Thanks for everyone's replies. The area that I'm looking at is mainly to do with the the reduction in footprint, and the effect that it has on the trucking of the show.
There was a study done about the carbon emissions of the UK music industry, and they found that 13,000 tonnes of carbon emissions were produced annually from transporting the show.
The UK live industry is responsible for 75% of the overall emissions produced by the UK music industry, with audience travel being the source of the majority of this. I agree with what you're saying in that the amount of emissions produced by the weight of the audio equipment is, in the grand scheme of things, a minute amount. But from what I have seen so far, it is seemingly one of the only things, with regards to audio, that the production team can change to try and the reduce environmental impact.
My study is to investigate what impact the use of a digital system has on this, because of its reduced footprint and weight. If the difference between the two is marginal, that's fine because I've still investigated the area, but there may be a difference, and if there is it will be an interesting subject to look into.
Lee