rift Zone. Before I read that, I had no clue that was true (or if it actually is). Nor do I have any idea why, in plate-tectonic terms, that should be so, or what effect it causes on Africa’s climate.

    Another bit of ignorance was dispelled after reading an article in The Economist, where I read that some rather significant part of inland Brazil is not rain forest, but is actually potentially quite rich farmland – and potentially dust bowl if managed wrong.

  8. Why it forms, I have no idea. I’d guess it has something to do with the edge of a continent, but why does it form off California instead of Oregon, or British Columbia?

    the latitude has to do with patterns of rising and descending air. the hot air where the sun is striking at the highest angle (directly above) at the equator rises, which means that air has to fall somewhere else (high pressure). that zone is to the north and south, in the subtropical zone. in the northern hemisphere that zone shifts south the winter, because the peak radiation is moving toward the tropic of capricorn. this means there is a dry season in the monsoonal zone, and a wet season in southern temperate zone as the high pressure shifts south.

  9. banerjee

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About Razib Khan

I have degrees in biology and biochemistry, a passion for genetics, history, and philosophy, and shrimp is my favorite food. In relation to nationality I'm a American Northwesterner, in politics I'm a reactionary, and as for religion I have none (I'm an atheist). If you want to know more, see the links at http://www.razib.com


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