Main Causes of Climate Change
The current period of rapid climate change is . Greenhouse gases absorb and re-emit infrared radiation, slowing the loss of heat from Earth into space. The Intergovernmental Panel on Climate Change (IPCC, 2023) concludes that human activities, principally through greenhouse-gas emissions, have unequivocally caused global warming.
The principal human causes of climate change are as follows:
- Overpopulation: puts greater pressure on the environment because more people require food, water, land, energy, housing and transportation. Meeting this increased demand can lead to faster extraction of forests, minerals, soil and freshwater, while greater energy use and land clearing contribute to climate change. At the same time, increased production and consumption create more sewage, plastic, chemicals and other waste, increasing air, water, and soil pollution. However, population size is only one factor—how much each person consumes and how resources are produced and managed also strongly determine environmental damage.
- Burning fossil fuels: Burning coal, oil, and natural gas for electricity, heating, transportation, and industrial activities releases large amounts of carbon dioxide (CO₂). The IPCC (2023) identifies fossil-fuel combustion and industrial processes as the largest sources of human-caused greenhouse-gas emissions.
- Deforestation and land-use change: Cutting or burning forests releases stored carbon dioxide and reduces the number of trees available to remove CO₂ from the atmosphere. The National Aeronautics and Space Administration (NASA, 2026) identifies both fossil-fuel burning and deforestation as major human sources of atmospheric carbon dioxide.
- Agriculture: Livestock digestion and manure management release methane, while rice cultivation also produces methane. The production and use of agricultural fertilizers release nitrous oxide. NASA (2026) explains that livestock, rice farming, manure, and fertilizer use are important human sources of methane and nitrous oxide.
- Industry and cement production: Industrial processes release carbon dioxide and fluorinated greenhouse gases. Cement production releases CO₂ both through fossil-fuel use and through the chemical conversion of limestone. The IPCC (2023) reports that industry, energy, transportation, and buildings together accounted for approximately 79% of global greenhouse-gas emissions in 2019.
- Waste disposal: Organic waste produces methane when it decomposes without sufficient oxygen in landfills. NASA (2026) identifies landfills as an important human source of atmospheric methane.
Natural factors—including volcanic eruptions, variations in solar activity, and natural ocean–atmosphere cycles—can affect Earth’s climate temporarily. However, these natural factors do not explain the sustained warming observed since the mid-20th century. NASA (2026) reports that solar energy has shown no sustained increase capable of explaining the observed temperature trend and that climate models cannot reproduce recent warming without including increased greenhouse-gas concentrations.
Evidence of Climate Change
1. Rising Global Temperatures
Measurements from weather stations, satellites, ships, and ocean buoys show a clear long-term increase in global surface temperature. The IPCC (2023) reports that the global surface temperature during 2011–2020 was approximately 1.1°C higher than the 1850–1900 average.
2. Increasing Greenhouse-Gas Concentrations
Direct atmospheric measurements and evidence from air trapped in ice cores show substantial increases in carbon dioxide, methane, and nitrous oxide since industrialization. The NOAA Global Monitoring Laboratory (2025) reports that the effective radiative forcing produced by long-lived greenhouse gases was 54% greater in 2024 than in 1990. It also reports that carbon dioxide was responsible for approximately 81% of this increase.
3. Warming Oceans
The oceans absorb most of the additional energy trapped by increased greenhouse-gas concentrations. NASA (2024b) reports that approximately 90% of the excess energy in Earth’s climate system is stored in the oceans and that the upper 100 metres of the ocean have warmed by approximately 0.33°C since 1969.
4. Melting Ice
Observations show that glaciers are retreating in many regions and that the Greenland and Antarctic ice sheets are losing mass. NASA (2024b) reports that Greenland lost an average of approximately 279 billion metric tons of ice annually between 1993 and 2019, while Antarctica lost approximately 148 billion metric tons annually during the same period.
5. Rising Sea Levels
Global sea level is rising because seawater expands as it warms and because melting glaciers and ice sheets add water to the oceans. NASA (2024b) reports that global sea level rose by approximately 20 centimeters during the 20th century and that the rate of rise during the most recent two decades has been nearly twice the average rate of the previous century.
6. Changes in Extreme Weather
Human-caused climate change is increasing the frequency and intensity of some extreme weather and climate events. NASA (2024a) reports that observed effects include longer and more intense heatwaves, increased wildfire conditions, longer droughts in some regions, and heavier rainfall associated with some tropical cyclones. The IPCC (2023) also concludes that human-caused climate change is already affecting weather and climate extremes in every region of the world.
7. Historical Climate Records
Scientists reconstruct past climates by examining ice cores, tree rings, corals, ocean sediments, rocks, and other natural records. NASA (2024b) explains that these independent records show a relationship between greenhouse-gas concentrations and Earth’s climate. They also indicate that the current warming is occurring approximately 10 times faster than the average warming following an ice age.
8. Ocean Acidification
Oceans absorb part of the carbon dioxide present in the atmosphere. As more CO₂ dissolves in seawater, it alters the chemical balance of the ocean, lowers pH, and reduces the availability of carbonate ions. These changes can make it more difficult for organisms such as corals, shellfish, and other marine species to build and maintain calcium carbonate shells or skeletons, and they may also affect marine food chains (U.S. Environmental Protection Agency [EPA], 2026).
9. Effects on Ecosystems and Biodiversity
Climate change can alter the geographic distribution of species, the timing of reproduction and migration, interactions among species, and the structure of ecosystems. Not all species are equally capable of adapting or moving rapidly enough in response to changing environmental conditions. As a result, some populations may decline, while the risk of extinction may increase for vulnerable species. The IPBES Global Assessment identifies climate change as one of the major direct drivers of changes in nature and biodiversity loss worldwide (Intergovernmental Science-Policy Platform on Biodiversity and Ecosystem Services [IPBES], 2019).
10. Human and Social Impacts
Climate change has both direct and indirect consequences for human health and can increase the risks of illness, mortality, malnutrition, and certain infectious diseases. Changing climatic conditions can also affect food production and access, water resources, and the livelihoods of communities, particularly those that are already vulnerable (World Health Organization [WHO], 2023; Food and Agriculture Organization of the United Nations [FAO], 2016).
References
Food and Agriculture Organization of the United Nations. (2016). The state of food and agriculture 2016: Climate change, agriculture and food security. https://openknowledge.fao.org/handle/20.500.14283/i6030e
Global Monitoring Laboratory. (2025, Fall). Annual Greenhouse Gas Index (AGGI). National Oceanic and Atmospheric Administration. Retrieved July 27, 2026, from https://gml.noaa.gov/aggi/aggi.html
Intergovernmental Panel on Climate Change. (2023). Climate change 2023: Synthesis report. Contribution of Working Groups I, II and III to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change. https://doi.org/10.59327/IPCC/AR6-9789291691647
Intergovernmental Science-Policy Platform on Biodiversity and Ecosystem Services. (2019). Global assessment report on biodiversity and ecosystem services of the Intergovernmental Science-Policy Platform on Biodiversity and Ecosystem Services (E. S. Brondízio, J. Settele, S. Díaz, & H. T. Ngo, Eds.). IPBES Secretariat. https://doi.org/10.5281/zenodo.3831673
National Aeronautics and Space Administration. (2024a, October 23). Effects. NASA Science. https://science.nasa.gov/climate-change/effects/
National Aeronautics and Space Administration. (2024b, October 23). Evidence. NASA Science. https://science.nasa.gov/climate-change/evidence/
National Aeronautics and Space Administration. (2026, July 13). Causes. NASA Science. https://science.nasa.gov/climate-change/causes/
World Health Organization. (2023, October 12). Climate change. https://www.who.int/news-room/fact-sheets/detail/climate-change-and-health
U.S. Environmental Protection Agency. (2026, April 21). Effects of ocean and coastal acidification on marine life. https://www.epa.gov/ocean-acidification/effects-ocean-and-coastal-acidification-marine-life