What is climate change and why does it matter?
Climate change refers to long-term shifts in temperatures and weather patterns, primarily warming observed since the mid-20th century. The dominant driver is an enhanced greenhouse effect from human activities that increase heat-trapping gases in the atmosphere. Natural factors also influence climate, but measurements and models show that human emissions are the primary cause of the rapid warming since the 1950s. This explainer outlines the physical mechanisms, key gases, and evidence used to attribute climate change.
Key greenhouse gases and their sources
Greenhouse gases absorb infrared radiation and warm the lower atmosphere. The most significant human-related emissions come from burning fossil fuels, industrial processes, agriculture, and land-use change. Each gas has a different capacity to trap heat and a different lifetime in the atmosphere. Tracking their concentrations and sources helps quantify responsibility and guide mitigation.
- Carbon dioxide (CO₂): emitted mainly by combustion of coal, oil, and natural gas; also by deforestation and some industrial processes.
- Methane (CH₄): released from livestock, rice cultivation, landfills, and fossil fuel extraction and use.
- Nitrous oxide (N₂O): from agricultural soils, fertilizer use, and some industrial activities.
- Fluorinated gases: synthetic gases used in refrigeration and industry with high heat-trapping potential.
Human activities that drive emissions
The primary human causes of rising atmospheric greenhouse gases are energy production, transportation, industry, agriculture, and land-use change. Burning coal, oil, and gas for electricity, heat, and vehicles accounts for the largest share of CO₂ emissions. Deforestation reduces carbon sinks and can add stored carbon to the atmosphere when trees are burned or left to decay. Industrial processes release both CO₂ and non-CO₂ gases, often with high global warming potential per unit mass.
How we know humans are the main cause
Scientists compare observations of warming with climate models that include either only natural factors or both natural and human factors. Models that include human greenhouse gas emissions reproduce the observed warming pattern, including the faster warming at night and in winter and the structure of warming in the upper atmosphere. Observations show atmospheric CO₂ increasing to levels not seen in millions of years, and the isotopic signature confirms the added carbon comes from fossil sources.
| Metric | Verified Detail | Source Type |
|---|---|---|
| Atmospheric CO₂ concentration (2024) | ≈420 ppm | Instrumental record (Keeling Curve) |
| Pre-industrial CO₂ level | ≈280 ppm | Ice-core records |
| Human contribution to CO₂ emissions | ≈99% from fossil fuels and industry | Carbon isotope analysis and inventory data |
| Global surface warming since late 19th century | ≈1.1°C | Multiple dataset compilations (NASA, NOAA, HadCRUT) |
| Share of warming attributable to human GHGs | >99% for observed net warming since mid-20th century | Detection and attribution studies (IPCC, NCA) |
Natural influences on climate
Natural factors have always influenced Earth’s climate, but their recent impact is small compared to human influences. Volcanic eruptions can temporarily cool the planet by ejecting aerosols that reflect sunlight. Changes in solar output produce minor variations over cycles of years to decades. Orbital shifts operate over tens to hundreds of thousands of years. Internal variability, such as El Niño and La Niña, causes year-to-year fluctuations but does not alter the long-term warming trend.
Climate feedbacks and amplifying changes
Feedback processes can amplify or dampen initial warming. Melting ice reduces reflectivity (albedo), causing more absorption of sunlight. Thawing permafrost can release stored CO₂ and methane, further increasing warming. Warmer air holds more water vapor, a potent greenhouse gas, which amplifies temperature changes. Ocean warming reduces its ability to absorb CO₂, leaving more in the atmosphere. These feedbacks are well established in climate science and are included in IPCC assessments.
Addressing common points of confusion
Not all warming is the same everywhere, and not all climate variation signals long-term change. Cold snaps and weather events still occur, but climate change shifts the baseline and increases the odds of extreme heat, heavy precipitation, and coastal high-water events. The role of CO₂ is not speculation; it is measured directly and supported by physics first demonstrated in the 19th century. Claims that recent warming is purely natural are inconsistent with the full body of evidence and fail to explain the observed pattern of warming and ocean heat uptake.
Summary of major causes and relative influence
The evidence consistently shows that greenhouse gases from human activities are the dominant cause of the rapid warming observed since the mid-20th century. Natural factors have small effects over the timescales of decades. The primary human sources are fossil fuel combustion and land-use change, with strong contributions from agriculture and some industrial gases. Attribution studies, isotopic data, and observed vertical warming patterns confirm that the increased greenhouse effect is from human emissions.
What this means for action
Because human activities are the main cause, reducing emissions from energy, transport, industry, and agriculture can limit future warming. Protecting and restoring natural carbon sinks, such as forests and wetlands, can enhance removal of CO₂. Understanding the causes clarifies responsibility and guides effective policies, technologies, and investments to stabilize the climate while supporting resilient communities and ecosystems.