2 Controls of Climate

Climate reflects interacting controls

Climate describes the long-term pattern of conditions such as temperature and precipitation in a region. Several controls interact to determine how much solar energy a place receives, how heat and moisture move, and where air rises or sinks. Together, they shape average conditions and seasonal ranges.

Latitude shapes sunlight and seasons

Latitude affects both the angle and duration of incoming sunlight. Near the equator, sunlight is more direct throughout the year, so average temperatures are generally high and seasonal temperature changes are relatively small. At higher latitudes, sunlight arrives at a lower angle and day length changes more between summer and winter, producing colder average conditions and larger seasonal contrasts toward the poles.

Latitude also relates to broad precipitation patterns. Warm, moist air often rises near the equator, supporting frequent rain. In subtropical belts, air commonly descends and dries, favoring arid climates. Winds, oceans, and landforms modify these broad patterns.

Elevation affects temperature and precipitation

Temperature generally decreases with increasing elevation because rising air expands as pressure falls and cools. As a result, a highland area can be much cooler than a nearby lowland at the same latitude.

Mountains may also receive more precipitation than surrounding lowlands when moist air is forced upward. Local conditions determine how much of that precipitation falls as rain or snow.

Land and water moderate temperatures

Land heats and cools more quickly than water. Oceans and large lakes therefore moderate nearby temperatures: coastal places often have cooler summers and warmer winters than inland places at similar latitudes. Inland locations tend to have a wider annual temperature range.

Water also supplies moisture to the air. Nearby water can support precipitation when winds carry moist air over land. For example, a coastal city and an inland city at similar latitudes may have similar annual average temperatures but very different seasonal extremes; the coastal city's winters and summers are often milder.

Ocean currents redistribute heat

Ocean currents transport heat. Warm currents carry heat toward higher latitudes and can raise temperatures along nearby coasts, while cold currents can cool coastal areas. Currents also affect evaporation and atmospheric moisture.

Cold-water upwelling occurs when deeper water rises to the surface. It can cool nearby air and often contributes to dry conditions along some coasts. The warm Gulf Stream carries heat northward across the Atlantic and helps moderate winter conditions in parts of northwestern Europe. The effects of currents depend on the current, prevailing winds, and regional geography.

Atmospheric circulation moves heat and moisture

Uneven solar heating drives large-scale air circulation. Warm air tends to rise, cool, and release moisture; descending air tends to warm and become drier. These rising and sinking zones help organize broad wet and dry climate belts.

Earth's rotation and the arrangement of continents and oceans shape prevailing winds and circulation patterns, which carry heat and moisture from one region to another. Trade winds carry air toward the tropics, while prevailing westerlies influence much of the middle latitudes. Seasonal shifts in circulation can bring wet and dry seasons to some regions.

Topography creates local climate differences

Mountains alter both temperature and precipitation. When moist air is forced up a mountain slope, it cools; water vapor may condense and fall as precipitation on the windward side. As air descends the leeward side, it warms and dries, creating a rain shadow with less precipitation. The direction of prevailing winds determines which slopes are windward or leeward.

Slope direction and exposure to sunlight can also create local temperature differences.

Climate controls work together

No single factor determines a region's climate. A high-elevation place near the equator may be cooler than a lowland at the same latitude; a cold current may cool a coastal desert; and a mountain range may make one side wet and the other dry.

To explain a regional climate, consider how latitude, elevation, distance from water, currents, atmospheric circulation, and landforms combine to shape temperature and precipitation over time.