Next year's international Climate Ambition Summit (COP 26, November 2021) is seeking to achieve a carbon neutral world as soon as possible. Suppose we are indeed able to become carbon neutral, will this stop atmospheric CO2 from rising?
The big problem facing those who want to reduce atmospheric CO2 concentrations is that man made (anthropogenic) CO2 is only 5% of total CO2 emissions so natural fluctuations could have important consequences and CO2 seems to have a very long lifetime in the atmosphere.
In 2019 the Intergovernmental Panel on Climate Change (IPCC) produced a summary of the current position on climate change: see summary. This made clear that tackling global warming had two components: lowering CO2 emissions to zero and extracting CO2 from the atmosphere.
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| Fixing global warming |
The IPCC calculated that reducing CO2 with forestry and land use changes would probably not be enough. Carbon capture and storage would also be needed.
I would not seek to gainsay the scientific findings or expertise of the IPCC but I would ask for their interpretation of the data to be reconsidered.
Reducing the emissions of CO2 will certainly reduce the growth in atmospheric CO2 concentrations. Carbon neutral policies for reducing atmospheric CO2 are not so obviously beneficial. As an example, if we cut down a large area of forest and replace it with Palm Oil plants there is a tricky calculation to be made about whether the Palm Oil will lock up more CO2 than the forest. If we use GM Palm Oil that is weedkiller resistant we can grow more oil but at the price of destroying organic matter in the soil. Using organic oils and sugars also produces agri-desert which is extremely bad for biodiversity. Carbon neutrality may not actually be carbon neutral, however, it will probably reduce the growth in atmospheric CO2 levels.
At present we inject enough CO2 into the atmosphere to raise concentrations by 2.5 ppm (parts per million) annually. About half of the CO2 that we release does not go into the atmosphere. The CO2 that does not go into the atmosphere is dissolved in the oceans or taken up by carbon sinks.
The carbon sinks are the processes that remove CO2 from the atmosphere for a long time. The most effective carbon sink is the mud in the sea at some continental margins. This mud is the stuff that eventually ends up as sedimentary rocks such as mudstones, sandstones, shales etc. Carbon in these rocks is permanently locked away until we start drilling, mining or fracking it.
The conventional wisdom is that CO2 stays in the atmosphere for a very long time. If we squirt some CO2 into the atmosphere how long does it remain? An unintentional experiment was performed in the 1950s when atomic bomb tests irradiated the atmosphere so that a small amount of the CO2 was changed to contain the radioactive isotope, C14. It turns out that about half of the C14 was gone from the atmosphere in less than 15 years.
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| The lifetime of C14 and hence CO2 in the Atmosphere |
The IPCC recognises the short turnover figure of around 5 years but uses a residence time of around 1000 years for the current concentration of CO2 in the atmosphere to be reduced by 63% (given zero CO2 emissions by people). The IPCC are not stupid so what is going on? The IPCC recognises that CO2 will flow into oceans and plants but also notes that this CO2 will be released again over decades and so will not be totally gone. So a picture emerges of CO2 being released by humans, flowing into plants etc and then being re-released. It is only the long term carbon sinks, such as the formation of sedimentary rock or expansion of forests, that will permanently remove the CO2 from the atmosphere. The IPCC view is that these carbon sinks, especially the short term sinks, have a low capacity and are virtually saturated.
The short term carbon sinks such as forests
can remove CO2 from the atmosphere but they are a "one-off" fix. The carbon becomes lodged in the trees and soils which means that the weight of carbon in newly planted forest is removed from the atmosphere and stays removed so long as we do not subsequently cut down or burn the forest. In a world where all of the pressure is to remove forests it will be difficult to increase the size of forests by 25% by 2050 to reduce
CO2 by about a quarter.
However, if the loss of tree cover over the past 250 years were corrected it would be almost enough to offset the CO2 in the atmosphere by about 50% and so return the earth to pre-industrial levels of CO2 or more (although the figures above are contested):
This introduces an interesting conundrum. If natural carbon sinks can be used to offset global warming then how far did the loss of these sinks create global warming in the first place? It is generally agreed that planting trees, restoring wetlands, river deltas etc. is essential to combat the rise of CO2. Over the past 200 years we have massively reduced tree coverage, wetlands and the transport of organic material to river deltas etc. How far has the disappearance of the carbon sinks caused the high atmospheric CO2 levels? As can be seen above, just the loss of forest might account much of the current 120 ppm excess CO2 without including industrial production. Half of all
wetlands have been lost since 1900 the remaining wetlands represent 12% of the world's carbon pool so perhaps the loss of 6% of the carbon pool, assuming replacement of 6% by farmland, can be added to the CO2 released by the destruction of the natural world.
A much better fix is to increase the area and health of productive continental shelf and river deltas. As anyone who has ever been "fossiling" knows, these wetlands and shallow seas produce mudstones, shales, chalk and limestone which lock away carbon. They created the rocks that are nowadays the source of oil, gas and shale oil. Even today the river deltas and shallow seas constitute about half of the global carbon sink.
The current burial rate of carbon by river deltas is about
0.1 Gigatonnes per year , equivalent to removing 0.32 Gt of CO2 that would otherwise have gone into the atmosphere. However, modern river deltas are a poor shadow of their former glory. Of the large river deltas only the Amazon and Congo are fairly pristine, the Indus, Ganges, Nile, Yangtze, Mississippi, Rhine etc. have all been dammed, with agriculture reaching to the river banks, flood plains drained etc. so that their transport of organic matter to the sea has been dramatically reduced. Flood plains, lakes, marshes and swamps globally have been drained. It is now difficult to see anywhere on the modern earth that could create the hydrocarbon producing rocks of the future. The standard texts for fossil creation always state that the fossilised creature died in a swamp, marsh, lake or shallow sea but where are the current places that create fossil bearing sedimentary rocks?
The fact that the growth curves for deforestation, population growth, CO2 accumulation and global temperature rise all overlie each other is not a coincidence. Global warming is an ecological crisis. If we "fix" it with carbon capture and storage and biofuels we will just hit another ecological or geophysical problem.
The only healthy long term fix is to reduce CO2 emissions, restore ecosystems and, most of all, reduce the population.
Glitches in the IPCC View
It is very important that the IPCC clear up a couple of problems with their analysis of the carbon cycle.
The most obvious problem with the IPCC view is the idea that the short term carbon sinks are saturated. 95% of CO2 emissions are natural so the IPCC is suggesting that a small disturbance of 5% in CO2 emission will overwhelm the carbon sinks. There are several proposed solutions to this problem of the carbon sinks being fixed. One possibility is that they are indeed fixed. Another is that the sinks are being removed by human beings (as we saw above). Yet another possibility is that natural CO2 emissions are increasing as the temperature rises.
There is abundant evidence of escalating damage to carbon sinks. As an example, forests would need to expand by around 2% per year to absorb the man made CO2 emissions but forest extent is controlled by humans and being reduced by around 0.2% a year. General air pollution also damages the productivity of vegetation everywhere and lowers its potential as a carbon sink. Add in wetlands, deltas, canalisation of rivers etc. and carbon sink damage could be responsible for the sinks appearing to be saturated.
There is indeed also some evidence that the release of CO2 from stores such as the ocean and soils is temperature dependent. This graph by
Hermann Harde demonstrates the co-dependency:
Harde interprets this as meaning that the rise in temperature is causing the rise in CO2. The IPCC view suggests that the opposite is largely true but it is very difficult to disentangle the two factors, however if both temperature and CO2 are in play, reinforcing each other's effects, it bodes ill for plans to control CO2. If Harde is right reducing anthropogenic CO2 will not solve global warming.
These glitches do not mean that we can just ignore anthropogenic CO2. It is a pollutant that we must cease emitting.
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16/12/2020
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