A53G-07 – Local Plant Physiological Responses to Increasing CO2 Contribute to a Zonally Asymmetric Pattern of Precipitation Change over Tropical Forests

Authors

Gabriel J Kooperman
University of California Irvine
James Tremper Randerson
University of California Irvine
Yang Chen
University of California Irvine
Abigail L. S. Swann
University of Washington Seattle Campus
Charles Koven
Lawrence Berkeley National Laboratory
Forrest M. Hoffman (forrest at climatemodeling dot org)
Oak Ridge National Laboratory
Keith T Lindsay
National Center for Atmospheric Research
Mike S Pritchard
University of California Irvine

Session

Atmospheric Circulation and Hydrological Cycle under a Changing Climate: Monsoons, Storm Tracks, and the ITCZ II
Friday, December 16, 2016 15:10–15:25
Moscone West 2022/2024

Abstract

Understanding how anthropogenic CO2 emissions may impact future precipitation patterns is a critical question for earth science and society, especially over tropical forests where changes affect drought conditions, ecosystem health, and the availability of freshwater. While there remains significant uncertainty about how tropical precipitation will change in the future, CMIP5 models robustly project a consistent zonally asymmetric pattern over land, amplifying differences between the Maritime Continent and Amazon. This pattern cannot be explained by mechanisms describing zonal mean changes to the hydrological cycle (e.g. Hadley strength, ITCZ shift, or wet-get-wetter response). Here we show, in CESM1(BGC), that the pattern is largely controlled by plant physiological responses to increased CO2, which setup local dynamic anomalies over each continent, rather than global-scale radiative forcing. Regional precipitation and associated circulation changes that manifest with global CO2 increases are also captured when CO2 increases are isolated to the land-surfaces of individual continents. Increased CO2 throttles stomatal conductance, reducing local transpiration and increasing sensible heating and surface temperature. Changes in heating over land drive regional circulations that influence vertical mixing and moisture fluxes over each continent, leading to greater moisture transport into the upper atmosphere and more precipitation over Indonesia, Central Africa and the west coast of South America, and less precipitation over the Amazon.


Forrest M. Hoffman (forrest at climatemodeling dot org)