If CO2 causes crime in the U.S., why has there been "a sharp and sustained drop in murders and other violent assaults since the mid-1990s"?

Study Shows That Cities Are Safer Than Rural Areas, Despite Crime | TIME.com

in New York City, where I live now, there were just 414 homicides [2012] in a city of 8.2 million, the lowest number in more than half a century. But those statistics aren’t convincing the country that cities are getting safer: a 2011 Gallup poll found that most Americans continue to believe that the nation’s crime rate is getting worse, even though there’s been a sharp and sustained drop in murders and other violent assaults since the mid-1990s. Perception — no doubt fueled in part by the media — beats reality...We already know that the best way to shrink your carbon footprint is to move to a dense city. Now it turns out that it might be the best way to stay alive too.

2012: How Climate Change Could Make Summer Crime Waves Worse | Mother Jones

One researcher predicts we could see as many as 30,000 more US murders over the next 90 years thanks to rising temperatures.