(Part of the How to Talk to a Global Warming Skeptic guide)
Objection: According to the IPCC, 150 billion tonnes of carbon go into the atmosphere from natural processes every year. This is almost 30 times the amount of carbon humans emit. What difference can we make?
Answer: It's true that natural fluxes in the carbon cycle are much larger than anthropogenic emissions. But for roughly the last 10,000 years, until the industrial revolution, every gigatonne of carbon going into the atmosphere was balanced by one coming out.
What humans have done is alter one side of this cycle. We put approximately 6 gigatonnes of carbon into the air but, unlike nature, we are not taking any out.
Thankfully, nature is compensating in part for our emissions, because only about half the CO2 we emit stays in the air. Nevertheless, since we began burning fossil fuels in earnest over 150 years ago, the atmospheric concentration that was relatively stable for the previous several thousand years has now risen by over 35%.
So whatever the total amounts going in and out "naturally," humans have clearly upset the balance and significantly altered an important part of the climate system.
On ‘climategate’
What to make of the new climate poll
‘Copenhagen Diagnosis’ offers a grim update to the IPCC’s climate science
Comments
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winterfrost Posted 6:48 am
02 Aug 2007
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Delay And Deny Posted 4:53 pm
02 Sep 2007
What humans have done is alter one side of this cycle. We put approximately 6 gigatonnes of carbon into the air but, unlike nature, we are not taking any out.
Wait a minute. If that's the case, then, as you say, it should take us 30 years to double the total CO2 in the atmosphere.
But Al Gore showed a graph with an exponential growth rate in a few years?!
John Bailo
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gzuckier Posted 3:24 am
06 Nov 2007
In fact, the IPCC model, to be conservative with respect to human effects, assumes that there has also been an increase in natural sources, at present unknown, of carbon dioxide of equal magnitude to human sources over the same period (i.e. another 270 Gtons of carbon over the preindustrial amount), which in turn mathematically requires that presently unknown natural sinks have absorbed an additional 380 Gton of carbon, or 120% of what humans have produced, more than their preindustrial amount.
If in fact these presently unknown sources do not exist or are smaller, then the effect of human activity must be larger than the IPCC estimates. Of course, if they are larger than assumed, then the effect of human activity will be smaller; but it's increasingly unlikely that such large unknown natural sources of carbon dioxide exist, particularly ones that have increased their activity in parallel with human output, by coincidence.
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airplanesocks Posted 10:37 am
10 May 2008
Since we have a good idea of how much carbon we've emitted since the Industrial Revolution (money makes people keep records), we have a pretty good idea of how much carbon ought to be in the atmosphere right now--and it isn't there. There is no certain answer at this point about where the carbon actually is; there are only three places that it can be hiding logically. The ocean; the terrestrial biosphere; or the atmosphere (and we know it's not there).
The greenhouse effect is causing a 'greening' at higher latitudes--plants that couldn't survive at high latitudes because of colder temperatures are now able to move there because the temperatures are right for them--but that is unlikely to draw down enough CO2 on its own to offset that 7 Gt per year of anthropogenic CO2 emissions. The ocean has a much faster turnover rate for CO2, so a number of people think that it might be there, as a dissolved gas.
In short, we know we're emitting about 7 Gt of CO2 per year (about 6 Gt in fossil fuel burning, and 1 Gt from deforestation), but only 3.5 Gt appears to stay in the atmosphere.
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megal Posted 6:51 pm
12 Oct 2008
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