The Earth has experienced seven cycles of glacial advance and retreat over the last 650,000 years. The last ice age ended 7,000 years ago. The current warming period is happening much faster than past changes, and 95% of climate scientists agree that human activity since the mid-20th century is the cause. Weather is the localized climate of any given location, and it changes frequently, and climate is the average long-term weather conditions.

The greenhouse effect is the phenomenon of Earth's atmosphere holding energy from the Sun. Solar energy reflected from Earth's surface is absorbed by the atmosphere instead of radiating back into space. Greenhouse gases in the atmosphere trap solar energy to direct back to Earth. The reflected energy heats the lower atmosphere and the planet's surface. Some trapped heat has to radiate back to Earth to maintain a temperature able to support life however the atmosphere is currently holding in too much solar energy.

The Greenhouse gases are carbon dioxide, methane, nitrous oxide, and fluorinated gases. Natural sources of carbon dioxide include volcanic eruptions and normal respiration of plants and animals, but natural sources are insignificant compared to carbon dioxide from human activity. Carbon dioxide in the atmosphere has increased by more than a third since the industrial revolution. Though the gases do dissipate on their own eventually, they stay in the atmosphere for a long time. If all human activity releasing greenhouse gases stopped today, it would take hundreds of years for the carbon dioxide in the atmosphere to drop back to pre-industrial levels.

Satellite data shows that global sea levels are rising by an average of 3 millimeters per year. A significant proportion of increased sea levels is from the thermal expansion of seawater. Molecules of water are packed together when they are cold. The water molecules spread out as temperatures rise, and this results in more volume in the oceans. Melting mountain glaciers and polar ice sheets are also contributing to rising sea levels. The majority of glaciers in temperate regions and the Antarctic Peninsula are shrinking by an average of 4% each decade. Some glaciers, such as those in the Greenland Ice Sheet, are melting much more quickly.

Methane is a hydrocarbon gas. It comes from natural sources and human activities such as decomposing waste in landfills and agriculture. Rice cultivation produces more methane than almost any other crop. Cattle digesting food and the management of manure add methane to the atmosphere as well. Methane is much more active and harmful than carbon dioxide, but there isn't much methane in the atmosphere. There are large pockets of methane frozen under ice sheets. Some pockets are very close to the surface now due to years of melting ice. Researchers are monitoring large pockets of gas under thin ice because the impact on the atmosphere if released could be devastating to the environment.

Chlorofluorocarbons, or CFCs, are a very potent and harmful greenhouse gas that also destroys the ozone layer. They are entirely synthetic, so there are no natural sources. CFCs used to be heavily utilized in industry, but their use is strictly regulated now. Unfortunately, the regulations are not standard worldwide. Nitrous oxide is produced by soil cultivation, especially when commercial or organic fertilizer is used. Other sources of nitrous oxide are fossil fuel combustion, nitric acid production, and burning of biomass.

Burning fossil fuels is the main culprit of increasing greenhouse gases. Burning coal and oil produces carbon dioxide by combining oxygen in the air with carbon. Clearing land for agriculture, industry, and other human activities contribute carbon dioxide to a lesser extent than fossil fuels. Human activities often occur in a manner that multiplies negative effects on the atmosphere. Each person uses resources, and the population of humans worldwide is rising steadily. The resources used by the larger population often involve burning fossil fuels, while more land may be cleared for agriculture. Carbon sinks, such as forested areas, decline as burning fossil fuels increase.

Satellites and other technology let scientists examine conditions on Earth on a large scale. Ice cores from Greenland, Antarctica, and glaciers on tropical mountains provide evidence that greenhouse gas concentrations influence Earth's climate. Ancient evidence is found in tree rings, ocean sediments, sedimentary rock layers, and coral reefs. The information obtained from these sources clearly shows that the current warming period is happening approximately ten times faster than the average warming period.

Climate change contributes to severe weather events and disasters in several ways. The mechanism driving these changes is extensively researched and documented by researchers. Warm air holds more water vapor than cool air. The extra moisture causes more severe storms. Warmer air and warmer oceans alter currents such as El Nino and the Gulfstream. Severe, long-term droughts influence weather as well. The right conditions for a polar vortex occur more often, and then the polar vortex influences the weather patterns too. Each weather event and change has an effect, and a feedback loop develops.