Strict air pollution rules could warm the planet by mid-century, study warns
Aggressive air quality policies that cut industrial emissions may paradoxically accelerate warming by removing aerosols that currently reflect sunlight, according to a new climate modeling study. The finding complicates policy tradeoffs: cleaner air improves public health but could require stronger climate action elsewhere to offset the warming effect.
Originaltitel: Decomposing the global and regional aerosol effective radiative forcing associated with strong versus weak air quality policies by Mid-21st century
Abstract The Regional Aerosol Model Intercomparison Project (RAMIP) is designed to quantify the forcing and climate impacts of mid-21st century anthropogenic aerosol and precursor gas (AA) emissions reductions (both industrial and biomass burning), by comparing a weak (SSP3-7.0) versus strong (SSP1-2.6) level of air quality control aerosol emissions pathway. AA emissions reductions experiments include global (GLO), East Asia (EAS), South Asia, Africa and the Middle East (AFR), and North America and Europe (NAE). Here, we use RAMIP time-slice simulations with fixed sea surface temperatures and sea-ice distributions from nine models to quantify the aerosol effective radiative forcing (ERF), including aerosol radiation (ERF ari ) and aerosol cloud interactions (ERF aci ). The multi-model global mean net ERF ari+aci is <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:mn>0.77</mml:mn> <mml:mo>±</mml:mo> <mml:mn>0.25</mml:mn> </mml:mrow> </mml:math> W m −2 for GLO, and three of the four regional perturbations yield a significant positive net ERF ari+aci (up to <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:mn>0.15</mml:mn> <mml:mo>±</mml:mo> <mml:mn>0.07</mml:mn> </mml:mrow> </mml:math> W m −2 for EAS). In all cases, net ERF ari+aci is dominated by aerosol-cloud interactions, which are largely due to reduced cloud scattering. Of the four regions, NAE yields the largest forcing efficiency whereas AFR yields the weakest. Although the areas outside our four target regions contribute 25% to the GLO aerosol optical depth reduction, they disproportionately contribute 44% to the GLO net ERF ari+aci . The multimodel regional mean net ERF ari+aci for three regional perturbations is much larger (up to <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:mn>1.64</mml:mn> <mml:mo>±</mml:mo> <mml:mn>1.36</mml:mn> </mml:mrow> </mml:math> W m −2 for EAS) than the corresponding global mean value. However, these regional values are even larger (up to <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:mn>2.69</mml:mn> <mml:mo>±</mml:mo> <mml:mn>1.72</mml:mn> </mml:mrow> </mml:math> W m −2 for EAS) under global aerosol reductions, implying remote emission reductions represent a sizable contribution (up to <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:mn>1.05</mml:mn> <mml:mo>±</mml:mo> <mml:mn>0.56</mml:mn> </mml:mrow> </mml:math> W m −2 for EAS). These large regional ERFs will in turn drive relatively large regional climate impacts, which continue to be underappreciated in most policy discussions.