The Mauna Loa Observatory, which has been monitoring carbon dioxide levels since the 1950s under NOAA, has recorded the steepest rise ever within a year-long period. Apparently, the average CO2 level for February 2016 is 404.02 parts per million, 3.76ppm higher than February 2015's and 50ppm higher than what scientists consider a safe level. It broke the previous record set in September 1998, when the observatory detected a 3.70ppm growth over the span of 12 months.
As New Scientist noted, CO2 levels grew this past year partly due to wildfires/deforestation caused by El Niño's warming effects. Thing is, the more carbon dioxide there is in the atmosphere, the hotter it is -- it becomes a cycle. That's why people are urging companies to conjure up ways to reduce carbon dioxide emissions from their factories or to capture the gas and put it to good use.
Want to know what a year's worth of carbon dioxide looks like? NASA released a video showing the gas swirling like ominous clouds over the planet back in 2014. Carbon dioxide levels were lower then, though, so you'll have to visualize even heavier clouds blanketing our home.