Hansen posited in a 2007 paper that 350 ppm (parts per million) of carbon dioxide in the atmosphere is a safe upper limit to avoid a climate tipping point. The current record level is 389 ppm of CO2, an almost 40-percent increase from the pre-industrial revolution level of 278 ppm. In 1988 the Earth's atmosphere surpassed the 350 ppm mark, while global CO2 emissions per capita rose.