Rising greenhouse gas concentrations reshape the planet through interconnected impacts. One of the most visible is sea level rise, driven by the thermal expansion of warming ocean water and the melting of glaciers and ice sheets. Sea levels have risen roughly 20 cm since 1900, and depending on emissions, they could rise another 0.3 m to over 1 m by 2100 according to IPCC estimates, threatening coastal communities worldwide. Climate change also intensifies the water cycle: warmer air holds more moisture, producing more intense precipitation events in some regions and prolonged droughts in others. A drought is a period of below-normal precipitation, and climate change is increasing both the severity and frequency of droughts in many areas, sometimes leading to desertification — the degradation of land in arid regions into desert through a combination of climate change, deforestation, and unsustainable farming.
Ecosystems and biodiversity are similarly affected. Shifting habitats, altered migration patterns, and coral bleaching stress species worldwide. Coral bleaching occurs when stressed corals expel their symbiotic zooxanthellae algae and turn white, primarily because of elevated sea temperatures. Permafrost thaw compounds the warming problem: as permanently frozen ground melts, it releases stored methane and CO₂, creating a dangerous positive feedback loop. Ocean warming also produces stratification, in which surface waters become less dense and vertical mixing with cooler deep water is reduced, limiting nutrient and oxygen circulation. On land, higher temperatures, prolonged droughts, and drier vegetation increase the frequency, size, and severity of wildfires. Climate feedback loops of these kinds are particularly concerning when they cross tipping points — critical thresholds beyond which changes become self-reinforcing and irreversible, such as the potential collapse of the West Antarctic Ice Sheet.
Human systems are increasingly strained. Agriculture faces altered growing seasons, increased droughts and floods, heat stress on crops, and shifting pest and disease ranges. People forced to leave their homes because of climate-related events such as sea level rise, extreme droughts, or recurring disasters are known as climate refugees. These cascading impacts underscore why scientists and policymakers focus on limiting warming, particularly beyond the 1.5°C threshold identified in the 2018 IPCC Special Report, after which risks of severe coral reef loss, extreme weather, and food insecurity increase dramatically.