Hysteresis and really big numbers

[GliderGuider]

One of the big concerns about global warming is (or should be) the notion of hysteresis. The definition of hysteresis is the lag in system behaviour from the time of any change in system inputs. This means either the application or the removal of an input. In the case of global warming, the current temperature rise is the result of CO2 that was put into the atmosphere up 50 years ago.

What concerns me most is that even if we stopped all global GHG production dead in its tracks this weekend, the natural hysteresis of the system ensures that it would be a further 30 to 50 years before the system responds to that change and stops heating up.

If GW is being helped along by excess CO2 (as is now pretty universally accepted), in order to stop the temperature from rising we would need to remove that excess. As the current atmospheric CO2 level is 380 ppm, we should aim to remove 100 ppm to get us back down to the pre-industrial level of 280 ppm. Given the mass of the atmosphere, this requires removing 530 gigatonnes of carbon dioxide, or about 140 gigatonnes of carbon. We currently generate 7 GT per year. In order to reverse the process we would need to immediately stop generating that amount, start removing the same amount every year, and keep that up for twenty years. And that 7 GT/yr has to be net removal. We'd also need to remove the CO2 we generated in whatever process we used to sequester the target amount, in addition to not doing anything else that generates CO2, like driving or flying or making plastics or concrete or heating our homes with natural gas.

The bottom line is that if anthropogenic CO2 is the culprit, we don't have a prayer of stopping the effect. And if the warming is entirely natural, we likewise don't have a prayer of stopping it.

Adapt or die.

[mike_c]

1. yep-- this is one of the concepts that I try really hard to get across...

...to my general ecology students. There is this prevailing view that system states respond predictably and similarly to driving forces in both directions. It just ain't so.

[bluerum]

2. Yes - I would expect a hysteresis loop that extends over a time frame

of many years - certainly on the scale of the input period. The system is massive and diverse and it makes sense that there would be some hysteresis.

One should also consider the concept of activation energy.

Once some critical level of atmospheric CO2 is reached events may take place so quickly that there is no turning back the clock. Not that there is any confirming evidence that this is the case, but we are in the midst of observing the largely unknown phenomena of global CO2 saturation. The mechanisms and trajectories are TBD.

[GliderGuider]

5. Activation energy

The manifestation of activation energy that is most obvious in this context is latent heat of fusion. It features prominently in two processes: the albedo change due to the melting of sea ice accelerating the absorption of further heat; and the release of methane (from hydrates or bacterial action) due to the melting of permafrost.

The phase change of water - the 0 degree tipping point.

[bluerum]

9. Interesting point. I was not thinking of such specific processes.

I was more or less postulating that as global warming continues unabated, and the overall thermal energy supply increases, we will observe reactions where CO2 either directly or indirectly acts as some kind of catalyst.

edit for sp.

[phantom power]

3. And then consider...

that each year we are releasing more CO2. The second derivative is still fucking positive. Forget "reversing" anything.

[Sinistrous]

4. Could you possibly give us non-cognoscenti a source for the statement::

"In the case of global warming, the current temperature rise is the result of CO2 that was put into the atmosphere up 50 years ago."

Sinistrous

[GliderGuider]

6. Sure.

This statement is the result of two facts. The most important one is the half-life of atmospheric CO2, which is estimated at about 30 years. This means that a significant portion of the CO2 released at any time stays in the atmosphere for 50 to 100 years. A source for this is this paper. The second factor is the point when significant amounts of CO2 started to be pumped into the air, and that would be post-WWII, or about 60 years ago.

Assuming a CO2 half-life of 30 years, then about 1/4 of all the CO2 pumped into the atmosphere in 1945 (60 years ago) is still there. As you can see from the graphs below, most of the rise in CO2 from pre-industrial levels has happened since 1945.


So most of the CO2 has been generated in the last 60 years, and much of what has been generated is still in the atmosphere. Therefore, the temperature rise we're seeing today is the result of CO2 that was generated since 1950 or so.

[bluerum]

8. Great pix. Disasterous implications - but nice graphics. nt

[longship]

7. The deniers will just call you hysterical.

Sorry bout that. Couldn't resist.
;-)