“At current emission rates it is possible we will pass the critical level of 450 parts per million CO2 in the atmosphere by 2040. That’s the level when, it is generally agreed, global climate change may become catastrophic and irreversible,” they add. “At that point we can expect to see the loss of most of our coral reefs and the arctic seas.”
http://www.sciencedaily.com/releases/2009/07/090729092538.htm
Since I hadn't heard before that there was a 450PPM line of death and a "generally agreed" one at that, I stopped to figure this one out. Since our current CO2 level is around 390PPM and increasing at around 2PPM, I would rate the chances of hitting 450PPM by 2040 as likely, rather than possible.
I went to find the paper and located it here:
http://www.cell.com/current-biology/fulltext/S0960-9822(09)01181-6#sec1
Oddly enough there wasn't anything in the paper that said exactly that, but there was this statement:
It has been suggested that a CO2[atm] of 450 ppm is a critical threshold beyond which catastrophic and irreversible change might occur [7]
this would bring a global mean temperature rise of 2
C above pre-industrial values. At present rates, this threshold will be passed by 2040, but climate-related systems are notoriously non-linear [14]. By 2040, some particularly sensitive marine ecosystems such as coral reefs and ice-covered polar seas could already have been lost, and other unexpected consequences may arise [15].Now to me, "suggested that" and "generally agreed" don't mean the same thing at all, so I was wondering where Science Daily got the quote from. I looked at the article more closely and found this "Adapted from materials provided by ARC Centre of Excellence in Coral Reef Studies.". That made it clearer, they are quoting from a press release about the paper and not from the paper itself. It also appears that whoever wrote the press release took some artistic license with the content of the paper. I found the press release and it implies that "generally agreed" is a direct quote from one of the authors.
http://www.coralcoe.org.au/news_stories/seachange.html
The whole 450ppm statement annoys me even more because I agree with a lot of the things the authors say. I'm a lukewarmer myself, so I think the biochemical impacts of CO2 increases will hit us before we actually start getting serious negative consequences from actual warming. The vague specificity of the 450ppm statement is alarming without giving any guidelines for actions. It makes them sound more like carnival fortune tellers and less like scientists. Assign a range of CO2 values where a certain catastrophe is likely and go through all the possible catastrophes and do the same for all of them. If you don't know enough to assign some probabilities, then go back and do some research and some experiments until you do know enough. It is worth spending billions of dollars to decrease that uncertainty.
Frankly a lot of things the authors say don't make any sense if they actually believe in the 450ppm catastrophe. How could ocean fertilization experiments be too risky if the alternative is a certain catastrophe? There are parts of the ocean that are near deserts any way and experiments could be done there with limited impact on other species. You need to balance the risk of actions against the risks of inaction.
If you truly believe that increases in CO2 is a clear and present danger, then what options should be off the table? Frankly every Nuclear reactor that is built should result in a coal plant of similar capacity being taken offline. The NRC shouldn't have any requirements for building a nuclear power plant except to verify that the containment is built to specification. It is sometimes hard to remember that no one died at Three Mile Island even though there was a complete core meltdown. Shucks the reactor next door is still operating.
BTW, would it have killed them to call it the "ARC Centre for Coral Reef Studies"? Organizations that use the the term "Excellence" or "Quality" in their title have the about the same effect on me as car dealers who have "Honest" in theirs.
