Upcoming GRL paper shows CO2 fraction is constant

[Wagmc]

contrary to AGW theory. I have not yet read the actual study.



http://bristol.ac.uk/news/2009/6649.html"

 

[Wagmc]

Conclusion from the paper:

Given the importance of the [the anthropogenic CO2 airborne fraction] for the degree of future climate change, the question is how to best predict its future course. One pre-requisite is that we gain a thorough understand of why it has stayed approximately constant in the past, another that we improve our ability to detect if and when it changes. The most urgent need seems to exist for more accurate estimates of land use emissions.

Another possible approach is to add more data through the combination of many detailed regional studies such as the ones by Schuster and Watson (2007) and Le Quéré et al. (2007), or using process based models combined with data assimilation approaches (Rayner et al., 2005). If process models are used, however, they need to be carefully constructed in order to answer the question of why the AF has remained constant and not shown more pronounced decadal-scale fluctuations or a stronger secular trend.

I read this as: if the models haven't gotten the past right, they can't be relied upon to accurately project the future.

 

[sylas]

With respect, you appear to have misunderstood this paper. It is in fact already published; it came out in the issue of 7 Nov. The press release came out just after the paper. The reference is

• Knorr, W. (2009), http://dx.doi.org/10.1029/2009GL040613, in Geophys. Res. Lett., 36, L21710, doi:10.1029/2009GL040613.

We already know that we can't accurately project the future. This is not news. That's why all projections give substantial uncertainties.

This paper is discussing the fraction of emissions which remains in the atmosphere. It's well known that roughly 40% of emissions remains in the atmosphere, with the rest being absorbed into the ocean and terrestrial land sinks. The question consider is whether this fraction can be expected to change.

The title you have given this thread might suggest to some readers that that the amount of CO₂ in the atmosphere is expected to be constant. That is, of course, not the correct reading. CO₂ levels are rising rapidly, being driven by anthropogenic emissions.

But for given emissions, how much of an increase in atmospheric carbon can you expect? Will it stay at about 40% of emissions, or increase to a larger fraction of emissions remaining in the atmosphere? The papers propose that this airborn fraction will remain roughly constant... meaning that atmospheric carbon will continue to increase at roughly 40% of the rate we are emitting carbon in the the atmosphere.

The climate effects of this is increased warming, due to a stronger greenhouse effect. This is also called anthropogenic warming. This is taken for granted. It is, after all, pretty fundamental physics. In order to figure out how much impact there will be from anthropogenic emissions, we need to know how carbon will be in the atmosphere. Some research has suggested that the fraction absorbed will drop as concentrations increase, and this would tend to mean a stronger impact than a simple linear relation between emissions and rising concentrations.

This has implications for how much warming we can expect, precisely because of what you would think of as "AGW theory" -- the conclusion that climate is warming primarily because of anthropogenic greenhouse gases in the atmosphere.

Cheers -- sylas

 

[Wagmc]

in the words of Knorr:

The results run contrary to a significant body of recent research which expects that the capacity of terrestrial ecosystems and the oceans to absorb CO2 should start to diminish as CO2 emissions increase, letting greenhouse gas levels skyrocket.

I think that's pretty clear, as is my understanding.

 

[sylas]

in the words of Knorr:



I think that's pretty clear, as is my understanding.

It is clear that this is about the workings of the carbon cycle.

It is precisely as I described for you above. The dispute described in your extract is a difference between various studies of the carbon cycle. All of this research takes completely for granted the following points, all of which stand as well supported scientific discoveries:

• A bit over 40% of anthropogenic CO₂ emissions remain in the atmosphere, with the rest absorbed into the ocean and land carbon sinks. This fraction is called the "AF", or "airborn fraction", in the paper.
• Almost of the current rapid rate of increase of CO₂ in the atmosphere is a consequence of anthropogenic emissions of CO₂; about 40% of which remain in the atmosphere to drive this increase, and the rest of which is being absorbed into other sinks in the ocean and land.
• The effect of increasing CO₂ levels is an increasingly strong greenhouse effect and an overall impact of warming the planet globally.

All of this is taken for granted in the paper.

Some research, to which you allude above, has suggested that airborne fraction of carbon may be increasing. If this is true, then the rate at which atmospheric carbon is increasing will tend to accelerate, even if emissions remain constant. This paper is arguing that the airborne fraction is remaining roughly constant (they do indicate a small increase; but less than some other investigators).

What you apparently still don't understand is that whatever way this particular issue gets resolved, there is no implication whatsoever for the basic underlying background conclusion that there is a strong anthropogenic warming effect from carbon dioxide emissions. I sympathize, somewhat. I note that this paper is being picked up rapidly by all the usual "denialist" blogs, and they nearly all are making precisely this mistake.

The extract you give speaks of a "significant body of research". This is research about the carbon cycle! It is cited in the paper. It is not a reference to the research that has established the existence of anthropogenic global warming.

There are a couple of issues worth discussing in this paper, but let's first see if we can get to a point of shared basic comprehension of the topic addressed in the paper!

Cheers -- sylas

 

[Xnn]

I've only read the abstract and press release, not the actual paper.

The following quote from the press release caught my attention:

Another result of the study is that emissions from deforestation might
have been overestimated by between 18 and 75 per cent.

Obviously the paper was reviewing emissions as part of the study.
However, this is a daunting task and as quoted above, there "might" be significant
errors. So, I wonder how much weight should be given to such a study.
Might it be best to place it in the low level of scientific understanding?

Dr Wolfgang Knorr at the University of Bristol found that in fact the trend in the
airborne fraction since 1850 has only been 0.7 ± 1.4% per decade, which is essentially
zero.

0.7 ± 1.4% sounds like a huge amount of uncertainty.
However, it's since 1850. That would be roughly 16 decades.

0.7*16 = 11

11% is huge!
So, I'd be curious to know how the uncertainty was calculated.
He may have made a mistake.

Bottom line, without the actual paper to read, there are a lot of open questions.

I've studied that monthly Mauna Loa CO2 data and it's seems that CO2
emissions probably exceeded the oceans absorption abilities sometime in the 1930's.
This is based on an Excel file on another computer, and I'll post a description
later of how this may be determined.

Clearly, atmospheric CO2 levels are accelerating.
It's a difficult task to determine how much of this is due
to increased emissions and how much is from reduced absorption.

 

[Wagmc]

At the current AF, it is not possible to support IPCC estimates of CO2 residence times on the order of ~100 years. It would be closer to 10-15 years, as other studies have found.

Thus, IPCC is overestimating how fast CO2 will accumulate and their warming scenarios are overstated.

 

[Xnn]

At the current AF, it is not possible to support IPCC estimates of CO2 residence times on the order of ~100 years. It would be closer to 10-15 years, as other studies have found.

Thus, IPCC is overestimating how fast CO2 will accumulate and their warming scenarios are overstated.

Sounds like an outrageous claim.
Do you have anything of substance to support this?

 

[Andre]

Sounds like an outrageous claim.
Do you have anything of substance to support this?

Essenhigh (2009), Potential Dependence of Global Warming on the Residence Time (RT) in the Atmosphere of Anthropogenically Sourced Carbon Dioxide, Energy Fuels, 2009, 23 (5), pp 2773–2784
DOI: 10.1021/ef800581r Publication Date (Web): April 1, 2009 Copyright © 2009 American Chemical Society[/url]

... the data source used was the outcome of the injection of excess 14CO2 into the atmosphere during the A-bomb tests in the 1950s/1960s, which generated an initial increase of approximately 1000% above the normal value and which then declined substantially exponentially with time, with τ = 16 years,...

 

[chriscolose]

Note that values of CO2 residence time in the atmosphere (several years) often refer to something much different than the perturbation lifetime, which refers to the amount of time CO2 levels remain elevated. There is no single number that describes how long CO2 levels remain elevated, since a significant portion is taken up on timescales of centuries, while roughly a quarter of it will stick around for thousands of years. Note that it makes absolutely no sense (either today, or in the past record) that large changes in CO2 are quickly brought back to initial levels on timescales of a few years to decades. Some useful reviews of this topic are:

Atmospheric lifetime of fossil-fuel carbon dioxide. D. Archer, M. Eby, V. Brovkin, A. Ridgwell, L. Cao, U. Mikolajewicz, K. Caldeira, K. Matsumoto, G. Munhoven, A. Montenegro, and K. Tokos, Annual Reviews of Earth and Planetary Sciences 37:117-134, doi 10.1146/annurev.earth.031208.100206, 2009.

Lifetime of anthropogenic climate change: Millennial time scales of potential CO2 and surface temperature perturbations, M. Eby, K Zickfield, A. Montenegro, D. Archer, K.J. Meissner, and A.J. Weaver. J. Climate 22(10): 1502-1511, 2009.

Millennial Atmospheric Lifetime of Fossil Fuel CO2, D. Archer and V. Brovkin, Climatic Change 90:283-297, 2008.