Travelling back to normal

One of the possibly unforeseen consequences of the coronavirus disease 2019-related lockdowns and changes in working practices was a reduction in CO2 production. With an average 6.4% (13% in the USA), or 2.4 billion tonnes, reduction in CO2 production in 2020, the virus achieved more in 2 years than humanity has in a quarter of a century (Friedlingstein et al., 2020). The sector most affected by the lockdowns was air travel, where CO2 emissions fell by 48% from their 2019 total (https://www.nature.com/articles/d41586-021-00090-3). However, the rebound was fast and furious; carbon emissions from burning fossil fuels rose by 4.9% to 36.4 billion tonnes a year in 2021 compared with 2020 (https://www.nature.com/articles/d41586-021-03036-x). As life returns to ‘normal’ and people start travelling to work, meetings and conferences, the expectation is that the carbon cost of transport will continue to increase. In The Physiological Society booklet Physiology and Climate Change (https://static.physoc.org/app/uploads/2021/11/01082431/Physiology-and-Climate-Change-October-2021_WEB.pdf), we suggest some actions people can take to reduce their carbon footprint. In an extension of this, we present in Table 1 the carbon costs of different forms of transport to help enable informed decisions about how, and if, to get from A to B as restrictions are removed. Unusually, we have included the carbon production (in grams per kilometre) associated with human self-propelled activities for information and as a comparator. These data are seldom reported in this form. In order to put these data into some kind of context, 1 kg of CO2 is ∼545 L (depending on temperature and humidity). One-fifth of that (nearly 110 L) will still be warming our planet in 33,000 years’ time, and 7% (38 L) 100,000 years from now. From Table 1, we see the data for CO2 production on long-haul flights. An estimation of CO2 production can also be obtained from fuel usage. A Boeing 747-400 travelling from London to New York (5556 km) with 80% occupancy (333 passengers), uses about 59,600 kg of fuel. The CO2 emission from aviation fuel is 3.15 kg per kg of fuel. This equates to about 187,740 kg or around 102,032,609 L of CO2. This CO2 is primarily emitted into the high atmosphere, where it is thought to have a greater greenhouse effect (two-fold) than CO2 released at sea level (https://www.carbonindependent.org/22.html). There are 15 companies offering ≤17 daily flights on this route alone. Incidentally, assuming all the passengers are resting, and a flight time of 8 h, adds another 82 kg (47,734 L, 0.38 g min−1) of human CO2 production. However, we ignore this as a contribution because it would be produced in all situations if alive. [Correction made on 1 May 2022, after first online publication: This paragraph has been updated to provide greater clarity on CO2 produced during a long-haul flight from London to New York.] As decisions are made about the future of meetings and conferences, it would be counter-intuitive, not to say hypocritical, for those concerned about human health and the immediate and grave threat posed by climate change not to consider how they organize meetings (of all sizes) and how they attend them. As part of this consideration, it is worth noting that whilst being regarded as a green alternative to in-person meetings, virtual meetings are not without costs in terms of the climate. It has been calculated (https://www.zdnet.com/article/how-much-co2-are-your-zoom-meetings-generating/) that the costs of such meetings (network operation, videoconferencing equipment use, maintenance and replacement, video quality and number of people at the meeting) are at most 7% of the energy/carbon footprint of in-person meetings. For example, the technology used by two people on an HD Zoom call for 1 h will generate ∼0.0037 kg of CO2. A weekly meeting with six participants, watching in HD 1080p for 1 h, releases 0.05 kg of CO2 or ≤2.6 kg over a year (https://www.zdnet.com/article/how-much-co2-are-your-zoom-meetings-generating/; https://gerrymcgovern.com/the-hidden-pollution-cost-of-online-meetings/). Replacing a video call with an email saves energy, and the extent of this can be calculated (https://www.utilitybidder.co.uk/business-electricity/zoom-emissions/). Of course, switching to a 100% renewable electricity supplier helps, and ‘green Internet service providers’ are also available. For information, a tree can draw down 10–40 kg of CO2 a year when mature, but perhaps only 5.9 kg while growing (https://ecotree.green/en/how-much-co2-does-a-tree-absorb). Finally, when organizing an in-person meeting, there are lots of things that can be done to minimize the damage to the climate associated with that meeting, from venue choice to the food and drink provided. This topic warrants separate consideration. There is no doubt that in-person meetings and conferences offer benefits not available by other means. Let us also not forget the negative impacts on mental and physical health of social isolation and sedentary lives and the carbon costs of health care when one is ill, while remembering the positive impacts that physical activity brings. Walking or cycling to a meeting has advantages too. Our aim in producing this short editorial is to help people calculate the cost/benefit of the type of meeting they run, how people travel to or attend such meetings, and the number of people who go. Just to be clear, the ‘cost’ here is defined in terms of the survival of our species and others; hence, worth a moment's thought. Many thanks to Dr Jo Corbett and Prof Jim Cotter for their input. None declared.