Why the Climate Is Changing: Natural Processes and Human Influence

Weather and Climate Are Not the Same

Weather describes the short-term state of the atmosphere: today's temperature, tomorrow's rain, a strong wind, or several cold days. Climate describes typical weather conditions and their variability over a long period. Modern climate is assessed using decades of observations rather than a single day, season, or year.

A cold winter in one region therefore does not disprove global warming, just as one hot day does not prove it on its own. What matters is the long-term pattern: changes in average temperatures, precipitation, season length, glaciers, sea level, ocean heat, and the frequency of particular extreme events.

Why Climate Changed in the Past

The climate system responds to how much energy Earth receives from the Sun, how much it reflects back to space, and how much heat the atmosphere retains. In the past, climate was influenced by slow changes in Earth's orbit and axial tilt, variations in solar activity, major volcanic eruptions, continental movement, and natural changes in atmospheric composition.

Oceans also redistribute enormous amounts of heat. Phenomena such as El Niño and La Niña can temporarily raise or lower global average temperature and alter rainfall in different regions. These variations mainly move heat within the climate system, however, and do not explain the sustained accumulation of additional energy across the planet.

Natural Factors Do Not Explain Current Warming

If stronger solar activity were the principal cause of modern warming, researchers would observe a corresponding long-term increase in incoming solar energy. Measurements do not show an increase large enough to explain the current temperature rise. Major volcanic eruptions usually produce short-lived cooling because particles in the atmosphere reflect part of the incoming sunlight.

Natural variability can make individual years warmer or cooler, but it is superimposed on the long-term trend. Current warming is occurring across the atmosphere, ocean, and land and is accompanied by ice loss, sea-level rise, and other consistent changes that match the expected effects of a strengthened greenhouse effect.

How Human Activity Changes Earth's Energy Balance

Burning coal, oil, and natural gas transfers carbon into the atmosphere that had been isolated in geological deposits for millions of years. Deforestation and forest degradation release stored carbon and reduce the capacity of ecosystems to absorb CO₂. Agriculture, waste management, and industrial processes increase emissions of methane, nitrous oxide, and fluorinated gases.

These gases absorb part of the infrared radiation Earth emits after being warmed by sunlight. More energy therefore remains in the climate system. This does not mean heat is distributed evenly: some regions warm faster, while atmospheric and ocean circulation, precipitation, soil moisture, and the likelihood of extremes all change.

How Scientists Separate Different Causes

Climate attribution combines observations, physical laws, evidence from past climates, and computer models. Researchers compare a climate influenced only by natural factors with simulations that also include human-caused emissions. Models reproduce the observed long-term trend much more accurately when human influence is included.

Different causes also leave characteristic fingerprints. An enhanced greenhouse effect warms the lower atmosphere while the upper stratosphere cools. In many locations, nights warm faster than days and winters faster than summers. The ocean stores most of the excess heat. These patterns allow conclusions to be tested through multiple independent lines of evidence.

Feedbacks and Climate-System Inertia

Initial warming triggers processes that can amplify or reduce it. As snow and ice melt, the surface reflects less sunlight and absorbs more heat. Warmer air can hold more water vapour, which is itself a greenhouse gas. Vegetation and the ocean absorb part of human CO₂ emissions, but their capacity is not unlimited.

Oceans warm slowly and retain heat for a long time, while a fraction of emitted carbon dioxide remains in the climate system for centuries. The effects of today's emissions do not disappear immediately after emissions are reduced. The longer high emissions continue, the more difficult and costly it becomes to limit further warming.

What Climate Change Means in Practice

Climate change is not only an increase in average temperature. It changes the probability and intensity of heat, heavy rainfall, drought, fire weather, and coastal flooding. The consequences vary by region and depend on infrastructure, ecosystems, health systems, and society's capacity to adapt.

Two types of action must work together. Mitigation reduces emissions and increases greenhouse gas removals. Adaptation reduces vulnerability to changes that can no longer be fully avoided — through early-warning systems, water protection, resilient buildings, urban greenery, and ecosystem restoration.