Posts Tagged ‘CO2’

*facepalm* comment of the day or why a theoretical accmulation of atmospheric CO2 ‘tipping point’ is not like boiling water

August 26, 2008

There was a comment buried below a dubious (as usual) article in Gristmill – regarding the even more dubious claim by the NOAA that July 2008 was warm.  I’d be curious to know exactly where in the world it was warmer than usual considering the number of places around the world that have been experiencing record cold this summer. NOAA data is suspect anyway because of the use of surface stations – not just their placement, but even the decline in stations that are even active.

The point of this article, however, isn’t to dispute that issue, but I’ve seen this sort of comment more than once:

Having this dissent is good for science, but it is not good for politics. They help to inflame the passions of uneducated people who know nothing about climate change or about evolution.

Coming back to the topic of CO2 levels, in physics phenomena happen when a threshold is reached. For example, water boils at 100 degree Centigrade. If you have a beaker of water which is at 100 centigrade, you can be sure that very soon all the water disappears as steam. Below 100 degrees, there is always some formation of steam but the content of water in your beaker remains stable.

Similarly, we know that there is a terrible chain reaction that might happen if CO2 levels in the atmosphere reach above 450 ppm. The temperature goes up and up in a spiral. Earth will then be uninhabitable for most life forms. There’s enough evidence for this chain reaction. It has been validated in lab experiments and in computer simulation. The only question is about what exactly is the required the threshold of CO2 levels : 450 ppm or 400 ppm or something else..

By the sounds of this comment one would think that 400 or 450ppm of CO2 in the atmosphere must initiate a phase change that turns carbon dioxide into plasma. He must mean that, since liquid water’s boiling is  an example of a phase change due to higher temperatures – from a liquid to a gas, and well, atmospheric CO2 is already a gas.  (Not that you ever see much liquid CO2 – ‘dry ice’ pretty much sublimates straight into that cool-looking smoke you see at nightclubs and parties)

See, water doesn’t actually boil at a fixed temperature in the way this person seems to imagine.  I recall learning that as far back as science class in primary school.  Someone up in the Colorado mountains could boil water at a lower temperature than 100 degrees Celsius. Why? Lower atmospheric pressure:
boiling point = 49.161 * Ln (Pressure in inches Hg) + 44.932.  So even with boiling water there isn’t a fixed temperature that could be seen as a ‘tipping point’ between phase changes.

One thing I appreciate, however is the reference to a ‘chain reaction’ rather than the usual ‘tipping point’. Much more suitably alarmist as it implies an out-of-control nuclear meltdown.

I’d be curious to see what lab experiments, however, have validated this claim, since Greenhouses routinely pump in CO2 in far higher concentrations with no consequence apart from higher yielding plants.