Pollard David

No Thumbnail Available
Last Name
Pollard
First Name
David
ORCID

Filters

2017 - 2020 3
2 1
3
Reset filters

Settings

Search Results

Now showing 1 - 3 of 3
  • Article
    A geostatistical framework for quantifying the imprint of mesoscale atmospheric transport on satellite trace gas retrievals
    (American Geophysical Union, 2019-07-29) Torres, Anthony D. ; Keppel-Aleks, Gretchen ; Doney, Scott C. ; Fendrock, Michaela ; Luis, Kelly M. A. ; De Mazière, Martine ; Hase, Frank ; Petri, Christof ; Pollard, David ; Roehl, Coleen M. ; Sussmann, Ralf ; Velazco, Voltaire A. ; Warneke, Thorsten ; Wunch, Debra
    National Aeronautics and Space Administration's Orbiting Carbon Observatory‐2 (OCO‐2) satellite provides observations of total column‐averaged CO2 mole fractions (XCO2 ) at high spatial resolution that may enable novel constraints on surface‐atmosphere carbon fluxes. Atmospheric inverse modeling provides an approach to optimize surface fluxes at regional scales, but the accuracy of the fluxes from inversion frameworks depends on key inputs, including spatially and temporally dense CO2 observations and reliable representations of atmospheric transport. Since XCO2 observations are sensitive to both synoptic and mesoscale variations within the free troposphere, horizontal atmospheric transport imparts substantial variations in these data and must be either resolved explicitly by the atmospheric transport model or accounted for within the error covariance budget provided to inverse frameworks. Here, we used geostatistical techniques to quantify the imprint of atmospheric transport in along‐track OCO‐2 soundings. We compare high‐pass‐filtered (<250 km, spatial scales that primarily isolate mesoscale or finer‐scale variations) along‐track spatial variability in XCO2 and XH2O from OCO‐2 tracks to temporal synoptic and mesoscale variability from ground‐based XCO2 and XH2O observed by nearby Total Carbon Column Observing Network sites. Mesoscale atmospheric transport is found to be the primary driver of along‐track, high‐frequency variability for OCO‐2 XH2O. For XCO2 , both mesoscale transport variability and spatially coherent bias associated with other elements of the OCO‐2 retrieval state vector are important drivers of the along‐track variance budget.
  • Article
    Future climate response to Antarctic Ice Sheet melt caused by anthropogenic warming
    (American Association for the Advancement of Science, 2020-09-23) Sadai, Shaina ; Condron, Alan ; DeConto, Robert M. ; Pollard, David
    Meltwater and ice discharge from a retreating Antarctic Ice Sheet could have important impacts on future global climate. Here, we report on multi-century (present–2250) climate simulations performed using a coupled numerical model integrated under future greenhouse-gas emission scenarios IPCC RCP4.5 and RCP8.5, with meltwater and ice discharge provided by a dynamic-thermodynamic ice sheet model. Accounting for Antarctic discharge raises subsurface ocean temperatures by >1°C at the ice margin relative to simulations ignoring discharge. In contrast, expanded sea ice and 2° to 10°C cooler surface air and surface ocean temperatures in the Southern Ocean delay the increase of projected global mean anthropogenic warming through 2250. In addition, the projected loss of Arctic winter sea ice and weakening of the Atlantic Meridional Overturning Circulation are delayed by several decades. Our results demonstrate a need to accurately account for meltwater input from ice sheets in order to make confident climate predictions.
  • Preprint
    Impact of climate change on New York City’s coastal flood hazard : increasing flood heights from the preindustrial to 2300 CE
    ( 2017-09) Garner, Andra J. ; Mann, Michael E. ; Emanuel, Kerry A. ; Kopp, Robert E. ; Lin, Ning ; Alley, Richard B. ; Horton, Benjamin P. ; DeConto, Robert M. ; Donnelly, Jeffrey P. ; Pollard, David
    The flood hazard in New York City depends on both storm surges and rising sea levels. We combine modeled storm surges with probabilistic sea-level rise projections to assess future coastal inundation in New York City from the preindustrial era through 2300 CE. The storm surges are derived from large sets of synthetic tropical cyclones, downscaled from RCP8.5 simulations from three CMIP5 models. The sea-level rise projections account for potential partial collapse of the Antarctic ice sheet in assessing future coastal inundation. CMIP5 models indicate that there will be minimal change in storm-surge heights from 2010 to 2100 or 2300, because the predicted strengthening of the strongest storms will be compensated by storm tracks moving offshore at the latitude of New York City. However, projected sea-level rise causes overall flood heights associated with tropical cyclones in New York City in coming centuries to increase greatly compared with preindustrial or modern flood heights. For the various sea-level rise scenarios we consider, the 1-in-500-y flood event increases from 3.4 m above mean tidal level during 1970–2005 to 4.0–5.1 m above mean tidal level by 2080–2100 and ranges from 5.0–15.4 m above mean tidal level by 2280–2300. Further, we find that the return period of a 2.25-m flood has decreased from ∼500 y before 1800 to ∼25 y during 1970–2005 and further decreases to ∼5 y by 2030–2045 in 95% of our simulations. The 2.25-m flood height is permanently exceeded by 2280–2300 for scenarios that include Antarctica’s potential partial collapse.