While most scientists today agree that global warming is indeed taking place, determining the severity and exact onset of its effects is the critical question facing these scientists because there are numerous variables involved with climate change. University Atmospheric, Oceanic and Space Sciences Prof. Joyce Penner is trying to predict the future of global climate change through the study of clouds.

Greenhouse gases, such as carbon dioxide, commonly released by industrial burning of fossil fuels and the burning of rainforests in the tropics, are the primary cause of increasing average global temperatures according to Penner. Although some critics of the global warming concept argue that the average global temperature may be rising due to a natural climate cycle, Penner is quick to dispute that view.

“Carbon dioxide is about 30 percent higher now than it was in the pre-industrial times. You cannot deny that there has been a huge change in the atmospheric composition,” Penner said.

Penner added that a common misconception about global climate change is that greenhouse gases are the only culprit. But she said virtually any pollutant released into the atmosphere, from the sulfur expelled from cars to gases released from landfills, can influence global climate.

“I am very confident that eventually we’ll see a pretty major change in earth’s temperature and weather. I think it’s important to figure out what kind of steps we should take to avoid very bad consequences, and it’s important to figure out how soon we need to take those steps,” she said.

Penner’s current research is focused on aerosols, which are particles expelled into the atmosphere. She became interested in aerosols while working at Lawrence Livermore National Laboratory in California. Penner and her colleagues were researching the possible cooling effects caused by aerosols in the atmosphere after a nuclear disaster, in what is known as nuclear winter. Afterward, she began searching for other areas to apply her aerosol research and found that her model could be applied to the effects of commonly emitted aerosols on clouds.

Ice clouds — which are the focus of Penner’s study — form at high altitudes in the atmosphere. It has been found that aerosols increase the production of ice clouds in high levels of the atmosphere by providing more particles for water to condense upon. Penner said that due to their structure, ice clouds absorb more radiation than they reflect so an increase in ice clouds could help fuel global warming.

In contrast, high levels of aerosols in low-level clouds help prevent global warming. These clouds are made of liquid water droplets instead of ice and help to cool the earth because they reflect more sunlight into space than onto the earth. Increased levels of aerosols cause more water droplets to form within low-level clouds, which makes them even more reflective and increases the radiation they reflect back into space.

“People have tried to look into ice clouds, but until you get a way to include them in a global model, you can’t really do it, so this will be a first,” Penner said.

She said climate researchers are working to incorporate more variables, such as aerosol levels, into climate models to more accurately model and predict future climate changes. Current models frequently are low resolution and are based mainly on first principals, or known science equations. To make more accurate predictions of the future climate, Penner is working to input real observed data into the models. The ice clouds left behind jet airplanes is yet another variable Penner is trying to input into the model.

“We’ve been looking at what kind of warming aircrafts might produce, and we are getting values three times higher than what other people have estimated. It is a major difference from previous estimates.”

Penner and her graduate student partners have discovered that many of the pollutants from flight tracks in the atmosphere drift down to the tropics, affecting more than the general region where the aircraft flew as previously thought.

“Because the clouds there are so much thicker in the tropics, you can have a bigger effect there,” she said. “Nobody’s looked at ice clouds in the tropics. I am trying to get to a place where I can write that up for publication because I think it will be smashing.”

Penner hypothesizes that there is a balance between greenhouse gases that cause warming and the cooling effect of aerosols, though exactly how much cooling is occurring is not yet known. Though aerosols may help cool the Earth’s climate, global warming becomes an issue because green house gases have a larger long-term effect than aerosols.

“To think to the future, maybe 100 years, we expect the aerosol effect to eventually be overwhelmed by greenhouse gases because they accumulate much more readily in the atmosphere and are not removed very easily, whereas aerosol is removed every time it rains,” Penner said.

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