Browsing by Author "Newman, Paul A"
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Item Early action on HFCs mitigates future atmospheric change(IOP, 2016-11-15) Hurwitz, Margaret M; Fleming, Eric L; Newman, Paul A; Li, Feng; Liang, QingAs countries take action to mitigate global warming, both by ratifying the UNFCCC Paris Agreement and enacting the Kigali Amendment to the Montreal Protocol to manage hydrofluorocarbons (HFCs), it is important to consider the relative importance of the pertinent greenhouse gases and the distinct structure of their atmospheric impacts, and how the timing of potential greenhouse gas regulations would affect future changes in atmospheric temperature and ozone. HFCs should be explicitly considered in upcoming climate and ozone assessments, since chemistry-climate model simulations demonstrate that HFCs could contribute substantially to anthropogenic climate change by the mid-21st century, particularly in the upper troposphere and lower stratosphere i.e., global average warming up to 0.19 K at 80 hPa. The HFC mitigation scenarios described in this study demonstrate the benefits of taking early action in avoiding future atmospheric change: more than 90% of the climate change impacts of HFCs can be avoided if emissions stop by 2030.Item Spatial heterogeneity in CO₂, CH₄, and energy fluxes: insights from airborne eddy covariance measurements over the Mid-Atlantic region(IOP, 2020-03-06) Hannun, Reem A; Wolfe, Glenn M; Kawa, S Randy; Hanisco, Thomas F; Newman, Paul A; Alfieri, Joseph G; Barrick, John; Clark, Kenneth L; DiGangi, Joshua P; Diskin, Glenn S; King, John; Kustas, William P; Mitra, Bhaskar; Noormets, Asko; Nowak, John B; Thornhill, K Lee; Vargas, RodrigoThe exchange of carbon between the Earth's atmosphere and biosphere influences the atmospheric abundances of carbon dioxide (CO₂) and methane (CH₄). Airborne eddy covariance (EC) can quantify surface-atmosphere exchange from landscape-to-regional scales, offering a unique perspective on carbon cycle dynamics. We use extensive airborne measurements to quantify fluxes of sensible heat, latent heat, CO₂, and CH₄ across multiple ecosystems in the Mid-Atlantic region during September 2016 and May 2017. In conjunction with footprint analysis and land cover information, we use the airborne dataset to explore the effects of landscape heterogeneity on measured fluxes. Our results demonstrate large variability in CO₂ uptake over mixed agricultural and forested sites, with fluxes ranging from −3.4 ± 0.7 to −11.5 ± 1.6 μmol m⁻² s⁻¹ for croplands and −9.1 ± 1.5 to −22.7 ± 3.2 μmol m⁻² s⁻¹ for forests. We also report substantial CH₄ emissions of 32.3 ± 17.0 to 76.1 ± 29.4 nmol m−² s−¹ from a brackish herbaceous wetland and 58.4 ± 12.0 to 181.2 ± 36.8 nmol m⁻² s⁻¹ from a freshwater forested wetland. Comparison of ecosystem-specific aircraft observations with measurements from EC flux towers along the flight path demonstrate that towers capture ~30%–75% of the regional variability in ecosystem fluxes. Diel patterns measured at the tower sites suggest that peak, midday flux measurements from aircraft accurately predict net daily CO₂ exchange. We discuss next steps in applying airborne observations to evaluate bottom-up flux models and improve understanding of the biophysical processes that drive carbon exchange from landscape-to-regional scales.