One of the reasons climate change is so difficult to address is the sheer range of sources and sectors that contribute to the problem. Some policies and measures are targeted to address certain sources, but one of the perceived advantages of carbon markets is that they allow a number of sources to be bundled under one policy and then allow the market to identify the lowest costs for reducing emissions.
While this may be an appropriate way to deal with certain industrial sectors, policymakers have often brought biological emissions (emissions from animals and plants) into the same market, treating them as equivalent to fossil emissions (manmade burning of fossil fuels), as “a tonne is a tonne” and it’s “what the atmosphere sees”. It is often done so on grounds of political expediency, to overcome the resistance to decarbonisation from vested fossil fuel interests. However, the two sources of carbon – fossil and biological – are not scientifically interchangeable, or ‘fungible’.
This is because the snapshot view of carbon fluxes – looking at only what the atmosphere sees – ignores the different dynamisms in the carbon cycles of fossil and biological carbon.
The fossil carbon found in fossil fuels was mostly laid down in the carboniferous period 359.2 to 299 million years ago, and is only now being released through human action – burning fossil fuels. The process for carbon to be stored geologically takes place on geological time scales. In other words thousands to millions of years!
In contrast, the shifts in quantities of carbon in the biosphere (the surface and atmosphere of the earth) operate over much shorter timescales than the geological ones, allowing rapid emissions to occur through land use change, fires, insect attacks, and reactions to rising temperatures.
In addition to the basic differences in the timescales of the two types of carbon, there are land area limits to how much land can be used to absorb fossil carbon. Furthermore, increases in carbon in the biosphere affect nutrient flows needed for plant life, especially nitrogen. This has the potential to affect plant life generally and eventually worsen climate change.
Another reason why relying on biological sinks (conserving and planting forests to store carbon) to offset fossil carbon is a bad idea is the issue of permanence: The IPCC has noted that “Carbon stored in terrestrial ecosystems is vulnerable to loss back to the atmosphere, resulting from increased fire frequency due to climate change and the sensitivity of ecosystem respiration to rising temperatures”. In other words, forests are not only stores of carbon but can also release it back into the atmosphere and this process is increased by over emission of greenhouse gases. Not burning fossil fuels is the only permanent means of not increasing atmospheric loading of CO2.
In reality, action to address emissions from both fossil and biological sources are needed. Humankind needs to end the fossil fuel era as soon as possible, and certainly by 2050. But there is also a biodiversity crisis, where loss of forests and other ecosystems contribute not only to the climate crisis, but also an impoverishment of life on earth.
 IPCC, 2014, Working Group 2: Impacts, Adaptation and Vulnerability
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