N2O - Let's have a laugh then properly take stock

This year the world takes stock of global GHG emissions, aggregated from national inventory reports (NIRs) published by countries. Countries aren't obligated to use the 2019 Refinement and will use the 2006 Guidelines which means that for N2O they can report nothing for N2O wastewater treatment emissions because the 2006 doesn't require reporting of these because we didn't realise how significant they were back then. They provided an optional EF but did not require that this be used as it was thought an insignificant source of emissions for our sector.

Since then, much more work has been done and hundreds of IPCC scientists have laboriously (and voluntarily - this always amazes me; we've relegated the writing of guidelines to help us save humanity something to be done in one's own time!) aggregated the best science into the 2019 Refinement. Including scientists and engineers we know and work with. For the first time this provided a tiered approach for wastewater N2O which provides a very significant change in the emission factor (EF) for N2O from wastewater treatment, which was made a required EF to be used in NIRs as well as providing clarity on the need for facility level (Tier 3) monitoring.

There is no obvious timeline for parties (countries) to apply the 2019 Refinement - they don't have to and they don't in their 2022 NIRs. In this great article, Michael Gillenwater, author and co-founder of not-for-profit GHG Institute says:

Ultimately, it is expected that all countries will use the?2019 Refinement?for GHG reporting under the Enhanced Transparency Framework (ETF) of the Paris Agreement. For this to happen, the?2019 Refinement?will have to be agreed upon through a decision of the Conference of the Parties serving as the Meeting of the Parties to the Paris Agreement.?

But even if not agreed by the countries, it has been adopted by the IPCC and provides the best available scientific consensus for treatment N2O emissions. The IPCC is always by nature conservative, though as we learn more about N2O emissions, year after year, this may not even be the case for the EF they proposed in the 2019 Refinement. More about the 2019 Refinement tiered framework imperative of facility level monitoring for N2O action another time but for now we can focus on the improved, recommended global EF which exists for N2O for handy application in stocktaking and baselining today!

Because our 2022 UK NIR doesn't take stock of N2O treatment emissions it underestimates N2O emissions from wastewater (by considering the 2006 Guidelines required effluent N2O EF only) by ~ a factor of 4 compared with if the UK Government adopted current best science. Rather than issue new fossil fuel licenses (seems ironic that N2O is the laughing gas!).

But adopting the not-yet-agreed-by-countries 2019 Guidelines isn't the only option for wastewater treatment N2O - countries can adopt the optional wastewater treatment N2O EF in the 2006 Guidelines (which was based on a single study from 1995 and is a factor of some 30 times lower than the 2019 Refinement) or they can also adopt an alternative methodology to calculate an EF if they choose to. In their NIR countries must also discuss gaps and areas for improvement in the inventories. The UK does none of this and neither do the large majority of reporting countries... with some notable exceptions we can be inspired by!

As you can read in the Danish NIR 2022, Denmark water and energy regulators have undertaken in-country monitoring of nitrous oxide and methane between 2018 - 2020 (links to a IWA webinar series on the 2 resulting National Monitoring Programmes carried out over the past 5 years). As a result of this climate action, Denmark are reporting country-specific EFs for both GHGs which means some emissions of N2O from treatment. The Swiss 2022 NIR also highlights that next year's NIR will implement the findings from their national N2O monitoring programme which developed new national EFs for N2O.

We actually have a sector level EF for N2O from wastewater treatment in the UK water sector - it's higher than the mandated 0 in the 2006 Guidelines, around 6 times higher than the optional 2006 EF but around 5 times lower than the 2019 Refinement EF (depending on assumptions about TN per capita). So our sector level N2O EF for treatment is not good though is better than nothing or the 2006 optional EF. But it's not used in UK national inventory reporting either.

This is discussed in the 2020 UKWIR report which reviewed this carbon accounting workbook EF for N2O. This work recommended a national monitoring programme to improve on the N2O EF, and on the basis of this prospective, imminent in-country monitoring programme, did not ultimately recommend a change in the under-estimated existing in-country EF. It did recommend the UK Government use the water sector reported EFs, despite their shortcomings, given it uses a number of the other specific water sector EFs in the NIR though at the current under-estimation this would make little difference anyway.

However, since this 2020 work, there has been an absolute wealth of new evidence around N2O emissions from treatment including emerging evidence from our own work as a sector in the UK (though alas no national monitoring programme yet).

A great step would be if our countries chose to take stock of the climate science and adopt the climate science and the 2019 Refinement N2O EF in their NIRs because this would give N2O emissions the magnitude and attention they deserve. Instead the UK NIR notes that whilst there is an EF in the 2019 Refinement, it is yet to be formally adopted. It mentions ongoing work and stakeholder engagement (erroneously it would seem, on the topic of effluent N2O but treatment N2O is what is meant). NIRs (or as they'll be called BTRs from the end of 2024 under the Enhanced Transparency Framework) definitely don't need to be perfect - as this great article discusses; fit for purpose is important.

Happily, in water, and as professionals of wastewater and process emissions and carbon accounting, we can take stock in the best way we can and move beyond inertia, delay, inaction! We can choose to adopt best science, even if our national governments do not. The GHG Institute article Should I use the new IPCC GHG inventory guidelines? concurs with a resounding yes (again, if you're a person!):

Technically speaking, there is every reason?anyone?engaged in estimating greenhouse gas (GHG) emissions or removals—from corporate, to facility, to project, to national scales — should use this updated guidance.?

There's a few reasons why we really should as professionals in water:

• as the above article highlights, because we know there is better science out there, summarised through consensus of an incredible global community exactly for this purpose - for us to use! We know this EF means we will have a more accurate starting point from which to reduce emissions and we might hope that a more accurate baseline will help draw the attention and funding required to the issue of N2O and wastewater (maybe even other fun areas like circular economy and what people eat and how we farm).
• we may genuinely fear for our children's future - already we can see current and future generations will not enjoy the stable climate we have. Life will be worse on the current trajectories for warming - both what we see now at 1.2 degrees and at 3 degrees. By acting within our professional capacities with the best science, we feel we are taking legitimate action.
• we all have an ethical obligation to society to act in a professional manner - as a professional Chemical Engineer, I have an obligation to act responsibly, in a sustainable manner and in the interests of the current and future global community - for example as set out in our Royal Charter. This means in line with best available evidence.
• we want to imagine a better life - despite our privilege, life without the burden of climate delay and inaction and with more wellbeing and less impact on our loved ones. For some of us, quieting that endless sense of urgency and distraction or more literally in the cleaner, greener places we will thrive in.

I can think of 2 main reasons why we may be hesitant as professionals in water to act to take stock as best we can when it comes to N2O:

1. others might take stock differently and what if their stocktaking is looking better than our stocktaking... we might be judged or penalised.
2. there is still high uncertainty and as engineers and scientists we just hate uncertainty; after land use and land use change, the waste NIR sector in which process emissions reside has the highest uncertainty in our NIR - we know this; we know the data we have to date has gaps and has high uncertainty too...

On point 1 - if anything our industry peers and stakeholders and citizens we impact in water (e.g. an entire population's worth) would surely judge us positively for taking stock in a science based manner and indeed would be surprised if we didn't. Once they realised, our children and future generations would be surprised and sad too if we didn't take stock the best way we knew how given the implications today (more accurate baseline, attention leading to support/funding for mitigation).

On 2 - we seem to miss the point here given the now greater than 50% chance of breaching the 'iconic threshold' of 1.5 degrees now within years. If we built an aeration system with 50% chance of being able to meet peak demand we'd be sent packing! What if we got on a plane that had 50% chance of landing safely! And anyway, luckily the IPCC has done the best science in 2019 here anyway so we don't need to be worried about adopting a more realistic but still uncertain EF for N2O, they're the experts!

Besides, we have some nice in-country emerging evidence around N2O emissions here in the UK. Which looks fairly well aligned with the IPCC best science (!). We also have excellent examples from the N2O monitoring programmes in Denmark and Switzerland (who have an N2O mitigation carbon offset scheme - more on that another time!) and from an entire EU level study Which (it's a pattern...) also aligns with IPCC best science!

In years to come we'll definitely seem improvements in our respective country NIRs - and when it comes to N2O EFs, we're already doing the work that will support this as professionals which is exciting. It may remain piecemeal and not very funded ... the need for a national monitoring programme to support this has now at least been discussed for the past 4 years but we are making some progress.

But happily we aren't countries, we're professionals in water. I believe this means we must find it in ourselves to look our kids in the eyes, really speak up and be advocates of taking proper stock of our N2O emissions today. This must be both through our day to day monitoring campaigns but also in our aggregated assessments, our assumptions in the absence of facility-level monitoring, our sector baselining, our projects and programme projections for today and tomorrow.... which will in turn help raise the issue within our sector globally, driving collaboration, progress and the facility level mitigation required.

PS. We have an IWA working group on the topic of N2O monitoring - open to all - please get in touch if you want to join up!