climate

Climate, in the scientific sense, refers to the long-term statistical properties of the atmosphere in a region or across the globe. It describes average conditions and their variability over extended periods, typically decades, in contrast to weather, which can change from hour to hour or day to day. Climate includes mean values such as average temperature and precipitation, as well as the distribution and frequency of extremes, seasonality, and other patterns.

The climate system consists of interacting components: the atmosphere, the hydrosphere (oceans, rivers, and groundwater), the cryosphere (ice and snow), the lithosphere (land surface), and the biosphere. Measurements from weather stations, satellites, and paleoclimate proxies are used to reconstruct past climates and monitor current changes. Climate is often summarized by metrics such as mean annual temperature, precipitation totals, and indices of variability; climate classification systems, such as Köppen, categorize regions by typical climate.

Climate is driven by internal variability and external forcings. Natural factors include orbital variations, volcanic eruptions, and fluctuations in ocean circulation. Human activities, notably the emission of greenhouse gases and land-use changes, alter the energy balance of the planet and are a major driver of recent warming. Climate models simulate the physics of the climate system and are used to project future changes under different emissions scenarios.

Observed changes in many regions include warming temperatures, altered precipitation patterns, retreat of glaciers, thawing of permafrost, changes in storm tracks, and rising sea levels. These changes affect ecosystems, agriculture, water resources, and infrastructure and interact with social and economic systems.

Addressing climate change involves monitoring and research, mitigation to reduce greenhouse gas emissions, and adaptation to reduce vulnerability to impacts. International cooperation and policy frameworks aim to align scientific knowledge with decision making.