As a chairperson, the biggest pitfall would be if you overpowered the group with your own views, especially as you know the subject well. You will need to keep yourself in check, offer your views, but no more forcefully than others, and listen for consensus.

In fact, coaxing a consensus will probably be the hardest task, if you have some strong personalities in the group. Especially in the early stages of the work (where you will be brainstorming and collecting possible ideas and options), your task will be for everyone to have a fair "shout". Some knowledgeable people may be too shy to speak up - you'll need to coax them gently.

At the start, make sure they all know each other; the usual thing is to go round and ask each to say something about themselves, especially with respect to the task in hand. Don't rush this bit too much. Half an hour is better than 5 minutes - let them settle into the group.

Agree the selection criteria second (after the brainstorming) - not before, otherwise people will be subconsciously filtering their ideas through the criteria during the brainstorming session, and you might miss some good ones.

Selection of criteria is in my view the most important task. Too often we glibly come up with the obvious ones (example: "The one that saves most emissions") and forget others that may be just as important (examples: "The one that is easiest to implement" or "The one that gives fastest results" etc). And if you miss a good criterion, don't be afraid to go back and change them - they are your criteria, and they are not holy; their only purpose is to let you select the best options.

Don't worry too much about prioritising your criteria, assigning weighting factors etc - that is false accounting and turns the whole thing into a numerical exercise, diverting attention. But DO identify any "make or break" criteria: the ones that absolutely MUST be satisfied.

After you have selected your preferred options/ideas according to the criteria, don't simply list them; you can do a little bit more. Prioritise them along a timeline, work out some target emission savings by quarter etc.

Finally - and this is the second biggest pitfall for a chairperson - make sure the workload of the group is divided; this is to ensure that everyone feels involved AND to avoid your becoming unofficial scribe-cum-presentation-developer-cum-general-dogsbody. Be a chairperson (willing to do some of the work, perhaps even more than others), not just the one on whom all the work is dumped.

And have fun!