Warm climates of the past—a lesson for the future?

Lunt, Daniel J.; Elderfield, Henry; Pancost, Richard D.; Ridgwell, Andy; Foster, Gavin L.; Haywood, Alan M.; Kiehl, J.; Sagoo, Navjit; Shields, Christine A.; Stone, E. J.; Valdes, Paul J.

doi:10.1098/rsta.2013.0146

Cited by 33 publications

(21 citation statements)

References 53 publications

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“…Getech Group plc (www.getech.com) have provided an alternative palaeogeographic reconstruction that may be used for sensitivity studies, in particular the simulation deepmip-sensgeoggetech (see Tables 1, 2). It is included digitally in Lunt et al (2016) as a netcdf file at a resolution of 3.75 • longitude × 2.5 • latitude, and is shown in Fig. 3c.…”

Section: Sensitivity To Palaeogeographymentioning

confidence: 99%

DeepMIP: experimental design for model simulations of the EECO, PETM, and pre-PETM

Lunt

Huber

Baatsen

et al. 2016

Preprint

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Abstract. Past warm periods provide an opportunity to evaluate climate models under extreme forcing scenarios, in particular high (> 800 ppmv) atmospheric CO2 concentrations. Although a post-hoc intercomparison of Eocene (~50 million years ago, Ma) climate model simulations and geological data has been carried out previously, models of past high-CO2 periods have never been evaluated in a consistent framework. Here, we present an experimental design for climate model simulations of three warm periods within the latest Paleocene and the early Eocene. Together these form the first phase of DeepMIP – the deeptime model intercomparison project, itself a group within the wider Paleoclimate Modelling Intercomparison Project (PMIP). The experimental design consists of three core paleo simulations and a set of optional sensitivity studies. The experimental design specifies and provides guidance on boundary conditions associated with palaeogeography, greenhouse gases, orbital configuration, solar constant, land surface parameters, and aerosols. Initial conditions, simulation length, and output variables are also specified. Finally, we explain how the geological datasets, which will be used to evaluate the simulations, will be developed.

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Section: Sensitivity To Palaeogeographymentioning

confidence: 99%

DeepMIP: experimental design for model simulations of the EECO, PETM, and pre-PETM

Lunt

Huber

Baatsen

et al. 2016

Preprint

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“…Paleoclimate is a useful testbed for simple and complex climate models [400][401][402][403][404][405] and numerous studies have estimated climate sensitivity from past periods, in particular the Last Glacial Maximum or the last few glacial cycles, but also the Holocene and warm periods millions of years back 95,102,400, . Uncertainties in some individual studies are small but the range across studies is similar to the range derived from other methods.…”

Section: Paleoclimatementioning

confidence: 99%

Beyond equilibrium climate sensitivity

2017

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Equilibrium climate sensitivity characterizes the Earth' long-term global temperature response to an increased atmospheric carbon dioxide concentration. It has reached almost iconic status as the single number that describes how severe climate change will be. The consensus 'likely' range for climate sensitivity of 1.5-4.5 o C today is the same as given by Jule Charney in 1979, but is now based on quantitative evidence from across the climate system, and through climate history. The quest to constrain climate sensitivity has revealed important insights into the timescales of the climate system response, natural variability, limitations in observations and climate models, but also concerns about the simple concepts underlying climate sensitivity and radiative forcing, which open avenues to better understand and constrain the climate response to forcing. Estimates of the transient climate response are better constrained by observed warming and are more relevant for predicting warming over the next decades. Newer metrics relating global warming directly to the total emitted CO2 show that in order to keep warming to within 2 o C, future CO2 emissions have to remain strongly limited, irrespective of climate sensitivity being at the high or low end.If we increase the amount of CO2 in the Earth's atmosphere and wait for climate to respond, how much warmer would surface temperatures eventually get? What seems like a simple but important question to ask given current and projected human-induced CO2 emissions, is an issue that scientists have struggled with since the first rough estimates were made more than a century ago 1,2 . To answer that question, starting in the 1960s, scientists have used energy balance arguments combined with observed changes in the global energy budget, evaluated comprehensive climate models against observations, and analyzed the relationship between external forcing and climate change over different climate states in the past (see Methods for a list of early publications). The idea of using those different lines of evidence has not changed, but progress in simulating climate, a longer and more accurate observed record of past warming, and better constrained paleoclimate reconstructions now offer more possibilities to evaluate and constrain models. However, recent research has pointed out previously unknown limitations in some of the concepts and assumptions underlying a single constant climate sensitivity 3 . While publications have appeared using various methods, arguably the most important conceptual recent insights is that feedbacks change with equilibration time, an insight that is based on studies in comprehensive climate models. Other recent insights show that the treatment of observations is important 4 . Knowing, to first order, how the global climate will warm in response to increased CO2 is critical: for unabated emissions, it is the difference between a hot and an extremely hot future. The value of halving the uncertainty in that projection may be in the trillions of dollars 5 . Here w...

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“…The onset of the PETM, at approximately 55.9 Ma (Westerhold et al, 2009), is recognised as the boundary between the Palaeocene and Eocene epochs (Aubry et al, 2007), and is characterised by a large CIE, indicating large GHG emissions, accompanied by a sudden rise in global temperature (Kennett and Stott, 1991), extensive extinction and origination of nanoplankton (Gibbs et al, 2006) and widespread ocean anoxia (Dickson et al, 2012). There is some evidence from analysis and modelling of the timing and duration of variations in δ 13 C and δ 18 O observed in nanoplankton fossils that some of the GHG emissions were initially in the form of CH 4 (Dickens, 2011;Lunt et al, 2011;Thomas et al, 2002), which is rapidly oxidised in the atmosphere to CO 2 . The PETM is also marked by enhanced precipitation and continental weathering (Carmichael et al, 2016;Chen et al, 2016;Penman, 2016), rapid and sustained surface ocean acidification (Penman et al, 2014;Zachos et al, 2005), and shares many features of the global-scale oceanic anoxic events of the Cretaceous and Jurassic periods (Jenkyns, 2010); see McInerney and Wing (2011) for a review of PETM research.…”

Section: Climate Of the Early Eocenementioning

confidence: 99%

“…The CIEs of the early Eocene show similar regularity in their timing to periodic changes in the Earth's orbit around the Sun , and the search for causal relationships between orbital cycles and Paleogene climate is an active area of research (e.g. Lauretano et al, 2015;Laurin et al, 2016;Lunt et al, 2011).…”

Section: Introductionmentioning

confidence: 99%

Sensitivity of the Eocene climate to CO<sub>2</sub> and orbital variability

Keery

Edwards

2018

Clim. Past

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The early Eocene, from about 56 Ma, with high atmospheric CO 2 levels, offers an analogue for the response of the Earth's climate system to anthropogenic fossil fuel burning. In this study, we present an ensemble of 50 Earth system model runs with an early Eocene palaeogeography and variation in the forcing values of atmospheric CO 2 and the Earth's orbital parameters. Relationships between simple summary metrics of model outputs and the forcing parameters are identified by linear modelling, providing estimates of the relative magnitudes of the effects of atmospheric CO 2 and each of the orbital parameters on important climatic features, including tropical-polar temperature difference, ocean-land temperature contrast, Asian, African and South (S.) American monsoon rains, and climate sensitivity. Our results indicate that although CO 2 exerts a dominant control on most of the climatic features examined in this study, the orbital parameters also strongly influence important components of the ocean-atmosphere system in a greenhouse Earth. In our ensemble, atmospheric CO 2 spans the range 280-3000 ppm, and this variation accounts for over 90 % of the effects on mean air temperature, southern winter high-latitude oceanland temperature contrast and northern winter tropical-polar temperature difference. However, the variation of precession accounts for over 80 % of the influence of the forcing parameters on the Asian and African monsoon rainfall, and obliquity variation accounts for over 65 % of the effects on winter ocean-land temperature contrast in high northern latitudes and northern summer tropical-polar temperature difference.Our results indicate a bimodal climate sensitivity, with values of 4.36 and 2.54 • C, dependent on low or high states of atmospheric CO 2 concentration, respectively, with a threshold at approximately 1000 ppm in this model, and due to a saturated vegetation-albedo feedback. Our method gives a quantitative ranking of the influence of each of the forcing parameters on key climatic model outputs, with additional spatial information from singular value decomposition providing insights into likely physical mechanisms. The results demonstrate the importance of orbital variation as an agent of change in climates of the past, and we demonstrate that emulators derived from our modelling output can be used as rapid and efficient surrogates of the full complexity model to provide estimates of climate conditions from any set of forcing parameters.

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Warm climates of the past—a lesson for the future?

Cited by 33 publications

References 53 publications

DeepMIP: experimental design for model simulations of the EECO, PETM, and pre-PETM

DeepMIP: experimental design for model simulations of the EECO, PETM, and pre-PETM

Beyond equilibrium climate sensitivity

Sensitivity of the Eocene climate to CO<sub>2</sub> and orbital variability

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Warm climates of the past—a lesson for the future?

Cited by 33 publications

References 53 publications

DeepMIP: experimental design for model simulations of the EECO, PETM, and pre-PETM

DeepMIP: experimental design for model simulations of the EECO, PETM, and pre-PETM

Beyond equilibrium climate sensitivity

Sensitivity of the Eocene climate to CO&lt;sub&gt;2&lt;/sub&gt; and orbital variability

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Sensitivity of the Eocene climate to CO<sub>2</sub> and orbital variability