The Earth & Planetary Sciences Department hosted climatologist and aerosol specialist Lorraine Remer of the NASA Goddard Space Flight Center on Thursday. The Bromery lecture, held in Olin Hall, was titled, “Aerosols and Climate Forcing: New Thoughts, Future Direction,” and focused on how aerosols contribute to the global heating and cooling cycle.
According to Remer, some aerosols cool the atmosphere, while others warm it, making it impossible to lump all aerosols into one category based on their impact on Earth’s climate.
“Aerosols are traced clearly to industrial human activity. Aerosols are a much more complicated problem than greenhouse gases,” Remer said.
She discussed a variety of aerosols, such as dust, smoke, and soot from volcanic eruptions. Dark and light aerosols affect the atmosphere in different ways. Light aerosols act like clouds, Remer explained, reflecting incoming solar radiation as a result of high albedo, which is the amount of radiation that a body reflects. Dark aerosols can absorb more solar radiation, leading to more warming. When mixed with different types of clouds, the effects can be unexpected and complex.
One point that Remer discussed was the connection between the amount of clouds and the amount of aerosol particulates in the air. A small change in the amount of aerosols in the atmosphere can cause the composition, color and albedo, or reflectivity, of the clouds to change. Aerosols can both destroy clouds, such as by introducing smoke into them, or they can create particulates that the water vapor clings to, forming clouds. It is often hard to tell whether an increase in aerosols will destroy or create clouds, according to Remer.
As environmental laws become stricter and pollution decreases, the amount of aerosols in the atmosphere are rapidly decreasing, given that they stay in the atmosphere for a short amount of time.
“Aerosols are both increasing and decreasing,” Remer said. “Particles are significantly decreasing across the United States. We have never lived in a cleaner environment.”
Even though one would think that decreasing aerosols in the atmosphere is always a good option, there are some benefits of having increased aerosol levels. Respiratory diseases are decreasing across the developed world as air quality restrictions are tightened. However, as human health increases, the earth is losing some of its most powerful reflectors and is therefore absorbing more solar radiation through the darker colored oceans and lands.
Remer and her team have found that the cloud fraction, or the amount of clouds in the atmosphere, has decreased significantly over parts of the U.S. in the last 40 years. The albedo of the U.S. has decreased 15 to 20 percent in the last decade because of the decreasing cloud fraction caused by the decrease of human-produced aerosols in the atmosphere.
Remer was quick to point out that while the decrease of aerosols may be helping global warming, it is not a bad thing that aerosol levels are decreasing. The better air quality is visible from a wide range of locations, including the mountain peaks and the tops of the skyscrapers in Los Angeles. Fewer people are getting ill from respiratory diseases, and the atmosphere is cleaner now than it ever has been before.
Remer cautioned that the results were preliminary and far from conclusive.
“The associations are so strong [we cannot overlook them],” Remer said.
The conclusion she reached was that the events of global warming are decreasing cloud formation. Cleaning up the atmosphere may lead to an increased rate of warming, and greenhouse gases are a much simpler matter to explain than the complicated problem of aerosols, whose global levels can be radically shifted by something as trivial as a volcanic eruption in Iceland. Aerosols are a complex problem that are only now being studied by the leading scientists in the field of climatology.
