What’s in a number?

For those who didn’t heard the news yet, since shortly CO₂ levels in Mauna Loa starting to reach 400 ppm. It was hailed as an important number, some even talked about a tipping point. So I thought it would be an interesting project to look into this a bit more in detail and find how much is too much when CO₂ is concerned.

First things first, the 400 ppm level. I read about it in a paper last Tuesday. I could trace back the origin to a media alert by Christina Figueres, executive Secretary of UNFCCC.

“With 400 ppm CO2 in the atmosphere, we have crossed an historic threshold and entered a new danger zone. The world must wake up and take note of what this means for human security, human welfare and economic development. In the face of clear and present danger, we need a policy response which truly rises to the challenge. We still have a chance to stave off the worst effects of climate change, but this will require a greatly stepped-up response across all three central pillars of action: action by the international community, by government at all levels, and by business and finance.”

“Historic threshold”, “new danger zone”, “in the face of clear and present danger”! No hyperboles were spared in this one. But hey, we lucky people, we still have a chance to evade this bullet!

The big question we started with: how much is too much? I remember that this is not the first time the media reported major tipping points. I remembered values of 350 ppm, 650 ppm and the pre-industrial level. Picture my surprise when I hit Google with some search terms and found loads of links to statements which involves numerous CO₂ tipping points. Next you will find one or two examples of each level. There are loads more to be found on the internet.

Let’s start with a very known level. There is of course the 350 org organization, which states 350 ppm is the upper limit and we should return to that to be on the safe side.

350 means climate safety. To preserve our planet, scientists tell us we must reduce the amount of CO2 in the atmosphere from its current level of 392 parts per million to below 350 ppm. But 350 is more than a number-it’s a symbol of where we need to head as a planet.

We passed that for already 2 decades now. Seems less dangerous than originally thought. But there are even lower tipping points predicted. Some scientists like for example James Hansen states that 300 ppm is the real safe limit. Read more about this on the
300.org google site and some contemplation about whether 300 ppm or 350 ppm is a safe limit.:

2. Urgent reduction of atmospheric CO₂ to a safe level of about 300 ppm as recommended by leading climate and biological scientists.

These are probably levels from almost 70 years ago! Even that seems too high. What about 280 ppm? Earth was, ahum, “in balance” with that, so it would be straight forward to aim for that level. According to State of Nature

If burning fossil fuels like coal and oil during industrialization has created the mess we’re in with climate change, it seems only logical that we should aim for pre-industrial levels of atmospheric CO2 of 280 ppm.

or the book Climate Challenge: 101 Solutions to Global Warming by Guy Daunce p31:

We need a target that guarantees the safety of our planet – in other words 280 ppm.

That’s more than 150 years ago we had that level. Apparently mayhem takes its time. And even that is much too high. Professor Schellnhuber says that we need to be less than 280 ppm!

Schellnhuber states that we need to go to pre-industrial levels of CO2 emissions (less than 280ppm) to save the planet

How much lower?

global emissions to be reduced to 220-225ppm.

Oops, earth must have experienced loads of dangerous tipping points during the last 800,000 years! Who knew?

Not much chance for tipping points higher than currently stated 400 ppm, you think.

You would be wrong.

Giss states levels above 450 ppm would be dangerous:

According to study co-author Makiko Sato of Columbia’s Earth Institute, “the temperature limit implies that CO2 exceeding 450 ppm is almost surely dangerous, and the ceiling may be even lower.

Step it up a notch: 500 ppm.
The book Understanding Environmental Pollution by Hill (p406):

500 ppm is considered a “tipping point” beyond which humanity must not allow itself to go before irrevocable changes could take place in our climate.

What about 550 ppm:
According to Avoiding dangerous climate change-page at Wikipedia

“Avoiding Dangerous Climate Change: A Scientific Symposium on Stabilisation of Greenhouse Gases” was a 2005 international conference[16] that examined the link between atmospheric greenhouse gas concentration, and the 2 °C (3.6 °F) ceiling on global warming thought necessary to avoid the most serious effects of global warming. Previously this had generally been accepted as being 550 ppm

560 is also a real nice number (twice the pre-industrial level of 280). On the climate avenue website:

It is calculated that if the carbon dioxide concentration reaches 560 ppm, the world will be in great danger.

Yikes! It is even calculated! Are there higher bidders?

Yes, there are. 650 ppm:
Golden Rules Report (pdf)

The Golden Rules Case puts CO 2 emissions on a long-term trajectory consistent with
stabilizing the atmospheric concentration of greenhouse-gas emissions at around
650 parts per million, a trajectory consistent with a probable temperature rise of more
than 3.5 degrees Celsius (°C) in the long term, well above the widely accepted 2°C target.

But it doesn’t stop there: what about tripling or quadrupling the pre-industrial level (840 – 1120 ppm)? NY Times reports:

Some experts think the level of the heat-trapping gas could triple or even quadruple before emissions are reined in.
[…]
Even if climate sensitivity turns out to be on the low end of the range, total emissions may wind up being so excessive as to drive the earth toward dangerous temperature increases

Here I stopped my search. This was a dizzying experience. So many declared tipping points and I even didn’t searched for increments of 25 yet. From 220 to 1120, that is quite a difference! Some advice for those who want to declare a new tipping point: 50 at the end is nice, but increments of 100 or increments of 280 are even better.

Why so many declared tipping points? Let’s go back to the media alert of the UNPCCC:

Governments will be meeting 3 – 14 June in Bonn for the next round of climate change talks
under the umbrella of the UNFCCC. A central focus of the talks will be negotiations to build a new
global climate agreement and to drive greater immediate climate action.

So, why 400 ppm? Well, if it is there, why not just using it? The 400 ppm is a political move, those meeting Governments will get that rubbed in to steer the negotiations into a certain direction. The other declared tipping points probably also had their specific purpose. They are probably more symbolic in nature than scientific.

Speaking of numbers with a symbolic meaning, this is the 13^th post on this blog. Should I start getting nervous? 😉

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