Climate variability and change refer to alterations in the statistical distribution of climate elements over an extended period. Long-term averages of weather patterns define a region's climate, while variations lasting decades or longer constitute climate change.
The balance between incoming solar radiation and outgoing thermal radiation determines whether the planet warms or cools. When more energy enters than leaves, the planet warms, whereas if more energy escapes than arrives, global temperatures drop.
Human activities have increased greenhouse gas concentrations since the Industrial Revolution. The US Geological Survey estimates that human emissions exceed volcanic outputs by one hundred to three hundred times.
Scientists analyze tree rings to infer past precipitation and temperature trends through dendroclimatology. Ice cores drilled from Antarctic sheets contain trapped air bubbles that reveal historical carbon dioxide variations dating back hundreds of thousands of years.
Ocean basins like the Pacific exhibit decadal oscillations such as the El Niño Southern Oscillation cycle which repeats every two to seven years. These cycles influence rainfall patterns and storm tracks worldwide during warm phases when tropical sea surface temperatures rise across the eastern Pacific.