Do Low CO2 Concentrations Affect Pollen-Based Reconstructions of LGM Climates? A Response to “Physiological Significance of Low Atmospheric CO2 for Plant–Climate Interactions” by Cowling and Sykes

Williams, John W.; Webb, Thompson; Shurman, Bryan N.; Bartlein, Patrick J.

doi:10.1006/qres.2000.2131

Cited by 22 publications

(14 citation statements)

References 29 publications

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“…The use of fossil pollen records to reconstruct climate has a long history in eastern North America (Bartlein and Webb, 1985;Gajewski, 1988;Prentice et al, 1991;Webb et al, 1993Webb et al, , 1998Jackson et al, 2000;Williams et al, 2000;Bartlein et al, 2011;Viau et al, 2012;Wahl et al, 2012). Pollen data have been used to reconstruct climate variables such as mean temperature of the coldest month, mean temperature of the warmest month, mean annual temperature, and mean annual precipitation and bioclimatic variables.…”

Section: Fossil Pollenmentioning

confidence: 99%

Climatic history of the northeastern United States during the past 3000 years

et al. 2017

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Abstract. Many ecosystem processes that influence Earth system feedbacks -vegetation growth, water and nutrient cycling, disturbance regimes -are strongly influenced by multidecadal-to millennial-scale climate variations that cannot be directly observed. Paleoclimate records provide information about these variations, forming the basis of our understanding and modeling of them. Fossil pollen records are abundant in the NE US, but cannot simultaneously provide information about paleoclimate and past vegetation in a modeling context because this leads to circular logic. If pollen data are used to constrain past vegetation changes, then the remaining paleoclimate archives in the northeastern US (NE US) are quite limited. Nonetheless, a growing number of diverse reconstructions have been developed but have not yet been examined together. Here we conduct a systematic review, assessment, and comparison of paleotemperature and paleohydrological proxies from the NE US for the last 3000 years. Regional temperature reconstructions (primarily summer) show a long-term cooling trend (1000 BCE-1700 CE) consistent with hemispheric-scale reconstructions, while hydroclimate data show gradually wetter conditions through the present day. Multiple proxies suggest that a prolonged, widespread drought occurred between 550 and 750 CE. Dry conditions are also evident during the Medieval Climate Anomaly, which was warmer and drier than the Little Ice Age and drier than today. There is some evidence for an acceleration of the longer-term wetting trend in the NE US during the past century; coupled with an abrupt shift from decreasing to increasing temperatures in the past century, these changes could have wide-ranging implications for species distributions, ecosystem dynamics, and extreme weather events. More work is needed to gather paleoclimate data in the NE US to make inter-proxy comparisons and to improve estimates of uncertainty in reconstructions.

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Section: Fossil Pollenmentioning

confidence: 99%

Climatic history of the northeastern United States during the past 3000 years

et al. 2017

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“…Moreover, if these variations in c a have caused changes that are detectable in compositional data, such as pollen assemblages, then conventional approaches to reconstructing past climate using statistical or analogue methods -if applied to periods with c a different from that of the late Holocene -are certain to yield incorrect results. Although this potential problem in palaeoclimate reconstruction has been known in principle for more than two decades (Solomon, 1984;Idso, 1989;Farquhar, 1997;Street-Perrott, 1994;Street-Perrott et al, 1997;Sykes, 1999, 2000;Bennett and Willis, 2000;Williams et al, 2000;Loehle, 2007), until recently few systematic attempts have been made to rectify it.…”

Section: Introductionmentioning

confidence: 99%

Ecosystem effects of CO2 concentration: evidence from past climates

2009

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Abstract. Atmospheric CO 2 concentration has varied from minima of 170-200 ppm in glacials to maxima of 280-300 ppm in the recent interglacials. Photosynthesis by C 3 plants is highly sensitive to CO 2 concentration variations in this range. Physiological consequences of the CO 2 changes should therefore be discernible in palaeodata. Several lines of evidence support this expectation. Reduced terrestrial carbon storage during glacials, indicated by the shift in stable isotope composition of dissolved inorganic carbon in the ocean, cannot be explained by climate or sea-level changes. It is however consistent with predictions of current processbased models that propagate known physiological CO 2 effects into net primary production at the ecosystem scale. Restricted forest cover during glacial periods, indicated by pollen assemblages dominated by non-arboreal taxa, cannot be reproduced accurately by palaeoclimate models unless CO 2 effects on C 3 -C 4 plant competition are also modelled. It follows that methods to reconstruct climate from palaeodata should account for CO 2 concentration changes. When they do so, they yield results more consistent with palaeoclimate models. In conclusion, the palaeorecord of the Late Quaternary, interpreted with the help of climate and ecosystem models, provides evidence that CO 2 effects at the ecosystem scale are neither trivial nor transient.

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“…These studies suggest that previous pollen-based estimates of temperature decreases during the LGM may have been overestimated. A modeling approach combined with appropriate data is thus necessary to understand these discrepancies (15,16).In this paper, we describe our use of an improved inverse vegetation modeling approach (17) by a physiological processbased vegetation model, BIOME4 (18), in an inverse mode (15), and the BIOME6000 pollen data (19) to examine how changes in atmospheric CO 2 concentration and climate might account for the observed distribution of African mountain vegetation during the LGM. …”

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Dominant factors controlling glacial and interglacial variations in the treeline elevation in tropical Africa

Guiot

Brewer

et al. 2007

Proc. Natl. Acad. Sci. U.S.A.

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The knowledge of tropical palaeoclimates is crucial for understanding global climate change, because it is a test bench for general circulation models that are ultimately used to predict future global warming. A longstanding issue concerning the last glacial maximum in the tropics is the discrepancy between the decrease in sea-surface temperatures reconstructed from marine proxies and the high-elevation decrease in land temperatures estimated from indicators of treeline elevation. In this study, an improved inverse vegetation modeling approach is used to quantitatively reconstruct palaeoclimate and to estimate the effects of different factors (temperature, precipitation, and atmospheric CO 2 concentration) on changes in treeline elevation based on a set of pollen data covering an altitudinal range from 100 to 3,140 m above sea level in Africa. We show that lowering of the African treeline during the last glacial maximum was primarily triggered by regional drying, especially at upper elevations, and was amplified by decreases in atmospheric CO 2 concentration and perhaps temperature. This contrasts with scenarios for the Holocene and future climates, in which the increase in treeline elevation will be dominated by temperature. Our results suggest that previous temperature changes inferred from tropical treeline shifts may have been overestimated for low-CO2 glacial periods, because the limiting factors that control changes in treeline elevation differ between glacial and interglacial periods.biome model ͉ biome pollen scores ͉ palaeoclimatology ͉ pollen ͉ vegetation model inversion P ollen data show a lowering of treeline elevations during the last glacial maximum (LGM) by Ϸ1,000-1,700 m in mountains at a wide range of tropical and subtropical locations (1, 2). Assuming this decrease corresponds to a decrease in mean temperature and given a lapse rate of 5-6°C km Ϫ1 , this would imply a substantial cooling of Ϸ5-10°C in these areas, particularly at high elevations in the tropics (1, 2). However, a new faunal reconstruction of sea surface temperature (Multiproxy approach for the reconstruction of the glacial ocean surface: MARGO) for the tropics indicates a more limited cooling of Ϸ2°C at low elevations during this period (3, 4), which is slightly more than the Ϸ1.5°C estimated by using CLIMAP (5). These reconstructions are clearly not consistent, and although the differences could in principle be explained by a steeper atmospheric lapse rate, this parameter needs further validation by using more reliable data (6-8). Nonetheless, this lack of agreement leaves considerable uncertainty about what the tropical climate was really like during the last ice age.Physiological data and models have demonstrated that the processes that modify carbon and water uptake in plants are highly dependent on CO 2 concentrations (9, 10). This suggests that modern plant-climate relationships are not representative of interactions between plants and climate in the past (9 -11), because the atmospheric CO 2 concentration has f luctuated ...

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Do Low CO₂ Concentrations Affect Pollen-Based Reconstructions of LGM Climates? A Response to “Physiological Significance of Low Atmospheric CO₂ for Plant–Climate Interactions” by Cowling and Sykes

Cited by 22 publications

References 29 publications

Climatic history of the northeastern United States during the past 3000 years

Climatic history of the northeastern United States during the past 3000 years

Ecosystem effects of CO<sub>2</sub> concentration: evidence from past climates

Dominant factors controlling glacial and interglacial variations in the treeline elevation in tropical Africa

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Do Low CO2 Concentrations Affect Pollen-Based Reconstructions of LGM Climates? A Response to “Physiological Significance of Low Atmospheric CO2 for Plant–Climate Interactions” by Cowling and Sykes

Cited by 22 publications

References 29 publications

Climatic history of the northeastern United States during the past 3000 years

Climatic history of the northeastern United States during the past 3000 years

Ecosystem effects of CO&lt;sub&gt;2&lt;/sub&gt; concentration: evidence from past climates

Dominant factors controlling glacial and interglacial variations in the treeline elevation in tropical Africa

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Do Low CO₂ Concentrations Affect Pollen-Based Reconstructions of LGM Climates? A Response to “Physiological Significance of Low Atmospheric CO₂ for Plant–Climate Interactions” by Cowling and Sykes

Ecosystem effects of CO<sub>2</sub> concentration: evidence from past climates