Connecting the dots on aerosol details

July 27, 2011, Pacific Northwest National Laboratory
Pollution aerosols and their effect on the Earth’s energy budget are part of the picture that climate scientists are focusing on in multi-scale climate modeling.

Predicting future climate change hangs on understanding aerosols, considered the fine details in the atmosphere. Researchers at Pacific Northwest National Laboratory and the National Center for Atmospheric Research used a new modeling tool to bring the picture of aerosols and their actions on clouds into sharper focus.

The multi-scale aerosol-climate model, an extension of a multi-scale modeling framework, examined specific aerosol-cloud interactions and their effects on the Earth's energy budget, one of the toughest climate forecasting problems. Their results show that the cooling effect of human-caused is smaller than previously thought.

Current global climate models used to predict account for large-scale climate processes, typically at scales greater than 100 kilometers, or about 62 miles. This means small-scale and regional features in the climate tend to be averaged out, or estimated through parameterization, a technique used to represent complex small-scale systems. Because small-scale climate features, such as clouds and atmospheric aerosol particles, have a large impact on , it's important to improve the methods used to represent those climate features in the models. This study has advanced scientists' capabilities to model and predict those complex aerosol-cloud interactions on the Earth's energy budget, for a balanced and energy-sustainable future.

Scientists at PNNL developed a new aerosol-climate model as an extension of a multi-scale modeling framework model that embeds a cloud-resolving model (CRM) within each grid column of a . This model, called the PNNL-Multi-scale Modeling Framework, depicts aerosol-cloud interactions in both stratiform and convective clouds in a more realistic way than conventional global models. In addition, the PNNL-MMF is much more computationally feasible for running multi-year than a global CRM.

The cloud response to aerosols shows only one-third as strong as it did in previous modeling in the study using the PNNL-MMF. Scatter plots show changes in liquid water path response (LWP) versus cloud condensation nuclei (CCN) perturbation from anthropogenic aerosols in a) MMF (new model), and b) CAM5 (previous model). Anthropogenic, or human-caused aerosols are primarily the result of fossil fuel burning.

The team evaluated simulated cloud fields from the multi-scale aerosol-climate model and examined how specific human-caused aerosols, such as sulfate, black carbon (soot), and organic carbon affect those clouds and, in turn, the climate. The PNNL-MMF is a more physically based way to represent the indirect effects of aerosols compared to parameterization, typically used to represent small-scale climate details in global models. The significant computational resources available to the team at the National Center for Computational Sciences at Oak Ridge National Laboratory enabled this improvement in modeling.

The study compared pre-industrial and present-day results in current global models to the newer high-resolution model with the PNNL-MMF extension. Comparisons show a lesser effect on the Earth's energy budget, considering the additional burden of human-caused aerosols. These results confirm the need to use global high resolution models to study the aerosol indirect effects.

The researchers are working to understand the differences found between global models and the more detailed PNNL-MMF results. In future work, the team will tackle the aerosol effects on precipitation.

Explore further: Down-and-dirty details of climate modeling

More information: Wang M, et al. "Aerosol Indirect Effects in a Multi-scale Aerosol-climate Model PNNL-MMF." 2011. Atmospheric Chemistry and Physics, 11, 5431-5455. DOI: 10.5194/acp-11-5431-2011.

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1.8 / 5 (5) Jul 27, 2011
Translation: So far climate change predictions are just Wild Ass Guesses.
5 / 5 (2) Jul 27, 2011
The paper demonstrated that the aerosol cooling effects in current climate models is over-estimated and that their model of lower cooling effects from human created aerosols better matches observations.
From the Abstract "The smaller response in LWP to anthropogenic aerosols in the MMF model is consistent with observations..... "The simulated total anthropogenic aerosol effect in the MMF is -1.05 W m-2, which is close to the Murphy et al. (2009) inverse estimate of -1.1±0.4 W m-2 (1s) based on the examination of the Earth's energy balance."
not rated yet Jul 27, 2011
NotParker, they may be guesses, but they're better guesses than you or I could make. I think this is good science, equitably reported, and should be supported by us scientists.
A lot of work has gone into them and a lot of our tax money has been spent to arrive at where we are now.
Let's at least try to get some of our money's worth out of all this research investment. Being dismissive of good work is not the way to do that.

I would think that you should be heartened by this BBC news item:

I was particularly struck by the last sentence in that report.
not rated yet Jul 28, 2011
They should add to the list of aerosols under study barium and aluminum oxides, which are probably the main components of the mid-level schmutz that can be seen as a thin haze at about 10,000 feet (?)_on a clear day.

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