What Do We Want?
We call upon the UNFCCC to adopt a dual-term GWP20 and GWP100 greenhouse gas accounting standard for all of its activities, as well as future IPCC reporting.
This shift in greenhouse gas accounting standards will help mitigating short-lived climate pollutants (SLCPs), primarily methane, which in turn would reduce short term anthropogenic warming, providing the time and attention needed for the key objective, namely reducing CO2 emissions so as to limit global warming to 1.5°C. Reductions of SLCPs must of course be made in parallel with, and not diminish the existential urgency of decarbonizing global society by reducing emissions of the principal anthropogenic GHG, CO2.
The key impetus for immediate SLCPs reductions is provided by so-called ‘climate tipping points’, the possibility of rapid climatic regime changes into climate states completely unlike the conditions under which human societies evolved and that thus require a thorough and hasty, costly and challenging societal re-evolution. A key example of such regime changes is offered by rapid collapse of the Greenland ice sheet caused by intense transient radiative forcing by SLCPs that is fully preventable in their absence. Rapid reduction of SLCPs is thus a forceful application of the precautionary principle.
There are also many benefits to both developed and developing countries from this intervention, such as potentially reducing the cost of the global energy transition by up to 25%, as well as helping developing countries reach their SDGs by drastically limiting temperature rise for up to 25 years.
The metrics utilised by the UNFCCC to assess the global warming effect of GHGs play a critical role in defining the course of global climate action. They frame our understanding of climate change as well as choice and timing of responses.
The 100-year Global Warming Potential (GWP100) adopted by UNFCCC is widely used today as a default metric. Like any other metric, GWP100 has its shortcomings and is based on value judgments, which have implications for the climate mitigation strategies considered. GWP is a metric that compares the amount of radiative forcing caused by various GHGs over a chosen period of time – 20, 100 or 500 years – with that of carbon dioxide (CO2). The choice of a time frame affects the weighting of different GHGs depending on their lifespan. Thus, GWP20 ignores climate effects beyond 20-years, and, therefore, is not appropriate for reporting long-lived gases, such as nitrous-oxide. Meanwhile, GWP100 and GWP500 obscure the effects of SLCPs, such as methane and certain short-lived fluorinated gases. For example, the GWP100 multiplier of methane is 34, meaning that it is estimated that over 100 years, one tonne of methane produces 34 times more warming than one tonne of CO2. However, methane only lasts in the atmosphere for around 10 years, hence by averaging out its warming over 100 years we grossly underestimate its impact during those first 10 years. If we were to use a 20-year time frame to measure the impact of methane on the climate, one tonne of methane would provide 86 times more warming than one tonne of CO2.
Widespread implementation of GWP100 as the “gold standard” of GHG accounting emphasises CO2 as the primary target of climate action, correspondingly defining the timing and direction of mitigation activities at both the international and national level. CO2 is, indeed, the main driver of long-term warming and, therefore, targeting it is vital for long-term mitigation strategies if we aim to preserve a safe and healthy environment for future generations.
However, focusing on long-term climate impacts places weight on CO2 policy actions only and deemphasizes the vital role of SLCPs in driving near-term warming, one that must be considered in climate policy agendas. Though being largely discounted by the current GHG accounting system and despite their short lifespans, if produced continuously, these greenhouse emissions create a cumulative long-term warming effect, comparable to that of long-lived pollutants. In fact, 42% of current warming is due to SLCPs. While addressing SLCPs can only be legitimate in parallel with efforts to reduce CO2 emissions, neglecting them can increase the risk of reaching a temperature overshoot and tipping points for runaway climate change sooner. SLCPs can push the earth into a different climatic regime, which might reduce the climate change mitigation potential of cutting CO2.
Conversely, addressing SLCPs alongside CO2 represents a powerful opportunity to create a more immediate impact, which cannot be achieved through CO2 reductions alone, even under very ambitious mitigation strategies. Early mitigation of SLCPs can be beneficial in many important ways. It can help reduce damages due to climate change over the next few decades (e.g., biodiversity loss), slow down amplifying feedbacks (e.g., snow-and-ice albedo), and decrease the risk of potential non-linear changes (e.g., massive GHG release from thawing permafrost), eventually increasing the probability of staying below 2.0 °C through mid-century, stimulating progress towards the long-term 2.0 °C target and reducing long-term cumulative climate impacts. For example, it is estimated that moderate mitigation of SLCPs can slow global warming by 15 years and at least 0.5 °C.
Moreover, actions targeting SLCP reduction in near term also tend to be linked to human health, development and sustainability benefits, which can provide additional support to developing countries with the achievement of Sustainable Development Goals. Finally, action on SLCPs can contribute to cutting costs of overall climate change mitigation – for example, reducing methane emissions through cutting ruminant production could reduce the costs of the energy transition by 25%.
However, because of the inadequate messaging about the causes of climate change and the required responses, deriving from GWP100-centrism, these mitigation opportunities are significantly overlooked. Climate mitigation debates primarily focus on the sectors which are the dominant sources of CO2 – energy, industry and transportation. At the same time, the need for equally pressing action in other sectors which are the main sources of the short-lived climate pollutants – for example, agriculture, specifically, such activities as pasture and stubble fires, deforestation and industrial livestock management and expansion – is underplayed. Fugitive emissions from natural gas extraction is another major source of methane emissions not currently being addressed under the current greenhouse gas accounting framework.
To achieve the goal set by the Paris Agreement, we need to equip ourselves with a diverse portfolio of climate change mitigation strategies covering all pollutants and all contributing sectors. This requires bringing SLCPs into focus and updating the GHG accounting system, so that it would more adequately represent both long-lived and short-lived climate pollutants.
We suggest that it is time to acknowledge the fact that a single timescale GWP metric serves poorly the purpose of informing effective climate action. We propose using dual GWP20/GWP100 reporting, which will mitigate against the biases associated with a single time frame and will ensure we have a fuller picture of ongoing changes. It will highlight more opportunities for action and will help avoid policy and ethical trade-offs between near-term and long-term objectives.
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