J.-F. Lamarque

Assessing future nitrogen deposition and carbon cycle feedback using a multimodel approach: Analysis of nitrogen deposition

n this study, we present the results of nitrogen deposition on land from a set of 29 simulations from six different tropospheric chemistry models pertaining to present-day and 2100 conditions. Nitrogen deposition refers here to the deposition (wet and dry) of all nitrogen-containing gas phase chemical species resulting from NOx (NO + NO2) emissions. We show that under the assumed IPCC SRES A2 scenario the global annual average nitrogen deposition over land is expected to increase by a factor of ∼2.5, mostly because of the increase in nitrogen emissions. This will significantly expand the areas with annual average deposition exceeding 1 gN/m2/year. Using the results from all models, we have documented the strong linear relationship between models on the fraction of the nitrogen emissions that is deposited, regardless of the emissions (present day or 2100). On average, approximately 70% of the emitted nitrogen is deposited over the landmasses. For present-day conditions the results from this study suggest that the deposition over land ranges between 25 and 40 Tg(N)/year. By 2100, under the A2 scenario, the deposition over the continents is expected to range between 60 and 100 Tg(N)/year. Over forests the deposition is expected to increase from 10 Tg(N)/year to 20 Tg(N)/year. In 2100 the nitrogen deposition changes from changes in the climate account for much less than the changes from increased nitrogen emissions.

Projected changes of extreme weather events in the eastern United States based on a high resolution climate modeling system

This study is the first evaluation of dynamical downscaling using the Weather Research and Forecasting (WRF) Model on a 4 km 4 km high resolution scale in the eastern US driven by the new Community Earth System Model version 1.0 (CESM v1.0). First we examined the global and regional climate model results, and corrected an inconsistency in skin temperature during the downscaling process by modifying the land/sea mask. In comparison with observations, WRF shows statistically significant improvement over CESM in reproducing extreme weather events, with improvement for heat wave frequency estimation as high as 98%. The fossil fuel intensive scenario Representative Concentration Pathway (RCP) 8.5 was used to study a possible future mid-century climate extreme in 2057‐9. Both the heat waves and the extreme precipitation in 2057‐9 are more severe than the present climate in the Eastern US. The Northeastern US shows large increases in both heat wave intensity (3.05 C higher) and annual extreme precipitation (107.3 mm more per year).

Response of a coupled chemistry‐climate model to changes in aerosol emissions: Global impact on the hydrological cycle and the tropospheric burdens of OH, ozone, and NOx

[1] In this study, we analyze the response of the coupled chemistry-climate system to changes in aerosol emissions in fully coupled atmospheric chemistry-climate-slab ocean model simulations; only the direct radiative effect of aerosols and their uptake of chemical species are considered in this study. We show that, at the global scale, a decrease in emissions of the considered aerosols (or their precursors) produces a warmer and moister climate. In addition, the tropospheric burdens of OH and ozone increase when aerosol emissions are decreased. The ozone response is a combination of the impact of reduced heterogeneous uptake of N2O5 and increased ozone loss in a moister atmosphere. Under reduced aerosol emissions, the tropospheric burden of NOx (NO + NO2) is strongly reduced by an increase in nitric acid formation but also increased by the reduced N2O5 uptake. Finally, we discuss the significant difference found between the combined impact of all aerosols emissions and the sum of their individual contributions. Citation: Lamarque, J.-F., J. T. Kiehl, P. G. Hess, W. D. Collins, L. K. Emmons, P. Ginoux, C. Luo, and X. X. Tie (2005), Response of a coupled chemistryclimate model to changes in aerosol emissions: Global impact on the hydrological cycle and the tropospheric burdens of OH, ozone, and NOx, Geophys. Res. Lett., 32, L16809, doi:10.1029/ 2005GL023419.

Toward an Earth system model: atmospheric chemistry, coupling, and petascale computing

Atmospheric chemicals and aerosols are interactive components of the Earth system, with implications for climate. As part of the SciDAC climate consortium of labs we have implemented a flexible state-of-the-art atmospheric chemistry and aerosol capability into the Community Climate System Model (CCSM). We have also developed a fast chemistry mechanism that agrees well with observations and is computationally more efficient than our more complex chemistry mechanisms. We are working with other colleagues to couple this capability with the biospheric and aerosol-cloud interaction capabilities that are being developed for the CCSM model to create an Earth system model. However, to realise the potential of this Earth system model will require a move from terascale to petascale computing, and the greatest benefit will come from well balanced computers and a balance between capability and capacity computing.

Variability of fire emissions on interannual to multi-decadal timescales in two Earth System models

Connections betweenwildfires andmodes of variability in climate are sought as ameans for predicting fire activity on interannual tomulti-decadal timescales. Severalfire drivers, such as temperature and local drought index, have been shown to vary on these timescales, and analysis of tree-ring data suggests covariance betweenfires and climate oscillation indices in some regions. However, the shortness of the satellite record of globalfire events limits investigations on larger spatial scales. Here we explore the interplay between climate variability andwildfire emissions with the preindustrial long control numerical experiments and historical ensembles of CESM1 and theNOAA/GFDLESM2Mb. Wefind that interannual variability infires is underpredicted in both Earth Systemmodels (ESMs) compared to present dayfire emission inventories.Modeled fire emissions respond to the ElNiño/ southern oscillation (ENSO) andPacific decadal oscillation (PDO)with increases in southeast Asia and borealNorthAmerica emissions, and decreases in southernNorthAmerica and Sahel emissions, during the ENSOwarmphase in both ESMs, and the PDOwarmphase inCESM1. Additionally, CESM1produces decreases in boreal northern hemisphere fire emissions for thewarmphase of the AtlanticMeridionalOscillation. Through analysis of the long control simulations, we show that the 20th century trends in both ESMs are statistically significant,meaning that the signal of anthropogenic activity on fire emissions over this time period is detectable above the annual to decadal timescale noise. However, the trends simulated by the two ESMs are of opposite sign (CESM1decreasing, ESM2Mb increasing), highlighting the need for improved understanding, proxy observations, and modeling to resolve this discrepancy.