If you’re not quite sold on the link between man-made pollutants, toxic air and climate change, this lecture will extinguish any remaining doubts. Charles Kolb has chased buses, trucks and cars in Mexico City and New York City with a state-of-the-art mobile detection unit, and measured the precise quantity of gases and particulates released in the vehicles’ exhaust plumes. The picture is neither pretty nor predictable: in Mexico City, vehicles released not only carbon dioxide (implicated in global warming), but a surprising amount of formaldehyde, (a known carcinogen), and ammonia. New York City diesel buses engineered to reduce soot exhaust ended up producing large quantities of an even more disagreeable pollutant. Kolb reminds us to pay attention to the really big picture—the troposphere and stratosphere—where many of these human chemicals do their damage. It turns out that fossil fuel combustion (from vehicles, heating, cooling and industries) sends about 28 gigatons of carbon dioxide into the atmosphere on an annual basis. Green plants act as “sinks,” soaking up about half of that excess, but civilization is inexorably building up this gas and driving up global temperatures.