Reporting emissions the way we currently do obscures some key differences between the greenhouse gases emitted by agriculture, and we cannot use these figures to estimate temperature changes over time. New LEAP research demonstrates how an alternative means of relating different gases to carbon dioxide (CO2) can provide a straightforward means of overcoming these limitations.
When we hear about the climate impacts of agriculture and livestock, we are generally told the amount of ‘carbon dioxide equivalent (CO2e)’ greenhouse gas emissions these activities emit, either totalled per country or across the world, or the ‘carbon footprint’ of individual products. But current reporting methods cannot tell us if we will meet our climate change commitments. Our latest research, in the journal Environmental Research Letters, demonstrates an alternative and uncomplicated way of overcoming these limitations.
It might be assumed that the challenge in providing a simple link between emissions and global temperatures is complexity: that the physical science is so complicated it requires a high level of expertise and access to supercomputers. The details of exactly how climate change will manifest across the world, changing local weather patterns and increasing the frequency of extreme events, for example, are indeed very complex.
But at the level of global average temperature increases, we can distil the full complexity models down to some fairly straightforward principles. For many purposes this simplified picture will provide a sufficient level of detail, as global average temperature increases are generally agreed to be a good indicator of the more specific impacts through which climate damages are realised. This is why the Paris Agreement’s overarching goal is keeping global temperature increases below a 1.5-2°C threshold.
For CO2, the biggest contributor to global warming, a surprisingly simple picture emerges. Each individual CO2 emission adds an essentially permanent amount of warming that is only undone if we manage to actively remove past emissions from the atmospheric carbon cycle. Other greenhouse gases, with much shorter atmospheric lifetimes than CO2, do not work in the same way. If a gas only has a short atmospheric lifetime, then we have to consider natural removals of the gas balanced against ongoing emissions.
The standard way of communicating ‘Carbon dioxide equivalent’ emissions is to use the ‘100-year Global Warming Potential’, or GWP100. The GWP100 imagines a one-off pulse emission of different gases, and scales the total climate impact this emission would have relative to CO2, for the first 100-years after the emission of either gas. This can provide one indication of the effect of individual emissions, but because it comes down to weighting each gas by a single number, the GWP100 essentially means that you have to treat each gas in exactly the same way.
If we have a single reported ‘CO2e’ emission total, we don’t know how much is CO2, where each emission will add a permanent increment to global temperature, or how much is, for example, methane (CH4), where the gas will break down and much of its temperature impact will automatically be undone after a few decades. In turn, if we want to know how different emission scenarios contribute to global temperature increases over time, we cannot use the GWP100.