I want to do research in A about its applications in B. Don't know exactly what people in B need from A. What's a good way to acquire this knowledge? Issues related to climate change, mitigating it and making humans deal better with its negative consequences are super important to me. I am not an environmental scientist though - I'm an engineer. I have a varied background and experience, which fits in well with a discipline I'm very interested in - robotics. I feel like pursuing a PhD in robotics, researching its application in environmental science would be good for me and for the field(s).

Now, the problem is I don't know the exact problems (in environmental science) that I could propose to work on in my research proposals. I really want to have a conversation with someone in the field about this, but I don't know how to go about this. I'm one year out of school now, so it's not like I can swing by a relevant professor's office and drop in for a chat. On the other hand sending a "cold-call" email also seems not fully appropriate, because asking "What kinds of problems do you have that can be solved by technology?" seems far too general.

So the question is - what is a good way to acquire this kind of knowledge?
You don't know what they need and they don't know what you can offer. One of you has to give and start getting hands dirty in the other's field. And in this case you'll probably have to do that. Here are some possibilities. I study in the US so there could be some cultural/practical differences, but I would like to believe that they should not be big, if any.


Go to some university research seminars. Most of them are open to public and schedules are often posted online. Stay and chat with the presenter.
Take a few introductory classes. This allows you to acquire proper lingoes to communicate. If possible, I'd also suggest taking it for credit because later when you do your PhD, the issue of not having any coursework in this new area will come up. Some programs allow 1-2 credits transfer so you may be able to hit two birds with one stone.
Identify prominent research organizations in this area. For example, internationally there is IPCC, and in the US there is EPA. These organizations periodically produce evidence-based statements and reports, in which you can glean important research needs.
Regularly do some brief literature surveys in this area and perhaps even the combined area. Sign up for customizable article alert. Pay attention to the studies' limitations and applications. Take good notes and review them time to time when brainstorming.
Examine grant availability by visiting funding agency websites. In the US there is grants.gov and I'm sure there must be a UK or European equivalence. Look for related grant announcements. In most of these announcements, you'll often find problem statements and suggested areas from which the agency would like to see some grant proposals. Having a research plan that appeals to your future supervisor and funding agencies can make your PhD journey a lot smoother.
In the above processes, also pay attention to who are the leading institutes and researchers in this field (or the combined field.) Consider contacting them for a short information interview (15-min or so.) Don't dread doing it because eventually you'll need a person in the env. sci. to be in your committee; might as well start scouting earlier.