Higher ozone concentrations could lead to more school absences.Photo: Ole OlsonA new study puts a hefty price tag on climate change by linking it to the air you breathe. The report, published last Thursday by the Union of Concerned Scientists (UCS), concludes that CO2-induced temperature increases will worsen ground-level ozone concentrations (the kind coming from power plants and exhaust pipes, not the kind that shields the Earth from UV rays). Higher concentrations of ground-level ozone threaten the health of millions of Americans, an impact that could cost the U.S. $5.4 billion in 2020. If that's not compelling enough, here's what …