InsideClimate: Carbon dioxide concentrations in the atmosphere once again exceeded 400 parts per million Monday, but this time they may never fall back down, according to scientists.
While not a tipping point that signals climate catastrophe, the 400 ppm mark is an important symbolic threshold in the fight against climate change. It represents a 43 percent jump in greenhouse gases since pre-industrial times and underscores governments' inaction and worsening global warming impacts.
Scientists at the Mauna...