Climate Forcing

IPCC AR4 Global Mean Radiative Forcing

Global Mean Radiative Forcing (W/m2)

Radiative Forcing Components IPCC AR4

Radiative Forcing Components IPCC AR4 SPM – Figure SPM.2. Global average radiative forcing (RF) estimates and ranges in 2005 for anthropogenic carbon dioxide (CO2 ), methane (CH4 ), nitrous oxide (N2O) and other important agents and mechanisms, together with the typical geographical extent (spatial scale) of the forcing and the assessed level of scientific understanding (LOSU). The net anthropogenic radiative forcing and its range are also shown. These require summing asymmetric uncertainty estimates from the component terms, and cannot be obtained by simple addition. Additional forcing factors not included here are considered to have a very low LOSU. Volcanic aerosols contribute an additional natural forcing but are not included in this figure due to their episodic nature. The range for linear contrails does not include other possible effects of aviation on cloudiness. {2.9, Figure 2.20} – Source (page 4): http://ipcc-wg1.ucar.edu/wg1/Report/AR4WG1_Print_SPM.pdf

Forcing Crowley 2000

The figure below shows time series of these forcings used in a climate model simulation of the last millennium. The size of these forcings is expressed in terms of Watts (a flux of energy) per square meter of the Earth's surface. Positive forcing warms the Earth, while negative forcing cools the Earth. http://www.ncdc.noaa.gov/paleo/globalwarming/gw-forcing.html

Net solar radiation at Mauna Loa Observatory relative to 1958

Net solar radiation at Mauna Loa Observatory, relative to 1958, showing the effects of major volcanic eruptions. Annual variations are due to transport of Asian dust and air pollution to Hawaii. http://www.esrl.noaa.gov/gmd/about/climate.html

Monthly and latitudinally varying volcanic forcing dataset in simulations of 20th century climate

A new monthly volcanic forcing dataset is included in a coupled GCM for a more physically consistent treatment of the stratospheric sulfate aerosol history from explosive volcanism. The volcanic forcing is different from previous versions in that there is an individual evolution of the aerosol for each event. Thus the seasonal and latitudinal dependence of the volcanic aerosol can affect global climate in a more realistic way prior to the satellite period, compared to earlier volcanic forcing datasets. Negative radiative forcing from volcanic activity is greatest in the early 20th century prior to 1915 and in the late 20th century after 1960. The combination of volcanic and solar forcing contributes to an early-20th century warming, followed by relative cooling in late 20th century. Consequently, the addition of natural forcing factors to the anthropogenic GHG forcing in late 20th century is required to simulate the observed late 20th century warming. http://www.ncdc.noaa.gov/paleo/pubs/ammann2003/ammann2003.html

The Physical Science Basis of Climate Change

Radiative forcings and simulated temperatures during the last 1.1 kyr. Global mean radiative forcing (W/m^2) used to drive climate model simulations due to (a) volcanic activity, (b) solar irradiance variations and (c) all other forcings (which vary between models, but always include greenhouse gases, and, except for those with dotted lines after 1900, tropospheric sulphate aerosols). (d) Annual mean NH temperature (°C) simulated under the range of forcings shown in (a) to (c), compared with the concentration of overlapping NH temperature reconstructions (shown by grey shading, modified from Figure 6.10c to account for the 1500 to 1899 reference period used here). All forcings and temperatures are expressed as anomalies from their 1500 to 1899 means and then smoothed with a Gaussian-weighted filter to remove fluctuations on time scales less than 30 years; smoothed values are obtained up to both ends of each record by extending the records with the mean of the adjacent existing values. http://www.ncdc.noaa.gov/paleo/pubs/ipcc2007/fig613.html