Environment on Crossref

A second look at Crossref's carbon footprint - the 2024 report

Ed Pentz — Mon, 15 Sep 2025 00:00:00 +0000

In 2022, we wrote a blog post “Rethinking staff travel, meetings, and events” outlining our new approach to staff travel, meetings, and events with the goal of not going back to ‘normal’ after the pandemic and said that in the future we would report on our efforts to balance online and virtual events, work life balance for staff, and track our carbon emissions. In December 2024, we wrote a blog post, “Summary of the environmental impact of Crossref,” that gave an overview of 2023 and provided the first report on our carbon emissions. Our report on 2023 only just made it into 2024, so we are happy to report on 2024 a little sooner in the year.

On the positive side, there are a few things:

Our spending on travel and meetings (a proxy for emissions) in 2024 was 56% of what it was in 2019, keeping below the target of not more than 60% of our 2019 spend
We were better at tracking hotel nights in 2024 compared to 2023
We managed to balance in-person, regional, and online meetings to engage with our global community while still not having returned to the pre-pandemic “normal”

In practice, our approach means thinking carefully about how to make the most of each trip. For example, when organising our Crossref Jakarta event, we travelled via Singapore and used the opportunity to meet with members there. Once in Jakarta, we combined our two-day event with an OJS workshop with colleagues from PKP, and another event with Universitas Indonesia. Similarly, when our colleague travelled by train to a conference in Amsterdam, they combined it with a day of visits to members in the area. These kinds of combinations reduce the need for separate trips and maximise the value of in-person travel.

Some of the less positive things were:

As our membership continues to grow globally and we expand our staff, (which are both great things in themselves), our emissions have also increased. Not only do we have more staff, but some staff travelled more in 2024 than in 2023. We’ll keep a close eye on this to avoid ever-increasing travel.
Taking a train instead of flying can take longer, and clashes with our desire for staff needing to be away from home as little time as possible.
It is difficult to find reliable data for some calculations - for example, we have decided not to try to calculate the impact of our Zoom use because there is no reliable way to do this.
We don’t have good options for offsetting our emissions, and it’s unclear whether we would want to do this even if they were available.

There is also the issue of whether it is worth it, or possible, to collect certain data, or whether it would change what we do. An example is Zoom. The estimate for the emissions from Zoom meetings in 2024 was 100 kg (that’s kilograms, not tonnes), but the calculations were made using a tool from 2020 that made many assumptions and estimates. We have no way of verifying whether the tool we used is accurate, so we decided not to update our previous calculation. In any case, we aren’t going to ration or reduce our teleconferencing, since it’s an essential tool, and especially if we want to fly less, have fewer in-person meetings, and operate effectively as a distributed organisation in multiple countries with no offices.

In summary, our total reported carbon emissions increased 40% from 105 tCO2e in 2023 to 147 tCO2e in 2024 (see below for the details). The positive aspect of this is that the increase is partly due to our improved ability to track our travel and hotel stays. The more concerning side of this is that we are travelling more. This enables us to engage with our growing community. We are still thinking strategically about our travel and meetings, following the approach outlined in our 2022 blog post. However, we need to carefully consider air travel in 2026, as it is our largest source of emissions (93%).

Total travel and carbon spending

Year	Amount	Percentage of 2019	Total carbon spent	Total hotel nights covered
2019 actuals	$585,482	100%	did not record	did not record
2020 actuals	$91,700	16%	did not record	did not record
2021 actuals	$19,066	3%	did not record	did not record
2022 actuals	$74,416	13%	did not record	did not record
2023 actuals	$305,737	52%	105 tCO2e	did not record
2024 actuals	$327,939	56%	147 tCO2e	415
2025 budget	$417,767 (reforecast)	71%	68 tCO2e (YTD)	256 (YTD)
2026 budget	$439,817	75%	TBD	TBD

In 2024, we met the target of keeping our travel expenses below 60% of our 2019 level. In 2025, we will exceed this. There are a number of reasons for this. We have more staff, more members, inflation has been high, and we are subsidising a lot more travel for others, such as our ambassadors, speakers, and collaborators at local events, and some board members (since 2019, we reduced from three to one in-person board meeting per year). This aligns with our goals of inclusivity for Crossref meetings, but we have to recognise there is a trade-off. The cost of travel, particularly airfare, has increased since 2019. Using US Bureau of Labor Statistics data from 2019 to 2025 the inflation multiplier for a dollar is 1.26 so adjusted for inflation the comparison figure for 2025 spending is $737,000 and forecasted 2025 spending is 60% of this. While we use cost as a proxy for travel volume, now that we’re better at tracking actual carbon emissions, we can try to set targets of keeping under a certain carbon tonne equivalent total instead of (only) a financial target.

Total Carbon Emissions for 2024

Our total reported carbon emissions increased 40% from 105 tCO2e in 2023 to 147 tCO2e in 2024. In 2023, we didn’t report on the estimated emissions from hotel stays, but for 2024, we have. We recorded 415 hotel nights in 2024 for 4 tCO2e using an average of Europe/US hotel per night emissions estimates (Circular Ecology). The most carbon-intensive activity was flying. There were about 215 flights in 2024, accounting for emissions of 138 tCO2e - 93% of our total. Crossref staff and community members we covered took 88 train journeys with carbon emissions of .47 tCO2e - so the more travel by train, the better, but this isn’t always possible or feasible. We haven’t included estimates of the impact of home working (Crossref is fully distributed), but we have an initial estimate below and will look to improve this analysis for the 2025 analysis and going forward.

Estimate of carbon footprint for distributed staff

Crossref is fully distributed with staff in 11 countries. We used Claude from Anthropic to calculate the emissions from home working for our staff in 2024 and asked for sources to be cited. It provided some approaches for how to go about the calculations but the results were not reliable - for our 46 staff in 10 countries (this is for 2024 - we now have 49 staff in 11 countries) estimates ranged from 5 tCO2e to 28 tCO2e depending on various assumptions such as whether to account for the grid intensity of the countries where staff are based (Our World in Data has grid intensity figures) and what estimate is used for the amount of energy an employee working from home uses each day. Circular Ecology uses UK DEFRA figures to come up with 2.67 kgCO2e/day for home working. So a simple calculation of 46 staff working 230 days per year arrives at the 28 tCO2e amount. This is much less than the equivalent figure for office-based work, which is 70 tCO2e. A number of things aren’t factored into these calculations: staff with green energy tariffs, staff with solar panels and home batteries, or other renewable energy sources, and the different needs for heating and air conditioning in different countries.

We decided not to include these figures in our overall emissions for 2024, but we are looking at a more reliable way to estimate this for 2025. However, we need to consider what we would do with the information and whether we would, or could, do anything to reduce this.

Hosting services

We use AWS for hosting our REST APIs, Metadata Search, and the website. In 2024, our main metadata registry was in a data centre in Massachusetts, which is not included in our calculations. In July 2025, we transitioned fully to AWS, so from 2025 onwards, our emissions from AWS will be higher and will encompass our entire system.

In 2023, Amazon reports Crossref’s carbon emissions were 0.216 tCO2e compared with 0.266 tCO2e in 2022. In 2024, emissions were 0.132 tCO2e.

Compared to travel, the footprint from AWS is minimal.

Online meetings

As a distributed, remote-first organisation, Crossref is a heavy Zoom user––it’s essential for staff and for engaging with our community. However, Zoom doesn’t provide tools or estimates of the carbon impact of Zoom meetings. We used a tool last year to provide an estimate, but we aren’t confident it’s accurate or meaningful. The tool was built in 2020 and made a lot of assumptions and guestimates.

Tools we used

To calculate emissions for flights and train journeys, we chose to use Carbon Calculator. For hotel stays and home working estimates, we used Circular Ecology. For AWS, we used the Customer Carbon Footprint Tool (CCFT) provided by AWS.

Offsetting

We don’t offset our emissions from travel or other operations and don’t have plans to do this. Offsetting emissions is problematic in a number of different ways, so we don’t feel confident in doing it.

In conclusion

In general, it feels good to have had a few years of tracking this, learning more, finding the right tools, and trying to stick to a target to limit our increases. While of course there are always reasons for the target to increase—as we grow and are able to subsidise others beyond our staff more—we remain committed to not just monitoring our carbon spend but also maintaining it at a reasonable level and finding ways to limit and mitigate our impact on the environment. This kind of sustainability isn’t included in the POSI Principles for open scholarly infrastructures, but we’d love to see other similar organisations share their tips and measurements so that, as a community, we can learn how to do even better.

Summary of the environmental impact of Crossref

Ed Pentz — Thu, 05 Dec 2024 00:00:00 +0000

In June 2022, we wrote a blog post “Rethinking staff travel, meetings, and events” outlining our new approach to staff travel, meetings, and events with the goal of not going back to ‘normal’ after the pandemic. We took into account three key areas:

The environment and climate change
Inclusion
Work/life balance

We are aware that many of our members are also interested in minimizing their impacts on the environment, and we are overdue for an update on meeting our own commitments, so here goes our summary for the year 2023!

To be honest, the picture is mixed. On the positive side, we are traveling less and differently compared with 2019. Most of our events have been online, with some regional in-person ones, reducing our carbon footprint and increasing inclusivity with more people attending Crossref events. On the negative side, it hasn’t been easy to collect the data and figure out the best tools for calculating emissions, and we certainly haven’t captured all of our carbon emissions. Our approach has been to not let the perfect be the enemy of the good and we’ve focused on our largest source of carbon emissions - air travel.

Some of the positive things:

We have maintained our strategic approach to consider environmental, inclusion, and work/life balance issues when we plan travel and to make the most of in-person events by focusing on those that involve interaction, such as listening and learning from our members and users, deepening relationships, co-creating, and forming new alliances
Crossref Annual Meetings and community updates have been online and in different time zones.
Crossref board meetings have been reduced from three in-person meetings per year to one face-to-face and two online meetings per year.
We had an optional all-staff in-person meeting in June 2023 (and this year too).
For the in-person board and staff meetings, we have selected locations that minimize the overall amount of travel and maximize direct flights.
We have maintained our country focus for in-person local meetings supported by regional Ambassadors.
We met our goal of keeping total travel and meeting expenses below 60% of 2019 costs even though we have more staff and membership growth has continued. The amount of money spent is a rough proxy for our carbon impact.
We no longer have an office in Oxford and will not renew the lease on our Lynnfield, MA office, so we will have no physical offices by the end of 2024. This is not a large carbon emission reduction and is more a result of being a “distributed first” organisation with staff in 11 different countries.
We recorded data on staff travel (flights, trains, cars, hotels) for 2023 to use as a baseline for comparison with future years. In 2023 the carbon emissions from travel and meetings was about 105 tCO2e.
We used tools provided by Amazon Web Services (AWS) and Zoom to estimate the impact of these services. In 2023 this was 0.266 tCO2e for AWS and .1 tCO2e for Zoom.

Some challenges

Compiling data is difficult and time-consuming for a small organisation
There are many different calculators and metrics to use and it’s difficult to decide which to use and how much detail to go into
We haven’t yet estimated the carbon footprint of staff home working
We were able to calculate the emissions from AWS but not our data center
We didn’t estimate the emissions from our offices. We had a small office in Oxford until November 2023, and we have an office near Boston - we won’t be renewing the lease in 2025 so won’t have any offices.

Total travel and meetings spending

Year	Amount	Percentage of 2019
2019 actuals	$585,482	100%
2020 actuals	$91,700	16%
2021 actuals	$19,066	3%
2022 actuals	$74,416	13%
2023 actuals	$305,737	52%
2024 budget	$333,500	56%

We have recorded carbon emissions from travel at about 105 tCO2e, so we will compare 2023 with future years. Now that we have started collecting travel data, it will be easier—staff can do it as they travel throughout the year.

Our Executive Director, Ed Pentz, looked at his personal and work flights and the carbon emissions in 2019 were 18 tCO2e and in 2023 were 2.7 tCO2e so this is a big change in the right direction.

Hosting services

We use AWS for hosting our REST APIs, Crossref Metadata Search, the website, and Labs projects. Our main metadata registry is still in a data center, which is not included in this calculation. For 2023 Amazon reports Crossref’s carbon emissions were 0.216 tCO2e compared with 0.266 tCO2e in 2022. Crossref is planning to move out of the data center and fully to AWS by the end of 2024 so this will increase our AWS usage and therefore our emissions from related activities will increase. Compared to travel, the footprint from AWS is minimal.

Online meetings

As a distributed, remote-first organisation Crossref is a heavy Zoom user –– it’s essential for staff and for engaging with our community. However, Zoom doesn’t provide tools or estimates of the carbon impact of Zoom meetings. We used a tool provided by Utility Bidder, which makes a lot of estimates and assumptions. In 2023 Crossref had almost 800,000 meeting minutes. This translated into an average of 1.92 kg of CO2 emissions per week, or 100 kg per year.

Some studies have estimated that turning off video reduces the carbon footprint of meetings. However, this can be a false savings since video is often important for creating a connection and having a productive meeting, and a Zoom meeting with video is still much, much better than traveling, particularly if flying is involved.

Tools we used

In order to calculate emissions for flights and train journeys, we chose to use Carbon Calculator. We didn’t calculate emissions from hotel stays but looked at the Hotel Footprinting tools and may add hotels to calculations in the future.

Offsetting

We don’t offset our emissions from travel or other operations and don’t have plans to do this. Offsetting emissions is problematic in a number of different ways so we don’t feel confident in doing it.

We did tree-planting as a “thank you” for the time of respondents in our metadata survey. Intended as an alternative to more commercial types of incentives rather than off-setting for our emissions, this resulted in 921 trees planted for the Gewocha Forest, Ethiopia via Ecologi.

Wrapping up

Moving forward, we’ve learned a lot over the last couple of years. Collecting accurate data is challenging and time-consuming, especially for a small organisation. For us, this has been a new lens for viewing our activities, and it remains a true learning journey and we have made permanent changes. In 2024 and beyond we are going to continue to follow our travel, meetings, and events policies that we announced in 2022. We will continue to capture our air travel emissions, and in 2025 we will more accurately capture train journeys and hotel stays. We will also continue calculating our Zoom and AWS emissions as best as we can. What we’ve learnt in the process of capturing and calculating our 2023 emissions helped us set things up to enable more prompt reporting on these impacts in the future.

We expect that many of our members and our community at large assess their environmental impact or are embarking on similar projects, to understand and curb emissions. We’re keen to discuss this and learn together to reduce our environmental impact as an organisation.