Not quite 400 ppm
But Hawaiian readings of CO2 levels are close enough
Although scientists at a Hawaiian observatory have revised their recent reading that carbon-dioxide levels had passed the symbolic milestone of 400 parts per million—the accurate reading was 399.89 ppm, they now say—the reality remains the same: The planet is warming up precipitously. Current ratios of carbon dioxide in the Earth’s atmosphere remain at levels not seen in more than 3 million years, when sea levels were as much as 80 feet higher than current levels. This chart dramatizes the rate of increase in the past 2,000 years.
Source: National Oceanic and Atmospheric Administration