Rapid adjustments cause weak surface temperature response to increased black carbon concentrations

Area of Science:

• Climate Science
• Atmospheric Chemistry
• Climate Modeling

Background:

• Black carbon (BC) is a potent climate forcer.
• Understanding BC's climate impact is crucial for climate change mitigation.
• Previous studies have varied in their assessment of BC's climate effects.

Purpose of the Study:

• To investigate the climate response to increased black carbon concentrations using a multi-model ensemble.
• To quantify the effective radiative forcing (ERF) and resulting temperature changes.
• To analyze the role of rapid adjustments in the BC climate response.

Main Methods:

• Simulations of a tenfold increase in BC concentrations using 9 global coupled-climate models.
• Calculation of effective radiative forcing (ERF) and global/Arctic temperature changes.
• Analysis of radiative forcing, rapid adjustments, and cloud feedback mechanisms.

Main Results:

• Model-median ERF of 0.82 Wm⁻², with a global warming of 0.67 K and Arctic warming of 1.24 K.
• Rapid adjustments significantly dampen the surface temperature response.
• Increased low-level clouds and decreased high-level clouds observed across models.
• Strong warming above 400 hPa, with increased atmospheric stabilization and reduced cloud cover.

Conclusions:

• Substantial increase in BC concentrations significantly impacts the climate system.
• Offsetting effects between forcing and adjustments lead to a smaller global warming per unit forcing compared to CO2.
• The present-day impact of anthropogenic BC on global warming is estimated to be minimal (0.07 K).