Carbon dioxide levels in the atmosphere passed 400 parts per million (ppm) on Thursday for the first time in human history. But one thing hasn't changed: false balance still crops up in climate change stories.

False balance occurs when journalists give equal weight to arguments from both sides, regardless of where the facts lie. Climate change is a textbook example of this problem -- in fact, the term was coined in academic papers to criticize climate coverage in the 1990s.

Yet 20 years later, we still get articles like this from Bloomberg News, reporting on the 400 ppm milestone:

Happy Plants

“The Earth has had many-times-higher levels of CO2 in the past,” said Marc Morano, former spokesman for Republican Senator James Inhofe and executive editor of Climate Depot, a blog that posts articles skeptical of climate change. “Americans should welcome the 400 parts-per-million threshold. This means that plants are going to be happy, and this means that global-warming fearmongers are going to be proven wrong.”

That position is disputed by many researchers, said Melanie Fitzpatrick, climate scientist at the Union of Concerned Scientists.

“This needs to be a wake-up call,” she said in a statement. “Reaching 400 parts per million represents a dire experiment with the climate system. As long as humans have walked the Earth, we've never seen carbon dioxide levels this high.”

Marc Morano is not a scientist and has no scientific education. He is paid by an oil-industry funded organization to confuse the public about climate change, and has compared climate science to the Mayan calendar, Nostradamus, and medieval witchcraft. Moreover, his argument is laughable: by focusing on how carbon dioxide stimulates plant growth in a controlled environment, he ignores that our huge emissions of it and other greenhouse gases are warming up the planet, thereby increasing the risk of extreme rainfall and drought to the detriment of agriculture. A Wall Street Journal op-ed made the same argument on Thursday, leading to a deluge of condemnation.

So why is Bloomberg News not only featuring Morano, but giving his discredited argument equal weight to the extensive evidence presented by scientists?

Bloomberg News didn't stop there, trotting out another thoroughly discredited “skeptic” argument:

Skeptics of man's influence on warming temperatures note that while CO2 levels in the atmosphere have continued to rise since the 1990s, no year has been statistically warmer on average than 1998, with higher levels for 2005 and 2010 falling within the margin of error for that year, according to data compiled by the U.K. Met Office.

Even if the UK Met Office's ranking of 2010 and 2005 as the warmest years on record globally is within the margin of error for 1998 (U.S.'s NASA and NOAA both rank 2010 and 2005 as statistically warmer than 1998), the fact that the difference between these individual years is small illustrates again that we should pay more attention to the long-term trend. As NASA explained, “all three [surface temperature datasets] show the last decade is the warmest in the instrumental record.”