Publications by authors named "Christopher J Poulsen"

14 Publications

  • Page 1 of 1

Past climates inform our future.

Science 2020 11;370(6517)

Department of Oceanography, Texas A&M University, College Station, TX, USA.

As the world warms, there is a profound need to improve projections of climate change. Although the latest Earth system models offer an unprecedented number of features, fundamental uncertainties continue to cloud our view of the future. Past climates provide the only opportunity to observe how the Earth system responds to high carbon dioxide, underlining a fundamental role for paleoclimatology in constraining future climate change. Here, we review the relevancy of paleoclimate information for climate prediction and discuss the prospects for emerging methodologies to further insights gained from past climates. Advances in proxy methods and interpretations pave the way for the use of past climates for model evaluation-a practice that we argue should be widely adopted.
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http://dx.doi.org/10.1126/science.aay3701DOI Listing
November 2020

Orbital climate variability on the northeastern Tibetan Plateau across the Eocene-Oligocene transition.

Nat Commun 2020 10 16;11(1):5249. Epub 2020 Oct 16.

State Key Laboratory of Loess and Quaternary Geology, Institute of Earth Environment, Chinese Academy of Sciences, Xi'an, China.

The first major build-up of Antarctic glaciation occurred in two consecutive stages across the Eocene-Oligocene transition (EOT): the EOT-1 cooling event at ~34.1-33.9 Ma and the Oi-1 glaciation event at ~33.8-33.6 Ma. Detailed orbital-scale terrestrial environmental responses to these events remain poorly known. Here we present magnetic and geochemical climate records from the northeastern Tibetan Plateau margin that are dated precisely from ~35.5 to 31 Ma by combined magneto- and astro-chronology. These records suggest a hydroclimate transition at ~33.7 Ma from eccentricity dominated cycles to oscillations paced by a combination of eccentricity, obliquity, and precession, and confirm that major Asian aridification and cooling occurred at Oi-1. We conclude that this terrestrial orbital response transition coincided with a similar transition in the marine benthic δO record for global ice volume and deep-sea temperature variations. The dramatic reorganization of the Asian climate system coincident with Oi-1 was, thus, a response to coeval atmospheric CO decline and continental-scale Antarctic glaciation.
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http://dx.doi.org/10.1038/s41467-020-18824-8DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7567875PMC
October 2020

Glacial cooling and climate sensitivity revisited.

Nature 2020 08 26;584(7822):569-573. Epub 2020 Aug 26.

Department of Earth and Environmental Sciences, University of Michigan, Ann Arbor, MI, USA.

The Last Glacial Maximum (LGM), one of the best studied palaeoclimatic intervals, offers an excellent opportunity to investigate how the climate system responds to changes in greenhouse gases and the cryosphere. Previous work has sought to constrain the magnitude and pattern of glacial cooling from palaeothermometers, but the uneven distribution of the proxies, as well as their uncertainties, has challenged the construction of a full-field view of the LGM climate state. Here we combine a large collection of geochemical proxies for sea surface temperature with an isotope-enabled climate model ensemble to produce a field reconstruction of LGM temperatures using data assimilation. The reconstruction is validated with withheld proxies as well as independent ice core and speleothem δO measurements. Our assimilated product provides a constraint on global mean LGM cooling of -6.1 degrees Celsius (95 per cent confidence interval: -6.5 to -5.7 degrees Celsius). Given assumptions concerning the radiative forcing of greenhouse gases, ice sheets and mineral dust aerosols, this cooling translates to an equilibrium climate sensitivity of 3.4 degrees Celsius (2.4-4.5 degrees Celsius), a value that is higher than previous LGM-based estimates but consistent with the traditional consensus range of 2-4.5 degrees Celsius.
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http://dx.doi.org/10.1038/s41586-020-2617-xDOI Listing
August 2020

Carboniferous plant physiology breaks the mold.

New Phytol 2020 08 8;227(3):667-679. Epub 2020 Apr 8.

Center for Integrative Geosciences, University of Connecticut, Storrs, CT, 06269, USA.

How plants have shaped Earth surface feedbacks over geologic time is a key question in botanical and geological inquiry. Recent work has suggested that biomes during the Carboniferous Period contained plants with extraordinary physiological capacity to shape their environment, contradicting the previously dominant view that plants only began to actively moderate the Earth's surface with the rise of angiosperms during the Mesozoic Era. A recently published Viewpoint disputes this recent work, thus here, we document in detail, the mechanistic underpinnings of our modeling and illustrate the extraordinary ecophysiological nature of Carboniferous plants.
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http://dx.doi.org/10.1111/nph.16460DOI Listing
August 2020

Simulation of Eocene extreme warmth and high climate sensitivity through cloud feedbacks.

Sci Adv 2019 09 18;5(9):eaax1874. Epub 2019 Sep 18.

Department of Geosciences, The University of Arizona, Tucson, AZ 85721, USA.

The Early Eocene, a period of elevated atmospheric CO (>1000 ppmv), is considered an analog for future climate. Previous modeling attempts have been unable to reproduce major features of Eocene climate indicated by proxy data without substantial modification to the model physics. Here, we present simulations using a state-of-the-art climate model forced by proxy-estimated CO levels that capture the extreme surface warmth and reduced latitudinal temperature gradient of the Early Eocene and the warming of the Paleocene-Eocene Thermal Maximum. Our simulations exhibit increasing equilibrium climate sensitivity with warming and suggest an Eocene sensitivity of more than 6.6°C, much greater than the present-day value (4.2°C). This higher climate sensitivity is mainly attributable to the shortwave cloud feedback, which is linked primarily to cloud microphysical processes. Our findings highlight the role of small-scale cloud processes in determining large-scale climate changes and suggest a potential increase in climate sensitivity with future warming.
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http://dx.doi.org/10.1126/sciadv.aax1874DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6750925PMC
September 2019

Amplification of heat extremes by plant CO physiological forcing.

Nat Commun 2018 03 15;9(1):1094. Epub 2018 Mar 15.

Ocean and Climate Physics, Lamont-Doherty Earth Observatory, 61 Route 9W, P.O Box 1000, Palisades, NY, 10964, USA.

Plants influence extreme heat events by regulating land-atmosphere water and energy exchanges. The contribution of plants to changes in future heat extremes will depend on the responses of vegetation growth and physiology to the direct and indirect effects of elevated CO. Here we use a suite of earth system models to disentangle the radiative versus vegetation effects of elevated CO on heat wave characteristics. Vegetation responses to a quadrupling of CO increase summer heat wave occurrence by 20 days or more-30-50% of the radiative response alone-across tropical and mid-to-high latitude forests. These increases are caused by CO physiological forcing, which diminishes transpiration and its associated cooling effect, and reduces clouds and precipitation. In contrast to recent suggestions, our results indicate CO-driven vegetation changes enhance future heat wave frequency and intensity in most vegetated regions despite transpiration-driven soil moisture savings and increases in aboveground biomass from CO fertilization.
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http://dx.doi.org/10.1038/s41467-018-03472-wDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5854667PMC
March 2018

Dynamic Carboniferous tropical forests: new views of plant function and potential for physiological forcing of climate.

New Phytol 2017 Sep 25;215(4):1333-1353. Epub 2017 Jul 25.

Center for Integrative Geosciences, University of Connecticut, Storrs, CT, 06269, USA.

Contents 1333 I. 1334 II. 1335 III. 1339 IV. 1344 V. 1347 VI. 1347 1348 1348 References 1348 SUMMARY: The Carboniferous, the time of Earth's penultimate icehouse and widespread coal formation, was dominated by extinct lineages of early-diverging vascular plants. Studies of nearest living relatives of key Carboniferous plants suggest that their physiologies and growth forms differed substantially from most types of modern vegetation, particularly forests. It remains a matter of debate precisely how differently and to what degree these long-extinct plants influenced the environment. Integrating biophysical analysis of stomatal and vascular conductivity with geochemical analysis of fossilized tissues and process-based ecosystem-scale modeling yields a dynamic and unique perspective on these paleoforests. This integrated approach indicates that key Carboniferous plants were capable of growth and transpiration rates that approach values found in extant crown-group angiosperms, differing greatly from comparatively modest rates found in their closest living relatives. Ecosystem modeling suggests that divergent stomatal conductance, leaf sizes and stem life span between dominant clades would have shifted the balance of soil-atmosphere water fluxes, and thus surface runoff flux, during repeated, climate-driven, vegetation turnovers. This synthesis highlights the importance of 'whole plant' physiological reconstruction of extinct plants and the potential of vascular plants to have influenced the Earth system hundreds of millions of years ago through vegetation-climate feedbacks.
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http://dx.doi.org/10.1111/nph.14700DOI Listing
September 2017

Minerals: A rescue package for imperilled collection.

Nature 2017 06;546(7657):210

Stanford University, California, USA.

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http://dx.doi.org/10.1038/546210bDOI Listing
June 2017

Pacific North American circulation pattern links external forcing and North American hydroclimatic change over the past millennium.

Proc Natl Acad Sci U S A 2017 03 13;114(13):3340-3345. Epub 2017 Mar 13.

Department of Geology and Geophysics, University of Utah, Salt Lake City, UT 84112;

Land and sea surface temperatures, precipitation, and storm tracks in North America and the North Pacific are controlled to a large degree by atmospheric variability associated with the Pacific North American (PNA) pattern. The modern instrumental record indicates a trend toward a positive PNA phase in recent decades, which has led to accelerated warming and snowpack decline in northwestern North America. The brevity of the instrumental record, however, limits our understanding of long-term PNA variability and its directional or cyclic patterns. Here we develop a 937-y-long reconstruction of the winter PNA based on a network of annually resolved tree-ring proxy records across North America. The reconstruction is consistent with previous regional records in suggesting that the recent persistent positive PNA pattern is unprecedented over the past millennium, but documents patterns of decadal-scale variability that contrast with previous reconstructions. Our reconstruction shows that PNA has been strongly and consistently correlated with sea surface temperature variation, solar irradiance, and volcanic forcing over the period of record, and played a significant role in translating these forcings into decadal-to-multidecadal hydroclimate variability over North America. Climate model ensembles show limited power to predict multidecadal variation in PNA over the period of our record, raising questions about their potential to project future hydroclimatic change modulated by this circulation pattern.
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http://dx.doi.org/10.1073/pnas.1618201114DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5380075PMC
March 2017

Response to Comment on "Long-term climate forcing by atmospheric oxygen concentrations".

Science 2016 Jul;353(6295):132

Department of Biology, Baylor University, Waco, TX 76798, USA.

Goldblatt argues that a decrease in pressure broadening of absorption lines in an atmosphere with low oxygen leads to an increase in outgoing longwave radiation and atmospheric cooling. We demonstrate that cloud and water vapor feedbacks in a global climate model compensate for these decreases and lead to atmospheric warming.
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http://dx.doi.org/10.1126/science.aad8550DOI Listing
July 2016

Tracking the migration of the Indian continent using the carbonate clumped isotope technique on Phanerozoic soil carbonates.

Sci Rep 2016 Mar 2;6:22187. Epub 2016 Mar 2.

Dept. of Earth and Environmental Sciences, University of Michigan, Ann Arbor, MI 48109-1005.

Approximately 140 million years ago, the Indian plate separated from Gondwana and migrated by almost 90° latitude to its current location, forming the Himalayan-Tibetan system. Large discrepancies exist in the rate of migration of Indian plate during Phanerozoic. Here we describe a new approach to paleo-latitudinal reconstruction based on simultaneous determination of carbonate formation temperature and δ(18)O of soil carbonates, constrained by the abundances of (13)C-(18)O bonds in palaeosol carbonates. Assuming that the palaeosol carbonates have a strong relationship with the composition of the meteoric water, δ(18)O carbonate of palaeosol can constrain paleo-latitudinal position. Weighted mean annual rainfall δ(18)O water values measured at several stations across the southern latitudes are used to derive a polynomial equation: δ(18)Ow = -0.006 × (LAT)(2) - 0.294 × (LAT) - 5.29 which is used for latitudinal reconstruction. We use this approach to show the northward migration of the Indian plate from 46.8 ± 5.8°S during the Permian (269 M.y.) to 30 ± 11°S during the Triassic (248 M.y.), 14.7 ± 8.7°S during the early Cretaceous (135 M.y.), and 28 ± 8.8°S during the late Cretaceous (68 M.y.). Soil carbonate δ(18)O provides an alternative method for tracing the latitudinal position of Indian plate in the past and the estimates are consistent with the paleo-magnetic records which document the position of Indian plate prior to 135 ± 3 M.y.
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http://dx.doi.org/10.1038/srep22187DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4773985PMC
March 2016

CLIMATE CHANGE. Long-term climate forcing by atmospheric oxygen concentrations.

Science 2015 Jun 11;348(6240):1238-41. Epub 2015 Jun 11.

Department of Biology, Baylor University, Waco, TX 76798, USA.

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.
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http://dx.doi.org/10.1126/science.1260670DOI Listing
June 2015

Onset of convective rainfall during gradual late Miocene rise of the central Andes.

Science 2010 Apr 1;328(5977):490-3. Epub 2010 Apr 1.

Department of Geological Sciences, University of Michigan, Ann Arbor, MI 48109, USA.

A decrease in the ratio of 18O to 16O (delta18O) of sedimentary carbonate from the Bolivian Altiplano has been interpreted to indicate rapid surface uplift of the late Miocene Andean plateau (AP). Here we report on paleoclimate simulations of Andean surface uplift with an atmospheric general circulation model (GCM) that tracks oxygen isotopes in vapor. The GCM predicts changes in atmospheric circulation and rainfall that influence AP isotopic source and amount effects. On eastern AP slopes, summer convective precipitation increases by up to 6 millimeters per day (>500%) for plateau elevations that are greater than about 2000 meters. High precipitation rates enhance the isotope amount effect, leading to a decrease in precipitation delta18O at high elevations and an increase in delta18O lapse rate. Our results indicate that late Miocene delta18O depletion reflects initiation and intensification of convective rainfall.
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http://dx.doi.org/10.1126/science.1185078DOI Listing
April 2010

Palaeoclimate: a balmy Arctic.

Nature 2004 Dec;432(7019):814-5

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http://dx.doi.org/10.1038/432814aDOI Listing
December 2004