Wetlands create their own local climate that is cooler, more humid, and more temperature-stable than the surrounding landscape. Modeling studies show that areas with abundant wetlands can be roughly 1 to 3 degrees Celsius cooler in summer than equivalent areas without them, thanks to the enormous amount of energy wetlands absorb through evaporation. But the climate story of wetlands is not just about local cooling. These ecosystems also pump moisture into the atmosphere, store vast quantities of carbon, and release methane at rates that make them a major player in the global greenhouse gas budget.
How Wetlands Cool the Air Around Them
The fundamental reason a wetland feels cooler than a dry field on a hot day comes down to where solar energy goes. When sunlight hits dry ground, most of that energy heats the surface and the air above it. When it hits a wetland, a large share of that energy is spent evaporating water instead. That shift from heating the air to evaporating water is the core mechanism behind wetland cooling. Climate modeling that compares landscapes with and without wetlands finds that the wetlands ramp up evaporation while suppressing the heat that would otherwise radiate into the atmosphere, producing a cooling effect of about 1 to 3°C in summer where wetlands are widespread.1Water Resources Research. Cooling Effects Revealed by Modeling of Wetlands and Land‐Atmosphere Interactions
Satellite observations confirm this pattern in real-world conditions. During the day, natural wetlands absorb slightly more solar radiation than surrounding drylands, but they channel a greater proportion of that energy into evaporation rather than directly warming the air. The effect is especially pronounced in semi-arid regions, where the contrast in soil moisture between wet and dry ground dramatically shifts the energy balance.2Science of Remote Sensing. Satellite observation reveals wetland-induced local cooling moderated by regional climate gradients In practical terms, standing near a marsh or bog on a hot afternoon, you feel the difference. The air is tangibly cooler and heavier with moisture compared to just a few hundred meters away on bare soil.
This cooling is not uniform across seasons or times of day. Wetlands have the strongest cooling influence during warm months, when evaporation rates are highest. On winter days or at night, when evaporation slows, the temperature difference between wetland and non-wetland landscapes shrinks considerably. The effect also depends on wetland size and how saturated the ground is: a small, drying seasonal pool cools its surroundings far less than a large, permanently flooded marsh.
Humidity and Moisture That Travels Downwind
Wetlands do not just modify the climate immediately around them. The moisture they release into the atmosphere gets carried by wind and can contribute to rainfall hundreds of kilometers away. Research tracking atmospheric moisture transport over China found that wetlands have a widespread impact on both local and downwind precipitation. The moisture they recycle supports enough rainfall to sustain thousands of square kilometers of forest growth and provides freshwater for hundreds of millions of people. Strikingly, the benefits are not mainly local: roughly three-quarters or more of the forest growth, economic activity, and population supported by wetland-derived moisture are in downwind regions, not adjacent to the wetlands themselves.3Journal of Hydrology. Wetlands as a critical water source for local and downwind ecosystems and societies over China through atmospheric moisture transport
This means that draining or destroying a wetland does not just dry out its immediate surroundings. It can reduce rainfall for communities and ecosystems far away that depend on the moisture the wetland once released. The climate influence of a large wetland, in other words, extends well beyond its physical borders, making it a kind of regional water pump.
The Methane Side of the Equation
For all their cooling benefits, wetlands have a complicated relationship with climate. Freshwater wetlands cover a relatively small fraction of Earth’s land surface, yet they are the single largest natural source of atmospheric methane, contributing an estimated 25 to 45 percent of global natural methane emissions.4PubMed Central. Effect of Dry-Wet Cycling on Methanotrophs in Wetland Soils Methane is a potent greenhouse gas, far more effective at trapping heat than carbon dioxide over short time scales, so this is not a minor detail.
The methane comes from microbes that thrive in waterlogged, oxygen-poor soils. When a wetland is flooded, oxygen cannot reach the soil, and particular microorganisms break down organic material and produce methane as a byproduct. The warmer and wetter the conditions, the more active those microbes become and the more methane they release. Peatlands, which are a specific type of wetland with thick layers of partially decomposed plant material, are an especially significant source.5PubMed Central. Divergent Responses of Methane Emission to Warming in Waterlogged Versus Drained Alpine Peatlands
This creates a tension in how we think about wetlands and climate. On one hand, wetlands cool their surroundings, store carbon in their soils, and recycle moisture. On the other, they produce methane that warms the planet. Whether a given wetland is a net climate cooler or warmer depends on the balance between the carbon it locks away and the methane it emits, and that balance shifts with temperature, water level, and the type of vegetation growing there. Peatlands, for example, play a major role in long-term carbon storage, but sustained nitrogen pollution from agriculture and industry can weaken their ability to sequester carbon, diminishing their cooling effect over time.6PubMed Central. Long-Term Nitrogen Addition Eliminates the Cooling Effect on Climate in a Temperate Peatland
What Happens When Water Levels Shift
Wetland climate depends heavily on hydrology. Even small changes in how wet or dry the soil is can dramatically alter what gases the wetland releases. Research in Amazonian wetland soils found that when the water table drops during drought, methane emissions fall because the oxygen-free conditions that methane-producing microbes need are disrupted. But the trade-off is that carbon dioxide emissions can rise as oxygen reaches previously submerged soil and accelerates decomposition. Then, when a heavy rain arrives after a dry spell, the sudden re-wetting can trigger a burst of nitrous oxide, another powerful greenhouse gas.7Wetlands. Effects of Water Table Fluctuation on Greenhouse Gas Emissions from Wetland Soils in the Peruvian Amazon
The local climate of a wetland, in other words, is not fixed. It fluctuates with the seasons, with rainfall patterns, and with any human activity that alters drainage. A wetland that is permanently saturated has a different atmospheric signature than one that dries out every summer. The drying-and-rewetting cycle matters enormously, both for the microclimate you would experience standing in the wetland and for the gases it sends into the broader atmosphere.
Coastal Wetlands and the Marine Edge
Salt marshes, mangroves, and tidal flats sit at the boundary between land and sea and have a distinct climate profile. These coastal wetlands are continuously shaped by tides, saltwater intrusion, and wind off the ocean. They tend to have more moderate temperature swings than inland wetlands because the surrounding ocean buffers extremes. Coastal wetlands intercept pollutants flowing from land, regulate local microclimates, and play a major role in carbon cycling.8Land. An Improved Method for Estimating Blue Carbon Storage in Coastal Salt Marsh Wetlands
The carbon stored in coastal wetland soils is called “blue carbon,” and mangroves and salt marshes are among the most efficient ecosystems on Earth at locking carbon away in sediment. Long-term studies of mangrove and salt marsh carbon storage in southern China have tracked how these ecosystems have gained and lost carbon over decades, showing that their capacity to act as carbon sinks depends on whether they are expanding or shrinking.9Land. Temporal and Spatial Patterns of Blue Carbon Storage in Mangrove and Salt Marsh Ecosystems in Guangdong, China As sea levels rise, some coastal wetlands migrate inland, while others are squeezed out by development. The fate of blue carbon storage depends on whether those transitions are possible.
Salinity itself shapes the microclimate of coastal wetlands. In subtropical tidal marshes, evaporation concentrates salt in the upper soil layers, creating hypersaline zones that stress plants and alter how water and heat move through the system. Tidal flushing periodically washes some of that salt away, preventing the marsh from becoming a barren salt flat. The interplay between evaporation, tidal flow, and density-driven circulation of salty water underground creates a dynamic environment where conditions can change dramatically between high and low tide.
Wetlands in Cities
Urban planners have increasingly looked to wetlands as tools for cooling cities, and the evidence suggests they are among the most effective green infrastructure options available. A global synthesis of studies on urban heat mitigation found that wetlands cooled the air by an average of about 5°C, ranking alongside botanical gardens as the most efficient cooling features in cities.10PubMed Central. Urban heat mitigation by green and blue infrastructure: Drivers, effectiveness, and future needs That is a bigger effect than street trees or green roofs, on average, because the open water and saturated soils of wetlands are especially effective at converting heat energy into evaporation.
Size and design matter. A study of urban wetlands in Chengdu, China found that the cooling intensity of a wetland increases with its size, but the efficiency per unit area peaks at a surprisingly small threshold of roughly 1.5 hectares. Beyond that, making a wetland bigger still helps, but you get diminishing returns. Connecting small wetlands to each other through channels or waterways boosted their cooling effect further, with hydrological connectivity accounting for about 28 percent of the total cooling influence. The researchers concluded that building several small, interconnected wetlands in densely built-up neighborhoods is more efficient than constructing a single large, isolated wetland on the outskirts of town.11Building and Environment. The effects of the cooling efficiency of urban wetlands in an inland megacity: A case study of Chengdu, Southwest China
Tropical Wetlands and Seasonal Extremes
The climate inside a tropical wetland can swing between extremes that would be hard to imagine in a temperate setting. The Pantanal in Brazil, the world’s largest tropical seasonal wetland, floods extensively during the rainy season and then dries out dramatically during drought. These shifts are so severe that plants living there have to survive both standing water and genuine water stress within a single year. Research on trees in the Pantanal found that drought conditions slashed photosynthetic activity by around 80 percent compared to the wet season, as trees shifted their energy toward reinforcing leaf structure rather than growing.12Trees. Physiological adjustments of an invasive tree species to extreme hydrological events in a tropical seasonal wetland
The climate you experience in such a wetland is accordingly variable. During the flood season, the landscape is a warm, humid world of slow-moving water and dense vegetation, with evaporative cooling tempering the tropical heat. During the dry season, the same area can become parched, with higher air temperatures, lower humidity, and soils cracking under the sun. This annual transformation is one reason seasonal tropical wetlands support such unusual biodiversity: organisms that thrive there have evolved to handle both aquatic and terrestrial conditions.
Arctic Wetlands and Thawing Ground
At the other end of the temperature spectrum, Arctic wetlands are forming in new places as permafrost thaws. When permanently frozen ground collapses, it creates low-lying depressions called thermokarst that fill with water and become wetlands. These new wetlands have a distinct climate signature: they are warmer and wetter than the frozen tundra they replace, and they release significant amounts of methane. Research across thermokarst landscapes found that these wetlands emitted enough methane to create a net warming effect on the atmosphere, even though they were also absorbing carbon dioxide through plant growth.13PubMed. Changing Interactions Between Trace Gas Fluxes, Belowground Chemistry, and Plant Traits Across an Arctic Thermokarst Landscape
This is one of the feedback loops climate scientists worry about. Warming thaws permafrost, which creates wetlands, which release methane, which drives further warming. The Arctic is warming faster than the rest of the planet, so the rate at which new thermokarst wetlands form is accelerating. The local climate effect is straightforward: where there was once frozen, dry tundra, there is now a damp, relatively mild microenvironment. But the global effect may push temperatures higher.
When Wetlands Burn
Perhaps the most dramatic way climate and wetlands interact is through fire. In Southeast Asia, widespread deforestation and drainage of tropical peatlands have created conditions where what was once a permanently waterlogged, fire-resistant landscape becomes flammable during droughts. When El Niño-driven dry spells hit drained peatlands, catastrophic fires can ignite that burn not just vegetation but the peat itself, releasing enormous quantities of stored carbon and blanketing entire regions in hazardous smoke.14Environmental Research Letters. Climate change-induced peatland drying in Southeast Asia
Paleoecological records and charcoal analysis show that tropical peatland fires have surged in recent decades compared to the previous two thousand years, driven by the combination of land drainage and more intense droughts under a warming climate.15PubMed Central. Unprecedented Burning in Tropical Peatlands During the 20th Century Compared to the Previous Two Millennia The fires transform the local climate overnight: smoke blocks sunlight, air quality plummets, and the once-cool, humid wetland environment is replaced by a scorched landscape that heats up rapidly, no longer buffered by standing water. Once the peat is burned, the carbon that accumulated over centuries or millennia enters the atmosphere in weeks, and the cooling services that wetland once provided vanish with it.
Wetlands Through Deep Time
Wetlands have shaped Earth’s atmosphere for far longer than human civilization has existed. Ice core records spanning hundreds of thousands of years show that tropical wetlands and seasonally flooded plains were the dominant drivers of atmospheric methane changes across glacial and interglacial cycles. The amount of methane in the atmosphere rose and fell with changes in temperature, rainfall, and water tables, which expanded and contracted wetlands across the tropics.16PubMed Central. Glacial/interglacial wetland, biomass burning, and geologic methane emissions constrained by dual stable isotopic CH4 ice core records Peatlands have persisted globally for at least 130,000 years, appearing and disappearing across continents as ice sheets advanced and retreated.17PubMed Central. Widespread global peatland establishment and persistence over the last 130,000 y
This deep history matters because it shows that wetlands are not a passive backdrop to climate. They are active participants in a feedback loop that has been running for hundreds of millennia: warming expands wetlands, which release more methane, which drives further warming, until other factors push the system the other way. Today’s wetlands are responding to the same physics they always have. The difference now is that human activity, through drainage, pollution, and greenhouse gas emissions, is altering the system faster than it has shifted in tens of thousands of years, and the climate consequences are correspondingly harder to predict.