The University of Arizona

Global Climate

satellite photo of the Earth

Credit: ©NASA Visible Earth

Basic Concepts
The climate system is dynamic and complex. While weather details changes over short periods of time, like when anvil-shaped clouds burst in the late afternoon during monsoon season, climate describes average conditions over longer intervals. Understanding this distinction and other basic concepts such as radiative forcing and the enhanced greenhouse gas effect can clarify how the climate is changing and how humans have contributed to that change.

Climate Dynamics
Energy from the Sun powers the climate system, driving forceful winds and ocean currents that redistribute the energy around the globe. Many regions are connected, and changes that occur in one area can alter climate and weather in regions thousands of miles away. Although the climate system is always in motion, many patterns are recognizable, such as the El Niño–Southern Oscillation (ENSO) phenomenon.

Climate Controls
The climate system is controlled by the amount of solar energy available to drive it. Changes in solar energy driving the Earth's climate are primarily due to variations in the Sun’s solar output, changes in the Earth’s position in space, periodic volcanic eruptions, and alterations in atmospheric concentrations of greenhouse gases. Changes in these controls incite feedbacks that also affect the climate.

Past and Present Climate
Widespread monitoring has helped document recent climate change and has enabled scientists to detail ancient climatic conditions. Pre-historic and modern records reveal that prolonged glaciations and shorter warmer periods have occurred during the past two million years—as have temperature swings of 15 degrees F within a decade—while confirming that recent warming is greater than at any other time in the past 1,000 years.

El Niño-Southern Oscillation
El Niño and La Niña are phrases frequently tossed around to explain weather conditions in the Southwest. The sibling events, born thousands of miles away in the tropical Pacific Ocean, can deliver copious rain and snow to the region or cause widespread drought.