A region’s climate is determined by how much energy it receives from the Sun, how that energy is distributed through the atmosphere and oceans, and how local geography influences temperature and precipitation. Latitude, elevation, proximity to oceans, and prevailing winds are among the most important factors. Together, they help explain why some places are hot year-round, others experience dramatic seasonal changes, and still others receive abundant rainfall while nearby areas remain dry.
Climate differs from weather. Weather describes atmospheric conditions over short periods, such as a rainy afternoon or a cold winter morning. Climate describes the long-term patterns of temperature, precipitation, humidity, and other atmospheric conditions in a region, typically assessed over periods of several decades. Although daily weather can vary widely, a region’s climate reflects the recurring patterns shaped by its location and physical environment.
These influences do not operate independently. Latitude affects the amount of solar energy available, elevation changes atmospheric pressure and temperature, oceans redistribute heat and moisture, and winds transport air masses from one place to another. Understanding how these factors interact reveals why climates differ across the United States and around the world.
Latitude determines how directly sunlight reaches the surface
Latitude, the distance north or south of the equator measured in degrees, is one of the fundamental influences on climate. It affects the angle at which sunlight strikes Earth and the length of daylight throughout the year. These differences influence how much solar energy a region receives and how its temperatures change with the seasons.
Near the equator, sunlight arrives at a relatively high angle throughout the year. Solar energy is concentrated over a smaller surface area, helping maintain warm temperatures. Near the poles, sunlight arrives at a lower angle, spreading the same incoming energy over a larger area. Sunlight also travels through more of the atmosphere before reaching the surface, allowing more energy to be scattered or absorbed along the way.
These differences help explain the broad pattern of decreasing average temperatures from the tropics toward the poles. Tropical regions generally remain warm throughout the year, while polar regions experience much colder conditions. However, latitude alone cannot predict the climate of a particular location. Ocean currents, elevation, prevailing winds, and landforms can substantially modify the temperature patterns expected from latitude.
Earth’s axial tilt adds another important dimension. Because Earth’s rotational axis is tilted relative to its orbit around the Sun, the hemisphere tilted toward the Sun receives more direct sunlight and longer days. The opposite hemisphere receives less direct sunlight and shorter days. This produces the seasons.
Seasonal contrasts are generally greater at higher latitudes, where daylight duration changes dramatically over the year. Some polar locations experience periods of continuous daylight in summer and continuous darkness in winter. Near the equator, day length varies much less, so seasonal temperature changes tend to be smaller.
The seasons result primarily from Earth’s axial tilt, not from changes in its distance from the Sun. In fact, Earth is closest to the Sun during the Northern Hemisphere’s winter. The changing angle and duration of sunlight explain why summer is warmer than winter in both hemispheres, even though the two hemispheres experience opposite seasons.
Latitude also influences global atmospheric circulation. Uneven solar heating creates temperature and pressure differences that help drive large-scale air movements. Warm air tends to rise in regions where heating is strong, while cooler air tends to sink in other areas. These movements contribute to broad patterns of wet and dry climates, making latitude important not only for temperature but also for rainfall.
Elevation changes temperature and atmospheric conditions
Elevation, or height above sea level, is another major climate factor. As altitude increases, temperatures generally decrease in the lower atmosphere. This is why mountain peaks can remain snow-covered even when nearby valleys are warm, and why high-elevation communities can have cooler summers than lowland areas at the same latitude.
The primary reason is that atmospheric pressure decreases with altitude. Air near the surface is compressed by the weight of the atmosphere above it. Higher in the atmosphere, pressure is lower, allowing rising air to expand. Expansion requires energy, which the air supplies through its own internal energy, causing it to cool. This process is called adiabatic cooling.
The reverse happens when air descends. Increasing pressure compresses the air, warming it. These processes help explain temperature differences across mountain slopes and play a central role in the formation of clouds and precipitation.
Under typical conditions, rising air that has not reached saturation cools at about 5.5°F per 1,000 feet of elevation gain, although the actual rate varies with atmospheric moisture and other conditions. This approximate environmental relationship is useful for understanding why mountain climates often differ substantially from those of nearby lowlands. It is not a universal rule for every slope, season, or weather situation.
Elevation also affects precipitation. When moist air encounters a mountain range, the terrain forces it upward. As the air rises and cools, water vapor may condense into cloud droplets or ice crystals. If these grow sufficiently, precipitation falls on the windward side of the mountains, the side facing the incoming air.
After crossing the mountain crest, the air often descends, warms, and becomes less humid relative to its temperature. This can suppress cloud formation and reduce precipitation on the leeward side. The resulting dry region is known as a rain shadow.
Rain shadows help explain striking contrasts between neighboring landscapes. Parts of the Pacific Northwest receive abundant precipitation from moist air moving inland from the Pacific Ocean, while areas east of the Cascade Range are considerably drier. Similar effects occur east of the Sierra Nevada, where descending air contributes to the arid conditions of parts of the Great Basin.
Elevation also influences snow cover, growing seasons, and the timing of spring runoff. Cooler highlands may retain snow well into spring, supplying water to rivers and reservoirs as temperatures rise. The combination of lower temperatures and increased precipitation at some elevations can create distinct ecological zones over relatively short horizontal distances.
Oceans moderate temperature and supply moisture
Large bodies of water have a powerful influence on the climates of nearby regions. Coastal areas often experience smaller seasonal temperature ranges than inland locations at similar latitudes. Oceans warm and cool more slowly than land, so they reduce the extremes that would otherwise occur near the coast.
Water has a high specific heat, meaning it can absorb or release substantial amounts of energy without undergoing an equally large temperature change. During warm months, ocean water absorbs heat while limiting how quickly its surface temperature rises. During cooler months, the water releases stored heat, helping moderate the air above it.
Land surfaces generally heat and cool more quickly. As a result, inland areas often experience hotter summers and colder winters than coastal areas at comparable latitudes. This difference is especially noticeable in regions with strong seasonal contrasts.
Along the U.S. West Coast, the Pacific Ocean helps moderate temperatures in many coastal communities. Inland locations, particularly those far from marine influence, can experience much larger temperature swings. On the East Coast, the Atlantic Ocean and nearby water bodies also influence temperatures, although the extent of their effects varies with local geography and prevailing winds.
Oceans also provide the moisture that fuels much of the world’s precipitation. Water evaporates from the ocean surface and enters the atmosphere as water vapor. When moist air rises and cools, some of that vapor condenses, forming clouds and potentially producing rain or snow.
The amount of moisture available does not guarantee abundant precipitation. Air must also rise or cool sufficiently for condensation to occur, and atmospheric conditions must allow cloud droplets or ice crystals to grow. A coastal region may therefore remain relatively dry if stable air suppresses rising motion or if winds carry moisture elsewhere.
Ocean currents further complicate the relationship between oceans and climate. These currents transport heat from one region to another, influencing sea-surface temperatures and the properties of the air above them. Warm currents can help maintain warmer and more humid coastal conditions, while cold currents can cool nearby air and affect cloud formation.
Cold ocean currents are often associated with coastal regions that receive little rainfall. When cool air lies beneath warmer air, the atmosphere may become stable, limiting vertical motion. Moisture can still produce low clouds or fog, but substantial rainfall may be limited. This helps explain the presence of some coastal deserts, including parts of the western coast of South America and southwestern Africa.
The effects of oceans extend far beyond the shoreline. Sea-surface temperatures influence atmospheric circulation, storm development, and the movement of moisture across continents. Changes in ocean temperatures can also shift rainfall patterns over large areas, demonstrating that ocean conditions are an essential part of regional climate.
Prevailing winds transport heat and moisture
Winds connect distant parts of the climate system by moving air from one region to another. They transport heat, moisture, and other atmospheric properties, influencing the temperatures and precipitation patterns of the places they reach.
Prevailing winds are the dominant wind directions in a region over a period of time. Their patterns are shaped by differences in atmospheric pressure, Earth’s rotation, and the arrangement of continents and oceans. The large-scale circulation of the atmosphere creates broad wind belts, while local geography modifies the direction and strength of winds near the surface.
The trade winds generally blow from the east toward the west in the tropics. The prevailing westerlies dominate much of the middle latitudes, carrying air predominantly from west to east. Near the poles, polar easterlies generally carry air from east to west. These are broad patterns rather than unchanging rules; actual winds vary with weather systems, seasons, and regional conditions.
Prevailing winds help determine whether a region receives moist maritime air or comparatively dry continental air. When winds blow from an ocean toward land, they can carry water vapor inland and moderate temperatures. When winds blow from dry land toward a coast, they may bring less moisture and produce different temperature effects.
In much of the contiguous United States, weather systems commonly move from west to east under the influence of the prevailing westerlies. Air moving inland from the Pacific can bring moisture to western mountain ranges, where it rises and produces precipitation. After crossing the mountains, some of that air descends and dries, contributing to the arid conditions of interior western regions.
Winds also influence temperature by transporting air masses. An air mass is a large body of air with relatively consistent temperature and moisture characteristics. Air arriving from the Arctic can bring sharply colder conditions, while air moving north from the Gulf of Mexico can carry warmth and humidity into the central and eastern United States.
These movements explain why two places at the same latitude can experience very different weather and climate patterns. One location may be frequently exposed to moist oceanic air, while another receives dry continental air. Over time, the typical frequency and direction of these air movements contribute to differences in average temperature, humidity, and precipitation.
Winds can also affect rainfall by controlling where air rises and sinks. Rising air tends to cool, encouraging condensation and cloud formation. Sinking air tends to warm, reducing relative humidity and making clouds less likely to develop. These vertical movements, combined with the transport of moisture, help determine the locations of many wet and dry climate zones.
Atmospheric circulation creates broad wet and dry regions
Latitude, winds, and the uneven heating of Earth work together to create global patterns of rising and sinking air. These circulation patterns are central to understanding why some regions receive heavy rainfall while others are persistently dry.
Near the equator, strong solar heating warms the surface and encourages warm, humid air to rise. As the air rises, it expands and cools. Water vapor condenses into clouds, often producing frequent and heavy rainfall. This process contributes to the humid climates found in many equatorial regions.
After rising high into the atmosphere, much of this air moves away from the equator and eventually descends in the subtropics. Descending air warms as pressure increases, making it less likely to reach saturation. This suppresses cloud development and precipitation, helping create broad belts of dry climates around the subtropics.
These circulation patterns help explain why many of the world’s major deserts occur in subtropical regions. The Sahara in northern Africa and large desert areas of Australia lie within regions strongly influenced by descending air. Local factors, including cold ocean currents and mountain rain shadows, can intensify dryness further.
Between the tropics and the poles, atmospheric circulation is more variable. The prevailing westerlies, migrating areas of high and low pressure, and the movement of weather systems create a mix of wet and dry conditions. Midlatitude regions often experience changing weather as air masses with different properties meet and interact.
These global patterns are not fixed in place. Seasonal shifts in solar heating cause major circulation zones and rain belts to move north or south. Monsoons are a prominent example. A monsoon is a seasonal change in prevailing winds that can produce a marked shift between wet and dry periods. In some regions, summer winds bring moist air from the ocean onto land, resulting in substantial rainfall.
Atmospheric circulation therefore links the local climate of a region to processes occurring thousands of miles away. A change in ocean temperatures or the position of a large atmospheric circulation pattern can alter the winds and rainfall that a region typically experiences.
Mountains and landforms redirect air and precipitation
The shape of the land can strongly influence climate by directing winds, forcing air to rise, and creating barriers to moisture transport. Mountains are particularly important, but valleys, plateaus, and broad plains also affect local temperature and precipitation.
When air encounters a mountain range, it may be forced upward, producing the cooling and precipitation associated with orographic lifting. The amount of precipitation depends on the air’s moisture content, the strength and direction of the wind, and the height and orientation of the terrain.
Mountain ranges can also block or redirect air masses. A range may limit the movement of moist air into an interior basin or alter the path of storms. Where several mountain ranges lie in succession, the air may lose much of its moisture before reaching the regions farther inland.
Valleys introduce additional effects. Cold, dense air can drain downslope and collect in low-lying areas, especially on clear, calm nights. This can make a valley colder than nearby slopes and sometimes produce temperature inversions, in which air near the ground is colder than air above it. Inversions can influence frost risk, fog, and the accumulation of air pollution.
The orientation of a slope also matters. In the Northern Hemisphere, south-facing slopes generally receive more direct sunlight than north-facing slopes, while the opposite pattern occurs in the Southern Hemisphere. These differences can affect snowmelt, soil moisture, vegetation, and local temperature.
Together, these effects can create distinct microclimates: localized climate conditions that differ from those of the surrounding area. A shaded mountain hollow, a sunny hillside, and a nearby valley floor may have noticeably different growing conditions even though they are geographically close.
Land cover changes how the surface absorbs and releases energy
The characteristics of the ground also influence local climate. Soil, vegetation, snow, water, and built surfaces differ in how they absorb sunlight, store heat, reflect energy, and transfer moisture into the atmosphere.
Albedo is the fraction of incoming sunlight that a surface reflects. Snow and ice generally have high albedo, reflecting much of the sunlight they receive. Darker surfaces tend to absorb more solar energy. This difference affects how quickly surfaces warm and how much energy remains available to heat the air or melt snow and ice.
Vegetation influences temperature through both shading and evaporation. Plants draw water from the soil and release water vapor through their leaves, a process called transpiration. Together with evaporation from soil and other surfaces, transpiration contributes to evapotranspiration. This process transfers energy into the atmosphere as water changes from liquid to vapor, limiting how much energy directly heats the surface.
Where soil moisture is abundant, more available energy can go toward evaporation and transpiration. Where the ground is dry, less energy is used for these processes, so surface temperatures can rise more quickly. This helps explain why dry landscapes often experience intense daytime heating.
Urban areas can develop distinct local climates. Roads, roofs, and buildings absorb and store heat, while limited vegetation and altered surface drainage can reduce evaporative cooling. Waste heat from vehicles, buildings, and industrial activity adds to the effect. These influences contribute to the urban heat island effect, in which built-up areas are often warmer than surrounding rural areas, particularly at night.
Land cover can also influence humidity, runoff, and the local movement of air. However, its effects depend on regional climate and geography. Replacing vegetation with a different surface may have a substantial local impact without necessarily changing the larger-scale climate patterns governed by latitude, oceans, and atmospheric circulation.
Why nearby regions can have different climates
The strongest explanation for regional climate differences often comes from the interaction of several factors rather than from any single one. Latitude establishes broad patterns of solar energy, but elevation can cool a location considerably. Oceans moderate temperatures and supply moisture, while winds determine how much of that moisture reaches the land. Mountains can then force the air upward, extract moisture, and leave dry conditions on the opposite side.
Consider two locations at similar latitudes. A coastal community exposed to moist ocean winds may have mild temperatures and frequent rainfall. An inland community at the same latitude may have hotter summers, colder winters, and less precipitation because it lies farther from the ocean and receives drier air. If a mountain range separates the two, the contrast may become even greater.
The same combination of factors helps explain climate differences across the United States. The Pacific coast often benefits from ocean moderation, while parts of the interior West experience arid conditions shaped by distance from moisture sources and mountain rain shadows. The central plains are exposed to air masses arriving from different directions, producing large temperature changes and variable precipitation. The southeastern states generally receive abundant moisture from the Gulf of Mexico and the Atlantic, while higher elevations in the Appalachian and Rocky Mountains tend to be cooler than surrounding lowlands.
These are broad tendencies, not uniform conditions. Coastal California, for example, has a different rainfall pattern from the Pacific Northwest, despite both regions bordering the Pacific Ocean. The difference reflects the combined influence of latitude, seasonal atmospheric circulation, ocean conditions, and local geography.
Scientists describe climate using several variables, including average temperature, precipitation, humidity, wind, cloud cover, and the frequency of extreme conditions. Two regions with similar average temperatures may still have very different climates if one receives rainfall throughout the year while the other has a pronounced wet season and dry season. Likewise, annual precipitation totals alone do not reveal whether water arrives as frequent light rain, intense storms, or winter snow.
Understanding a region’s climate therefore requires examining both averages and patterns. Seasonal changes, day-to-day variability, and the distribution of rainfall can be just as important as annual temperature.
Climate changes over time, but its basic controls remain important
Latitude, elevation, oceans, and winds provide a foundation for understanding climate, but regional climates are not permanently fixed. They can change as atmospheric composition, ocean circulation, land cover, and other parts of the climate system change.
The increasing concentration of greenhouse gases in the atmosphere, primarily from human activities, is warming the planet. These gases absorb and reemit infrared radiation, reducing the rate at which Earth loses energy to space. As the planet warms, the atmosphere and oceans change, influencing temperature patterns, evaporation, precipitation, snow cover, and the distribution of some weather extremes.
The consequences vary by region. A warmer atmosphere can hold more water vapor, increasing the potential for heavier precipitation when conditions support rainfall. In other places, changes in evaporation and atmospheric circulation can contribute to greater drying. Shifts in snowpack and the timing of snowmelt can affect water supplies, while rising ocean temperatures influence marine heat conditions and the energy available to some storms.
These changes do not mean that every location will warm at the same rate or become uniformly wetter or drier. Regional outcomes depend on local geography and on how the atmosphere, oceans, and land interact. Scientists can explain many of the underlying mechanisms with confidence, but the magnitude and timing of some local changes remain uncertain.
The basic controls of climate continue to operate within this changing system. Latitude determines the broad distribution of solar energy. Elevation shapes temperature and atmospheric pressure. Oceans store and transport heat while supplying moisture. Winds move air masses and influence where heat and precipitation are distributed. Landforms and surface characteristics modify these effects at local and regional scales.
A region’s climate emerges from the combined action of all these influences over time. No single factor tells the entire story, but understanding how they work together provides a clear explanation for the remarkable variety of climates found across Earth.