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Climate Tipping Point? Concentration of Carbon Dioxide Tops 400 ppm for First Time in Human History

The 400 ppm threshold is widely recognized as a dangerous level that could drastically worsen human-caused global warming.
 
 
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AMY GOODMAN: Scientists are warning the planet has now reached a grim climate milestone not seen for two or three million years. The National Oceanic and Atmospheric Administration says the amount of heat-trapping carbon dioxide in the atmosphere has topped 400 parts per million. The 400 ppm threshold has been an important marker in U.N. climate change negotiations, widely recognized as a dangerous level that could drastically worsen human-caused global warming.

The environmentalist group 350.org takes its name after the 350 parts per million threshold that scientists say is the maximum atmospheric concentration of carbon dioxide for a safe planet. In a statement on the parts per million number hitting 400, 350.org co-founder Bill McKibben said, quote, "The only question now is whether the relentless rise in carbon can be matched by a relentless rise in the activism necessary to stop it."

To find out more about the impacts of crossing the threshold, we’re joined now by leading climate scientist Michael Mann, distinguished professor of meteorology at Penn State University, author of the recent book,  The Hockey Stick and the Climate Wars: Dispatches from the Front Lines.

We welcome you to  Democracy Now! Thank you for joining us from the public television station in State College, WPSU. Thanks so much, Michael Mann. Talk about the significance of this threshold being passed.

MICHAEL MANN: Thanks. It’s great to be with you.

So, this number, 400 parts per million, what does it mean? It’s the number of molecules of CO2 for every million molecules of air; 400 of them are now CO2. Just two centuries ago, that number was only 280 parts per million. So if we continue to add carbon to the atmosphere at current rates, we’ll reach a doubling of the pre-industrial levels of CO2 within the next few decades.

Now, 400, what does that round number, 400, mean? Well, what it means is that, as you alluded to, we have to go several million years back in time to find a point in earth’s history where CO2 was as high as it is now. And, of course, we’re just blowing through this 400 ppm limit. If we continue to burn fossil fuels at accelerating rates, if we continue with business as usual, we will cross the 450 parts per million limit in a matter of maybe a couple decades. We believe that with that amount of CO2 in the atmosphere, we commit to what can truly be described as dangerous and irreversible changes in our climate.

AMY GOODMAN: Like what?

MICHAEL MANN: So, what we are already witnessing, in fact, the effects of climate change. If we look at the past year here in the U.S., last summer, the record heat, the record drought, the record wildfire that destroyed large forest areas in Colorado, New Mexico. We saw, you know, tremendous damage to our crops in the breadbasket of the country. We saw Arctic sea ice diminish to the lowest level we’ve ever seen, and it’s on a trajectory where there will be no ice in the Arctic at the end of the summer in perhaps a matter of 10 years or so. We also saw the devastation of Superstorm Sandy. Now, we can’t say that Hurricane Sandy was caused by climate change, but many of its characteristics are precisely the kinds of characteristics that we predict tropical storms and hurricanes will have if we continue to warm the planet. We will see more destructive tropical storms. We’ll see more flooding. We’ll see more drought. And that’s just the tip of the iceberg, because, remember, we’ve only just crossed 400 now. We will reach 450 ppm in a matter of a couple decades if we continue with business as usual.

 
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