Climate change represents a significant long-term alteration in global or regional climate patterns, primarily driven by human activities, particularly the emission of greenhouse gases. The Earth’s average surface air temperature has risen by at least 1.1° Celsius (1.9° Fahrenheit) since 1880, with the majority of this warming occurring since 1975 at a rate of roughly 0.15 to 0.20°C per decade.
Changes to Earth’s Physical Systems
Global temperatures continue to rise, with the decade from 2014 to 2023 warming to an average of 1.19 °C compared to the pre-industrial baseline of 1850–1900. This warming is not uniform; land temperatures generally increase more than sea surface temperatures, and the Arctic experiences the most pronounced warming.
Rising temperatures drive widespread melting of ice and glaciers. Glaciers and ice sheets, including those in Greenland and Antarctica, are shrinking and receding, contributing to sea level rise. Warmer air causes ice to melt more quickly and flow faster towards the sea. Warmer ocean waters also contribute by melting the base and edges of ice sheets, accelerating the calving process where ice breaks off to form icebergs.
Rising sea levels result from the thermal expansion of warming ocean water and melting ice. Since the early 1970s, global mean sea level has increased, primarily due to thermal expansion and ice loss from glaciers and ice sheets. The rate of sea level rise has accelerated, from 1.3 mm per year between 1901 and 1971 to 3.7 mm per year between 2006 and 2018.
Oceans are experiencing significant changes beyond just rising levels. They absorb about 90 percent of the excess heat generated by rising greenhouse gas emissions. This ocean warming contributes to the formation of oxygen-depleted dead zones, making large coastal and open ocean areas uninhabitable for marine life. Additionally, as oceans absorb more carbon dioxide, the seawater becomes more acidic, a process known as ocean acidification. This increased acidity makes it harder for marine organisms, such as corals, shellfish, and plankton, to build and maintain their calcium carbonate shells and skeletons.
Climate change is also altering the frequency and intensity of extreme weather events. Heat waves, droughts, heavy rainfall, and powerful storms are becoming more common and severe. For instance, heatwaves, like the one in Europe in 2003 which caused over 70,000 deaths, have been found to be at least twice as likely due to human influence on global temperatures.
Effects on Natural Ecosystems
Climate change impacts natural ecosystems significantly. Rising temperatures, sea level rise, and extreme weather events contribute to widespread habitat loss and degradation. For example, warmer ocean temperatures cause massive coral bleaching, leading to the collapse of these ecosystems which support vast numbers of fish. Coastal habitats like saltmarshes and mudflats are being lost to rising sea levels and erosion, with the UK losing 100 hectares annually. Wildfires, fueled by higher temperatures and increased dry fuel from dead trees, also destroy forest habitats.
Species are forced to shift their geographic ranges and migration patterns as their traditional habitats become unsuitable. Many species, including mammals like moose, are moving towards higher latitudes or elevations in search of cooler climates. Marine species are also shifting, generally northward, eastward, or into deeper waters in response to warming ocean temperatures. These shifts can disrupt the timing of life-cycle events, such as breeding and migration, if species rely on environmental cues that are no longer aligned with their food sources.
Rapid environmental change increases the risk of biodiversity loss and extinction. Climate change is becoming a significant driver of biodiversity loss, alongside overexploitation and habitat destruction. At least 3,500 animal species are directly threatened by climate-related stresses, with invertebrates and marine species facing particular danger. Populations unable to migrate or adapt, such as some plant and insect species, face local extinction.
Disruptions to food webs occur when changes in one species’ life cycle or population cascade through an entire ecosystem. For instance, in Arctic tundra and boreal forests, warming temperatures have altered food webs, leading to small mammals shifting their primary energy source from plants to fungi. In marine environments, warming and acidification can weaken food webs by reducing energy flow to higher trophic levels.
Changes in plant life cycles are also evident, affecting growing seasons and agricultural yields. Increased temperatures can accelerate plant life cycles, leading to quicker maturation but less time for photosynthesis, resulting in smaller yields for crops like corn and soybeans. While some crops like wheat and rice may benefit from increased CO2 levels, extreme weather events such as heat waves and droughts can offset these gains, potentially causing significant yield reductions. Warmer temperatures also allow pests and diseases to reproduce more generations or invade new territories, further impacting plant health and agricultural productivity.
Consequences for Human Well-being
Climate change directly and indirectly impacts human societies, affecting food and water security. Droughts, floods, and altered growing seasons directly affect agricultural production and access to clean drinking water. Rising temperatures can reduce crop water productivity, requiring more water input to achieve the same yields, while also depleting freshwater sources from rivers, lakes, and reservoirs. Extreme weather events can damage crops, disrupt planting and harvesting, and erode fertile topsoil, further jeopardizing food supplies.
Human health faces multiple challenges from a changing climate. Temperature and precipitation changes enhance the spread of vector-borne diseases like malaria and dengue fever, as warmer conditions facilitate the establishment of vectors in new regions. Heat-related illnesses are also increasing, with heat-related deaths among those over 65 rising by 70% in two decades. Climate-related disasters can also lead to respiratory problems from air pollution and significant mental health impacts, including anxiety and post-traumatic stress.
Displacement and migration are increasingly linked to climate change. Sudden events like floods and landslides, as well as slow-onset processes such as desertification and sea level rise, force people from their homes. In 2022, over 32 million climate-linked internal displacements were recorded, primarily due to floods and storms. Projections suggest an additional 250 million people could be displaced by environmental factors over the next 35 years.
Infrastructure is vulnerable to damage from extreme weather events and rising sea levels. Coastal infrastructure, including roads, bridges, and water supplies, faces risks from sea level rise and increased high-tide flooding. Intense rainfall can overwhelm outdated sewer systems, leading to untreated wastewater flowing into local water bodies. Heat waves can put immense pressure on electric grids, causing power outages, while permafrost thaw in northern regions damages roads and building foundations.
Economic impacts are substantial, including costs for disaster recovery and losses across various industries. Climate disasters have cost North America $415 billion in the last three years, largely due to wildfires and hurricanes. Warmer temperatures, sea level rise, and extreme weather negatively affect sectors such as agriculture, forestry, fisheries, and tourism. For instance, ocean warming and acidification threaten fisheries, impacting food security and the livelihoods of coastal communities.