"Global warming" redirects here. For other uses, see Climate change

Temperature records prior to global warming
Main articles: Climate variability and change and Paleoclimatology
Global surface temperature reconstruction over the last 2000 years using proxy data from tree rings, corals, and ice cores in blue.^[55] Directly observed data is in red.^[56]
Human beings evolved over the last few million years in a climate that cycled through ice ages, with global average temperature ranging between current levels and 5–6 °C colder than today.^[57][58] The temperature record prior to human evolution includes hotter temperatures and occasional abrupt changes, such as the Paleocene–Eocene Thermal Maximum 55.5 million years ago.^[59]
Historical patterns of warming and cooling, like the Medieval Warm Period and the Little Ice Age, did not occur at the same time across different regions. Temperatures may have reached as high as those of the late 20th century in a limited set of regions.^[60]
There was little net warming between the 18th century and the mid-19th century. Climate information for that period comes from climate proxies, such as trees and ice cores.^[61] Thermometer records began to provide global coverage around 1850.^[62]
Attribution of recent temperature rise
Main article: Attribution of recent climate change
Drivers of climate change from 1850–1900 to 2010–2019. There was no significant contribution from internal variability or solar and volcanic drivers.
The climate system experiences various cycles on its own which can last for years (such as the El Niño–Southern Oscillation (ENSO)), decades or even centuries.^[63] Other changes are caused by an imbalance of energy that is "external" to the climate system, but not always external to the Earth.^[64] Examples of external forcings include changes in the concentrations of greenhouse gases, solar luminosity, volcanic eruptions, and variations in the Earth's orbit around the Sun.^[65]
To determine the human contribution to climate change, known internal climate variability and natural external forcings are ruled out. Unique "fingerprints" for all potential causes are determined and compared with observed patterns of climate change.^[66] For example, solar forcing—whose fingerprint involves warming the entire atmosphere—is ruled out because only the lower atmosphere has warmed.^[67] Attribution of recent climate change shows that the climate's main driver is elevated greenhouse gases, with aerosols having a dampening effect.^[68]