Rainforests, whether tropical or temperate, represent some of the planet’s most diverse biological systems. These complex environments, home to a vast percentage of the world’s plant and animal species, govern regional weather patterns and help stabilize the global climate. The continuous pressures from a changing climate are now actively disrupting the sensitive internal workings of these forests, threatening their ability to sustain life and perform their global ecological functions. Understanding how these ecosystems are responding to a warming world illuminates the scale of the challenge to preserve these irreplaceable biomes.
Thermal and Moisture Stress on Ecosystems
Climate change directly attacks the physiological function of rainforest plants by increasing heat and altering water availability. Rising average temperatures push trees past their thermal optimum, forcing them to use more energy for survival through a process called respiration. This accelerated metabolic rate can lead to an energy deficit, reducing the net carbon gain that fuels growth and overall biomass accumulation. The result is a slow, systemic weakening of the forest canopy.
The hydrological cycle is simultaneously disrupted by intensifying extremes. Prolonged, severe droughts are becoming more frequent and intense, particularly in regions like the Amazon, causing widespread leaf shedding and reduced stream flow. Conversely, other regions experience more intense rainfall events, which increase surface runoff and accelerate the erosion of the nutrient-poor topsoil.
Shifts in Species Distribution and Biodiversity
The biological consequences of thermal and moisture stress manifest as forced migrations and a breakdown of synchronized life cycles. Many species, particularly those highly sensitive to temperature like amphibians and insects, are attempting to move their ranges uphill in a phenomenon known as elevation shift. Tropical species are migrating upslope faster than their temperate counterparts, following cooler temperatures higher up the mountainsides. This movement is problematic because organisms with limited dispersal ability or those living on isolated mountain peaks may run out of suitable habitat, a situation scientists describe as the “escalator to extinction.”
For species that cannot move, the overall species richness of a given area declines as heat-sensitive organisms die out, while climate cues are also desynchronizing interdependent life events, creating “trophic mismatch.” For example, a change in temperature may cause a plant to flower earlier, disrupting the availability of nectar for specialized pollinators. When the plant’s flowering period no longer coincides with the pollinator’s peak activity, the reproductive success of both species is compromised, weakening the food web structure.
Increased Vulnerability to Fire and Pest Outbreaks
Climate-induced stress amplifies the risk of large-scale destructive events that fundamentally alter the rainforest structure. The severe droughts described earlier dry out the forest floor, transforming the typically damp environment into a flammable landscape. This fuel, combined with higher temperatures, allows fires—often ignited by human activity—to spread uncontrollably into areas that were historically fire-resistant. Once burned, the forest is severely degraded and becomes even more susceptible to future fires.
Trees weakened by prolonged water and heat stress lose the ability to fend off natural threats, making them highly vulnerable to insect pests and pathogens. A stressed tree cannot produce enough defensive compounds, such as resins, to deter borers and other insects. This increased susceptibility can lead to widespread die-offs, accelerating the pace of canopy loss and forest degradation beyond what is caused by drought alone.
Rainforests as a Carbon Cycle Regulator
Rainforests play a significant global role as massive carbon sinks, absorbing and storing vast amounts of atmospheric carbon dioxide in their extensive woody biomass. This function helps to mitigate the rate of global warming by drawing down greenhouse gases. However, the growing stress from heat and drought is diminishing the forest’s capacity to absorb carbon and is pushing some regions toward a dangerous “tipping point”.
When tree mortality rates increase due to climate extremes, the forest’s net carbon uptake declines. Research on Australian tropical rainforests, for example, has shown that increased tree deaths caused the ecosystem to transition from a net carbon sink to a net carbon source around the year 2000. Between 2010 and 2019, these forests lost close to a thousand kilograms of carbon per hectare annually from their above-ground biomass, releasing more carbon through decomposition and death than they absorbed through growth. If other major rainforests, such as the Amazon, follow this trend, the loss of this natural climate buffer will accelerate the rise of atmospheric carbon dioxide, intensifying global warming.