Aerosols Must be Included in Climate Risk Assessments
Aerosols are hugely important to the climate, globally and regionally. The details are however complicated. Some aerosols warm the atmosphere, and others cool it, depending on their type, height above ground, and impact on clouds. Since the start of the industrial age, aerosols have had a profound cooling effect by reflecting sunlight. Without them, the global warming we see today would be 30–50% greater. It is not clear, however, whether aerosol emissions are set to rise, fall or stabilize. The amount of uncertainty about aerosol levels by 2050 is as large as the total increase since pre-industrial times. Over the next 20–30 years, we might—or might not—see aerosol-driven climate changes as large as those that have played out over the past 170 years, adding as much as 0.5 °C to global warming, rapidly changing the likelihood of extreme events occurring in many regions, with a geographical pattern that is very different from what greenhouse gas emissions bring. When it comes to climate risk, aerosols are wickedly more complicated than greenhouse gases.
Because evolving aerosol emissions will be a major driver of climate change, they need to be accounted for. Unfortunately, when policymakers turn to consultancy companies, non-governmental organizations (NGOs), or even reports from the Intergovernmental Panel on Climate Change (IPCC), seeking assessments of climate-change risk, the impact of aerosols is often lost along the way.
In this paper, researchers from the University of Texas at Austin, the CICERO Center for International Climate Research, and the University of Reading (along with co-signatories) are calling for funding agencies, foundations, universities, and national laboratories to prioritize collaboration to better determine the impacts of aerosols on regional climate change. They also urge consultants and NGOs to invest in and adopt new ‘aerosol aware’ methods of estimating climate risk, and for policymakers to recognize that changing regional aerosol emissions are transforming the landscape of climate risk and should demand projections accounting for this critical source of uncertainties.