According to the Intergovernmental Panel on Climate Change (IPCC), the temperature of the Earth increased by about 0.74 °C over the past century.
The IPCC also concluded that most of the observed increase in global average temperatures since the mid-20th century is very likely due to the observed increase in anthropogenic GHG concentrations.
Scientists use the concept of radiative forcing for quantitative comparisons of the strength of different agents in causing climate change. Radiative forcing is a measure of how the energy balance of the Earth-atmosphere system is influenced when factors that affect climate are altered. The word "radiative" signifies that the factors affect the balance between incoming solar radiation and outgoing infrared radiation within the Earth’s atmosphere. Positive forcing tends to warm the surface while negative forcing tends to cool it. Forcing values are expressed in watts per square meter (Wm-2).
The total anthropogenic radiative forcing (cooling and warming) is estimated to be +1.6 Wm-2, indicating that, since 1750, it is extremely likely that humans have exerted a substantial warming influence on climate. What about the effects of energy-related emissions? The IPCC concluded that the global mean concentration of CO2 in 2005 (about 379 ppm) generated a radiative forcing of +1.66 Wm-2. In addition, past emissions from fossil fuel combustion and cement production have likely contributed about three-quarters of the current radiative forcing, with the remainder caused by land use changes.
These conclusions are unequivocal: carbon dioxide emissions from energy use are the single largest human contribution to the observed increase in the Earth’s temperature.
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- Nodvin, Stephen C. (Lead Author); Kevin Vranes (Topic Editor). 2007. Radiative forcing. In: Encyclopedia of Earth. Eds. Cutler J. Cleveland (Washington, D.C.: Environmental Information Coalition, National Council for Science and the Environment). [First published in the Encyclopedia of Earth March 21, 2007; Last revised June 14, 2007; Retrieved May 18, 2009].