Variability, timescales, and nonlinearity in climate responses to black carbon emissions

Abstract

Abstract. Black carbon (BC) particles exert a potentially large warming influence on the Earth system. Reductions in BC emissions have attracted attention as a possible means to moderate near-term temperature changes. For the first time, we evaluate regional climate responses, nonlinearity, and short-term transient responses to BC emission perturbations in the Arctic, midlatitudes, and globally based on a comprehensive set of emission-driven experiments using the Community Earth System Model (CESM). Surface temperature responses to BC emissions are complex, with surface warming over land from midlatitude BC perturbations partially offset by ocean cooling. Climate responses do not scale linearly with emissions. While stronger BC emission perturbations have a higher burden efficiency, their temperature sensitivity is lower. BC impacts temperature much faster than greenhouse gas forcing, with transient temperature responses in the Arctic and midlatitudes approaching a quasi-equilibrium state with a timescale of 2–3 years. We find large variability in BC-induced climate changes due to background model noise. As a result, removing present-day BC emissions results in discernible surface temperature changes for only limited regions of the globe. In order to better understand the climatic impacts of BC emissions, both the drivers of nonlinear responses and response variability need to be assessed across climate models.

Surface temperature response to regional black carbon emissions: do location and magnitude matter?

“…In the Arctic the effect of high-altitude BC is particularly strong, even causing a cooling at the surface for positive regional DRF, because of the strong vertical stability in this area (Flanner, 2013;Sand et al, 2013). A similar weaker temperature efficiency with stronger emission perturbations has also been found in Yang et al (2019), but for much higher emission perturbations. Figure 4a shows the climate sensitivity in terms of regional surface air temperature change per global DRF, i.e.…”

Evaluating climate emulation: fundamental impulse testing of simple climate models

“…Finally, we do not have a definitive reference for the timedependent response to BC forcing perturbations. Instead, we compare the SCMs using the difference from the average of both MAGICC models, which both differentiate aerosol forcing between land and ocean, resulting in a faster overall climate response to aerosols compared to greenhouse gases (Shindell, 2014;Sand et al, 2016;Yang et al, 2019). In the case of BC, we note that all of the SCM responses should be taken critically because none show the fast temporal response to a BC step recently found in more complex models.…”

“…In the case of BC, we note that all of the SCM responses should be taken critically because none show the fast temporal response to a BC step recently found in more complex models. An experiment using NorESM found a very short temporal response to a global step perturbation in black carbon (BC) with minimal long-term response (Sand et al, 2016) and with a similarly short timescale found for BC perturbations in the Arctic and midlatitudes (Yang et al, 2019). A more definitive evaluation of climate system responses to aerosol perturbations in general would be useful.…”

“…S9). * For BC specifically, we note that none of the SCMs reflect the temporal response for BC seen in two complex models (Sand et al, 2016;Yang et al, 2019; see Sect. S13).…”

“…BC has a unique set of atmospheric interactions as an absorbing aerosol, causing warming within the atmosphere but potentially also surface cooling (Stjern et al, 2017;Yang et al, 2019). The response to a step change in BC emissions in two coupled model experiments has been found to have a flat long-term temperature response (Sand et al, 2016;Yang et al, 2019). In contrast, the comprehensive simple models continue to respond over a much longer timescale (Sect.…”