Climate has a profound impact on the development of soils. Indeed, Tom L. McKnight, in "Physical Geography: A Landscape Appreciation" (1999), suggests it is the premier influence on soil traits but one that tends to play out over long periods of time and over large regions, which can make it less tangible to the human observer than other factors like topography and biology. A map of the world's climate zones will overlap significantly with one of its major soil types.
Mechanisms of weathering -- the breakdown or transformation of rock -- play a role in soil building and are impacted by climate. For example, chemical weathering, which involves changes to rock structure via chemical reactions, is typically enhanced in warmer and moister climates like the tropics. The percolation of rainwater through soil acts upon unconsolidated rock bits and lower bedrock layers, exerting a chemical weathering influence. Forces of mechanical weathering, like repetitive freeze/thaw cycles and exfoliation (where strips of rock peel away, possibly due to a release of pressure at Earth's surface), provide the soil with erratic chunks of rock.
Precipitation, one of the most significant climatic aspects, also has a big impact on soils. In areas that experience a lot of rainfall, water percolating down through soil tends to leach nutrients and organic matter out of the upper layers, unless modified by other soil components like plant roots. The soils underlying tropical rain forests tend to be nutrient-poor because of intensive leaching due to heavy rains; most of the nutrients are stored in the lush vegetation itself. Conversely, in arid regions with little annual precipitation, high rates of evaporation encourage the accumulation of salts in the soil.
Climate heavily influences the distribution and composition of vegetation communities. In cold, semi-arid climates, plant litter may take a long time to decompose, while warmer, wetter conditions can promote rapid release of nutrients from such detritus into the soil. Temperate, humid climates may be more conducive to earthworms, which have a significant effect on soil composition and fertility through their tunneling, excrement and nutrient transfer.
In high latitudes and some alpine regions, soil that remains below freezing year-round forms permafrost. This frozen underground belt is found across large area of Siberia, Alaska, Canada, Greenland and Scandinavia. In these regions, surface soil layers may be warmed in the summer to well above freezing, but below a certain point the annual temperature variations are far less and some deep soil is permanently frozen.