What Passing 400 ppm CO2 Means to Climate Scientists

NASA | A Year in the Life of Earth's CO2 (source). Note first that emissions are greater in the industrialized northern hemisphere, which probably explains why the Arctic is melting first. Then note the difference between winter emissions in the north, which remain airborne, and summer emissions, which are partially withdrawn by growing vegetation.

by Gaius Publius

This is written for anyone who is climate-concerned, but specifically for our DC readers in the policy-making community. This is the issue at which cautious incrementalism collides with urgency. If a meteor were headed for earth and due to crash in a year between 2020 and 2040, I doubt our policymakers would be talking about how long to delay before acting.

The climate emergency is that meteor. 2020 is five years away. I don't know about anyone else, but I'm not feeling lucky. Neither are these folks.

What Passing a Key CO2 Mark Means to Climate Scientists

From Andrea Thompson and Brian Kahn at Climate Central comes this, a series of comments from prominent climate scientists on our passing a key climate milestone, a persistent 400 ppm of atmospheric CO2.

As the animation above shows, CO2, one of several greenhouse gases and the longest lived, passes into the atmosphere from the burning of fossil fuels (primarily), then is partially draw out by the activity of plants in the summer, and other factors, such as dissolution in the ocean. More remains in the air than is drawn out, however, which counts for increasing atmospheric concentrations, year by year.

Here is the authors' introduction to the scientists' comments:

Humans have burned enough fossil fuels to drive atmospheric CO2 to levels that world hasn’t seen in at least 400,000 years. That’s driven up temperatures, melted ice and caused oceans to acidify. Some extreme weather events around the world have become more likely and stronger because of it, and some will likely only get worse as the planet continues to warm. [Note the unnecessary conservativism in the use of "likely." The word they want is "certainly."]

Because CO2 sits in the atmosphere long after it’s burned, that means we’ve  likely lived our last week in a sub-400 ppm world. It also means that the reshaping of our planet will continue for decades and centuries to come, even if climate talks in Paris in two weeks are successful.

To get some perspective on what this means for the world, we asked leading climate scientists for their insight on passing this milestone as well as what it means for their particular areas of research. Below are their answers, some edited lightly for clarity or length.

And now a few of the comments:

How Do You Feel About CO2 Levels Passing This Threshold?
 
Ralph Keeling, director of the Scripps CO2 Program: “It will take some getting used to psychologically, like a round-numbered birthday. For someone who remembers when CO2 was only around 330 ppm, it's a pretty big change.”

Jason Box, ice researcher at the Geologic Survey of Denmark and Greenland: “I feel very concerned because the last time atmospheric CO2 was this high, global sea levels were at least six meters higher. You can see a recent study by Andrea Dutton and others on sea level rise due to polar ice-sheet mass loss during past warm periods.”

Katharine Hayhoe, atmospheric scientist at Texas Tech University: “As a scientist, the difference between 399 ppm vs. 401 ppm is negligible.

As a human, though, passing both the 400 ppm and (potentially) the 1°C threshold within such a short time period makes it clear we are already living in a different world. We have blown past targets that were being considered as viable when I entered graduate school. We have significantly reduced the options available to us in the future. If we aren’t going to blow past the next set of thresholds — 500 ppm and 2°C — within just a few more decades, we have a lot of work to do in Paris in two weeks and beyond.”

Peter Gleick, president of the Pacific Institute: “In some ways, the number 400 ppm is no different than 395 ppm or 390 ppm — it is just that we like watching our odometers turn over at even numbers with lots of zeros. But this feels far more important than pure symbolism. The truth is, when I was born, atmospheric CO2 levels were around 300 ppm. Today — maybe even this week — will be the last time anyone alive experiences a level below 400 ppm, and no one born in the coming century or even longer will ever see less than 400 ppm again. That is a deep, deep observation, with ramifications for our children and for every future generation.”

Pieter Tans, head of the Carbon Cycle Greenhouse Gases Group at the Environmental System Research Laboratory: “What do I feel about this? Awe! To me, it demonstrates the continuing and unavoidable rise of CO2 as long as mankind continues to burn coal, oil, and natural gas in quantities so large that natural systems are being overwhelmed.”

There are more questions and more comments, all of them interesting. The questions include "What Does Reaching This Level Mean For Your Area Of Climate Science?" and "Do You Think This Milestone Will Spur Action On Climate Change?" Please read the rest.

Four Takeaways

To make it simple, here are four takeaways from the article:

1. From Jason Box, quoted above: The last time atmospheric CO2 was this high, global sea levels were at least six meters higher.
    
2. Katherine Hayhoe, above: If we aren’t going to blow past the next set of thresholds — 500 ppm and 2°C — within just a few more decades, we have a lot of work to do in Paris in two weeks and beyond.
    
3. John Church, from an unquoted part of the article: The oceans, glaciers and ice sheets are all out of balance so sea level will rise for centuries, and more.
    
4. Julienne Stroeve, from an unquoted part: Any action on climate change will be driven by economics; sadly that's the way the world currently works.

All four statements are true — "we have a lot of work to do" is of course a huge understatement — but the fourth statement is only conditionally correct. In "incremental times" the fourth is spot-on. In revolutionary times, however, times in which the villagers opt for an "Easter Island solution," there are choices other than protecting the wealth of our "leaders":

You're a villager on Easter Island. People are cutting down trees right and left, and many are getting worried. At some point, the number of worried villagers reaches critical mass, and they go as a group to the island chief and say, "Look, we have to stop cutting trees, like now." The chief, who's also CEO of a wood products company, checks his bottom line and orders the cutting to continue.

Do the villagers walk away? Or do they depose the chief?

There's always a choice ...

Six meters or more of sea level rise before 2100 is at least 19 feet. The seas continuing to rise "for centuries" is the end of coastal living worldwide, the absolute end, except in easily moved villages. Me, I like the Easter Island solution more and more. Simply depose the chief.

What Does "Depose the Chief" Mean?

Until the Democratic primary is over, "depose the chief" means replacing the "carbon friendly" and "solution at the margins" Barack Obama with only Bernie Sanders, at least until Hillary Clinton stops being a carbon candidate herself.

You can help in two ways. First, contribute to Bernie Sanders campaign, and optionally, the campaigns of all candidates who have endorsed him. (Adjust the split any way you like at the link.)

Second, understand that moving quickly means just that — a World War II-style national mobilization. Consider adding your name, voice and effort to this group and signing the pledge to mobilize.

Otherwise, we could end up here:

Climate translation:

"I know what you're thinking, Mr. & Ms. American. You're thinking, 'Do we have until 2020 to stop making Exxon and Big Oil rich, or can we wait till 2040 to take them on?' Now, to tell you the truth, no one really knows. But being this is civilization-ending CO2 emissions we're talking about, which will blow your grandchildren right back to the stone age while you watch, you've got to ask yourselves a question — Do you feel lucky?" 

Me, I don't feel lucky.

"You are here" and rising at >2.1 ppm/year. Atmospheric CO2 across a span of time longer than our species has existed (source; click to enlarge).

Not lucky at all. (One solution here.)

GP