Climate change refers to long-term shifts in temperatures and weather patterns. While the climate has changed naturally throughout Earth's history, the scientific consensus is that human activity has been the main driver of warming observed since the mid-20th century.
The greenhouse effect, briefly
Certain gases in the atmosphere, including carbon dioxide and methane, trap heat from the sun that would otherwise radiate back into space -- a natural process known as the greenhouse effect that keeps Earth's climate habitable. Burning fossil fuels, deforestation, and industrial processes have significantly increased the concentration of these gases in the atmosphere since the Industrial Revolution.
How scientists measure and track change
- Direct temperature records from weather stations and ocean buoys, going back roughly a century and a half.
- Satellite measurements of temperature, ice cover, and sea level.
- Ice cores and tree rings, which provide indirect ("proxy") records of past climate conditions.
What the evidence shows
Major scientific organizations, including NASA and the National Oceanic and Atmospheric Administration, report that global average temperatures have risen over the past century, with the majority of that increase occurring in recent decades. Associated changes include rising sea levels, shrinking ice sheets, and shifts in precipitation patterns.
Why this is considered an area of scientific consensus
Multiple independent lines of evidence, gathered by researchers across many countries and institutions, point to the same broad conclusions about the causes and trajectory of recent warming. Major scientific bodies worldwide have released assessments affirming this consensus, even as researchers continue to refine specific projections and regional impacts.
What remains actively studied
Active areas of research include regional climate projections, the pace of ice-sheet loss, and the effectiveness of different mitigation and adaptation strategies -- questions where scientific understanding continues to develop as more data becomes available.
The main greenhouse gases
Carbon dioxide, released primarily through burning fossil fuels like coal, oil, and natural gas, is the largest contributor to human-caused warming by volume. Methane, released from sources including agriculture, landfills, and natural gas systems, is far less abundant but traps substantially more heat per molecule over a shorter timeframe. Other gases, including nitrous oxide and various industrial gases, contribute smaller shares.
Observed effects
- Rising average global temperatures, with the last several decades ranking among the warmest on record.
- Melting glaciers and polar ice, contributing to rising sea levels.
- Shifts in precipitation patterns, including changes in the frequency of some extreme weather events.
- Ocean warming and increased acidity as oceans absorb both heat and excess carbon dioxide.
Mitigation versus adaptation
Policy responses to climate change are generally grouped into two categories: mitigation, which means reducing greenhouse gas emissions to limit future warming, and adaptation, which means adjusting infrastructure and practices to cope with changes already underway or considered unavoidable. Governments, businesses, and researchers pursue both approaches simultaneously, and debates over the right balance and pace of each remain a significant part of climate policy discussions.
How this differs from past natural climate shifts
Earth's climate has changed many times over geological history due to natural factors like volcanic activity and variations in the planet's orbit. What distinguishes the current warming trend, according to climate scientists, is both its pace -- occurring over decades rather than millennia -- and the strong correlation with the timing and scale of human greenhouse gas emissions since industrialization, which is why the recent trend is attributed primarily to human activity rather than natural variability alone.
The shift toward renewable energy
Because energy production is one of the largest sources of greenhouse gas emissions, the transition toward renewable sources like solar, wind, and hydropower is widely viewed by researchers and policymakers as a central part of mitigation efforts. The cost of solar and wind power has fallen substantially over the past decade, making renewables increasingly competitive with fossil fuels in many markets, though questions about energy storage, grid infrastructure, and the pace of transition remain active areas of engineering and policy work.
