Comment on “Heat capacity, time constant, and sensitivity of Earth's climate system” by S. E. Schwartz

Knutti, Reto; Krähenmann, Stefan; Frame, David J.; Allen, Myles

doi:10.1029/2007jd009473

Cited by 52 publications

(54 citation statements)

References 38 publications

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“…In this section we choose to focus on uncertainties in TCR estimates rather than in ECS estimates. This is both because dependence of uncertainties in observationally-based estimates of ECS are already well-established (Knutti et al, 2008), and because the varying radiative forcing in the TCR definition is more relevant to policy decisions that have to be taken over the next few decades in which the radiative forcing is likely to still be increasing and the climate system is substantially out of equilibrium due to heat uptake by the oceans. Indeed, the analysis in section 4 shows that when TCR and ECS are considered independent the TCR is more important for climate projections out until around 2150.…”

Section: Estimating Tcr and Ecs From Observations And Simple Modelsmentioning

confidence: 99%

“…These methods, which incorporate direct observations of the climate system and do not use GCMs, are often referred to as observational estimates of TCR and ECS, which incorrectly implies they are modelindependent. It is well-established that inferences about ECS using such methods depend on the structure of the simple model used as shown by Knutti et al (2008) in response to Schwartz (2007). However, it is often assumed that estimates of TCR are more-or-less independent of the specifics of the simple climate model.…”

Section: Introductionmentioning

confidence: 99%

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Model structure in observational constraints on transient climate response

et al. 2015

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The transient climate response (TCR) is a highly policy-relevant quantity in climate science. We show that recent revisions to TCR in the IPCC 5th Assessment Report have more impact on projections over the next century than revisions to the equilibrium climate sensitivity (ECS). While it is well known that upper bounds on ECS are dependent on model structure, here we show that the same applies to TCR. Our results use observations of the planetary energy budget, updated radiative forcing estimates and a number of simple climate models. We also investigate the ratio TCR:ECS, or realised warming fraction (RWF), a highly policy-relevant quantity. We show that global climate models (GCMs) don't sample a region of low TCR and high RWF consistent with observed climate change under all simple models considered. Whether the additional constraints from GCMs are sufficient to rule out these low climate responses is a matter for further research.

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Section: Estimating Tcr and Ecs From Observations And Simple Modelsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Model structure in observational constraints on transient climate response

et al. 2015

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“…Estimates of the GMAST response time have varied from less than 1 year to several decades and, in reality, the role of the oceans means that a spectrum of response times is to be expected. Knutti et al (2008) discuss the time constants of different parts of the climate system: short time scales (1 year or less) apply to atmospheric adjustments and land surface processes; medium time scales (of order decades) to the melting of sea ice; and long time scales (many decades) to warming of the whole ocean surface layer. Ocean warming effects are complex because of mixing behaviour (Hansen et al 1985), but an effective timescale of 5-20 years has been predicted by Dickinson and Schaudt (1998).…”

Section: Solar Variability and Global Climate Response Timescalesmentioning

confidence: 99%

Solar Influence on Global and Regional Climates

Lockwood

2012

Surv Geophys

149

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The literature relevant to how solar variability influences climate is vast-but much has been based on inadequate statistics and non-robust procedures. The common pitfalls are outlined in this review. The best estimates of the solar influence on the global mean air surface temperature show relatively small effects, compared with the response to anthropogenic changes (and broadly in line with their respective radiative forcings). However, the situation is more interesting when one looks at regional and season variations around the global means. In particular, recent research indicates that winters in Eurasia may have some dependence on the Sun, with more cold winters occurring when the solar activity is low. Advances in modelling ''top-down'' mechanisms, whereby stratospheric changes influence the underlying troposphere, offer promising explanations of the observed phenomena. In contrast, the suggested modulation of low-altitude clouds by galactic cosmic rays provides an increasingly inadequate explanation of observations.

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“…However, these approaches assume that the climate response function has a very simple shape and is well described by a single e-folding time. They are therefore believed to produce inaccurate estimates of this function (Wigley et al 2005a;Foster et al 2008;Knutti et al 2008; see also Sect. 3.4).…”

Section: Introductionmentioning

confidence: 99%

A fractal climate response function can simulate global average temperature trends of the modern era and the past millennium

Hateren

2012

Clim Dyn

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A climate response function is introduced that consists of six exponential (low-pass) filters with weights depending as a power law on their e-folding times. The response of this two-parameter function to the combined forcings of solar irradiance, greenhouse gases, and SO 2 -related aerosols is fitted simultaneously to reconstructed temperatures of the past millennium, the response to solar cycles, the response to the 1991 Pinatubo volcanic eruption, and the modern 1850-2010 temperature trend. Assuming strong long-term modulation of solar irradiance, the quite adequate fit produces a climate response function with a millennium-scale response to doubled CO 2 concentration of 2.0 ± 0.3°C (mean ± standard error), of which about 50 % is realized with e-folding times of 0.5 and 2 years, about 30 % with e-folding times of 8 and 32 years, and about 20 % with e-folding times of 128 and 512 years. The transient climate response (response after 70 years of 1 % yearly rise of CO 2 concentration) is 1.5 ± 0.2°C. The temperature rise from 1820 to 1950 can be attributed for about 70 % to increased solar irradiance, while the temperature changes after 1950 are almost completely produced by the interplay of anthropogenic greenhouse gases and aerosols. The SO 2 -related forcing produces a small temperature drop in the years and an inflection of the temperature curve around the year 2000. Fitting with a tenfold smaller modulation of solar irradiance produces a less adequate fit with millenniumscale and transient climate responses of 2.5 ± 0.4 and 1.9 ± 0.3°C, respectively.

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Comment on “Heat capacity, time constant, and sensitivity of Earth's climate system” by S. E. Schwartz

Cited by 52 publications

References 38 publications

Model structure in observational constraints on transient climate response

Model structure in observational constraints on transient climate response

Solar Influence on Global and Regional Climates

A fractal climate response function can simulate global average temperature trends of the modern era and the past millennium

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