Posted by: ericgrimsrud | April 20, 2013

Is warming by CO2 irreversible, unstoppable, and/or inevitable?

These are three separate and very important questions that have different and commonly misunderstood answers.  Therefore, in this post, I will try to explain each of them.  Additional details concerning them have been provided recently by a post on 19 April 2013 by Andy Skuce at skepticalscience.com as well as in the literature articles referenced there.

First, is the global warming caused by CO2 emissions irreversible?  Unfortunately, on any time scale of relevance to existing human civilizations, the answer to this question is “no”, the warming we cause is not reversible.   There are two reasons for this.  One is that even if we stopped all man-causes CO2 emissions today, it would take about 200 years for today’s elevated level of atmospheric CO2, approaching 400 ppm, to naturally decay down to a level of about 340 ppm, a level we had in 1980 – still much higher than the preindustrial level of 280 ppm. Yes, it takes a long time for the extra biological carbon we put into the Earth’s carbon cycle to dissipate into stable geological reservoirs of carbon such as limestone.  And yes, it will take about 200 years to undo the CO2 increase we have caused over the last 30 years.

In addition, the heating of the Earth is delayed by the huge thermal inertia of our oceans, and the timescale of that delay just happens to be nearly equal to the rate of CO2 decay just described.  Thus, these two slow processes described above go in opposite directions and tend to cancel each other’s effect so that the Earth’s temperature will remain approximately constant after that envisioned point in time when all anthropogenic CO2 emissions have been eliminated.  Then, of course, what has taken a long time to warm up (the oceans primary) also takes a long time to cool off.  Putting all of this together, the warming we have created to date is approximately what we are stuck with in the future.  That is, the temperature change that has been caused up to present is already set and is not reversible.

Secondly, is warming by CO2 unstoppable?  Fortunately, the answer to this question is “yes”.  As explained above, if all man-caused CO2 emissions were stopped today, the additional warming caused by this specific greenhouse gas would be stopped.   Due to the two opposing effects described above, the temperature of the Earth would be remain unchanged at the present level for many centuries.

Lastly, is warming by CO2 inevitable?  Another way this question is commonly put is “is there additional warming already in the pipeline” – that will play out no matter what we do?  The answer to this question must be broken into two parts.  If one is referring only to the scientific factors involved, the answer is fortunately “no”, additional warming is not inevitable.  As explained above, future warming can be stopped by stopping all of mankind’s emissions of CO2.  Thus, in a scientific only sense, there is no additional warming already in the pipeline.

We also know, however, that we will not be able to eliminate today or even within the next year all future emissions of CO2. Therefore, at least some and probably a lot of future warming by CO2 is inevitable.  The magnitude of that future warning depends entirely on the amount of fossil fuels presently residing in all of the reserves of the world that  will eventually be delivered to the energy markets of the world where they will be burned and converted into CO2.

In summary, we do not necessarily have to despair about the inevitability of future global warming.  The amount of warming “already in the pipeline” is something we have control over – that associated with man’s intended use of fossil fuels in the future.  The more fossil fuels we leave in the ground, the better.   Unfortunately, mankind’s use of fossil fuels for energy production is increasing, not decreasing, thereby making more future warming inevitable – if appropriate actions to cut off our addition to fossil fuels are not taken.

Therefore, as has always been the case, man-kind will reap what he sows.  Hopefully, this post explains both why this adage applies to the subject of climate change and what can be done to minimize future damage associated with the steadily increasing levels of CO2 in our atmosphere.


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