The rising level of carbon dioxide in the atmosphere has averaged 400 parts-per-million (ppm) for the third time in a row last June and this could scale up global warming effects beyond human adaptation, climate change scientists have said. History was made in June when average levels of carbon dioxide emitted into the atmosphere were above 400 ppm for the third month in a row, just 50ppm less than the 450 ppm mark which scientists have described as “unhabitable’’ for some humans. As noted by scientists from the National Oceanic and Atmospheric Administration’s Mauna Loa observatory in Hawaii, the trend is clearly an indication that humans are still pumping too much carbon dioxide into the sky - a rather worrying scenario considering the already challenging impact of a warming climate.