In terms of software engineering alone, your best bet may just be to find an organization you support and work hard while under their employ. Even if you're not _directly_ affecting emissions etc., you're supporting those who do. As a bonus, passion for a cause can be very motivational. (Though keep in mind you may be discouraged if the organization feels dysfunctional or ineffective. Be ready to switch jobs if need be.)

As for finding those organizations, that's a different question and may be better asked without reference to software engineering so as to receive the widest spectrum of orgs.