At one o'clock that afternoon, a mere 45 minutes after they had been alerted, scientists at Sweden's National Defense Research Institute, by retracing the trajectories of air parcels arriving at the country's eastern border, were able to pinpoint the source of radiation as "somewhere in the Ukraine." Later in the afternoon, specially equipped jets and helicopters flying over the Baltic Sea gathered samples of radioactive air, giving scientists precious data that would point them in the right direction. By evening, Swedish meteorologists had identified the Soviet nuclear reactor at Chernobyl, near Kiev, as the probable source - a fast, forensic solution to one of the most compelling detective stories in all of history. With a sense of emergency, all of Europe was warned about radioactive fallout from Chernobyl.

The Swedish warning, bolstered by confirmations from neighboring countries, was crucial because the Soviets were still keeping quiet about the nuclear accident, which had occurred more than 40 hours earlier on April 26. Peter Gould, a Professor of Geography at Penn State University, wrote in his book Fire in the Rain:

"At 1 hour, 23 minutes, and 43 seconds after midnight on April 26, 1986, Reactor 4 at Chernobyl went into a soaring and uncontrolled chain reaction. Two seconds later the resulting steam explosion tore the concrete housing apart, blew the thousand ton "safety" cover off the top of the reactor, and spewed materials high into the night sky equal to all the atomic tests ever conducted above ground."

Six days after the meltdown, hot, radioactive gases still escaping from the ruptured reactor were carried southeast in the wake of a compact low pressure system moving east over the Soviet Union. Just like jet aircraft flying through a deck of cirrus can clear a path through the clouds as hot engine exhaust evaporates droplets and ice crystals, hot radioactive gases cut a swath of clear skies through the overcast, creating a nuclear distrail (see the white arrows near Chernobyl in Figure 7.1), the first ever photographed (a distrail is a trail of clear skies surrounded by clouds; a contrail, discussed in Chapter 5, is a cloudy trail surrounded by clear skies).

Figure 7.2 shows the spread of radioactive particles in the first few days after the Chernobyl disaster, with emissions dispersed by shifting winds associated with changing patterns of air pressure across Europe. Such winds are like local rental trucks, responsible for regional transport of air. They are a small cog in a system of global winds, both at the surface and aloft, that acts like a connecting fleet of moving vans, relaying and transporting air around the earth. Back in May 1986, the interlocking system of global winds carried traces of Chernobyl's radioactivity to places as far away as the western United States (Figure 7.3). This global system of winds not only is accountable for the planetary transport of air, it also has an impact on climate, repercussions that we will now investigate.