tl;dr: The virtual GUADEC 2020 conference had negligible carbon emissions, on the order of 100× lower than the in-person 2019 conference. Average travel to the 2019 conference was 10% of each person’s annual carbon budget. 2020 had increased inclusiveness; but had the downside of a limited social scene. What can we do to get the best of both for 2021?

It’s been several weeks since GUADEC 2020 was held, and this release cycle of GNOME is coming to a close. It’s been an interesting year. The conference was a different experience from normal, and despite missing seeing everyone in person I thought it went very well. Many thanks to the organising team and especially the sysadmin team. I’m glad an online conference was possible, and happy that it allowed many people to attend who can’t normally do so. I hope we can incorporate the best parts of this year into future conferences.

Measuring things

During the conference, with the help of Bart, I collected some data about the resource consumption of the servers during GUADEC. After a bit of post-processing, it looks like the conference emitted on the order of 0.5–1tCO2e (tonnes of carbon dioxide equivalent, the measure of global warming potential). These emissions were from the conference servers (21% of the total), network traffic (55%), and an estimate of the power used by people’s home computers while watching talks (24%).

By way of contrast, there were estimated emissions of 110tCO2e for travel to and from GUADEC 2019 in Thessaloniki. Travel emissions are likely to be the bulk of the emissions from that conference (insufficient data is available to estimate the other costs, such as building use, food, events, etc.). Of those travel emissions, 98% were from flights, and 79% of attendees flew. The lowest emissions for a return flight were a bit under 0.3tCO2e, the highest were around 3tCO2e, and the mode was the bracket [0.3, 0.6)tCO2e.

This shows quite a contrast between in-person and virtual conferences — a factor of 100 difference in carbon emissions. The conference in Thessaloniki (which I’m focusing on because I’ve got data for it from the post-conference survey, not because it was particularly unusual) had 198 registered attendees, and modal transport emissions per attendee of 0.42tCO2e.

Does it matter?

The recommended personal carbon budget for 2019/2020 is 4.1tCO2e, and it decreases each year until we reach emissions which are compatible with 2°C of global warming in 2050. That means that everyone should only emit 4.1tCO2e or less, per year. Modal emissions of 0.42tCO2e per person attending the 2019 conference is 10% of their carbon budget.

Other emissions pathways give lower budgets sooner, and perhaps would be better goals (2°C of global warming is a lot).

Everyone is in charge of their own carbon budgeting, and how they choose to spend it. It’s possible to spend 10% of your annual budget on one conference and still come in under-budget for the year, but it’s not easy.

For this reason, and for the reasons of inclusiveness which we saw at GUADEC 2020, I hope we keep virtual participation as a first-class part of GUADEC in future. It would be good to explore ways of keeping the social aspects of an in-person conference without completely returning to the previous model of flying everyone to one place.

What about 2021?

I say ‘2021’, but please take this to mean ‘next time it’s safe to host an international in-person conference’.

Looking at the breakdown of transport emissions for GUADEC 2019 by mode, flights are the big target for emissions reductions (note the logarithmic scale):

Splitting the flights up by length shows that the obvious approach of encouraging international train travel instead of short-haul flights (emissions bins up to 1.2tCO2e/flight in the graph below) would not have got us more than 38% reduction in transport emissions for Thessaloniki, but that’s a pretty good start.

Would a model where we had per-continent or per-country in-person meetups, all attending a larger virtual conference, have significantly lower emissions? Would it bring back enough of the social atmosphere?

Something to think about for GUADEC 2021! If you have any comments or suggestions, or have spotted any mistakes in this analysis, please get in touch. The data is available here.

Thanks to Will Thompson for proofreading.