By Patrick Snodgrass ’13, thurj Staff

Although not completely accepted by the public, the idea that humans can adversely affect global climate is fast becoming a commonplace notion. Yet the subject of atmospheric chemistry research addressing climate change did not even exist just thirty years ago.

Since the 1970s, the tools available to researchers in the field have evolved from rudimentary weather balloons to complex, infrared satellite instruments. At the same time, Harvard has emerged as one of the leading worldwide research centers in atmospheric chemistry and climate change.

Housed in Harvard’s Department of Earth and Planetary Sciences, atmospheric chemists are investigating everything from how to model the effect of pollution on global warming to how to develop optical instruments to create an accurate climate record. Their research provides insight into how policy-makers can help mitigate the effect of human activity on the environment.

Illustration by Casey Alcantar '13
Illustration by Casey Alcantar '13

Lasers and Satellites
In addition to the continued work on global warming, research is now transitioning toward understanding the broader effects that changes in atmospheric composition have on the climate. James Anderson, the Philip S. Weld Professor of Atmospheric Chemistry, recognizes that research in the field requires more robust as well as more accurate climate data. He has witnessed the development of the field and made many of the measurements that established the existence of the Antarctic ozone hole.

Anderson was instrumental in the passage of the Montreal Protocol, a document banning the use of chlorofluorocarbons (the main agents causing depletion of the ozone layer). He understands that the public remains largely unconvinced that humans have directly caused climate change such as global warming. However, he stresses that the majority of the scientific community supports the view that climate change is primarily caused by human factors.

However, it is necessary to generate data to demonstrate the connection between human activity and climate to influence public policy. This is the motivation for many of Anderson’s current research endeavors.

“Setting in place a very high accuracy record of how the entire coupled climate structure was of paramount importance,” says Anderson. “And so, in 1996, we proposed to build a highly accurate small satellite that would be in the infrared spectrum.”

Although he faced some setbacks along the way, Anderson successfully built this instrument. The device will hopefully create a long-term global record of climate, while achieving a new level of accuracy.

This device measures the spectra of infrared radiation emitted by the earth. The data can be used to generate global temperature distributions, atmospheric composition, and radiative forcing, all of which are necessary to create a precise picture of global climate change.

This instrument is meant to help create a climate monitoring system, key to the development of the field. “This country doesn’t have a climate observing system,” says Anderson. “It only has pieces of what you would call a very rickety system, and it’s simply not capable of providing hard scientific evidence for public policy.”

The infrared satellite instrument will hopefully provide the data necessary to better understand the earth’s dynamic climate structure.

Modeling of Atmospheric Chemicals and Climate
Collecting data with atmospheric instruments is not an end in itself. Rather, atmospheric chemists use climate and chemical models to interpret the raw data supplied by researchers like Professor Anderson with the intent of understanding the interaction between the atmosphere and climate.

The Harvard Atmospheric Chemistry Modeling Group, led by Professor Daniel Jacob and Dr. Jennifer Logan, is at the helm of atmospheric modeling with the novel GEOS-Chem chemical transport model. The GEOS-Chem model calculates three-dimensional atmospheric composition using estimates of emissions of various chemicals into the atmosphere. It simulates the flow of these chemicals when they are blown by winds and when they react with other chemicals.

Central to this model is the data collected by satellites. “Satellites, for a modeler like myself,” says Professor Jacob, “are very exciting because satellite observations mean nothing without a good model.”

Discrepancies between the measured satellite data and the data simulated with the GEOS-Chem model are revealed when the two sets of data are compared. The GEOS-Chem model is subsequently modified to reduce the discrepancy between the measured and simulated data, and ultimately to improve the model’s ability to forecast atmospheric composition. This demonstrates why the instruments developed by the Anderson Group are so important to this field.

Chemical transport models like GEOS-Chem are crucial to an understanding of climate systems since they can reveal how chemicals released into the environment affect climate. By pairing these models with climate change models, scientists discovered that the release of greenhouse gasses like CO2 into the atmosphere may be a major cause of global warming.

Eric Leibensperger, a graduate student in the lab group, recently demonstrated how these chemical transport models can be used to understand changes in climate. Leibensperger simulated the changes over time in the atmospheric concentration of aerosols (particles of air pollution). He then used a global climate model to translate these changes into their effects on global temperatures. In the process, Leibensperger showed that “if you remove the U.S. sources of aerosols, you actually warm the United States.” He also verified that this warming effect would be felt only locally above the US.

An Interconnected Climate System
Despite improvements in modeling technology and data collection, climate and chemical models still struggle to replicate the complex climate structure. Professor Steven Wofsy, who studies sources and sinks of CO2 and other chemicals in the atmosphere, is well acquainted with the challenges of climate models.

“What I think is the most important scientific issue that slops over to the policy and social realms is that the [climate] system is highly interactive and nonlinear and that the one thing we really know about these systems is that they are hard to predict,” says Wofsy. “In fact, they are generally thought of as being unpredictable.”

The reason that these complex models often break down is that the atmosphere is intricately connected to the environment in ways we do not yet understand. The atmospheric changes caused by chemical emissions do not stop with changes in global temperatures.

Professor Anderson explains this phenomenon: “I like to make the analogy that a 1°C increase in global mean temperature, global warming, is to the climate as a 2% default rate on a mortgage is to the financial structure. It triggered a sequence of events in the climate and financial structures that led to collapse, but the feedbacks in the financial system are what really caused the system to implode.”

The new frontier of climate change research is shifting toward understanding these climate feedbacks. Although the Anderson Group is continuing to work on their infrared satellite instrument, the group is now also exploring these feedbacks.

Two main focuses of the Anderson Group’s new research are the Arctic ice caps and the glaciers on Greenland. The melting and collapse of these systems have the potential to exacerbate climate change and global warming.

To better forecast the future of the Greenland glaciers, the Anderson Group is developing instruments to map the topography and three-dimensional structure of the glaciers. In addition, the group is developing underwater instruments to gather information about the Arctic ice caps.

The endeavors of Professor Wofsy and the Anderson Group are providing the field with much-needed information on the interaction between the climate and environment. This information is critical to the development of the field since it is necessary to develop more accurate models and to understand the mechanisms through which human activity affects the environment.

What Now?
Although there are already noticeable consequences due to climate change, its future effects promise to be far worse than any observed to date. “Something bad is going to happen,” says Wofsy. “What, I don’t know, but I do know that it is going to be sudden.”

Both Wofsy and Anderson agree that establishing public policy sooner rather than later is necessary to curb the effect of human activity on climate. “The role of government here is unprecedented,” says Anderson. “For economic competitiveness, for national security, we have to move very quickly to renewable energy and fortunately, we have it.” The United States has the resources to power two thirds of its energy with solar and wind power. It just requires time to develop.

However, with climate research in an early stage of development, it seems unlikely that politicians would support changes in environmental public policy based on current findings. Establishing unequivocal evidence is a huge feat, let alone drafting legislation with a price tag that taxpayers would approve.

Yet, Anderson is optimistic about the future: “I have no doubt that we can do it. But the government has got to step in and develop the economic infrastructure.”

But Anderson is not the only one with this positive attitude. Rather, it pervades Harvard’s atmospheric chemistry and climate change research groups. These researchers are determined to not only understand the complex climate system but also to fight for its preservation.

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