With passengers numbers massively down, and likely to be permanently affected by the "Zoom revolution" driven by lockdown, any planned expansion of the airport, making the Western Access rail scheme essential/highly desirable/politically necessary, looks a loooong way off.
Indeed, however with a limited range of options to reduce carbon in the actual flying element (and many of the greenest at least a decade away) flying may look at ways of reducing the non flying carbon emissions. That may include making it easier for people to get to the airport by public transport.
As the big emissions for lots of companies will still be staff travel, so the airlines may try spinning that by getting their staff to work by public transport they have reduced their emissions whilst those "carbon neutral" companies are still creating lots of carbon through their staff driving to work.
Many will call it out as greenwashing, however the airlines will have a point. In that how can companies be carbon neutral if for them to exist their staff all have to create significant amounts of carbon getting to and from work.
I suspect that we may see different tiers of carbon neutral companies:
In operations - the company is carbon neutral in what it does, including business trips
In operations and supply chain - as above plus through their supply chain
In operations, supply chain and staff commuting - as above plus they account for their staff travel to and from work
The last will be the hardest to achieve and will not be something that will be used for a few years yet, however as more companies claim carbon neutrality more questions will be asked about just how green they really are. With little else to go on staff commuting will start to be the next thing to be asked about.