Sulfate Geoengineering Impacts on Agriculture

Sulfate geoengineering has been discussed frequently as anthropogenic global warming is continuing, and currently we lack an adequate mitigation strategy to keep global average temperature from rising above 2 °C relative to the pre-industrial level. With sulfate geoengineering, climate factors important for agriculture will change, including temperature, precipitation, total solar radiation, diffuse radiation, ultraviolet radiation and surface ozone. Currently, there are only four regional agriculture impacts studies using process-based crop models under different geoengineering scenarios. Those results are varied and difficult to compare with each other. To understand this issue more comprehensively, we use an ensemble of state-of-the-art mechanistic crop models at global level, uniformly forced by a standard geoengineering scenario. Sulfate injections are evaluated based on an overshoot scenario proposed by Tilmes et al. (2016). It uses one of the Tier 2 scenarios for CMIP6, SSP5-34-OS as the reference case, in which temperature gradually increases to > 2 °C above present by 2060, and then slowly declines to ~1 °C higher than present by 2100. Sulfate geoengineering is applied to keep the global average surface air temperature at the pre-defined target of 1.5 °C. We use AgMERRA (1980-2010) as the control climate for historical crop models simulations. Climate anomalies from the reference and geoengineering simulations are applied to AgMERRA to create a bias-corrected forcing data set that maintains its natural variability. Three crop models (CLM5crop, pDSSAT and LPJmL) simulate the same reference and geoengineering scenarios during 2050-2070 in a harmonized way. Results indicate that cooling from geoengineering benefits irrigated crop growth compared with the reference case over tropical regions, while over mid-high latitude areas, cooling shows slightly negative impacts. CLM5crop shows that dimming from geoengineering tends to reduce crop yield, but more diffuse radiation from aerosol scattering balances this reduction. We present preliminary results to demonstrate different crop models responses to these complex atmospheric anomalies. We explicitly invite additional crop modeling groups to contribute to this effort of understanding of global agricultural responses under stratospheric sulfate geoengineering.

Reference:

Tilmes, S., B. M. Sanderson, and B. C. O’Neill (2016), Climate impacts of geoengineering in a delayed mitigation scenario, Geophys. Res. Lett., 43, 8222-8229, doi:10.1002/2016GL070122.