Global Warming

Global Mean Temperature over Land and Ocean (Jan-Dec). (Source: NCDC/NESDIS/NOAA)
According to the World Meteorological Organization (WMO), the decade of the 2000s (2000–2009) is the warmest on record. The global mean surface temperature for 2009 is currently estimated at 0.44°C/0.79°F above the 1961-1990 annual average of 14.00°C/57.20°F. WMO states that in 2009 above-normal temperatures were recorded in most parts of the continents. Only North America (United States and Canada) experienced conditions that were cooler than average.
n order to attempt to answer why the Earth is currently warming, scientists have conducted accountings of each of the fluxes of heat into (warming) and out of (cooling) the Earth's climate system. Since the measured data show that annual average temperatures of the Earth have been increasing in recent decades, the year-to-year annual flux of heat into the climate system must be greater than the annual flux of heat out of the system. By accounting for each of the fluxes of heat into and out of the system, scientists are able to assess which fluxes and processes are contributing to net annual warming of the Earth's surface. By conducting such accountings, scientists are able to quantify the influence that each natural and human factor has in altering the balance of incoming and outgoing energy in the Earth-atmosphere system and can calculate an index of the importance of each of the factor as a potential climate change mechanism. Each of the factors are called climate drivers and the relative impact or index of each factor's importance to climate change is called its radiative forcing.