Fitting all the different pieces of the climate change puzzle together is one of the major challenges of our age.  Aerosol is a key piece of this puzzle, but the size and shape of its effect is still unclear – a fact that jeopardises the reliability of all current predictions of climate change.

Now, a new £630,000 project has been launched at the University of Leeds to tackle the conundrum of how aerosol affects climate. 

Aerosols are small particles suspended in the atmosphere, such as soot in smoke or chemicals emitted by trees, and are known by experts to have a huge cooling effect on our planet.  This is because these particles act as tiny mirrors that reflect sunlight back into space. 

This effect is thought to be so large that, since the industrial period, the climactic cooling effect of aerosols has largely cancelled out the warming effect of greenhouse gases. This phenomenon has often been referred to as global dimming.

“Aerosol is the most important factor that affects climate after greenhouse gases,” says Professor Ken Carslaw from the University of Leeds, who is leading the research.

“Aerosol pretty much counteracts a large part of global warming caused by greenhouse gases, meaning that temperature changes over the industrial period would have been a lot more intense if it weren’t for aerosol,” explains Professor Carslaw.

Aerosol has been described by the IPCC as the biggest source of uncertainty in climate change models. Being able to reduce uncertainty in climate models is important because it affects how confident we can be in models that predict the intensity of future climate changes. 

“The potentially catastrophic consequences of climate change mean that policy makers are no longer satisfied with climate scientists explaining that they have ten models that give a range of answers,” adds Professor Carslaw.

Currently there is very little understanding of why aerosol is such an uncertain factor in climate change.   But unlike greenhouse gases, which have clear sources and spread evenly through the atmosphere, aerosols are affected by a range of complex factors including weather patterns, so it is much harder to predict their climatic effect. 

The project, which also involves the Met Office Hadley Centre and the University of Oxford, aims to design advanced global models of aerosols by identifying specific processes that lead to aerosol production and try and quantify the levels of uncertainty of each.

The work will draw heavily on existing data sets from aircraft, surface observatories and satellites that have yet to be fully exploited and the global aerosol model that has already been developed at Leeds (Global Model of Aerosol Processes).

The Aerosol Model Robustness and Sensitivity Study (AEROS) is a 3-year study funded by the Natural Environment Research Council in the UK.