Earth's Geography and Climate

A mountain range splits a climate in two because of what rising air does. Moist air blowing off an ocean hits the slope and is forced upward. As it rises it cools, and cool air holds less water vapor, so the vapor condenses into clouds and falls as rain on the windward side, the side facing the wind. By the time that air crosses the peak it has dumped most of its moisture. It then descends the leeward side, and descending air compresses and warms, which pulls it further from condensation. The result is a rain shadow: lush windward slopes, dry leeward basins or deserts, sometimes only a few tens of kilometers apart.

Large lakes and oceans moderate nearby land because water resists temperature change far better than land or air does. Water takes longer to heat up and longer to cool down, so a coastal town stays cooler in summer and milder in winter than an inland town at the same latitude, since onshore breezes carry that stored warmth or coolness inland. A cold ocean current running along a coast pushes this further: it chills the air above it, which can suppress rainfall and even create coastal fog and deserts, like the cool, dry stretches along some western coastlines fed by cold currents.

This explains why elevation alone cannot predict climate. Higher elevation reliably means colder air, since temperature drops as you climb. But rainfall depends on moisture supply and position relative to mountains and water, not height itself. A high valley sitting in a rain shadow can be cold and bone dry, while a lower coastal spot soaked in onshore moisture stays mild and wet. Geography, not altitude alone, sets the full climate picture.