Inadequacy of effective CO<sub>2</sub> as a proxy in assessing the regional climate change due to other radiatively active gases

Wang, Wei‐Chyung; Dudek, Michael P.; Liang, Xin‐Zhong

doi:10.1029/92gl01157

Cited by 28 publications

(16 citation statements)

References 9 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: 81%

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: 81%

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

“…Halocarbons and ozone changes may not fit this simple constant-sensitivity picture. Climate models typically show different responses to equivalent forcings from WMGHG changes and CO 2 (Wang et al, 1991(Wang et al, , 1992Govindasamy et al, 2001). In particular, Hansen et al (1997) found halocarbons to have a ∼20% larger climate sensitivity than CO 2 , mainly due to a stronger positive cloud feedback in their halocarbon experiments.…”

Section: Climate Sensitivitymentioning

confidence: 99%

“…This, combined with a typical vertical temperature profile, means that halocarbons usually warm the atmosphere locally, as opposed to carbon dioxide, which generally cools (the atmosphere only warms as a response to the induced surface warming). Further, this effect is largest at the tropical tropopause, where temperatures are most different from those of the underlying surface (e.g., Dickenson, 1978;Wang et al, 1992;Forster et al, 1997).…”

Section: Introductionmentioning

confidence: 97%

The Role Of Halocarbons In The Climate Change Of The Troposphere And Stratosphere

Forster

Joshi

2005

Climatic Change

View full text Add to dashboard Cite

Releases of halocarbons into the atmosphere over the last 50 years are among the factors that have contributed to changes in the Earth's climate since pre-industrial times. Their individual and collective potential to contribute directly to surface climate change is usually gauged through calculation of their radiative efficiency, radiative forcing, and/or Global Warming Potential (GWP). For those halocarbons that contain chlorine and bromine, indirect effects on temperature via ozone layer depletion represent another way in which these gases affect climate. Further, halocarbons can also affect the temperature in the stratosphere. In this paper, we use a narrow-band radiative transfer model together with a range of climate models to examine the role of these gases on atmospheric temperatures in the stratosphere and troposphere. We evaluate in detail the halocarbon contributions to temperature changes at the tropical tropopause, and find that they have contributed a significant warming of ∼0.4 K over the last 50 years, dominating the effect of the other well-mixed greenhouse gases at these levels. The fact that observed tropical temperatures have not warmed strongly suggests that other mechanisms may be countering this effect. In a climate model this warming of the tropopause layer is found to lead to a 6% smaller climate sensitivity for halocarbons on a globally averaged basis, compared to that for carbon dioxide changes. Using recent observations together with scenarios we also assess their past and predicted future direct and indirect roles on the evolution of surface temperature. We find that the indirect effect of stratospheric ozone depletion could have offset up to approximately half of the predicted past increases in surface temperature that would otherwise have occurred as a result of the direct effect of halocarbons. However, as ozone will likely recover in the next few decades, a slightly faster rate of warming should be expected from the net effect of halocarbons, and we find that together halocarbons could bring forward next century's expected warming by ∼20 years if future emissions projections are realized. In both the troposphere and stratosphere CFC-12 contributes most to the past temperature changes and the emissions projection considered suggest that HFC-134a could contribute most of the warming over the coming century.

show abstract

“…In addition to calculating the response of climate to ozone changes, the impact of a homogeneous change in methane is also computed because, as explained earlier, methane is affected by the changed emissions. We are not aware of other GCM calculations of the climate sensitivity to methane changes alone; Wang et al (1991, 1992) and Govindasamy et al (2001) have compared the climate sensitivity to increases in a range of well‐mixed greenhouse gases, compared with equivalent CO 2 , with conflicting conclusions. Wang et al (1991, 1992) showed that the global‐mean sensitivity is similar in both cases, while Govindasamy et al (2001) found that explicit consideration of the well‐mixed gases led to a 20% increase in climate sensitivity.…”

Section: Surface Temperature Response and Climate Sensitivitymentioning

confidence: 99%

Response of climate to regional emissions of ozone precursors: sensitivities and warming potentials

Berntsen¹,

Fuglestvedt²,

Joshi³

et al. 2005

Tellus B

View full text Add to dashboard Cite

The response of climate to ozone perturbations caused by regional emissions of NOx or CO has been studied through a sequence of model simulations. Changes in O3 and OH concentrations due to emission perturbations in Europe and southeast Asia have been calculated with two global 3‐D chemical tracer models(CTMs; LMDzINCA and Oslo‐CTM2). The radiative transfer codes of three general circulation models (GCMs; ECHAM4, UREAD and LMD) have been used to calculate the radiative forcing of the O3 perturbations, and for a subset of the cases full GCM simulations have been performed with ECHAM4 and UREAD. The results have been aggregated to a global number in two ways: first, through integrating the global‐mean radiative forcing of a sustained step change in emissions, and second through a modified concept (SGWP*) which includes possible differences in the climate sensitivity of O3, CH4 and CO2 changes. In terms of change in global tropospheric O3 burden the two CTMs differ by less than 30%. Both CTMs show a higher north/south gradient in the sensitivity to changes in NOx emission than for CO. We are not able to conclude whether real O3 perturbations in general have a different climate sensitivity from CO2. However, in both GCMs high‐latitude emission perturbations lead to climate perturbations with higher (10–30%) climate sensitivities. The calculated SGWP*, for a 100 yr time horizon, are negative for three of the four CTM/GCM combinations for European emissions (−9.6 to +6.9), while for the Asian emissions the SGWP* (H= 100) is always positive (+2.9 to +25) indicating a warming. For CO the SGWP* values (3.8 and 4.4 for European and Asian emissions respectively, with only the Oslo‐CTM2/ECHAM4 model combination) are less regionally dependent. Our results support the view that for NOx, regionally different weighting factors for the emissions are necessary. For CO the results are more robust and one global number may be acceptable.

show abstract

Inadequacy of effective CO₂ as a proxy in assessing the regional climate change due to other radiatively active gases

Cited by 28 publications

References 9 publications

Limitations of the equivalent CO₂ approximation in climate change simulations

Limitations of the equivalent CO₂ approximation in climate change simulations

The Role Of Halocarbons In The Climate Change Of The Troposphere And Stratosphere

Response of climate to regional emissions of ozone precursors: sensitivities and warming potentials

Contact Info

Product

Resources

About

Inadequacy of effective CO2 as a proxy in assessing the regional climate change due to other radiatively active gases

Cited by 28 publications

References 9 publications

Limitations of the equivalent CO2 approximation in climate change simulations

Limitations of the equivalent CO2 approximation in climate change simulations

The Role Of Halocarbons In The Climate Change Of The Troposphere And Stratosphere

Response of climate to regional emissions of ozone precursors: sensitivities and warming potentials

Contact Info

Product

Resources

About

Inadequacy of effective CO₂ as a proxy in assessing the regional climate change due to other radiatively active gases

Limitations of the equivalent CO₂ approximation in climate change simulations

Limitations of the equivalent CO₂ approximation in climate change simulations