Chemistry-driven changes strongly influence climate forcing from vegetation emissions

Area of Science:

• Atmospheric Chemistry
• Climate Science
• Earth System Modeling

Background:

• Biogenic volatile organic compounds (BVOCs) influence climate by altering aerosols, aerosol-cloud interactions (ACI), ozone, and methane.
• BVOCs are sensitive to climate and land use, creating feedback loops with uncertain net climatic impacts.
• The representation of BVOC chemistry is a key source of uncertainty in climate projections.

Purpose of the Study:

• To quantify the influence of BVOC chemistry on climate feedbacks.
• To compare the climatic impact of BVOCs using standard versus state-of-science chemistry descriptions.
• To investigate the mechanisms driving aerosol-cloud interactions (ACI) under altered BVOC chemistry.

Main Methods:

• Utilized the Earth System Model UKESM1 to simulate climate responses.
• Compared model runs with doubled pre-industrial BVOC emissions under two chemistry schemes: standard and state-of-science.
• Analyzed changes in aerosols, ACI, ozone, methane, and cloud droplet number concentration (CDNC).

Main Results:

• Doubling BVOC emissions resulted in a net positive climate forcing, driven by increases in ozone and methane, and altered ACI, outweighing enhanced aerosol scattering.
• The ACI response was primarily driven by CDNC reductions due to suppressed gas-phase sulfur dioxide (SO2) oxidation.
• State-of-science chemistry reduced the net feedback by 43% due to lower oxidant depletion, leading to smaller increases in methane and CDNC.

Conclusions:

• BVOC chemistry significantly influences the net climatic impact of biogenic emissions.
• The pathways through which BVOCs affect climate are more complex than previously recognized, particularly concerning ACI.
• Accurate representation of BVOC chemistry is crucial for reliable climate change projections.