What Is Climate Change?
Climate change refers to long-term shifts in Earth's temperatures and weather patterns. The climate has changed naturally before — ice ages came and went — but today the term almost always means the r New to the topic? Start with our plain-language explainer on what climate change is.apid warming driven by human activity since the mid-1800s.
The key distinction is between weather and climate. Weather is today's rain or this week's heat wave; climate is the average pattern over decades. When scientists say the climate is changing, they mean those long-term averages are shifting. Earth has warmed roughly 1.2°C (2.1°F) since the late 19th century, and the pace is accelerating.
The Greenhouse Effect: How Earth Regulates Its Temperature
To understand climate change, start with the greenhouse effect — a natural process that makes Earth habitable. Sunlight warms the planet's surface, and Earth radiates some of that energy back toward space as heat. Greenhouse gases in the atmosphere absorb this outgoing heat and re-radiate it back down. Without this effect, Earth's average temperature would be about −18°C (0°F) instead of the comfortable 15°C (59°F) we enjoy.
The main greenhouse gases are carbon dioxide (CO₂), methane (CH₄), and nitrous oxide (N₂O). The problem is concentration, not existence: human activities have raised atmospheric CO₂ about 50% since the Industrial Revolution began, from roughly 280 to more than 420 parts per million — a level not seen in at least 800,000 years. More greenhouse gases mean more trapped heat.
What Causes Climate Change?
The overwhelming driver of today's climate change is human activity, especially the burning of fossil fuels. Multiple independent assessments have found that essentially all of the warming since the mid-20th century is attributable to human influence. Here are the main contributors.
Burning Fossil Fuels
Coal, oil, and natural gas stored carbon underground for millions of years; burning them for electricity, heating, transportation, and manufacturing releases it as CO₂. Fossil fuel combustion is by far the largest source of greenhouse gas emissions — roughly three-quarters of the total — led by electricity and heat production, followed by transportation and industries like steel and cement.
Deforestation and Land-Use Change
Forests act as carbon sinks: trees absorb CO₂ as they grow and store the carbon in wood, roots, and soil. When forests are cleared — often for farmland or grazing — that stored carbon returns to the atmosphere, and the planet loses a sink that would have kept absorbing more. Tropical deforestation alone accounts for roughly 10% of human-caused CO₂ emissions, and draining peatlands releases carbon that accumulated over thousands of years.
Agriculture and Industry
Livestock, especially cattle, produce methane during digestion — and methane traps more than 80 times as much heat as CO₂ over a 20-year period. Synthetic fertilizers release nitrous oxide, another potent greenhouse gas, and rice paddies emit methane as well. Beyond agriculture, industries release fluorinated gases used in refrigeration and manufacturing that are thousands of times more potent than CO₂, though in much smaller quantities.
Why Natural Causes Cannot Explain It
Volcanoes, solar changes, and orbital cycles have altered the climate in the past, but none account for the current warming. Solar output has actually declined slightly in recent decades while temperatures rose — the opposite of a Sun-driven change. Only rising greenhouse gases from human activity explain the observed pattern, including the telltale signature of a warming lower atmosphere and a cooling upper atmosphere, exactly as greenhouse physics predicts.
Effects of Climate Change
A warmer planet does not just mean slightly hotter days. Extra heat sets off a chain of consequences that touch nearly every aspect of life on Earth.
Rising Temperatures and Heat Waves
Average global temperatures keep setting new records, but the most dangerous change is in extreme heat. Heat waves are becoming more frequent, longer, and more intense across North America, Europe, Australia, and Asia. Prolonged extreme heat is already the deadliest weather hazard in many countries, putting outdoor workers, older adults, and people without cooling at serious risk.
Rising Seas and Coastal Flooding
As temperatures rise, seawater expands and glaciers and ice sheets melt, pushing sea levels higher. The average sea level has risen more than 20 centimeters (about 8 inches) since 1900, and the rate of rise has more than doubled in the last three decades — bringing more frequent coastal flooding, saltwater intrusion into freshwater supplies, and a growing threat to low-lying nations and coastal cities.
More Extreme Weather
A warmer atmosphere holds about 7% more water vapor for every 1°C of warming, fueling heavier downpours and severe flooding. Meanwhile, shifting rainfall and faster evaporation are intensifying droughts in the western United States, the Mediterranean, and parts of Australia. Warmer oceans energize hurricanes into stronger, wetter storms, while longer dry spells make wildfire seasons more destructive.
Pressure on Ecosystems and Wildlife
Species are being forced toward the poles or to higher elevations as habitats warm, but many cannot move fast enough. Coral reefs are among the hardest hit: warmer oceans cause coral bleaching, and mass bleaching events now occur too frequently for reefs to recover. Ocean acidification — driven by the oceans absorbing excess CO₂ — is additionally threatening shellfish, plankton, and the marine food webs that depend on them.
Effects on People and Economies
Shifting rainfall and extreme heat are reducing crop yields in some of the world's most productive farming regions, while drought and shrinking snowpack stress water supplies. The economic costs are mounting: climate-related disasters now cause hundreds of billions of dollars in damage each year, and the burden falls hardest on lower-income communities and developing countries that contributed least to the problem.
How Scientists Know: The Evidence
Climate science rests on multiple independent lines of evidence. Direct temperature records go back to the 1800s; satellites have measured the planet's energy balance from space since the late 1970s; and Antarctic and Greenland ice cores preserve ancient air bubbles showing how CO₂ and temperature moved together over hundreds of thousands of years.
Scientists can even "fingerprint" atmospheric CO₂: fossil fuels carry a distinctive ratio of carbon isotopes from ancient plant matter, and that exact signature is showing up in the rising CO₂ — proof it comes from burning fossil fuels, not volcanoes or oceans. Models that include human emissions reproduce the observed warming almost exactly; models that leave them out do not.
Solutions to Climate Change
The good news: climate change has known solutions. The cause is understood — greenhouse gas emissions from human activity — so the answer is clear: cut emissions to zero as quickly as possible, and remove some of what is already in the air.
Clean Energy and Electrification
The fastest-growing solution is replacing fossil fuels with clean electricity. Wind and solar are now the cheapest sources of new electricity in most of the world. Electric vehicles, heat pumps, and electric industrial processes let that clean electricity replace oil and gas across transportation and buildings, while modernized grids and battery storage keep the power flowing around the clock.
Protecting Forests and Changing Land Use
Stopping deforestation and restoring degraded forests, wetlands, and grasslands pulls CO₂ out of the atmosphere while protecting biodiversity. Farming practices that build soil carbon — cover cropping, reduced tillage, better grazing management — can turn farmland from an emissions source into a carbon sink. Cutting methane from livestock and food waste is another high-impact lever, since methane is so potent in the short term.
What Individuals Can Do
Individual actions matter most when they add up and shift larger systems. The highest-impact personal steps include:
- Switching to clean electricity for your home and choosing an electric vehicle or public transit when possible.
- Reducing air travel, one of the most carbon-intensive activities per person.
- Eating more plant-rich meals and reducing food waste — about a third of all food produced is never eaten.
- Improving home insulation and using energy-efficient appliances to cut heating and cooling demand.
- Supporting organizations, businesses, and policies that are working on climate solutions.
Policy and Collective Action
History shows the largest emission cuts come from policy: clean-energy standards, carbon pricing, methane regulations, and international agreements that align countries' efforts. Scientists say global emissions need to roughly halve by 2030 and reach net zero around mid-century to limit warming to 1.5°C. Every fraction of a degree of avoided warming prevents real harm.
Keep exploring: browse more explainers in our Science section, including how vaccines work and how photosynthesis powers the planet's carbon cycle.