##  1 Mobility

Mobility constitutes a significant portion of the emissions of a hecap
researcher. This includes short daily commutes between the home and the
workplace, and longer-distance business travel (see fig:Intro-
ComparativeEmissions).

Transport accounted for almost a fifth of total global emissions in 2016
[OWIDsector], and is the sector that saw the highest growth in pre-COVID years
[SLOCAT]. Demand for car, rail and air transport is expected to continue to
increase over time with increasing global population and income levels.

Unsurprisingly, self-powered mobility, such as walking and cycling, are the
most carbon-efficient means of transportation, with train travel being the
next best. A quantitative comparison between these and other options requires
further details to be specified, such as the distance travelled, the fuel
efficiency of the vehicle used and the number of passengers carried, and the
underlying electricity mix for the country of travel. In the UK, for instance,
driving alone in a medium-sized petrol-fuelled car yields smaller ghg
emissions than air travel for distances shorter than 1,000 km, whereas flying
in economy class beats driving over longer distances [OWIDtravel] (data taken
from Ref. [BEIS]).111These estimates include a “radiative forcing” factor of
1.9 for air travel, which accounts for a larger warming effect due to
aeroplanes emitting GHGs high in the atmosphere. For a detailed comparison of
emissions due to various forms of transport within France, see
fig:emiMobility.

When and how we travel, however, are not always free choices, being
constrained by existing transport infrastructure, local geography, our
research, finances, and caring responsibilities. Universities and
institutions, with their large and progressive workforce, can help tip the
balance in favour of the more environmentally sustainable option with a
judicious combination of policy, incentives, on-site infrastructure and
advocacy.

Our current societal infrastructure is set up to facilitate individual travel
by car, to the detriment of a large part of the population. Universities, as
large employers with a relatively progressive workforce, have the potential to
act as instigators of change in this. Making public transport and cycling the
preferred options when possible will increase demand for these more
sustainable forms of transport and thus encourage cities to improve the
infrastructure for them.

Nevertheless, efforts to limit emissions resulting from travel must be
balanced against legitimate needs for mobility: the establishing and
maintenance of close collaborative relationships, sharing of research outputs,
individual exposure and career development, and travel to research facilities.
Changes to our travel culture and policies must be implemented so as to
benefit and, at the very least, not to worsen barriers to inclusion, by
avoiding the disenfranchisement of members of our community such as early-
career researchers, members of our community from the Global South or those
otherwise geographically isolated.

  * [leftmargin=6 mm]

  * •

Re-assess business travel needs, using remote technologies wherever
practicable.

  * •

Choose environmentally sustainable means of transport for daily commutes as
well as unavoidable business travel, amalgamating long-distance trips where
possible.

  * [leftmargin=6 mm]

  * •

Define mobility requirements and travel policies that minimise emissions,
while accounting for the differing needs of particular groups, such as early-
career researchers or those who are geographically isolated.

  * •

Re-assess needs for in-person meetings, and prioritise formats that minimise
travel emissions and diversify participation by making use of hybrid, virtual
or local hub participation, and optimising the meeting location(s).

  * [leftmargin=6 mm]

  * •

Support environmentally sustainable commuting by improving on-site bicycle
infrastructure, subsidising public transport and providing shuttle services.

  * •

Disincentivise car travel where viable alternatives exist, facilitate car
pooling, and provide on-site charging stations.

  * •

Incentivise the reduction of business travel, e.g., by implementing carbon
budgets with appropriate concessions.

  * •

Ensure unavoidable travel is made via environmentally sustainable means
through flexible travel policies and budgets, and the use of travel agents
that offer multi-modal itineraries. Employ carbon offsetting only as a last
resort.

  * •

Remove any requirement on past mobility as an indication of quality in hiring
decisions.

  * •

Lobby for improved and environmentally sustainable local and regional
transport infrastructure.

###  1.1 Commuting

Changes in commuting patterns are typically affected by life circumstances,
including changes in education, employment and residence [BEIGE2017179]. The
viability of environmentally sustainable mobility, like walking, cycling and
taking the train, depends crucially on characteristics of the home and
workplace locations, including the distance between them, and their local
environment. These properties are seen to influence the relative importance of
commuting and business emissions for different institutions.

For example, cern, fnal, and the Department of Physics at eth have wildly
different emission profiles due to personal transportation. While emissions
due to commuting were roughly equal to those for business travel at FNAL,
commuting outweighed business travel for CERN, and conversely, business travel
swamped commuting emissions for ETHZ. This reflects the unique environment and
characteristics of each these research centres:

  * •

ETHZ is located in an urban centre and is well connected to the local public
transport. In 2008, only 1,700 tco2e were recorded for commuting, with 7.5 to
10 times larger emissions attributable to business travel (using numbers from
2006–2012). It is clear here that the emissions per capita for all staff
(including researchers) are significantly smaller than those for FNAL or CERN.

  * •

FNAL and CERN have more rural settings, with a 77% majority of CERN employees
commuting by car from France. FNAL’s commuter emissions [FermilabEnvReport] of
about 6,000 are approximately on par with business travel emissions,222In a
typical year, FNAL’s approximately 1,900 staff members commute an average
distance of 15.6 miles each way mostly by car. This translates into 5,987
tonnes of when assuming 250 working days per years and using 404 g of per mile
as per US Environmental Protection Agency [USEPA]. This is only 5% less than
FNAL’s emissions from air travel, calculated from 8.2 million (or 42%) fewer
miles flown in 2020 using 200 g per air km [RefAGU]. whilst CERN quotes 5,836
of commuter emissions compared to 3,330 business travel emissions for its
approximate 4,000 staff members. The small amount of travel emissions compared
to emissions from commuting reflects to some extent the status of CERN as a
scientific centre, to which other members of the community are expected to
travel and where travel is easier to avoid, also because the experiments are
located at CERN.

Whilst ETHZ, FNAL and CERN face different boundary conditions, all three of
them, and institutions in general, should aim to reduce emissions from
commuting, even if these contribute to their overall budget to a different
degree.

This reduction requires an interplay of institutional and individual actions:
while institutions cannot force employees to choose more environmentally
sustainable commuting habits, they can incentivise them through various
measures, from the availability of bicycle-friendly infrastructure, such as
showers and secured/covered parking, to financial incentives for greener
transportation. They can also allow employees to avoid long commutes by
formalising telecommuting options, which have become more normalised since the
start of the COVID-19 pandemic, and use their standing to push local
authorities towards better public transit/cycling/carpool infrastructure.
Individuals and groups can, on the other hand, push for these actions at the
institutional level. Table 1 collects some means by which ETHZ, FNAL and other
academic and institutes promote ‘green’ transport. An estimate of the
emissions per distance of different forms of transport in France is presented
in fig:emiMobility.

1.05

Table 1: Institutional/country-wide measures to encourage sustainable
commuting amongst employees. This is a non-exhaustive list; similar
initiatives are also offered by other employers.

Institute | Initiative | Comments
---|---|---
DESY | Reduced-price ticket for public transport for all employees |  The non-transferable ticket, with a 30% subsidy for employees, is also usable outside working hours, and allows free network-wide travel for an additional adult and up to 3 children (age 14 and under) on weekends and holidays. This requires a subscription of more than 6 months. Once suspended, a cooling-off period of 9 months is required to be eligible for re-subscription. This is problematic if the employee is posted abroad for a few months. With the implementation of the ”Deutschlandticket” in Germany, the terms have slightly changed [DESYsustainableReport2022, hvvJobticket1, hvvJobticket2].
FNAL | Shuttle service to and from Chicago Metra trains for all employees |  There are two scheduled connections in the morning and three in the afternoon, on demand at other times, from 06:30 to 18:50. A ticket costs $2.25 (cash only), payable to the bus driver [FNALPace]. The regular shuttle does not connect to the Metra station serving the fast train to Chicago (Route 59); FNAL do not offer pre-tax public transport ticket purchase.
France |  Public transit subsidy [transitFR] or 300/year for all employees who cycle or carpool [mobdouceFR] |  Honours system for the 300/year. The adoption of the roughly 50 % reimbursement on public transport subscription depends on how well connected each institute is.
Germany | General tax reimbursement for commuting depending on distance |  For each km travelled to work, 0.30 is deducted from the taxable income (0.38 per km above 21 km per one way starting from 2022) [GermanyTax]. While this was originally thought to cover the expenses of private cars, it now applies to all means of transport, so that also cyclists or pedestrians obtain the same financial advantage even if they have no direct costs.
University of Sheffield | Bike to work scheme for all employees |  There is the possibility to borrow an e-bike (or a bike) for free for 2 months in order to test commuting by bike, to rent bikes throughout the semester and to buy reconditioned bikes. Over 1,400 cycle parking spaces are available throughout campus and at the residences. Services are provided for free bike checks and at-cost servicing and repairs for staff and students funded by the university. (All UK universities.) Financial help is available to buy an e-bike. (However, this is based on reducing the university’s financial contribution to the pension scheme over a set amount of time.) [shefbike]

Figure 1: GHG emissions for different means of transport (in g per km).
Emissions from electricity and vehicle production as well as fuel combustion
are included. All data is for 2019–2020, and comes from the database of Ref.
[labos1p5] — see, in particular, Ref. [labos1p5emi] — and assumes the
electricity comes from the French grid, which is a factor of 10 less carbon-
intensive than other countries [OWDintensity]. For a comparison with the UK,
see Ref. [OWIDtravel]. Note that emissions from personal transport do not
scale linearly with number of passengers.

###  1.2 Business Travel

A global scientific endeavour such as will mandate some amount of long-
distance travel, e.g., to experimental sites, or to build close working
relationships. However, the current academic culture, which rewards hyper-
mobility, is neither environmentally sustainable, nor equitable to all
scientists. Visa rules and prohibitive long-haul travel costs can make
participation in conferences extremely challenging, especially for researchers
from the Global South. Moreover, the freedom to travel can be heavily
restricted for people with disabilities, health impairments or caring
responsibilities. For example, the burden of childcare is still unequally
distributed, and this burden falls predominately on female shoulders
[McCarthy].

Emissions from commercial aviation is a long-recognised problem, contributing
2.5% of emissions and 3.5% of ‘effective radiative forcing’ (a closer measure
of aviation’s impact on warming as explained in footnote 1) [Rit20] in 2018.
Note that the majority of these emissions derive from the one-tenth of the
world’s population that can afford air travel. Almost all scientists belong to
the 4% of the population taking international flights, and many fall within
the 1% classified as the most frequent flyers [GOSSLING2020102194]. These
statistics highlight the inequalities inherent in travel emissions.

More troubling is that global aviation statistics belie the significance of
business travel emissions for many researchers, which are comparable to, and
in some cases even dwarf, their direct and indirect emissions (see fig:Intro-
ComparativeEmissions). This is clearly in tension with the push to net-zero
emissions, particularly given that we do not expect the aviation sector to
decarbonise at the same rate as the rest of the transport sector [Gota2019,
Science18].

Emissions related to conference travel have been studied in detail and
dominate conference-related emissions [Spinellis, nature_better_confs],
contributing annual emissions 30% larger than the total annual transportation
emissions for Geneva (720 kilotonnes [Geneve]). However, the emissions for a
single conference trip amount to about 7% of an average individual’s total
emissions [Spinellis]. This might be even worse for researchers, for whom
frequent trips to experimental sites and meeting venues to undertake
international collaborations are common. See also emissions estimates for
business travel of members of the LHCb experiment at CERN in case:LHCb.

Discussions about reducing business travel are highly charged, as active
engagement with other members of the scientific community is integral to
scientific practice. Any changes that we make to travel culture have to be
considered in the context of other aspects of our working practices, such as
hiring decisions, where any curbs on travel may, disproportionately impact
early-career researchers. At the same time, the reprioritisation of business
travel and a move toward a greater share of virtual/hybrid formats can have a
positive impact both on the climate and on inclusivity.

For necessary travel, sustainable alternatives to air travel should be
prioritised where possible, keeping in mind that the increased travel time and
costs of sustainable travel as compared with air travel could make this choice
difficult for researchers with caregiving responsibilities, or limited travel
budgets. In case:traveltoCERN, we compare emissions, travel time and cost of
different modes of travel to CERN, from various starting points within Europe,
for CMS Week in January 2022. institutions and funding bodies are beginning to
implement more sustainable travel policies, including travel top-ups for green
travel; we highlight two examples in bp:Erasmus and bp:DESY_travel.

If the community is to rethink this travel culture and move toward more
hybrid/virtual modes of engagement, we must recognise that these require
additional planning to maximise engagement, which amounts to much more than
streaming the in-person event format (see cs:CfH). It is also important to
appreciate that virtual participation requires an internet-ready device and
stable connection, and devices with which to connect, which may not be
universally available in lower-income countries. A possible remedy for this
might be the concept of hub conferences, where the conference has several
locations spread globally (see, Ref. [Parncutt]). In case:ICHEP, we study
travel emissions and participation in the context of the last 5 instances of
the International Conference for High Energy Physics (ICHEP) conference, and
assess the reduction in emissions from optimising the conference location,
moving to a hub model, or hybrid/virtual forms of attendance.

[Sustainable travel to CERN]Sustainable travel to CERNThe itineraries in
tab:CERNtravel were found for travel to cern for, e.g., CMS Week,
24${}^{\text}{th}$–28${}^{\text}{th}$ January 2022, as found on
30${}^{\text}{th}$ November 2021333Prices and carbon footprint rounded to
nearest whole number. For prices not given in euros, currency conversions were
made using Google currency converter. Carbon footprints for one-way travel
were calculated using Ref. [ecopassenger] and then doubled, using all default
assumptions, except for toggling on the climate factor for flights. Precise
departure and arrival information was not used for calculation of the flight
footprint. Since some airports are not included as possible destinations, the
footprint was calculated from the central train station in the origin city to
the central train station in the destination city, and the footprint of travel
to the airport is assumed negligible (in comparison to the flight). Train
fares quoted are for the most convenient train journeys from the central
station in the origin city to the central station at the destination. For
longer journeys, preference was given to itineraries with overnight trains to
maximise efficiency per euro spent, assuming savings on an additional night in
a hotel. For all overnight trains, quoted prices include reservation in shared
sleeper cabin. Female-only occupancy can be specified. Note that in many cases
there may be a limited number of ‘super saver’ tickets that are available for
purchase ahead of time. Air fares were for the ‘best’ option available on
Skyscanner [skyscanner], with the inbound flight arriving in time for an
assumed midday start of meetings at CERN, and the outbound flight departing
after 15:00 hours on Friday. Flight prices were taken directly from the
airline where possible, and include a standard-sized cabin bag, but not
necessarily a checked bag. Durations include flight time only and do not
include airport check-in times.. Although emissions were significantly smaller
for rail travel as compared with travel by car or air, as expected, this must
be weighed against the increased travel time, and in many cases, cost of rail
travel. Note that the air travel times are underestimated as they do not
include travel to the airports, which are usually distant from the city
centres, or the usual buffer time required for check-in and security
formalities. For itineraries that include sleeper trains, the additional cost
of the train could offset a night’s hotel accommodation at origin or
destination.

1.05 = =0pt =0pt type=table

gray!20Distance |  gray!20Origin |  gray!20Mode of Transport |  gray!20Travel time (one way) |  gray!20Itinerary |  gray!20Price (EUR) |  gray!20Emissions (kg )
---|---|---|---|---|---|---
1-7 $<600$ km |  Paris |  Pythongreen!30Train |  Pythongreen!303h15 |  Pythongreen!30Out: Mon 24th 08:18–11:29 In: Fri 28th 14:29–17:42 |  Pythongreen!30178 |  Pythongreen!3025
3-7 |  |  Flight ORY–GVA |  $\sim$1 hr |  Out: Mon 24th 08:20–09:25 In: Fri 28th 19:05–20:15 |  98 |  235
3-7 |  |  Car |  5h42 |  |  |  116
1-7 $>600$ km |  gray!10Hamburg |  Pythongreen!30Train (2 changes) |  Pythongreen!30$\sim$13.5 hrs |  Pythongreen!30Out: Sun 23rd 20:50–10:18 (+1 day) In: Fri 28th 18:15–07:54 (+1 day) |  Pythongreen!30258 |  Pythongreen!30 46
3-7 |  gray!10 |  gray!10Flight HAM–GVA (1 change) |  gray!10$\sim$3 hrs |  gray!10Out: Mon 24th 07:00–10:10 In: Fri 28th 19:10–22:35 |  gray!10261 |  gray!10497
3-7 |  gray!10 |  gray!10Car |  gray!109h50 |  gray!10 |  gray!10 |  gray!10 225
2-7 |  London |  Pythongreen!30Train (2 changes out; 1 change in) |  Pythongreen!30$\sim$8 hrs |  Pythongreen!30Out: Sun 23rd 15:31–23:29 In: Fri 28th 15:30–22:30 |  Pythongreen!30288 |  Pythongreen!30 25
3-7 |  |  Flight LTN–GVA |  1h40 |  Out: Mon 24th 08:00–10:45 In: Fri 28th 21:40–22:20 |  80 |  402
3-7 |  |  Car |  8h32 |  |  |  196
2-7 |  gray!10 Rome |  Pythongreen!30Train (1 change) |  Pythongreen!30$\sim$8.5 hrs |  Pythongreen!30Out: Sun 23rd 15:25–23:54 In: Friday 28th 13:39–21:40 |  Pythongreen!30238 |  Pythongreen!30 70
3-7 |  gray!10 |  gray!10Flight FCO–GVA |  gray!101h30 |  gray!10Out: Mon 24th 09:00–10:30 In: Friday 28th 18:45–20:20 |  gray!1077 |  gray!10392
3-7 |  gray!10 |  gray!10Car |  gray!10$\sim$8 hrs |  gray!10 |  gray!10 |  gray!10183
2-7 |  Barcelona |  Pythongreen!30Train |  Pythongreen!307-8 hrs |  Pythongreen!30Out: Sun 23rd 08:15–16:35 In: Fri 28th 12:35–19:32 |  Pythongreen!30147 |  Pythongreen!3018
3-7 |  |  Flight BCN–GVA |  $\sim$1.5 hrs |  Out: Mon 24th 08:40–10:20 In: Fri 28th 17:00–18:25 |  83 |  370
3-7 |  |  Car |  7 hrs |  |  |  164
1-7 $>1,200$ km |  gray!10Warsaw |  Pythongreen!30Train (2 changes) |  Pythongreen!3022.5–24.5 hrs |  Pythongreen!30Out: Sat 22nd 19:49–18:18 (+1 day) In: Fri 28th 18:42–19:15 (+1 day) |  Pythongreen!30319 |  Pythongreen!30 176
3-7 |  gray!10 |  gray!10Flight WAW–GVA |  gray!102h20 |  gray!10Out: Mon 24th 07:20–09:40 In: Fri 28th 19:45–21:55 |  gray!10185 |  gray!10531
3-7 |  gray!10 |  gray!10Car |  gray!1012.5 hrs |  gray!10 |  gray!10 |  gray!10398
|  |  |  |  |  |

Comparison of modes of travel to CERN from different origins. The mode giving
rise to the lowest emissions for each origin is highlighted in green.

[Comparative study of travel emissions for ICHEP conferences
(2012–2020)]Comparative travel emissions for ICHEP conferencesBased on the
study of the annual meetings of the American Geophysical Union (AGU) in Ref.
[RefAGU], and the methodology and software tools employed therein, we
undertake a survey of the past five editions of the ICHEP with the aim of
assessing the ghg emissions of conference travel to ICHEP, as well as the
(geographical) diversity of participants.

The International Conference for High Energy Physics (ICHEP) is a biannual
conference with a large and steadily growing participation, of order 1,000
researchers, and a location that alternates mainly between Europe, America and
Asia. We study the 5 most recent instances, with locations in Melbourne,
Australia (2012); Valencia, Spain (2014); Chicago, United States (2016);
Seoul, Korea (2018); and Prague, Czech Republic (2020, fully virtual).444At
the time of writing, the 2022 conference, held in Bologna, had not yet begun.

#### Methodology

Participant details were taken from the Indico conference system registration
pages [indico]. The departure location for each participant was assumed to be
the city of their affiliation, save for cases where it was clear that the
participant was based in Geneva, as is often the case for members of lhc
collaborations. Direct travel to and from the conference was assumed.
Distances were calculated as the great-circle distance using coordinates
obtained with Nominatim from the OpenStreet Map data base. Rail, car or bus
travel was assumed for all journeys with distances of less than 400 km, with
air travel assumed for longer distances. ‘Short-haul’ was defined as travel
distances of less than 1,500 km; distances up to 8,000 km are ‘long-haul’; and
longer distance still were classified as ‘super long-haul’.

1.1 type=table  AGU Fall Meeting 2019 ICHEP Melbourne 2012 ICHEP Valencia 2014
ICHEP Chicago 2016 ICHEP Seoul 2018 ICHEP Prague 2020 (virtual) 2-7 Number of
participants 24,009 764 966 1,120 1,178 2,877 GHG emissions per participant
[kg ] 2,883 8,432 1,902 2,699 2,648 0 Total number of participants of recent
ICHEP conferences and the GHG emissions per participant. The corresponding
numbers for the American Geophysical Union (AGU) Fall Meeting [RefAGU] are
shown for reference.

Table 1.2 shows the average GHG emissions per participant for the ICHEP
editions alongside those for the 2019 AGU Fall Meeting for reference. With the
exception of the 2012 Melbourne edition of ICHEP, the per-capita emissions
were significantly lower for ICHEP, which is a “travelling” conference, as
compared with the stationary AGU Meeting, which always takes place in San
Francisco. This indicates that moving a conference series between continents
naturally reduces the travel-related emissions as participants tend to wait
for the conference to be held near them to make the trip. Comparing the
geographical distribution of home institutes for each conference reinforces
this conclusion. Note that ICHEP Melbourne (2012) was the first and only ICHEP
conference taking place in Oceania.

The emissions for two typical ICHEP conferences, one in Europe (Valencia) and
one in Asia (Seoul) are displayed as a function of travel distance in
fig:EmmPerDistance. A large fraction of attendees at the Seoul conference had
to fly super long-haul, giving rise to the majority of the emissions.
Emissions for the remaining half of the attendees was nearly negligible. This
was not the case for Valencia, where as many attendees travelled short haul or
less. It is also clear that the bulk of the emissions is due to long-haul or
super long-haul air travel.

type=figure

Emissions per distance for ICHEP Valencia and ICHEP Seoul shown in (left axis)
and as share of the total emissions. Additionally, the emissions caused by the
17% and 36% of participants travelling furthest are shaded in green.

Reference [RefAGU] investigated possible optimisations of the conference
location for the given participant distribution in order to reduce
emissions.555Optimisations were carried out with a grid spacing, and hence
resolution, of 1 degree longitude and latitude Note that this is a slightly
artificial construction because of the basin of attraction phenomenon
discussed above, where participant distribution is self-selecting, based on
the conference location. Unlike the AGU example, where moving the conference
location to the middle of the country, rather than on a coast, significantly
decreased the travel-related emissions, we found that the ICHEP locations were
already pre-optimised, and further optimisation yielded at most a 10.2%
reduction of GHG emissions. (The real outlier again was Melbourne, where the
majority of participants had to fly super long-haul, and for which a 70.7%
reduction would be achievable given the same participants by changing the
location). If the location was optimised using participants from all 5 ICHEPs,
the optimal location would be close to Amsterdam.

Further emissions reductions are only possible with a hub-based conference,
and mandatory virtual participation above a certain distance from the hubs.
Reference [RefAGU] trialled hubs in Chicago, Seoul and Paris, with virtual
attendance for all participants with origins greater than 2,000 km from the
hubs. Having found that Chicago, Seoul and Paris were not far from the optimal
locations for the respective ICHEP conferences, we did the same, for the total
ICHEP participation over the 5 conferences. Simply using a 3-hub model can
reduce the carbon footprint of the conference to around 15–35% of a
traditional one. Adding compulsory virtual participation for more distant
participants reduces the carbon footprint further by 5–15% of a traditional
conference with 10–25% of the participants attending virtually. As a test
case, and without any prior optimization, we chose Rio de Janeiro,
Johannesburg, and Kolkata as alternative hubs. This, however, increased
virtual participation to 95%¸ mainly due to the strong European participation
in hep and the remoteness of Johannesburg from Western Europe. Switching Paris
for Johannesburg reduced the footprint to about 10% of the nominal one, with
40% of participants attending virtually. While the virtual fraction is still
relatively high, it might be acceptable in a bid to include more remote HEP
communities (like Melbourne), while keeping the emissions low.

Finally, one might expect a fully virtual conference to be more inclusive than
in-person ones, especially for underserved participants, such as those with
care-giving responsibilities, limited travel funding, or visa problems. We
studied this by classifying participants by the human development index (HDI)
[hdiref] of their country of affiliation, and dividing them into four
categories (low, medium, high and very high HDI).666Examples of countries with
very high HDI are Norway, Malaysia, Kuwait and Serbia, high HDI are, Trinidad
and Tobago, Albania, Egypt and Vietnam. Medium HDI countries include Morocco
and Pakistan, while low HDI countries are Nigeria, Chad and Niger. A brief
overview of the categories can be found in Ref. [hdiref]. The share of
participants in these categories for each of the ICHEP conferences is shown in
fig:DevelopmentIndex. Indeed, in addition to enjoying the largest number of
participants (by a factor of 2), the virtual ICHEP in Prague had the largest
proportion of participants from countries with high or medium human
development index, although it was not clear how much of this increase was due
to its virtual nature, as opposed to a steady increase in physics
participation from high and medium-HDI countries. There was virtually no
participation from low HDI countries in any of the ICHEP conferences studied.

type=figure  The fraction of participants, categorised by human development
index (HDI) [hdiref] attending the last 5 instances of ICHEP.

[Green travel top-ups on Erasmus+]Green travel top-ups on Erasmus+The EU
mobility and training programme Erasmus+ has implemented funding top-ups for
environmentally sustainable travel, which is more costly than point-to-point
air travel in many instances, in particular between hubs for low-cost
airlines. See tab:ErasmusGreenSupplement for exact supplements for
participants who receive travel funding, as excerpted from the 2022 programme
guide [Erasmus+]. Green travel over large distances can be more time-
consuming. The programme allows for this by providing travel support for an
additional 4 days of travel.

1.05 type=table

Travel distance
(km) |  Standard travel
(/participant) |  Green travel
(/participant)
---|---|---
10–99 |  23 |
100–499 |  180 |  210
500–1,999 |  275 |  320
2,000–2,999 |  360 |  410
3,000–3,999 |  530 |  610
4,000–7,999 |  820 |
¿ 8,000 |  1,500 |
|  |

Green travel supplements for Erasmus+ participants [Erasmus+].

[Internal regulations to reduce the impact of business travel at DESY
[DESYsustainableReport2022, privateKSchulz]]DESY sustainable travel
regulationsThe regulations at desy have been based on the goal of preserving
the excellence of science and career opportunities while reacting to the
necessity to save  and other emissions. With its directive for business trips
adopted in 2021, DESY relies on the climate policy principle: Avoid — Reduce —
Compensate.

Avoid: The number of business trips will be reduced by 30% compared to the
situation before the start of the COVID-19 pandemic. This means that all
travel planning is reviewed to identify whether the trip is needed to achieve
the intended purpose, whether a virtual meeting could be just as beneficial,
whether rotational changes between presence and digital are possible, and
whether and how appointments can be bundled. In addition to  savings and
travel time, it should also be considered how much of the time spent traveling
and for travel planning can actually be used as working time, and what costs
are incurred or saved. Ultimately, digital meetings also contribute to a
better flexibility between personal and work life. They also reduce travel-
related risks.

Reduce: For some time now, it has already been possible to use the train
instead of the plane, even if the costs were higher. With the new directive,
the use of the train is now mandatory if the destination can be reached within
six hours total travel time. It should also be noted that the usable working
time during the trip for rail travel is given as at least 50% of the travel
time (depending on the transfer frequency) and for flying it is assumed to be
about 25% of the travel time.

Compensate: Until recently, compensation was not possible under the Federal
Travel Expenses Act. However, since September 2020, there is a new regulation
on the reimbursement policy for carbon offsets from the German ministry of
science, whereby also grant recipients like DESY are allowed to offset their
emissions for business trips. Starting in 2021, DESY will compensate the
consequences of unavoidable air travel. There are established systems through
which the climate-damaging effects of travel can be offset. The money goes to
climate protection projects, including energy efficiency, biogas or biomass,
solar energy, and environmental education. The selection of the compensation
projects can be steered by DESY.

[Cosmology from Home This case study is, in part, adapted from the Cosmology
from Home website [CfHwebsite].]Cosmology from HomeCosmology from Home (CFH)
[CfHwebsite] is an “online by design” conference series that has been run on a
yearly basis since 2020. It exploits the advantages of digital communication
to accomplish things that have no analogue in traditional conference formats,
while staying true to the dynamic and social nature of traditional
conferences.

CfH is spread over two weeks, with two days per week dedicated to plenary and
parallel talks. Talks are pre-recorded and shared with the conference
participants ahead of the start of the conference. Other than a strict time
limit, CfH places few constraints on the format of the talks. Participants are
expected to watch the talks before the scheduled online discussion events. The
scheduled discussions last a maximum of three hours per day to mitigate online
fatigue, but multiple sessions can be scheduled to accommodate different time
zones.

Other days are reserved for themed discussions, which are proposed by the
participants. Topics have included content related directly to cosmology, to
scientific research more generally (i.e., technical or computational aspects),
and social aspects, such as inclusivity and outreach in science.

The live discussions are hosted in virtual conference venue spaces to create a
social atmosphere in which participants can wander around and join
conversations. Suitable conference spaces are, Sococo [Sococo], Welo [Welo]
and Gather [Gather]. In case the number of participants is such that the
conference spaces are too small to host everyone at once, break-out rooms of a
suitable video-conferencing platform can be used. In the specific case of CfH
so far, this has been Zoom [Zoom].

CfH is coordinated asynchronously through an online message board, and a large
part of the conference is dedicated to asynchronous text-based discussions.
These discussions can start before the official opening of the conference and
continue long after the conference has finished. In previous years, CfH used
Slack [Slack]. (Alternatives include MatterMost [MatterMost], Zulip [Zulip],
Microsoft Teams [Teams] or Discord [Discord].) Discussion channels are grouped
according to the scheduled live-talk discussion sessions (see below).
Participants can discuss points in dedicated threads in these channels. Once a
given discussion has grown sufficiently and has branched out into different
sub-discussions, it can be given its own dedicated channel.

In addition to scheduled talk discussions, CfH implements scheduled themed
discussions. These are moderated, workshop-style discussions on cosmological
themes that are of interest to the conference participants. The topics are
suggested, voted on and chosen via the Slack workspace. People can connect to
the session via the conference space, but the main session is hosted in Zoom
break-out rooms.

The final live discussion format featured by CfH is composed of spontaneous
and unscheduled777“Unscheduled” means that the discussions are not part of the
conference program. The participants can and do schedule these discussions on
the asynchronous platform. “informal” live discussions. The time allocated to
the scheduled live discussions is limited. The informal, breakaway sessions
allow the participants to engage in more detailed explorations of the topics
brought up by the live and asynchronous discussions.

The final live component of CfH consists of social events and interaction
formats, such as social games and casual get-togethers, which complement the
scientific discussion sessions on all days of the conference. These activities
aim to reproduce (at least partially) the evening interactions of in-person
conference social events.

One of the main advantages of the CfH format is that, compared to an in-person
conference, a much longer time can be spent debating the talks of the
participants. This allows for a much greater dissemination and understanding
of the research that is presented. Additionally, it removes the need for
travel. This keeps the participation costs low and offers the potential for
the conference to be carbon neutral or carbon negative (achieved, at present,
through carbon offsetting of residual emissions). The online format also makes
the conference accessible to researchers from all over the world, subject to
the availability of a suitable device and a stable internet connection by
which to connect. The geographical distribution of participants in the
previous three CfH conferences are shown in fig:CfH1.

type=figure  Geographical distribution of Cosmology from Home participants for
each of the installments by year.

Additionally, participants can watch the talks according to their own
schedules and personal obligations. Participants are able to pause and restart
the talks, take time to digest them and to look up background material. They
are also able to prepare and raise points for discussion in any of the
conference environments. The asynchronous discussions can be tailored exactly
to the schedule of the conference participants.

In the first CfH (2020), participants needed time to adjust to the format.
This was to be expected, and the organisers actively encouraged participants
to partake of the various aspects of the conference and actively modelled the
expected social norms. The activity and enthusiasm of participation increased
year on year. Speakers created innovative and accessible talk records, and
participants regularly referred to these in the live and text-based
discussions. Participants organised watch parties and impromptu discussions,
made use of the various breakout rooms, and gathered in the virtual
environments. The themed discussions proved to be particularly popular, and
parallel sessions were often necessary to accommodate the high number of topic
suggestions.

All participant feedback has been constructive and positive, and CfH has been
well attended. The number of CfH participants were 255, 427 and 275 in 2020,
2021 and 2022, respectively [CfHwebsite]. The format is easily tailored to
various topics: a conference featuring this format in HEP is expected to be
run in late 2023.