An underestimated negative cloud feedback from cloud lifetime changes

Mülmenstädt, J.; Salzmann, Marc; Kay, J. E.; Zelinka, Mark D.; Ma, Po‐Lun; Nam, Christine; Kretzschmar, J.G.; Hörnig, Sabine; Quaas, Johannes

doi:10.1038/s41558-021-01038-1

Cited by 85 publications

(86 citation statements)

References 93 publications

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“…with the SST via MBL processes, in which atmospheric humidity plays an important role. For example, the cloud feedback strongly depends on the description of warm-rain processes [173]. The aggregation state of cloud water is expected to shift from ice and mixed-phase to liquid clouds in a warmer atmosphere [173].…”

Section: Relative Humidity: Cause and Effect Of Evaporationmentioning

confidence: 99%

“…For example, the cloud feedback strongly depends on the description of warm-rain processes [173]. The aggregation state of cloud water is expected to shift from ice and mixed-phase to liquid clouds in a warmer atmosphere [173]. Warm clouds, however, have a higher albedo and longer lifetime and reduce the shortwave radiation flux absorbed by the Earth's surface, which constitutes a negative radiative feedback [173].…”

Section: Relative Humidity: Cause and Effect Of Evaporationmentioning

confidence: 99%

“…The aggregation state of cloud water is expected to shift from ice and mixed-phase to liquid clouds in a warmer atmosphere [173]. Warm clouds, however, have a higher albedo and longer lifetime and reduce the shortwave radiation flux absorbed by the Earth's surface, which constitutes a negative radiative feedback [173]. This cooling feedback was found to decrease from CMIP5 to CMIP6, which increases the greenhouse warming in CMIP6.…”

Section: Relative Humidity: Cause and Effect Of Evaporationmentioning

confidence: 99%

“…This cooling feedback was found to decrease from CMIP5 to CMIP6, which increases the greenhouse warming in CMIP6. If cloud liquid water precipitates too quick, the cloud lifetime shortens and negative lifetime feedbacks of warm clouds will be underestimated [173]. The modification of the warm-rain probability alone is sufficient to increase the cloud lifetime feedback by a factor of three as compared to the default model [173].…”

Section: Relative Humidity: Cause and Effect Of Evaporationmentioning

confidence: 99%

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Relative Humidity: A Control Valve of the Steam Engine Climate

Feistel

Hellmuth

2021

J. Hum. Earth Future

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In the words of Heinrich Hertz in 1885, the Earth is a “gigantic steam engine”. On average, of the planet’s cross section exposed to sunlight, 72 % belong to the global ocean. With a delay of only 2-3 months, most of the heat absorbed there is released by evaporation rather than by thermal radiation. Water vapour is the dominating “greenhouse gas” of the marine troposphere with a typical relative humidity (RH) of 80 % at the surface. Observing the heat transport across the ocean surface permits insight in the powerhouse of the “steam engine”, controlled by the RH at the surface, a quantity that is often considered the “Cinderella” among the climate data. RH of the troposphere also controls cloud formation that is equally fundamental as challenging for climate research. As a precise and perfectly consistent thermodynamic basis for the description of such processes, the new oceanographic standard TEOS-10 was introduced by UNESCO/IOC in 2010 and IUGG in 2011. Its equations cover all thermodynamic properties of liquid water, seawater, ice and humid air, as well as their mutual equilibria and phase transitions. For harmonisation of the inconsistent RH definitions of humid air between meteorology and climatology, the relative fugacity has been defined as a physically more reasonable RH substitute that does not rely on the approximation of ideal gases. Doi: 10.28991/HEF-2021-02-02-06 Full Text: PDF

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Section: Relative Humidity: Cause and Effect Of Evaporationmentioning

confidence: 99%

Section: Relative Humidity: Cause and Effect Of Evaporationmentioning

confidence: 99%

Section: Relative Humidity: Cause and Effect Of Evaporationmentioning

confidence: 99%

Section: Relative Humidity: Cause and Effect Of Evaporationmentioning

confidence: 99%

See 2 more Smart Citations

Relative Humidity: A Control Valve of the Steam Engine Climate

Feistel

Hellmuth

2021

J. Hum. Earth Future

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“…The advance that such models represent is trading a structural problem-a missing, or perhaps drowned out, physical mechanism-for a parametric one. While parametric uncertainty is a tough problem (Lee et al, 2016;Regayre et al, 2018;Tsushima et al, 2020), we have a hunch (Mülmenstädt et al, 2020(Mülmenstädt et al, , 2021 that the right types of observablesin this case, perhaps the regime-dependent liquid water path susceptibilities of Gryspeerdt et al (2019)make it more tractable than it currently appears.…”

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confidence: 99%

The Fall and Rise of the Global Climate Model

Mülmenstädt

Wilcox

2021

J Adv Model Earth Syst

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Global models are an essential tool for climate projections, but conventional coarse‐resolution atmospheric general circulation models suffer from errors both in their parameterized cloud physics and in their representation of climatically important circulation features. A notable recent study by Terai et al. (2020, https://doi.org/10.1029/2020ms002274 documents a global model capable of reproducing the regime‐based effect of aerosols on cloud liquid water path expected from observational evidence. This may represent a significant advance in cloud process fidelity in global models. Such models can be expected to give a better estimate of the effective radiative forcing of the climate. If this advance in cloud process representation can be matched by advances in the representation of circulation features such as monsoons, then such models may also be able to navigate the complex tangle between spatially heterogeneous aerosol–cloud interactions and regional circulation patterns. This tight link between aerosol and circulation results in anthropogenic perturbations of climate variables of societal importance, such as regional rainfall distributions. Upcoming global models with km‐scale resolution may improve the regional circulation and be able to take advantage of the Terai et al. (2020, https://doi.org/10.1029/2020ms002274 improvement in cloud physics. If so, an era of significantly improved regional climate projection capabilities may soon dawn. If not, then the improvement in cloud physics might spur intensified efforts on problems in model dynamics. Either way, based on the rapid changes in aerosol emissions in the near future, learning to make reliable projections based on biased models is a skill that will not go out of style.

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