Climate, Not Weather
Weather is what happened on Tuesday. Climate is the distribution weather is drawn from: the averages and the variance. For history, the variance matters more than the mean because populations live at the level bad years permit.
Wladimir Köppen classified climate by vegetation, since plants integrate temperature and rainfall.
| Group | Name | Character |
|---|---|---|
| A | Tropical | Hot, wet; no real winter |
| B | Arid | Evaporation exceeds precipitation |
| C | Temperate | Mild winters |
| D | Continental | Cold winters, warm summers |
| E | Polar | No warm season |
Arid (Group B) means evaporation exceeds precipitation. This is a budget, not a thermometer reading, which is why cold deserts exist.
Climate's Fingerprints
Paleoclimatology reads climate signatures: tree rings (growing season), ice cores (atmosphere), pollen cores (biomes), and speleothems (rainfall). These track events like the Medieval Climate Anomaly (c. 950–1250) and Little Ice Age (c. 1300–1850).
Climate is a stressor, not a script. The Norse abandoned Greenland during the Little Ice Age while the Inuit thrived under identical conditions:
same climate + different subsistence opposite outcomes
The methodological trap is correlation. A cold decade next to a revolt is a coincidence until you trace the mechanism through harvest yields, grain prices, and mortality.