“We will respond to the threat of climate change, knowing that the failure to do so would betray our children and future generations.” Barack Obama
“Climate change is a terrible problem, and it absolutely needs to be solved. It deserves to be a huge priority” Bill Gates
“We have to face the reality of climate change. It is arguably the biggest threat we are facing today” William Hague
“Climate Change is the greatest moral economic and social challenge of our time” Kevin Rudd
“Climate change is the major challenge facing the world”: David Attenborough
“Ellis Island, Jamestown and other U.S. landmarks' long-term future are at risk because of the consequences of climate change, a new report says”Time Magazine May 20 2014
“a change of climate which is attributed directly or indirectly to human activity that alters the composition of the global atmosphere and which is in addition to natural climate variability observed over comparable time periods”
Climate change refers to a change in the state of the climate that can be identified (e.g., by using statistical tests) by changes in the mean and/or the variability of its properties, and that persists for an extended period, typically decades or longer. Climate change may be due to natural internal processes or external forcings such as modulations of the solar cycles, volcanic eruptions and persistent anthropogenic changes in the composition of the atmosphere or in land use. Note that the Framework Convention on Climate Change (UNFCCC),in its Article 1, defines climate change as: ‘a change of climate which is attributed directly or indirectly to Human activity, that alters the composition of the global atmosphere and which is in addition to natural climate variability observed over comparable time periods’. The UNFCCC thus makes a distinction between climate change attributable to human activities altering the atmospheric composition, and climate variability attributable to natural causes.
Climate in a narrow sense is usually defined as the average weather, or more rigorously, as the statistical description in terms of the mean and variability of relevant quantities over a period of time ranging from months to thousands or millions of years.
The Classical period for averaging these variables is 30 years, as defined by the World Meteorological Organization..The Relevant quantities are most often surface variables such as temperature, Precipitation and wind.
Climate in a wider sense is the state, including a statistical description of the climate system.