How long does carbon dioxide emitted by human beings remain in the atmosphere? It turns out, it is a tricky question. Different mechanisms remove carbon at different rates, and the responses of each system to higher concentrations of carbon dioxide in the atmosphere differ.
Probably the most important distinction is between sinks that have a capacity that can be exhausted and those that are effectively limitless. Oceans the biosphere are of the first kind, and they respond to carbon dioxide in the atmosphere relatively quickly. That being said, there is a limit to how much carbon dioxide the ocean can absorb (and the fact that it becomes more acidic while doing so is problematic) and there is only so much biomass the planet can sustain. Weathering rock that absorbs carbon and then subducts below the seafloor is an example of the second type of sink: though it operates very slowly and volcanic eruptions can return carbon that has been locked into the lithosphere back to the atmosphere. Even without such eruptions to worry about, natural weathering is not the route to a stable climate on a human timescale. As the Nature article linked above explains: “it would take hundreds of thousands of years for these processes to bring CO2 levels back to pre-industrial values.”
The article also comments on how long the temperature anomaly from anthropogenic emissions will persist: “whether we emit a lot or a little bit of CO2, temperatures will quickly rise and plateau, dropping by only about 1°C over 12,000 years.” We should make no mistake in understanding that our choices about how much carbon dioxide we emit will have a big impact on a huge number of future generations.
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You might be better off writing these kinds of things somewhere where you would have a more specialized audience to provide responses. Perhaps on some sort of climate change group blog?
There is definitely something to that idea. Participating in a group blog would lead to a larger and more climate-focused readership, quite probably generating more extensive discussions.
I wonder how a person gets on board with something like that.
See also:
What it means to stabilize climate
January 22, 2009
Some climate damage already irreversible
RANDOLPH E. SCHMID
Associated Press
January 26, 2009 at 5:00 PM EST
WASHINGTON — Many damaging effects of climate change are already basically irreversible, researchers declared Monday, warning that even if carbon emissions can somehow be halted temperatures around the globe will remain high until at least the year 3000.
“People have imagined that if we stopped emitting carbon dioxide the climate would go back to normal in 100 years, 200 years – that’s not true,” climate researcher Susan Solomon said in a teleconference.
Ms. Solomon, of the National Oceanic and Atmospheric Administration’s Earth System Research Laboratory in Boulder, Colo., is lead author of an international team’s paper reporting irreversible damage from climate change, being published in Tuesday’s edition of Proceedings of the National Academy of Sciences.
Study shows that anthropogenic CO2 and the resulting climate change are longer lived than previously thought. Even after 10,000 years, 15% to30% of the anthropogenic CO2 perturbation persists in the atmosphere. The resulting climate changes last even longer.-
Eby, M., K. Zickfeld, A. Montenegro, D. Archer, K.J. Meissner and A.J. Weaver. 2009. Lifetime of anthropogenic climate change: millennial time scales of potential CO2 and surface temperature perturbation. Journal of Climate Vol 22, May 15, 2009, pp 2501-2511
“To go from the amount of CO2 emitted to the actual increase in the atmosphere, one needs to know what fraction of the emissions remains in the air: the “airborne fraction”. Broecker simply assumed, based on past data of emissions and CO2 concentrations (Keeling’s Mauna Loa curve), that the airborne fraction is a constant 50%. I.e., about half of our fossil fuel emissions accumulates in the atmosphere. That is still a good assumption today, if you look at the observed CO2 increase as fraction of fossil fuel emissions. Broecker calculated that about 35% of the emissions is taken up by the ocean and the other 15% by the biosphere (again not far from modern values, see Canadell et al.). On this basis he argued that if the ocean is the main sink, the airborne fraction would remain almost constant for the decades to come (his calculations extend to the year 2010).
Thus, with a 3% increase in emissions per year and 50% of that remaining airborne, it is easy to compute the increase in CO2 concentrations. He obtains an increase from 295 to 403 ppm from 1900 to 2010. The actual value in 2010 is 390 ppm, a little lower than Broecker estimated because his forecast cumulative emissions were a little too high.”
“Yes, there can be natural climate changes over thousands or millions of years that are large compared to what we are experiencing now. But in fact, our actions have risen well above the level of any natural variations because of their pace. Without our use of fossil fuels, we should be descending into another glacial maximum – albeit slowly, over tens of thousands of years (the pace of natural global climate change in the Pleistocene). And instead our actions have interfered with this natural cycle and we are in the process of completely deglaciating the planet.
Indeed, if one takes David Archer’s calculations seriously (and we should), roughly 20 percent of the CO2 that comes from burning fossil fuel will be there tens of thousands of years from now, and so if we end up well above 400 parts per million for tens of thousands of years, there is much less doubt that Greenland will melt in its entirety and that Antarctica may well deglaciate as well. The idea that the climate system is so powerful that it is beyond human influence is simply incorrect.”
“After years of research, the basic structure of the climate change problem is clear. The lifestyle of the global middle class is committing people for the next thousand years to a chaotic world significantly different from the one in which most human cultures developed and flourished. Even if we were to eliminate our emissions overnight, excess carbon would remain in the atmosphere for centuries, affecting climate and altering Earth systems. For those who can afford dikes, health care, food, and the possibility of migration, climate change will merely raise the price of the good life, if they are lucky. For those who cannot afford these goods, the consequences will be devastating. “
Climate change to continue to year 3000 in best case scenarios
New research indicates the impact of rising CO2 levels in the Earth’s atmosphere will cause unstoppable effects to the climate for at least the next 1000 years, causing researchers to estimate a collapse of the West Antarctic ice sheet by the year 3000, and an eventual rise in the global sea level of at least four metres. The study, to be published in the Jan. 9 Advanced Online Publication of the journal Nature Geoscience, is the first full climate model simulation to make predictions out to 1000 years from now. It is based on best-case, ‘zero-emissions’ scenarios constructed by a team of researchers from the Canadian Centre for Climate Modelling and Analysis (an Environment Canada research lab at the University of Victoria) and the University of Calgary.
“We created ‘what if’ scenarios,” says Dr. Shawn Marshall, Canada Research Chair in Climate Change and University of Calgary geography professor. “What if we completely stopped using fossil fuels and put no more CO2 in the atmosphere? How long would it then take to reverse current climate change trends and will things first become worse?” The research team explored zero-emissions scenarios beginning in 2010 and in 2100.
THE natural processes which dispose of carbon dioxide are, in aggregate, rather slow, which means that an increase in the atmosphere’s carbon-dioxide level will, left to itself, last a long time. David Victor, a professor at the University of California, San Diego, has a keen eye for such simple basics and the uncomfortable ways they may fit together. He sees this one as underlying all three of the things that make climate change a particularly pernicious sort of problem.
In the face of such slow removal, the level of the gas can’t be lowered simply by stabilising the rate of emission; instead emissions must be cut nearly to zero. Because the harm the gas does is slow and cumulative, the benefits for any such cuts in emission will be delayed and uncertain, whereas the costs are all up front. And gas’s longevity means it is spread more or less evenly around the world, with the result that the fate of a country’s climate depends not on its own emissions, but on those of the world as a whole. A challenge that requires fundamental shifts in the energy economy for the sake of benefits that will be both a long time coming and subject to a pernicious free-rider problem was never going to be an easy one to solve. Little surprise that the world isn’t up to it.
Rolling in the Deep
The global carbon cycle involves a constant exchange between oceans, biota, and the atmosphere. A large portion of the carbon cycle, however, extends deep into Earth’s solid interior, and exchange occurs over much longer time scales. Walter et al. (p. 54, published online 15 September; see the Perspective by Harte) show evidence, through the analysis of a unique set of Brazilian diamonds, that the deep carbon cycle extends further into Earth than previously anticipated. The isotopic signature of diamonds suggests that they formed from carbon that originated from subducted oceanic crust, but tiny mineral inclusions trapped within the diamonds reveal that they must have passed through the lower mantle before being sent back up to Earth’s surface.
http://www.sciencemag.org/content/334/6052/twis.full
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