Significant climate impacts of aerosol changes driven by growth in energy use and advances in emission control technology

Abstract

Abstract. Anthropogenic aerosols have increased significantly since the industrial revolution, driven largely by growth in emissions from energy use in sectors including power generation, industry, and transport. Advances in emission control technologies since around 1970, however, have partially counteracted emissions increases from the above sectors. Using the fully coupled Community Earth System Model, we quantify the effective radiative forcing (ERF) and climate response to 1970–2010 aerosol changes associated with the above two policy-relevant emission drivers. Emissions from energy-use growth generate a global mean aerosol ERF (mean ± 1 standard deviation) of -0.31±0.22 W m−2 and result in a global mean cooling (-0.35±0.17 K) and a precipitation reduction (-0.03±0.02 mm d−1). By contrast, the avoided emissions from advances in emission control technology, which benefit air quality, generate a global mean ERF of +0.21±0.23 W m−2, a global warming of +0.10±0.13 K, and global mean precipitation increase of +0.01±0.02 mm d−1. Despite the relatively small changes in global mean precipitation, these two emission drivers have profound impacts at regional scales, in particular over Asia and Europe. The total net aerosol impacts on climate are dominated by energy-use growth, from Asia in particular. However, technology advances outweigh energy-use growth over Europe and North America. Various non-linear processes are involved along the pathway from aerosol and their precursor emissions to radiative forcing and ultimately to climate responses, suggesting that the diagnosed aerosol forcing and effects must be interpreted in the context of experiment designs. Further, the temperature response per unit aerosol ERF varies significantly across many factors, including location and magnitude of emission changes, implying that ERF, and the related metrics, needs to be used very carefully for aerosols. Future aerosol-related emission pathways have large temporal and spatial uncertainties; our findings provide useful information for both assessing and interpreting such uncertainties, and they may help inform future climate change impact reduction strategies.

Multidecadal trend analysis of in situ aerosol radiative properties around the world

“…These observed ω 0 trends are in line with the modeled impact of aerosol on climate (Zhao et al, 2019). They found that a global cooling effect of −0.41 K due to growth of aerosol burden caused by an increase in energy use in the Northern Hemisphere (particularly in Asia) is counterbalanced by a global warming of +0.10 K caused by the decreased aerosol emissions due to technology advances particularly in North America and Europe.…”

“…The largest median slopes are found in Asia and in the Pacific (+0.13 and 0.14 % yr −1 , respectively), whereas the decreasing median slopes in other regions are relatively small (< 0.01 % yr −1 ). The beginning of the decrease in the aerosol burden varies with region; the earliest decrease is found in Europe in the 1980s (Tørseth et al, 2012), followed by North America in the 1990s (Bodhaine and Dutton, 1993;Hand et al, 2012) and by Asia some 10-15 years ago (Sogacheva et al, 2020;Zhao et al, 2019;Paulot et al, 2018). The median slope of the ω 0 trends seems to be proportional to the length of the mitigation efforts, which for some relevant pollutants (e.g., black carbon, SO 4 and NO x ) are still ongoing.…”

“…Further, the EMEP status report suggests that estimated increasing emissions of all pollutants since 2000 in eastern Europe are mainly influenced by emission estimates for the remaining Asian areas in the EMEP modeled domain. Similarly, Zhao et al (2019) used a model to attribute the AOD, ω 0 and å sp decreases in North America and Europe to considerable emission reductions in all major pollutants except in mineral dust and ammonia.…”

“…Over China, Yoon et al (2016) observe a disconnect between the model chemical composition and the measured AOD, which they explain by noting that the measurement sites they rely on in the region are far from the population centers where most of the emissions occur. Zhao et al (2019) use a model to attribute the increase in AOD followed by a decrease in AOD to emission increases induced by rapid economic development until 2008-2009 followed by decreases in both anthropogenic primary aerosols and aerosol precursor gases. Zhao et al (2017) suggest that the larger reductions in aerosol precursors (e.g., SO 4 and NO x emissions) rather than primary aerosols, including mineral dust and black carbon, can explain the decreases in ω 0 and å sp observed over Europe and the USA.…”

Multidecadal trend analysis of aerosol radiative properties at a global scale

“…Various satellite trend analyses present a picture of trends in aerosol optical depth for different regions of the world that is quite consistent across satellite (and ground-based) AOD datasets. For example, for the satellite literature that we surveyed, all found decreases in AOD over the USA and Europe (e.g., Hsu et al, 2012;Mehta et al, 2016;Zhao et al, 2017;Alfaro-Contreras et al, 2017;Wei et al, 2019) consistent with what we have reported for the AOD from ground-based, REM instruments. As we note above, this is also consistent with surface in situ scattering trends.…”