Curran M. A. J.

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M. A. J.

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  • Article
    Multi-model mean nitrogen and sulfur deposition from the Atmospheric Chemistry and Climate Model Intercomparison Project (ACCMIP) : evaluation of historical and projected future changes
    (Copernicus Publications on behalf of the European Geosciences Union, 2013-08-20) Lamarque, J.-F. ; Dentener, F. ; McConnell, Joseph R. ; Ro, C.-U. ; Shaw, M. ; Vet, R. ; Bergmann, D. ; Cameron-Smith, P. ; Dalsoren, S. ; Doherty, R. ; Faluvegi, G. ; Ghan, S. J. ; Josse, B. ; Lee, Y. H. ; MacKenzie, I. A. ; Plummer, D. ; Shindell, D. T. ; Skeie, R. B. ; Stevenson, D. S. ; Strode, S. ; Zeng, G. ; Curran, M. A. J. ; Dahl-Jensen, D. ; Das, Sarah B. ; Fritzsche, D. ; Nolan, M.
    We present multi-model global datasets of nitrogen and sulfate deposition covering time periods from 1850 to 2100, calculated within the Atmospheric Chemistry and Climate Model Intercomparison Project (ACCMIP). The computed deposition fluxes are compared to surface wet deposition and ice core measurements. We use a new dataset of wet deposition for 2000–2002 based on critical assessment of the quality of existing regional network data. We show that for present day (year 2000 ACCMIP time slice), the ACCMIP results perform similarly to previously published multi-model assessments. For this time slice, we find a multi-model mean deposition of approximately 50 Tg(N) yr−1 from nitrogen oxide emissions, 60 Tg(N) yr−1 from ammonia emissions, and 83 Tg(S) yr−1 from sulfur emissions. The analysis of changes between 1980 and 2000 indicates significant differences between model and measurements over the United States but less so over Europe. This difference points towards a potential misrepresentation of 1980 NH3 emissions over North America. Based on ice core records, the 1850 deposition fluxes agree well with Greenland ice cores, but the change between 1850 and 2000 seems to be overestimated in the Northern Hemisphere for both nitrogen and sulfur species. Using the Representative Concentration Pathways (RCPs) to define the projected climate and atmospheric chemistry related emissions and concentrations, we find large regional nitrogen deposition increases in 2100 in Latin America, Africa and parts of Asia under some of the scenarios considered. Increases in South Asia are especially large, and are seen in all scenarios, with 2100 values more than double their 2000 counterpart in some scenarios and reaching > 1300 mg(N) m−2 yr−1 averaged over regional to continental-scale regions in RCP 2.6 and 8.5, ~ 30–50% larger than the values in any region currently (circa 2000). However, sulfur deposition rates in 2100 are in all regions lower than in 2000 in all the RCPs. The new ACCMIP multi-model deposition dataset provides state-of-the-science, consistent and evaluated time slice (spanning 1850–2100) global gridded deposition fields for use in a wide range of climate and ecological studies.
  • Article
    Observed 20th century desert dust variability : impact on climate and biogeochemistry
    (Copernicus Publications on behalf of the European Geosciences Union, 2010-11-19) Mahowald, Natalie M. ; Kloster, S. ; Engelstaedter, S. ; Moore, J. Keith ; Mukhopadhyay, S. ; McConnell, Joseph R. ; Albani, S. ; Doney, Scott C. ; Bhattacharya, A. ; Curran, M. A. J. ; Flanner, M. G. ; Hoffman, Forrest M. ; Lawrence, David M. ; Lindsay, Keith ; Mayewski, P. A. ; Neff, Jason C. ; Rothenberg, D. ; Thomas, E. ; Thornton, Peter E. ; Zender, Charles S.
    Desert dust perturbs climate by directly and indirectly interacting with incoming solar and outgoing long wave radiation, thereby changing precipitation and temperature, in addition to modifying ocean and land biogeochemistry. While we know that desert dust is sensitive to perturbations in climate and human land use, previous studies have been unable to determine whether humans were increasing or decreasing desert dust in the global average. Here we present observational estimates of desert dust based on paleodata proxies showing a doubling of desert dust during the 20th century over much, but not all the globe. Large uncertainties remain in estimates of desert dust variability over 20th century due to limited data. Using these observational estimates of desert dust change in combination with ocean, atmosphere and land models, we calculate the net radiative effect of these observed changes (top of atmosphere) over the 20th century to be −0.14 ± 0.11 W/m2 (1990–1999 vs. 1905–1914). The estimated radiative change due to dust is especially strong between the heavily loaded 1980–1989 and the less heavily loaded 1955–1964 time periods (−0.57 ± 0.46 W/m2), which model simulations suggest may have reduced the rate of temperature increase between these time periods by 0.11 °C. Model simulations also indicate strong regional shifts in precipitation and temperature from desert dust changes, causing 6 ppm (12 PgC) reduction in model carbon uptake by the terrestrial biosphere over the 20th century. Desert dust carries iron, an important micronutrient for ocean biogeochemistry that can modulate ocean carbon storage; here we show that dust deposition trends increase ocean productivity by an estimated 6% over the 20th century, drawing down an additional 4 ppm (8 PgC) of carbon dioxide into the oceans. Thus, perturbations to desert dust over the 20th century inferred from observations are potentially important for climate and biogeochemistry, and our understanding of these changes and their impacts should continue to be refined.
  • Article
    Antarctic-wide array of high-resolution ice core records reveals pervasive lead pollution began in 1889 and persists today
    (Nature Publishing Group, 2014-07-28) McConnell, Joseph R. ; Maselli, Olivia J. ; Sigl, Michael ; Vallelonga, P. ; Neumann, T. ; Anschutz, H. ; Bales, R. C. ; Curran, M. A. J. ; Das, Sarah B. ; Edwards, R. ; Kipfstuhl, Sepp ; Layman, Lawrence ; Thomas, E. R.
    Interior Antarctica is among the most remote places on Earth and was thought to be beyond the reach of human impacts when Amundsen and Scott raced to the South Pole in 1911. Here we show detailed measurements from an extensive array of 16 ice cores quantifying substantial toxic heavy metal lead pollution at South Pole and throughout Antarctica by 1889 – beating polar explorers by more than 22 years. Unlike the Arctic where lead pollution peaked in the 1970s, lead pollution in Antarctica was as high in the early 20th century as at any time since industrialization. The similar timing and magnitude of changes in lead deposition across Antarctica, as well as the characteristic isotopic signature of Broken Hill lead found throughout the continent, suggest that this single emission source in southern Australia was responsible for the introduction of lead pollution into Antarctica at the end of the 19th century and remains a significant source today. An estimated 660 t of industrial lead have been deposited over Antarctica during the past 130 years as a result of mid-latitude industrial emissions, with regional-to-global scale circulation likely modulating aerosol concentrations. Despite abatement efforts, significant lead pollution in Antarctica persists into the 21st century.