In a rather testy exchange during a House hearing, Rep. Dana Rohrabacher tore into Environmental Protection Agency Administrator Gina McCarthy for not knowing what percentage of the atmosphere was made up of carbon dioxide.

“What percentage of the atmosphere is CO2?” the California Republican asked during a Thursday hearing.

“I don’t have that calculation for you, sir,” McCarthy replied. “I don’t make those guesses, sir.”

“You’re head of the EPA and you did not know,” Rohrabacher shot back in astonishment, “and now you are basing policies that impact dramatically on the American people and you didn’t know what the content of CO2 in the atmosphere was… the justification for the very policies you’re talking about.”

“If you’re asking me how much CO2 is in the atmosphere, not a percentage but how much, we have just reached levels of 400 parts per million,” McCarthy said, looking slightly annoyed with the lawmaker’s response.

“I think I was very clear on what I was asking,” Rohrabacher retorted. “I think it was very clear you didn’t know.”

Rohrabacher said carbon dioxide only makes up “one-half of one-tenth of one percent of the atmosphere,” adding that mankind only contributed to about 10 percent of the total amount of CO2.

“And you believe that this minimal, tiny element, and by the way only ten percent of that from what I understand is actually man-made… will have an impact on the weather to the point it that it will actually impact people’s health,” Rohrabacher said, before running out of time during the hearing.

The Earth’s atmosphere is 78 percent nitrogen, 21 percent oxygen and 1 percent other gases, including about 0.04 percent carbon dioxide. And yes, Earth’s CO2 concentration stood at 400 parts per million in May 2015.

Earth’s CO2 levels have been increasing in recent decades due to human activities and also natural factors, and some estimates say as little as 3 or 4 percent of carbon dioxide in the atmosphere is due to humans. Scientists, however, tend to argue that even though humans only contribute a tiny amount of CO2 into the atmosphere, it can’t all be absorbed by natural cycles.

This is not the first time a Republican lawmaker has tried to trip up McCarthy for not knowing some specifics about global warming. In March, Alabama Sen. Jeff Sessions criticized McCarthy for not knowing if predictions about extreme weather were right or wrong.

“This is a stunning development, that the head of the Environmental Protection Agency — who should know more than anybody else in the world, who is imposing hundreds of billions of dollars in cost to prevent this climate temperature increase — doesn’t know whether their projections have been right or wrong,” Sessions said after McCarthy said she didn’t know the specifics about hurricane data.

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