Climate is average atmospheric conditions over a period (usually 30 years). Climate constantly changes over various periods of decades, centuries and beyond. The causes include natural factors such as solar activity anomalies, volcano eruptions, and variations in the Earth's orbit, and human factors such as emissions of radiation-active gases and particles from fossil burning. The climate change concerned most recently is mainly related to the global warming induced by the increasing atmospheric CO2 concentrations since the industrial revolution. There are observational and simulation evidence for the climate change as indicated by the increasing trends in global temperature and extreme weather events in the past century. The scientific consensus on climate change described in the recent IPCC Assessment Report is that climate is changing and that these changes are in large part caused by human activities. The trends are likely to continue this century based on projections by climate models and future emission scenarios.
Climate change can dramatically impact ecosystems, likely leading to more frequent and intense forest disturbances such as wildfires. Weather and climate are determinants for wildfire characteristics along with fuel properties and topography. Under warm and dry conditions, a fire season becomes longer, and fires are easier to ignite and spread. Wildfires, especially catastrophic wildfires, have increased in recent decades in both the United States and other parts of the world. Among the converging factors were extreme weather events, such as extended drought. Wildfires are expected to continue to increase this century in response to the projected climate change.