page_title: Climate variability and change
section_title: Greenhouse gases
hierarchical_section_title: Climate variability and change / Causes / External climate forcing / Greenhouse gases
context_page_description: Climate variability includes all the variations in the climate that last longer than individual weather events, whereas the term climate change only refers to those variations that persist for a longer period of time, typically decades or more. In the time since the industrial revolution the climate has increasingly been affected by human activities that are causing global warming and climate change.
  The climate system receives nearly all of its energy from the sun. The climate system also radiates energy to outer space. The balance of incoming and outgoing energy, and the passage of the energy through the climate system, determines Earth's energy budget. When the incoming energy is greater than the outgoing energy, earth's energy budget is positive and the climate system is warming. If more energy goes out, the energy budget is negative and earth experiences cooling.
  The energy moving through Earth's climate system finds expression in weather, varying on geographic scales and time. Long-term averages and variability of weather in a region constitute the region's climate.
context_section_description: Whereas greenhouse gases released by the biosphere is often seen as a feedback or internal climate process, greenhouse gases emitted from volcanoes are typically classified as external by climatologists. Greenhouse gases, such as CO
  2, methane and nitrous oxide, heat the climate system by trapping infrared light. Volcanoes are also part of the extended carbon cycle. Over very long (geological) time periods, they release carbon dioxide from the Earth's crust and mantle, counteracting the uptake by sedimentary rocks and other geological carbon dioxide sinks. 
  Since the industrial revolution, humanity has been adding to greenhouse gases by emitting CO₂ from fossil fuel combustion, changing land use through deforestation, and has further altered the climate with aerosols (particulate matter in the atmosphere), release of trace gases (e.g. nitrogen oxides, carbon monoxide, or methane) . Other factors, including land use, ozone depletion, animal husbandry (ruminant animals such as cattle produce methane), and deforestation, are also play a role.
  The US Geological Survey estimates are that volcanic emissions are at a much lower level than the effects of current human activities, which generate 100–300 times the amount of carbon dioxide emitted by volcanoes. The annual amount put out by human activities may be greater than the amount released by supereruptions, the most recent of which was the Toba eruption in Indonesia 74,000 years ago.
caption: CO
  2 concentrations over the last 800,000 years as measured from ice cores (blue/green) and directly (black)