Inadequacy of effective CO2 as a proxy in simulating the greenhouse effect of other radiatively active gases

Wang, Wei‐Chyung; Dudek, Michael P.; Liang, Xin-Zhong; Kiehl, J. T.

doi:10.1038/350573a0

Cited by 90 publications

(44 citation statements)

References 20 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…In agreement with the previous studies [Wang et al, 1991[Wang et al, , 1992] the results presented here indicate that trace gases and equivalent CO2 produce different patterns of surface, tropospheric and stratospheric temperature change, which are significant at a 5% level. However, in contrast to their results, we find that the global annual-mean response also differs by as much as 20%.…”

Section: Discussionsupporting

confidence: 92%

Limitations of the equivalent CO₂ approximation in climate change simulations

Bala¹,

Taylor²,

Duffy³

et al. 2001

J. Geophys. Res.

View full text Add to dashboard Cite

Abstract. The "equivalent CO2" approximation often used to simulate the climatic effects of a suite of trace greenhouse gases is investigated using a recent version of the NCAR Community Climate Model. We performed present-day and preindustrial equilibrium climate simulations. The climate sensitivity is lower by -20% in the equivalent CO2 case compared to the control case in which the individual trace gases were treated explicitly. This is reflected in similar percentage differences in global-and annual-mean surface temperature, precipitation, precipitable water, and sea ice. The temperature changes are also different regionally in the tropical and subtropical troposphere and in the stratosphere. This difference in climate sensitivity originates from differences in the spatial pattern of radiative forcing. The equivalent CO2 forcing pattern differs from the control case forcing pattern for several reasons, but the dependence on temperature of the Planck emission spectrum appears to be fundamentally most important. The primary absorption bands of CH 4 and N20 are found at wavelengths more sensitive to the temperaturerelated shift of the wavelength of maximum emission than the absorption bands of CO 2. This leads to stronger spatial variations in absorption by trace gases than by CO2. We conclude that because of differences in the pattern of radiative forcing, the equilibrium response of global climate to increases in trace gases is larger than the response to an "equivalent" increase in CO2, and the patterns of response are also different. The global warming potential (GWP) for a trace gas attempts to account for two factors responsible for its climatic effects: the atmospheric lifetime of the gas and its radiative impact. The GWP is defined as the ratio of the time-integrated radiative forcing of a unit mass impulse of the gas to that of a unit mass impulse of COg. The GWP can be used to infer the relative strength of the surface temperature change with respect to COg if and only if the climate sensitivity factor X for the gas in question is the same as the sensitivity factor for COg. If the X values are different for different gases, the relative surface temperature change can still be inferred if we modify the definition of GWP to account for the different climate sensitivities.Wang et al. [1991, 1992] used the NCAR CCM1 to investigate the validity of the equivalent CO2 approximation. Though they obtained similar global mean climate change, significant differences in the pattern of regional climate change were noticed when they substituted equivalent COg for a suite of trace gases. They attributed the differences in the patterns of climate change to the different vertical distribution of longwave radiative forcing. Cox et al. [1995] found that the global and annual mean surface temperature changes depend only on global mean net forcing and are not highly sensitive to either the details of the spatial and seasonal patterns in forcing or the nature of the forcing (shortwave versus longwave). For equal and oppo...

show abstract

Section: Discussionsupporting

confidence: 92%

Limitations of the equivalent CO₂ approximation in climate change simulations

Bala¹,

Taylor²,

Duffy³

et al. 2001

J. Geophys. Res.

View full text Add to dashboard Cite

show abstract

“…Clearly, these forcing uncertainties translate into considerable uncertainty regarding the spatial pattern of the temperature response in the SC experiment, and in the relative contributions to this response from C02 and aerosols. Further signal uncertainties include the lack of a dynamic ocean, the neglect of the indirect effects of sulfate aerosols, the omission of the radiative effects of trace gases other than COZ (which may have temperature-change signatures that differ from that for C02 alone; see Wang et al, 1991), and failure to include the effects of carbonaceous aerosols generated by biomass burning, fossil fuel combustion, and industrial processes (Penner et al, 1992(Penner et al, , 1994b.15 .…”

Section: Model Integrations Recently Carried Out Bymentioning

confidence: 99%

Towards the detection and attribution of an anthropogenic effect on climate

Santer¹,

Taylor²,

Penner³

et al. 1995

101

View full text Add to dashboard Cite

“…A consistent finding of such studies is that the change in global mean temperature per forcing, that is the climate sensitivity, is, to a good approximation, independent of the nature of the forcing, for example, forcing because of changes in CO 2 mixing ratios, mixing ratios of other GHGs, 8 aerosol direct forcing, 9 or the solar constant, 10 and independent as well of the geographical distribution of the forcing. 9 These model-based studies are the basis of the climatesensitivity hypothesis.…”

Section: Radiative Forcing Of Climate Changementioning

confidence: 81%

Uncertainty Requirements in Radiative Forcing of Climate Change

Schwartz

2004

Journal of the Air & Waste Management Association

View full text Add to dashboard Cite

The continuing increase in atmospheric carbon dioxide (CO 2 ) makes it essential that climate sensitivity, the equilibrium change in global mean surface temperature that would result from a given radiative forcing, be quantified with known uncertainty. Present estimates are quite uncertain, 3 Ϯ 1.5 K for doubling of CO 2 . Model studies examining climate response to forcing by greenhouse gases and aerosols exhibit large differences in sensitivities and imposed aerosol forcings that raise questions regarding claims of their having reproduced observed large-scale changes in surface temperature over the 20th century. Present uncertainty in forcing, caused largely by uncertainty in forcing by aerosols, precludes meaningful model evaluation by comparison with observed global temperature change or empirical determination of climate sensitivity. Uncertainty in aerosol forcing must be reduced at least three-fold for uncertainty in climate sensitivity to be meaningfully reduced and bounded.

show abstract

Inadequacy of effective CO2 as a proxy in simulating the greenhouse effect of other radiatively active gases

Cited by 90 publications

References 20 publications

Limitations of the equivalent CO₂ approximation in climate change simulations

Limitations of the equivalent CO₂ approximation in climate change simulations

Towards the detection and attribution of an anthropogenic effect on climate

Uncertainty Requirements in Radiative Forcing of Climate Change

Contact Info

Product

Resources

About

Inadequacy of effective CO2 as a proxy in simulating the greenhouse effect of other radiatively active gases

Cited by 90 publications

References 20 publications

Limitations of the equivalent CO2 approximation in climate change simulations

Limitations of the equivalent CO2 approximation in climate change simulations

Towards the detection and attribution of an anthropogenic effect on climate

Uncertainty Requirements in Radiative Forcing of Climate Change

Contact Info

Product

Resources

About

Limitations of the equivalent CO₂ approximation in climate change simulations

Limitations of the equivalent CO₂ approximation in climate change simulations