San Diego, according to Mark Thiemens, is the birthplace of research on climate change: it was here where scientists first started to study the rising carbon dioxide levels in the atmosphere.Climate change was once again the subject of discussion in San Diego on Jan. 9, when the Natural History Museum hosted the third in its lecture series about climate change. Thiemens, a chemist and dean of physical sciences at the University of California, San Diego (UCSD), gave a presentation titled “How We Know the Climate is Changing.”According to Thiemens (who admits to a pro-San Diego bias), “One of the first papers of real substance on climate change was written by two people named Roger Revelle and Hans Suess.” Revelle and Suess, scientists at UCSD, published evidence of increasing atmospheric carbon dioxide in 1957.San Diego’s most well known climatologist is Charles Keeling. Keeling, at the Scripps Institute of Oceanography (SIO), began charting atmospheric carbon dioxide levels during the 1950s. The now-famous “Keeling Curve” clearly shows a continuing rise in carbon dioxide. Scientists at UCSD and SIO continue to lead research in climate change.Global climate change is a result of the greenhouse effect. The gases in our atmosphere trap heat around the planet. Without the greenhouse effect, Earth would be an uninhabitable snowball. However, increasing greenhouse gases mean an ever-warmer planet. Thiemens compared the gases around the Earth to a wetsuit, and, as he explained, “The thicker your wetsuit, the warmer you are.”To study climate change, Thiemens looks to so-called “canaries in the mine.” Certain climate systems are particularly sensitive to climate change and can provide a warning about big changes to come. For example, the upper levels of the atmosphere may show signs of change before the problem is apparent in the air we breathe.Thiemens measures isotopes to learn about his samples. Isotopes are atoms of the same material that have slightly different weights. By measuring isotope levels from air or ice samples, Thiemens can figure out what kind of chemical reactions produced his sample.How does one obtain samples of the upper atmosphere? The answer, Thiemens explained, is rocket science. Thiemens and his research team send their sample collectors to the upper reaches of the atmosphere using military-grade missiles, launched from White Sands Missile Range in New Mexico. The sample collectors open at the proper altitude, collect gases, then parachute back to the Earth. The scientists study the samples to determine what gases are up there and deduce where they came from.In addition to atmospheric samples, Thiemens also studies particles that have fallen from the air to the Earth. The challenge of this research is to find an undisturbed location where the particles will be preserved as they fell. As it turns out, the best location is the South Pole. Thiemens was careful to point out that a trip to the South Pole is no vacation. He advised the audience, “If you ever get a chance to go there”don’t!”Thiemens, his students and collaborators traveled to Antarctica to collect isotopes. After completing their survival training and flying in a cramped airplane to the South Pole, the scientists started digging in the ice. Of this part of his research, Thiemens said, “It’s not rocket science.” They dug holes reminiscent of icy graves, then donned sterile surgical garb to collect uncontaminated samples of the ice.By measuring the isotopes in the Antarctic ice, Thiemens and his colleagues were able to analyze the fallout from two previous volcanic eruptions. Within their samples, the scientists were able to identify particles from two eruptions: the 1963 eruption of Mount Agung in Bali and the 1991 eruption of Mount Pinatubo in the Philippines. The sulfur isotopes present in each sample indicated how high the volcanic ash traveled. If the particles rose above the ozone layer, they were exposed to ultraviolet radiation that changed the isotope composition of the molecules. The scientists were also able to calculate past ozone levels by examining the oxygen isotopes in the icy samples.Thiemens’ work is just a tiny piece of the climate research carried out by scientists in San Diego and around the world. Every bit of data helps them to understand how the Earth’s climate works and how it might change. As Thiemens noted, “To understand the present and predict the future, we must also know and understand the past.”The next lecture in the climate change series will be held Feb. 14, 6:30 p.m., at the Natural History Museum, 1788 El Prado. Dan Cayan of the Scripps Institution of Oceanography will speak on “Climate Change: A Looming Challenge to California’s Water Supply.”