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Topic: Radiative forcing


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In the News (Thu 20 Jun 19)

  
  Climate Change 2001: The Scientific Basis
The pattern of the radiative forcing is governed mainly by variations of surface temperature and water vapour and the occurrence of high level cloud (Section 6.3).
The exact switchover between areas of positive and negative radiative forcing are not well established owing to uncertainties in the modelled mineral aerosol optical properties and depends upon the assumed single scattering albedo (Miller and Tegen, 1998), the long-wave properties and altitude of the aerosol (Section 6.7.6).
The spatial distribution of the indirect radiative forcing is quite different from the direct radiative forcing with strong areas of forcing off the coasts of industrialised regions (note the change in scale of Figure 6.7h).
www.pnl.gov /aisu/pubs/eemw/papers/ipccreports/workinggroup1/253.htm   (1862 words)

  
 Recent Climate Change - Atmosphere Changes | Science | Climate Change | U.S. EPA
Radiative forcing is measured in Watts per square meter, which is a measure of energy.
The radiative forcing contribution from increasing tropospheric ozone, an unevenly distributed greenhouse gas, is estimated to be +0.35 Watts per square meter (on average), resulting in a relatively small warming effect.
The radiative forcing contribution from the observed depletion of stratospheric ozone is estimated to be -0.15 Watts per square meter, resulting in a relatively small cooling effect.
www.epa.gov /climatechange/science/recentac.html   (1785 words)

  
 Global Monitoring Division
The perturbation to radiative climate forcing which has the largest magnitude and the least scientific uncertainty is the forcing related to changes in long-lived and well mixed greenhouse gases, in particular carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O) and the halocarbons (mainly CFCs).
To determine the total radiative forcing of the greenhouse gases, we have used IPCC (2001) recommended expressions to convert greenhouse gas changes, relative to 1750, to instantaneous radiative forcing (see Table 1).
Radiative forcing of all the long-lived greenhouse gases, relative to 1750, and the NOAA Annual Greenhouse Gas Index (AGGI) on the right axis, which is indexed to 1 on January 1, 1990.
www.cmdl.noaa.gov /aggi   (1193 words)

  
 IGAC | Nuts and bolts of radiative forcing by mineral dust
Overall, the radiative impact of mineral aerosol is important relative to that of other types of aerosols'such as sulfates and smoke particles–due to the widespread distribution and large optical depth of mineral dust.
Part of the complexity in estimating dust radiative impact comes from the fact that dust sources and sinks are not uniformly distributed, and that the lifetime of mineral aerosol in the atmosphere is relatively short, at most a few weeks.
Therefore, incorporation of regionally and temporally varying size-resolved dust mineralogical composition into global and regional climate models is a desirable and promising approach to decrease the currently large uncertainties in the assessment of radiative forcing by the natural and anthropogenic components of the airborne mineral aerosol.
www.igac.noaa.gov /newsletter/17/dust.php   (2050 words)

  
 Climate Change : 2. What causes this climate change?
The radiative forcing due to increases of the well-mixed greenhouse gases from 1750 to 2000 is estimated to be 2.43 Wm-2:
The observed depletion of the stratospheric ozone(O3) layer from 1979 to 2000 is estimated to have caused a negative radiative forcing (–0.15 Wm-2).
Direct radiative forcing is estimated to be -0.4 Wm-2 for sulphate, -0.2 Wm-2 for biomass burning aerosols, -0.1 Wm-2 for fossil fuel organic carbon and +0.2 Wm-2 for fossil fuel fl carbon aerosols.
www.greenfacts.org /studies/climate_change/l_3/climate_change_2.htm   (2296 words)

  
 Radiative forcing - Wikipedia, the free encyclopedia
As a general concept, the term radiative forcing in climate science means any change in the radiation (heat) entering or leaving the climate system.
The radiation balance can be altered by factors such as intensity of solar energy, reflection by clouds or gases, absorption by various gases or surfaces, and emission of heat by various materials.
The term “radiative forcing” has been employed in the IPCC Assessments with a specific technical meaning to denote an externally imposed perturbation in the radiative energy budget of the Earth’s climate system, which may lead to changes in climate parameters [1].
en.wikipedia.org /wiki/Radiative_forcing   (491 words)

  
 Climate Change 2001: The Scientific Basis
Section 6.2 discusses the relationship between radiative forcing and climate response and describes recent studies that have supported the view that many different kinds of forcing agents (e.g., various greenhouse gases, sulphate aerosols, solar activity, etc.) yield similar globally averaged climate responses per Wm of forcing (albeit with different spatial patterns in some important cases).
Radiative properties control the absorption of radiation per kilogram of gas present at any instant, but the lifetime (or adjustment time, see Chapter 4) controls how long an emitted kilogram is retained in the atmosphere and hence is able to influence the thermal budget.
The direct relative radiative forcings per ppbv are derived from infrared radiative transfer models based on laboratory measurements of the molecular properties of each substance and considering the molecular weights.
www.pnl.gov /aisu/pubs/eemw/papers/ipccreports/workinggroup1/247.htm   (1424 words)

  
 Climate Ark: Radiative forcing
Radiative forcing is the change in the balance between radiation coming into the atmosphere and radiation going out.
A positive radiative forcing tends on average to warm the surface of the Earth, and negative forcing tends on average to cool the surface.
The figure shows estimates of the globally and annually averaged anthropogenic radiative forcing (in Wm-2) due to changes in concentrations of greenhouse gases and aerosols from pre-industrial times to present day and to natural changes in solar output from 1850 to present.
www.climateark.org /overview/04.asp   (172 words)

  
 Radiative forcing (via CobWeb/3.1 planetlab2.cs.unc.edu)   (Site not responding. Last check: 2007-10-03)
The generalised concept of radiative forcing in climate science is any change in the radiation (heat) entering the climate system or changes in radiatively active gases.
The term “radiative forcing” has been employed in the IPCC Assessments with a specific technical meaning to denote an externally imposed perturbation in the radiative energy budget of the Earth’s climate system, which may lead to changes in climate parameters http://www.grida.no.cob-web.org:8888/climate/ipcc_tar/wg1/212.htm.
Note that radiative forcing is intended as a useful mechanism to compare and explain different (CO ; land-use changes) perturbations to the climate system.
radiative-forcing.iqnaut.net.cob-web.org:8888   (427 words)

  
 Radiative forcing and climate response
The consistency of the response among different forcings is higher, within 20% or better, for most of the globally distributed forcings suspected of influencing global mean temperature in the past century, but exceptions occur for certain changes of ozone or absorbing aerosols, for which the climate response is less well behaved.
However, negative forcing due to the net ozone change since 1979 appears to have counterbalanced 30–50% of the positive forcing due to the increase of well-mixed greenhouse gases in the same period.
As the net ozone change includes halogen-driven ozone depletion with negative radiative forcing and a tropospheric ozone increase with positive radiative forcing, it is possible that the halogen-driven ozone depletion has counterbalanced more than half of the radiative forcing due to well-mixed greenhouse gases since 1979.
www.agu.org /pubs/crossref/1997/96JD03436.shtml   (454 words)

  
 Climate Change 2001: The Scientific Basis
This represents the subjective judgement about the reliability of the forcing estimate, involving factors such as the assumptions necessary to evaluate the forcing, the degree of knowledge of the physical/chemical mechanisms determining the forcing, and the uncertainties surrounding the quantitative estimate of the forcing (see Table 6.12).
The forcing associated with stratospheric aerosols from volcanic eruptions is highly variable over the period and is not considered for this plot (however, see Figure 6.8).
All the forcings shown have distinct spatial and seasonal features (Figure 6.7) such that the global, annual means appearing on this plot do not yield a complete picture of the radiative perturbation.
www.ipcc.ch /pub/taroldest/wg1/015.htm   (1033 words)

  
 Radiative Forcing of Climate Change:
Each forcing agent is associated with a level of scientific understanding, which is based on an assessment of the nature of assumptions involved, the uncertainties prevailing about the processes that govern the forcing, and the resulting confidence in the numerical values of the estimate.
Radiative Forcing of Climate Change: Expanding the Concept and Addressing Uncertainties Account for the Vertical Structure of Radiative Forcing The relationship between TOA radiative forcing and surface temperature is affected by the vertical distribution of radiative forcing within the atmosphere.
Adoption of surface radiative forcing as a new metric will require research to test the ability of climate models to reproduce the observed vertical distribution of forcing (e.g., from aircraft campaigns) and to investigate the response of climate to the vertical structure of the radiative forcing.
newton.nap.edu /books/0309095069/html/1.html   (3782 words)

  
 TARFOX Home Page   (Site not responding. Last check: 2007-10-03)
Radiative forcing is defined as the change in the net (downwelling minus upwelling) radiative flux at a given level in the atmosphere [IPCC, 1995].
Above an aerosol layer the dominant term in the aerosol radiative forcing is the increase in upwelling flux [Russell et al., 1997a].
The direct aerosol radiative forcing is then defined to be the difference between the case with aerosol particles present and that without.
geo.arc.nasa.gov /sgg/tarfox/direct.html   (3394 words)

  
 RealClimate » An Aerosol Tour de Forcing
Each published calculation of aerosol radiative forcing was a tour de force for integrating a wide variety of measurements ranging from absorption of radiation by individual particles to satellite estimates of aerosol amount.
Because radiation into the surface is mainly balanced by evaporation, except within extremely arid regions, the discrepancy has implications for the supply of moisture to the atmosphere.
For the calculation of anthropogenic climate forcing the exact value of natural emissions (or the discovery of new natural sources) is not that much relevant, because these emissions have been there before and do not change climate unless it is found that they have changed, too on the discussed timescale.
www.realclimate.org /index.php?p=245   (5128 words)

  
 Summary for Policymakers: The Science of Climate Change - IPCC Working Group I
The direct radiative forcing of the long­lived greenhouse gases (2.45 Wm­2) is due primarily to increases in the concentrations of CO2 (1.56 Wm­2), CH4 (0.47 Wm­2) and N2O (0.14 Wm­2) (values for 1992).
However, their net radiative forcing is reduced by about 0.1 Wm­2 because they have caused stratospheric ozone depletion which gives rise to a negative radiative forcing.
Radiative forcing is the perturbation to the energy balance of the Earth­atmosphere system (in Watts per square metre [Wm­2]).
www.ipcc.ch /pub/sarsum1.htm   (2951 words)

  
 William Kininmonth: Climate Change: A Natural Hazard?: Book Launch Address
Radiative forcing assumes that there was radiation balance at the top of the atmosphere before industrialisation commenced.
Radiative forcing is a simple, seductive hypothesis for how emissions of carbon dioxide, especially burning of fossil fuels, will lead to global warming.
The magnitude of the radiation errors in the computer models is up to five times the expected radiation forcing from doubling carbon dioxide concentration.
www.lavoisier.com.au /papers/articles/kininmonthlaunch.html   (2385 words)

  
 Pubs.GISS: Schulz et al. 2006. 'Radiative forcing by aerosols as derived from the AeroCom present-day and ...   (Site not responding. Last check: 2007-10-03)
Radiative forcing by aerosols as derived from the AeroCom present-day and pre-industrial simulations.
While the diversity in clear-sky forcing efficiency is impacted by factors such as aerosol absorption, size, and surface albedo, we can show that the all-sky/clear-sky forcing ratio is important because all-sky forcing estimates require proper representation of cloud fields and the correct relative altitude placement between absorbing aerosol and clouds.
With the current uncertainties in the modelling of the radiative forcing due to the direct aerosol effect we show here that an estimate from one model is not sufficient but a combination of several model estimates is necessary to provide a mean and to explore the uncertainty.
pubs.giss.nasa.gov /abstracts/2006/Schulz_etal.html   (438 words)

  
 Forcing
A simple radiative energy equilibrium model of the troposphere yields an IPCC-conforming radiative forcing which is here defined as the additional energy re-radiated to ground.
"The radiative forcing of the surface-troposphere system (due to a change, for example, in greenhouse gas concentration) is the change in net (solar plus longwave irradiance) in W/m² at the tropopause AFTER allowing the stratospheric temperatures to re-adjust to radiative equilibrium, but with surface and tropospheric temperature and state held fixed at the unperturbed values".
The often quoted additional absorption for CO doubling within the troposphere is not the forcing itself, as formerly often (mis)understood by non-specialists, but it is the source of the (thermal) re-emission to ground which is based on the atmospheric energy equilibrium.
www.john-daly.com /forcing/forcing.htm   (2537 words)

  
 Climate and Vegetation Research Group: Courses (GG 312 Fall 2002 Chapter 02)
Estimates of the globally averaged radiative forcing due to changes in greenhouse gases and aerosols from pre-industrial time to the present, and changes in solar variability from 1850 to the present are shown in Figure2.1.
The negative values for aerosols should not necessarily be seen as an offset against the greenhouse gas forcing because of uncertainities over the applicability of global mean radiative forcing in the case of non-homogeneously distributed species such as aerosols and ozone.
The direct radiative forcing due to increases in sulphate aerosol since 1850, averaged globally, is estimated to lie between -0.25 to -0.9 W/m2.
cybele.bu.edu /courses/gg312fall02/chap02/chap02.html   (3944 words)

  
 Cloud forcing - Wikipedia, the free encyclopedia
Cloud forcing (sometimes described as 'cloud radiative forcing') is the difference between the radiation budget components for average cloud conditions and cloud-free conditions.
These numbers should not be confused with the usual radiative forcing concept, which is for the change in forcing related to climate change: clouds remain one of the largest uncertainties in future projections of climate change by global climate models.
Trapping of the long-wave radiation due to the presence of clouds reduces the radiative forcing of the greenhouse gases compared to the clear-sky forcing.
en.wikipedia.org /wiki/Cloud_forcing   (352 words)

  
 Forcing
The total negative forcing is set to correct for the discrepancy between the previously predicted and the observed GHG forcings.
Chick Keller had cited Venus as 'evidence' for the strong CO2 radiative forcing estimated by the IPCC, and I was claiming that the 'Venus argument' could also be used as 'evidence' to oppose that estimate.
The point is however: The altitude of effective radiation to space has been shifted to an altitude of 10 km, and the lower foggy atmosphere adds another 97 K from the 255K-10km layer to ground.
www.john-daly.com /forcing/forcing2.htm   (9950 words)

  
 Intercomparison of models representing direct shortwave radiative forcing by sulfate aerosols
The normalized forcings (forcing per sulfate column burden) obtained with the several radiative transfer models were examined, and the discrepancies were characterized.
The relative standard deviation of the zenith-angle-averaged normalized broadband forcing for 15 models was 8% for particle radius near the maximum in this forcing (∼0.2 μm) and at low surface albedo.
However, the relatively small spread in these results suggests that the uncertainty in forcing arising from the treatment of radiative forcing of a well-characterized aerosol at well-specified surface albedo is smaller than some of the other sources of uncertainty in estimates of direct forcing by anthropogenic sulfate aerosols and anthropogenic aerosols generally.
www.agu.org /pubs/crossref/1998/98JD00997.shtml   (746 words)

  
 Images on Global Energy Balance, Radiative Forcing   (Site not responding. Last check: 2007-10-03)
Radiative forcing relative to CO per unit molecule change.
Decadal contributions to radiative forcing due to increases in greenhouse gas concentrations for periods between 1765 and 1990.
Changes in radiative forcing due to increases in greenhouse gas concentrations between 1765 and 1990.
www.iitap.iastate.edu /gccourse/forcing/images.html   (249 words)

  
 MAGICC
For reference, the 2100 forcing value for a 1% per year compounded increase in CO concentration from the 1990 level is shown by the arrow on the right.
This is the sum of forcing contributions from sulfate aerosols, plus forcings from organic carbon and fl carbon from both fossil and biomass-burning sources.
Total radiative forcing, the driver for future changes in global-mean temperature and sea level, is shown for the SRES illustrative scenarios in Fig.
www.cgd.ucar.edu /cas/ACACIA/projects/magicc.html   (5069 words)

  
 EO Observation Deck: Cloud Radiative Forcing Dataset View
The term "cloud radiative forcing" refers to the effects clouds have on both sunlight and heat in the atmosphere.
More precisely, cloud radiative forcing measures how much clouds modify the net radiation, at wavelengths ranging from 0.3 to 100 micrometers, of the Earth system.
The image above is a false-color map showing the magnitudes of cloud radiative forcing (in Watts per square meter) for the given month(s).
earthobservatory.nasa.gov /Observatory/Datasets/cldforc.erbe.html   (211 words)

  
 Radiative Forcing   (Site not responding. Last check: 2007-10-03)
Note that the magnitude of the increase in radiative forcing for the most recent decade on the previous graph is about 0.55 Wm figure 8).
From these comparisons, it should be apparent that human emission of greenhouse gases have increased the radiative forcing of the planet far in excess of natural variations.
Recent estimates of the effects of sulfate aerosol particles are shown in the next two global maps (figure 11) that give warming due to carbon dioxide with and without considering the sulfate cooling.
www.iitap.iastate.edu /gccourse/forcing/radiative.html   (987 words)

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