Article

Can climate feel the pressure?

Authors:
To read the full-text of this research, you can request a copy directly from the authors.

Abstract

see the figure). Under a scenario in which O 2 is at the low end of the range of estimates (see the figure), these differences between climate models and proxy data largely disappear. The results have important implications for assessing climate during other times in Earth history. The early Paleogene (66 to 50 million years ago) is one of the best-studied intervals of a hothouse planet, with proxy records indicating very warm and wet conditions in mid-latitude and polar regions (2, 7) and CO 2 levels below 2000 ppm (1) (see the figure). Despite decades of intensive research, climate models predict too cool and too dry climates , especially in polar regions (2), unless CO 2 concentrations greater than 2500 ppm are used. O 2 during this time was probably between ~15 and 25% (see the figure). If the low-end O 2 estimates are correct (~15%), the reduced density of the atmosphere relative to today would elevate surface temperatures and precipitation, particularly at the poles, likely reducing the model-proxy differences. During the late Carbon-iferous and Permian (315 to 255 million years ago), Earth experienced the largest and longest glacial period of the Phanerozoic (8), coincident with high O 2 (as much as 35%) and low CO 2 (~350 ppm) (see the figure). Climate models require CO 2 to drop below 560 ppm to initiate ice sheet growth (8) and are thus broadly compatible with CO 2 constraints from proxies and long-term carbon cycle models. Nevertheless , climate model results should be revisited in light of Poulsen et al.'s findings, because the high-pressure atmosphere at this time likely caused additional A

No full-text available

Request Full-text Paper PDF

To read the full-text of this research,
you can request a copy directly from the authors.

... Eras 4, 5, and 6, CO 2 is based on proxy estimates from five methods, originating from more than a hundred individual publications, summarized by Royer et al. (2012) and Peppe and Royer (2015). We have used a data file containing these observations sent to us by Dana Royer, senior author of these papers. ...
Book
This book is open access under a CC BY 4.0 license. This volume presents an Empirical Model of Global Climate developed by the authors and uses that model to show that global warming will likely remain below 2ºC, relative to preindustrial, throughout this century provided: a) both the unconditional and conditional Paris INDC commitments are followed; b) the emission reductions needed to achieve the Paris INDCs are carried forward to 2060 and beyond. The first section of the book provides a short overview of Earth’s climate system, describing and contrasting climatic changes throughout the planet’s history and anthropogenic changes post-Industrial Revolution. The second section describes the climate model developed by the authors (Canty et al., Atmospheric Chemistry and Physics, 2013) and contrasts the model with climate models used in the Intergovernmental Panel on Climate Change (IPCC) 2013 Report. Chapter 3 examines both the unconditional (i.e., firm commitments) and conditional Paris INDCs (commitments contingent on financial flow and/or technology transfer) through the lens of their climate model and concludes that if all of the Paris INDCs are followed, then they are indeed a beacon of hope for Earth’s climate. The fourth part of the book offers a perspective of energy needs and subsequent emissions reductions required to meet the Paris temperature goals, illuminating challenges faced both in the developing world and the developed world. Throughout the book, easy-to-understand charts and graphics illustrate concepts. The scientific basis of Chapters 2 and 3 was first presented in a keynote session of the 96th Annual Meeting of the American Meteorological Society in January, 2016.
... Additionally, some factors involved in long-term climate dynamics such as O 2 have been put forward to challenge this paradigm 4 . This raises questions about the extent to which we are correctly interpreting the relative influence of atmospheric pCO 2 forcing on climate 5 . ...
Article
Full-text available
CO2 is considered the main greenhouse gas involved in the current global warming and the primary driver of temperature throughout Earth’s history. However, the soundness of this relationship across time scales and during different climate states of the Earth remains uncertain. Here we explore how CO2 and temperature are related in the framework of a Greenhouse climate state of the Earth. We reconstruct the long-term evolution of atmospheric CO2 concentration (pCO2) throughout the Cretaceous from the carbon isotope compositions of the fossil conifer Frenelopsis. We show that pCO2 was in the range of ca. 150–650 ppm during the Barremian–Santonian interval, far less than what is usually considered for the mid Cretaceous. Comparison with available temperature records suggest that although CO2 may have been a main driver of temperature and primary production at kyr or smaller scales, it was a long-term consequence of the climate-biological system, being decoupled or even showing inverse trends with temperature, at Myr scales. Our analysis indicates that the relationship between CO2 and temperature is time scale-dependent at least during Greenhouse climate states of the Earth and that primary productivity is a key factor to consider in both past and future analyses of the climate system.
... Eras 4, 5, and 6, CO 2 is based on proxy estimates from five methods, originating from more than a hundred individual publications, summarized by Royer et al. (2012) and Peppe and Royer (2015). We have used a data file containing these observations sent to us by Dana Royer, senior author of these papers. ...
Chapter
Full-text available
This chapter provides an overview of the factors that influence Earth’s climate. The relation between reconstructions of global mean surface temperature and estimates of atmospheric carbon dioxide (CO2) over the past 500 million years is first described. Vast variations in climate on geologic time scales, driven by natural fluctuations of CO2, are readily apparent. We then shift attention to the time period 1765 to present, known as the Anthropocene, during which human activity has strongly influenced atmospheric CO2, other greenhouse gases (GHGs), and Earth’s climate. Two mathematical concepts essential for quantitative understanding of climate change, radiative forcing and global warming potential, are described. Next, fingerprints of the impact of human activity on rising temperature and the abundance of various GHGs over the course of the Anthropocene are presented. We conclude by showing Earth is in the midst of a remarkable transformation. In the past, radiative forcing of climate represented a balance between warming due to rising GHGs and cooling due to the presence of suspended particles (aerosols) in the troposphere. There presently exists considerable uncertainty in the actual magnitude of radiative forcing of climate due to tropospheric aerosols, which has important consequences for our understanding of the climate system. In the future, climate will be driven mainly by GHG warming because aerosol precursors are being effectively removed from pollution sources, due to air quality legislation enacted in response to public health concerns.
Article
Full-text available
The early Eocene "equable climate problem", i.e. warm extratropical annual mean and above-freezing winter temperatures evidenced by proxy records, has remained as one of the great unsolved problems in paleoclimate. Recent progress in modeling and in paleoclimate proxy development provides an opportunity to revisit this problem to ascertain if the current generation of models can reproduce the past climate features without extensive modification. Here we have compiled early Eocene terrestrial temperature data and compared with climate model results using a consistent and rigorous methodology. We test the hypothesis that equable climates can be explained simply as a response to increased greenhouse gas forcing within the framework of the atmospheric component of the Community Climate System Model (version 3), a climate model in common use for predicting future climate change. We find that, with suitably large radiative forcing, the model and data are in general agreement for annual mean and cold month mean temperatures, and that the pattern of high latitude amplification recorded by proxies can be largely, but not perfectly, reproduced.
Article
Full-text available
The percentage of oxygen in Earth's atmosphere varied between 10% and 35% throughout the Phanerozoic. These changes have been linked to the evolution, radiation, and size of animals but have not been considered to affect climate. We conducted simulations showing that modulation of the partial pressure of oxygen (pO2), as a result of its contribution to atmospheric mass and density, influences the optical depth of the atmosphere. Under low pO2 and a reduced-density atmosphere, shortwave scattering by air molecules and clouds is less frequent, leading to a substantial increase in surface shortwave forcing. Through feedbacks involving latent heat fluxes to the atmosphere and marine stratus clouds, surface shortwave forcing drives increases in atmospheric water vapor and global precipitation, enhances greenhouse forcing, and raises global surface temperature. Our results implicate pO2 as an important factor in climate forcing throughout geologic time. Copyright © 2015, American Association for the Advancement of Science.
Article
Full-text available
Estimating the partial pressure of atmospheric oxygen (pO2) in the geological past has been challenging because of the lack of reliable proxies. Here we develop a technique to estimate paleo-pO2 using the stable carbon isotope composition (d13C) of plant resins—including amber, copal, and resinite—from a wide range of localities and ages (Triassic to modern). Plant resins are particularly suitable as proxies because their highly cross-linked terpenoid structures allow the preservation of pristine d13C signatures over geological timescales. The distribution of d13C values of modern resins (n = 126) indicates that (a) resin-producing plant families generally have a similar fractionation behavior during resin biosynthesis, and (b) the fractionation observed in resins is similar to that of bulk plant matter. Resins exhibit a natural variability in d13C of around 8‰ (d13C range: -31‰ to -23‰, mean: -27‰), which is caused by local environmental and ecological factors (e.g., water availability, water composition, light exposure, temperature, nutrient availability). To minimize the effects of local conditions and to determine long-term changes in the d13C of resins, we used mean d13C values (d13C resin mean) for each geological resin deposit. Fossil resins (n = 412) are generally enriched in 13C compared to their modern counterparts, with shifts in d13C resin mean of up to 6‰. These isotopic shifts follow distinctive trends through time, which are unrelated to post-depositional processes including polymerization and diagenesis. The most enriched fossil resin samples, with a d13C resin mean between -22‰ and -21‰, formed during the Triassic, the mid-Cretaceous, and the early Eocene. Exper-imental evidence and theoretical considerations suggest that neither change in pCO2 nor in the d13C of atmospheric CO2 can account for the observed shifts in d13C resin mean . The fractionation of 13C in resin-producing plants (D13C), instead, is primarily influ-enced by atmospheric pO2 , with more fractionation occurring at higher pO2 . The enriched d13C resin mean values suggest that atmospheric pO2 during most of the Mesozoic and Cenozoic was considerably lower (pO2 = 10–20%) than today (pO2 = 21%). In addition, a correlation between the d13C resin mean and the marine d18O record implies that pO2 , pCO2 , and global temperatures were inversely linked, which suggests that intervals of low pO2 were generally accompanied by high pCO2 and elevated global temperatures. Intervals with the lowest inferred pO2 , including the mid-Cretaceous and the early Eocene, were preceded by large-scale volcanism during the emplacement of large igneous provinces (LIPs). This suggests that the influx of mantle-derived volcanic CO2 triggered an initial phase of warming, which led to an increase in oxidative weathering, thereby further increasing greenhouse forcing. This process resulted in the rapid decline of atmospheric pO2 during the mid-Cretaceous and the early Eocene greenhouse periods. After the cessation in LIP volcanism and the decrease in oxidative weathering rates, atmospheric pO2 levels continuously increased over tens of millions of years, whereas CO 2 levels and temperatures continuously declined. These findings suggest that atmospheric pO2 had a considerable impact on the evolution of the climate on Earth, and that the d13C of fossil resins can be used as a novel tool to assess the changes of atmospheric compositions since the emergence of resin-producing plants in the Paleozoic.
Article
Full-text available
The late Paleozoic archives the greatest glaciation of the Phanerozoic.Whereas high-latitude Gondwanan strata preserve widespread evidencefor continental ice, the Permo-Carboniferous tropics have longbeen considered analogous to today's: warm and shielded fromthe high-latitude cold. Here, we report on glacial and periglacialindicators that record episodes of freezing continental temperaturesin western equatorial Pangaea. An exhumed glacial valley andassociated deposits record direct evidence for glaciation thatextended to low paleoelevations in the ancestral Rocky Mountains.Furthermore, the Permo-Carboniferous archives the only knownoccurrence of widespread tropical loess in Earth's history;the volume, chemistry, and provenance of this loess(ite) ismost consistent with glacial derivation. Together with emergingindicators for cold elsewhere in low-latitude Pangaea, theseresults suggest that tropical climate was not buffered fromthe high latitudes and may record glacial-interglacial climateshifts of very large magnitude. Coupled climate-ice sheetmodel simulations demonstrate that low atmospheric CO2 and solarluminosity alone cannot account for such cold, and that otherfactors must be considered in attempting to explain this "best-known"analogue to our present Earth.
Article
Full-text available
The Eocene was the warmest part of the Cenozoic, when warm climates extended into the Arctic, and substantive paleobotanical evidence indicates broadleaf and coniferous polar forests. Paleontological temperature proxies provide a basis for understanding Arctic early Paleogene climates; however, there is a lack of corresponding proxy data on precipitation. Both leaf physiognomic analysis and quantitative analysis of nearest living relatives of an Arctic macroflora indicate upper microthermal to lower mesothermal moist climates (mean annual temperature ∼13–15 °C; cold month mean temperature ∼4 °C; mean annual precipitation >120 cm/yr) for Axel Heiberg Island in the middle Eocene. Leaf-size analysis of Paleocene and Eocene Arctic floras demonstrates high precipitation for the Paleogene western and eastern Arctic. The predicted enormous volume of freshwater entering the Arctic Ocean as a result of northward drainage of a significant region of the Northern Hemisphere under a high-precipitation regime would have strongly affected Arctic Ocean salinity, potentially supporting Arctic Ocean Azolla blooms. High Paleogene precipitation around the Arctic Basin is consistent with high atmospheric humidity, which would have contributed significantly to polar, and global, Eocene warming.
Article
Full-text available
The late Paleozoic represents Earth's last ice age. This review summarizes evidence for the timing, extent, and behavior of continental ice on Pangaea, and the climate and ecosystem response to glacial-interglacial conditions and ultimately the transition from icehouse to greenhouse conditions. In contrast to the traditional view, combined empirical and climate modeling studies argue for a dynamic ice age characterized by discrete periods of glaciation separated by ice contraction during intermittent warmings, moderate-size ice sheets emanating from multiple ice centers throughout southern Gondwana, and the possibility of northern hemisphere glaciation. The glacioeustatic response to fluctuations of these smaller ice sheets was likely less extreme than previously suggested. Both modeling studies and empirical evidence for changes in the geographic patterns and community composition of marine fauna and terrestrial flora as well as stratigraphic relationships suggest the potential for strong responses in oc...
Article
Full-text available
The early Eocene "equable climate problem", i.e. warm extratropical annual mean and above-freezing winter temperatures evidenced by proxy records, has remained as one of the great unsolved problems in paleoclimate. Recent progress in modeling and in paleoclimate proxy development provides an opportunity to revisit this problem to ascertain if the current generation of models can reproduce the past climate features without extensive modification. Here we have compiled early Eocene terrestrial temperature data and compared with climate model results with a consistent and rigorous methodology. We test the hypothesis that equable climates can be explained simply as a response to increased greenhouse gas forcing within the framework of the atmospheric component of the Community Climate System Model (version 3), a climate model in common use for predicting future climate change. We find that, with suitably large radiative forcing, the model and data are in general agreement for annual mean and cold month mean temperatures, and that the pattern of high latitude amplification recorded by proxies can be reproduced.
Article
Full-text available
Variations of the Earth's atmospheric oxygen concentration (pO2) are thought to be closely tied to the evolution of life, with strong feedbacks between uni- and multicellular life and oxygen. On the geologic timescale, pO2 is regulated by the burial of organic carbon and sulphur, as well as by weathering. Reconstructions of atmospheric O2 for the past 400million years have therefore been based on geochemical models of carbon and sulphur cycling. However, these reconstructions vary widely, particularly for the Mesozoic and early Cenozoic eras. Here we show that the abundance of charcoal in mire settings is controlled by pO2, and use this proxy to reconstruct the concentration of atmospheric oxygen for the past 400million years. We estimate that pO2 was continuously above 26% during the Carboniferous and Permian periods, and that it declined abruptly around the time of the Permian-Triassic mass extinction. During the Triassic and Jurassic periods, pO2 fluctuated cyclically, with amplitudes up to 10% and a frequency of 20-30million years. Atmospheric oxygen concentrations have declined steadily from the middle of the Cretaceous period to present-day values of about 21%. We conclude, however, that variation in pO2 was not the main driver of the loss of faunal diversity during the Permo-Triassic and Triassic-Jurassic mass extinction events.
Article
Full-text available
On the basis of a carbon isotopic record of both marine carbonates and organic matter from the Triassic-Jurassic boundary to the present, we modeled oxygen concentrations over the past 205 million years. Our analysis indicates that atmospheric oxygen approximately doubled over this period, with relatively rapid increases in the early Jurassic and the Eocene. We suggest that the overall increase in oxygen, mediated by the formation of passive continental margins along the Atlantic Ocean during the opening phase of the current Wilson cycle, was a critical factor in the evolution, radiation, and subsequent increase in average size of placental mammals.
Article
Long-term carbon and sulfur cycle models have helped shape our understanding of the Phanerozoic history of atmospheric CO2 and O2, but error analyses have been largely limited to testing only a subset of input parameters singly. As a result, the full ranges of probable CO2 and O2 are not quantitatively known. Here we investigate how variation in all 68 input parameters of the GEOCARBSULF model, both singly and in combination, affect estimated CO2 and O2. We improve formulations for land area, runoff, and continental temperature, the latter of which now excludes land area not experiencing chemical weathering. We find our resampled model CO2 and O2 estimates are well bounded and provide high confidence for a "double-hump" in CO2 during the Phanerozoic, with high values during the early Paleozoic and Mesozoic, and low values during the late Paleozoic and late Mesozoic-to-Cenozoic. Our analyses also support a distinct atmospheric O2 peak during the late Paleozoic (>30%) followed by low values near the Triassic-Jurassic boundary (∼10%). Most of the spread in CO2 is contributed by three factors: climate sensitivity to CO2-doubling and the plant-assisted chemical weathering factors LIFE and GYM. CO2 estimates during the Paleozoic to early Mesozoic are highly concordant with independent records from proxies, but are offset to lower values during the globally warm late Mesozoic to early Cenozoic. The model-proxy mismatch for the late Mesozoic can be eliminated with a change in GYM within its plausible range, but no change within plausible ranges can resolve the early Cenozoic mismatch. Either the true value for one or more input parameters during this interval is outside our sampled range, or the model is missing one or more key processes.
Chapter
The amount of CO2 and O2 in the atmosphere over long timescales (>105years) is largely controlled by several key processes. Reconstruction of atmospheric CO2 and O2 in the geologic past can be accomplished either with proxies or by modeling the long-term carbon and sulfur cycles. Application of these two independent approaches yields similar results. CO2 was high during the early Paleozoic (>2000ppm) and parts of the Mesozoic (~1000ppm) but low during the Carboniferous, Permian, and late Cenozoic (<500ppm). These CO2 patterns are strongly coupled to independent evidence for global temperature. O2 records show oscillating values (15-25%) with a distinct peak (>30%) during the Permian. There is a compelling link between this Phanerozoic peak in atmospheric O2 and a concomitant interval of insect gigantism.
Data
We explore the relationship between atmospheric O2 and CO2 evolution and seawater chemistry, with particular focus on the CO2-carbonic acid system and ocean ventilation, over the Phanerozoic Eon using a coupled biogeochemical Earth system model (MAGic). This model describes the biogeochemical cycles involving the major components of seawater (Ca, Mg, Na, K, Cl, SO4, CO2HCO3CO3), as well as components (O2, Fe, P, organic C, reduced S) central to long-term ecosystem productivity. The MAGic calculations show that the first-order input fluxes from weathering of continental rocks of Ca, Mg, and dissolved inorganic carbon (DIC) to the ocean varied in a cyclical manner over the Phanerozoic. The cyclicity is mainly the result of the impact of changing atmospheric CO2 levels, and hence temperature and runoff, on these fluxes, reflecting the nature of hothouse (greenhouse, high CO2 and warm) versus icehouse (low CO2, cool, and continental glaciation) conditions during the Phanerozoic. Uptake of DIC by seafloor basalt-seawater reactions also varied in a corresponding fashion to the weathering fluxes. The fluxes of Ca, Mg, DIC and other seawater constituents removed in oceanic sinks were also calculated and hence with calculated inputs and outputs of seawater constituents, the changes in seawater chemistry through Phanerozoic time could be obtained. Seawater pH increased irregularly during the Phanerozoic from just above 7 in the Cambrian Period, approaching modern average values in the most recent several millions of years. Calcite saturation state also increased with decreasing age. Both pH and calcite saturation state trends exhibited a cyclic overprint of hothouse and icehouse environmental conditions. Dissolved sulfate changed in a cyclical manner reflecting mainly variations in weathering and accretion rates and redox conditions, whereas dissolved potassium exhibited little variation in concentration.
  • R Tappert
R. Tappert et al., Geochim. Cosmochim. Acta 121, 240 (2013).
  • D L Royer
  • Y Donnadieu
  • J Park
  • J Kowalczyk
  • Y Goddéris
D. L. Royer, Y. Donnadieu, J. Park, J. Kowalczyk, Y. Goddéris, Am. J. Sci. 314, 1259 (2014).
  • G S Soreghan
G. S. Soreghan et al., Geology 36, 659 (2008).
  • P G Falkowski
P. G. Falkowski et al., Science 309, 2202 (2005).
  • C J Poulsen
  • C Tabor
  • J D White
C. J. Poulsen, C. Tabor, J. D. White, Science 348, 1238 (2015).
  • R A Berner
  • J M Vandenbrooks
  • P D Ward
R. A. Berner, J. M. Vandenbrooks, P. D. Ward, Science 316, 557 (2007).
  • I P Montañez
  • C J Poulsen
I. P. Montañez, C. J. Poulsen, Annu. Rev. Earth Planet. Sci. 41, 629 (2013).
  • R S Arvidson
  • F T Mackenzie
  • M W Guidry
R. S. Arvidson, F. T. Mackenzie, M. W. Guidry, Chem. Geol. 362, 287 (2013).