Impacts of land surface properties and atmospheric CO&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt; on the Last  Glacial Maximum climate: a factor separation analysis

Henrot, Alexandra; François, Louis; Brewer, Simon; Munhoven, Guy

doi:10.5194/cp-5-183-2009

Cited by 13 publications

(13 citation statements)

References 56 publications

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“…The interaction between vegetation and atmosphere was found 415 to produce a warmer Miocene independent of CO2 by Knorr et al (2011). The interaction between vegetation and paleogeography produced a higher climate sensitivity in the modelled Miocene in Bradshaw et al (2015) and warming independent of CO2 by Henrot et al (2010) due to vegetation and lower-elevation topography. Land surface cover and increased northern transient eddy heat transport were found to result in polar warming in a modelled late Miocene in a fully coupled GCM by Micheels et al (2010).…”

Section: Climate Forcing and Co2 Levelsmentioning

confidence: 89%

“…Modelling efforts of the Miocene find that reconciling the combined constraints of ocean temperature, CO2 indicators and Antarctic ice sheet dynamics is a non-trivial task (Micheels et al, 2009;Henrot et al, 2010, Bradshaw et al, 2012Sijp et al, 2014), with vegetation seemingly integral in creating the Miocene climatic conditions (Henrot et al, 2010;Knorr et al, 2011;50 Krapp and Jungklaus, 2011;Micheels et al, 2011;Bradshaw et al, 2015) along with bathymetry, topography and CO2.…”

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confidence: 99%

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Data-constrained assessment of ocean circulation changes since the middle Miocene in an Earth system model

Crichton¹,

Ridgwell²,

Lunt³

et al. 2020

Preprint

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Abstract. Since the middle Miocene, 15 Ma (million years ago), the Earth’s climate has undergone a long-term cooling trend, characterised by a reduction in sea surface temperatures by over 6 °C, with 4 to 6 °C cooling occurring in the deep ocean. The causes of this cooling are primarily thought to be linked to changes in ocean circulation due to tectonic plate movements affecting ocean seaways, together with and a drop in atmospheric greenhouse gas forcing (and attendant ice-sheet growth and feedback). In this study we assess the potential to constrain, using marine sediment proxy data, the evolving patterns of global ocean circulation and cooling of surface climate over the last 15 million years (Ma) in an Earth system model. We do this by compiling surface and benthic ocean temperature and benthic carbon-13 data in a series of seven time-slices spaced at approximately 2.5 million year intervals. We pair this with a corresponding series of seven tectonic and surface climate boundary condition reconstructions in the cGENIE (muffin release) Earth system model. In the cGENIE model, we adjust atmospheric CO2 together with the magnitude of North Pacific to North Atlantic salinity flux adjustment in a series of 2D parameter ensembles in order to match global temperature and benthic δ13C patterns in the model to the data. We identify that a relatively high CO2 equivalent forcing of 1120 ppm is required at 15 Ma in cGENIE to reproduce proxy temperature estimates in the model, noting that this CO2 forcing is dependent on cGENIEs climate sensitivity (which is as the present day) and that it incorporates the effects of all greenhouse gases. The required CO2 forcing progressively reduces throughout the subsequent six time slices delineating the observed long-term cooling trend. In order to match the evolving patterns of the proxy data, we require fundamental change in the mode of ocean circulation at 12.5 Ma with present-day-like benthic δ13C trends established by 10 Ma. We also find a general increasing strength of Atlantic overturning despite a reduction in salinity of the surface North Atlantic over the cooling period, attributable to falling intensity of the hydrological cycle and polar cooling caused by CO2-driven global cooling.

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Section: Climate Forcing and Co2 Levelsmentioning

confidence: 89%

mentioning

confidence: 99%

Data-constrained assessment of ocean circulation changes since the middle Miocene in an Earth system model

Crichton¹,

Ridgwell²,

Lunt³

et al. 2020

Preprint

View full text Add to dashboard Cite

show abstract

“…Factor separation studies have found that ice sheets primarily cool climate through their low albedo, with increased elevation having a smaller effect (Henrot et al 2009;Yin et al 2009). Temperature anomalies are smaller away from the ice sheets, but the widespread cooling in this experiment, especially in the SH, differs from past ice sheet experiments (Broccoli and Manabe 1987;Henrot et al 2009;Yin et al 2009), which show areas of warming in the SH or ocean areas. Those studies used EMICs or had simple oceans, however, so the current results suggest that widespread cooling may be a more realistic response to expanded NH and Antarctic ice sheets.…”

Section: Climate Response Fingerprintsmentioning

confidence: 96%

“…A method of investigating linearity in more detail is the factor separation approach, in which climate simulations are driven by separate forcings as well as every combination of forcings for a given time period (Stein and Alpert 1993;Henrot et al 2009;Yin andBerger 2010, 2012). While effective, a pure factor separation approach requires many simulations to separate out the interactions between multiple forcings, which can become computationally expensive.…”

Section: Introductionmentioning

confidence: 99%

Using Single-Forcing GCM Simulations to Reconstruct and Interpret Quaternary Climate Change

2015

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The long-term climate variations of the Quaternary were primarily influenced by concurrent changes in Earth's orbit, greenhouse gases, and ice sheets. However, because climate changes over the coming century will largely be driven by changes in greenhouse gases alone, it is important to better understand the separate contributions of each of these forcings in the past. To investigate this, idealized equilibrium simulations are conducted in which the climate is driven by separate changes in obliquity, precession, CO 2 , and ice sheets. To test the linearity of past climate change, anomalies from these single-forcing experiments are scaled and summed to compute linear reconstructions of past climate, which are then compared to mid-Holocene and last glacial maximum (LGM) snapshot simulations, where all forcings are applied together, as well as proxy climate records. This comparison shows that much of the climate response may be approximated as a linear response to forcings, while some features, such as modeled changes in sea ice and Atlantic meridional overturning circulation (AMOC), appear to be heavily influenced by nonlinearities. In regions where the linear reconstructions replicate the full-forcing experiments well, this analysis can help identify how each forcing contributes to the climate response. Monsoons at the mid-Holocene respond strongly to precession, while LGM monsoons are heavily influenced by the altered greenhouse gases and ice sheets. Contrary to previous studies, ice sheets produce pronounced tropical cooling at the LGM. Compared to proxy temperature records, the linear reconstructions replicate long-term changes well and also show which climate variations are not easily explained as direct responses to long-term forcings.

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“…More recent applications have studied the planetary climate system's response to, for instance, vegetation-atmosphere feedback mechanisms (Dekker et al, 2010;Bathiany et al, 2012), large-scale changes in orography (Garreaud et al, 2010;Schmittner et al, 2011), and variations in astronomical forcings (Boschi et al, 2013;Linsenmeier et al, 2015). The model has also been used for paleoclimate studies (Henrot et al, 2009) and snowball Earth experiments (Spiegl et al, 2015;Lucarini et al, 2013). Some of these studies have also explored the existence of alternative equilibrium states of the planetary climate system, as well as the mechanisms behind potential state transitions (Dekker et al, 2010;Bathiany et al, 2012;Boschi et al, 2013;Linsenmeier et al, 2015).…”

Section: Model Descriptionmentioning

confidence: 99%

Tipping the ENSO into a permanent El Niño can trigger state transitions in global terrestrial ecosystems

2019

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Abstract. Some large-scale components of the Earth's climate system have been identified as policy-relevant “tipping elements”, meaning that anthropogenic forcing and perturbations may push them across a tipping point threshold, with potential global scale impact on ecosystems and concomitant environmental and social phenomena. A pronounced change in the amplitude and/or frequency of the El Niño–Southern Oscillation (ENSO) is among such tipping elements. Here, we use the Planet Simulator (PlaSim), an Earth system model of intermediate complexity, to investigate the potential impact on global climate and terrestrial ecosystems of shifting the current dynamics of the ENSO into a permanent El Niño. When forced with sea surface temperature (SST) derived from observations, the PlaSim model yields a realistic representation of large-scale climatological patterns, including realistic estimates of the global energy and water balances, and gross primary productivity (GPP). In a permanent El Niño state, we found significant differences in the global distribution of water and energy fluxes, and associated impacts on GPP, indicating that vegetation production decreases in the tropics, whereas it increases in temperate regions. We identify regions in which these El Niño-induced changes are consistent with potential state transitions in global terrestrial ecosystems, including potential greening of western North America, dieback of the Amazon rainforest, and further aridification of south-eastern Africa and Australia.

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Impacts of land surface properties and atmospheric CO<sub>2</sub> on the Last Glacial Maximum climate: a factor separation analysis

Cited by 13 publications

References 56 publications

Data-constrained assessment of ocean circulation changes since the middle Miocene in an Earth system model

Data-constrained assessment of ocean circulation changes since the middle Miocene in an Earth system model

Using Single-Forcing GCM Simulations to Reconstruct and Interpret Quaternary Climate Change

Tipping the ENSO into a permanent El Niño can trigger state transitions in global terrestrial ecosystems

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