Reevaluation of global emissions from rice paddies of methyl iodide and other species

Abstract

We present new modeled estimates of global methyl halide emissions from rice cultivation. We extrapolate existing data on rice behavior, including temperature, seasonality and soil moisture effects, to the global scale and on a monthly basis. Our best estimates are 2.4 to 4.9 Gg yr-1 for methyl chloride, 0.5 to 0.9 Gg yr-1 for methyl bromide, and 16 to 29 Gg yr-1 for methyl iodide, with additional uncertainty ranges of ±73%, ±87% and ±75%, respectively. Our central range of estimates reflects the greatest remaining model uncertainty, emission response to soil halide concentrations. We find that peak emissions of methyl halides, especially methyl iodide, are sharply defined in regional and temporal extent. Ambient temperature strongly influences rice emissions of methyl bromide and methyl iodide, which rise by ∼10% for an increase of 1°C. Copyright 2005 by the American Geophysical Union.