We know that climate change is going to alter wine. In fact, we know that it already has. But we are still working toward a deeper understanding of what it will look like — and what can be done about it. The latest step toward that understanding is a study published Tuesday by the Union of Concerned Scientists, one of the most detailed forecasts to date of extreme heat across the U.S. As The Chronicle’s environmental correspondent Kurtis Alexander reported, the study warns that most of the country will see more than double the number of days with a 100 degree heat index by 2050, unless something drastic is done.