Rocks slowly break down over time through a set of chemical, physical and biological processes called weathering. Some of these processes are heavily dependent on climate, so certain kinds of rocks weather more rapidly in some climates than in others. The two key climate parameters that affect the rate of weathering are moisture and temperature.
Weathering occurs both through physical processes like freezing and thawing and through chemical processes like reactions with carbonic acid that turn silicate minerals into clays. The rate of most chemical reactions increases as the temperature increases, so rocks in warm climates experience faster rates of chemical weathering than rocks in cool climates. Cold climates, by contrast, increase rates of physical weathering, because different minerals expand and contract at different rates when they are heated, so repeatedly heating and cooling the rock eventually causes it to fracture. Desert and mountain climates experience a wide range of temperatures so physical weathering through fracturing accelerates in these environments.
Moisture and rainfall are the other critical factor. Some types of rocks weather more rapidly in humid climates, while dry climates make other rocks more susceptible to attack. Limestone, for example, weathers rapidly in areas with wet climates, where rainwater carrying carbonic acid dissolves the limestone to form caves and valleys. Sandstone, by contrast, weathers more rapidly in dry climates, because the quartz in the sandstone is largely invulnerable to chemical weathering, but can fall prey to fracturing caused by ice formed when water freezes and expands in cracks in the stone.
Chemical vs. Physical
Wet climates accelerate the rates of chemical weathering, so if a rock is prone to chemical weathering it will break down more rapidly in a wet climate. The mineral olivine, for example, is relatively unstable and vulnerable to chemical attack, so olivine-rich rocks will break down much more rapidly in a humid region. In general, hot wet climates accelerate chemical weathering while cold dry climates accelerate physical weathering. Although the rate of weathering depends on the type of rock, rocks in tropical climates experience the highest rates of weathering because of the combination of high heat and heavy rainfall.
Biological weathering occurs when living organisms break up rocks. Tree roots, for example, can fracture rocks in the same way they buckle pavement. Warm, humid climates are most favorable to life. Contrast the rich diversity of life in a rainforest, for example, with the scarcity of life in the dry Sahara or the frigid Antarctic. Consequently, rates of biological weathering are most rapid in warm humid climates like those in tropical regions.