Carbon Offsetting
A lot of the greenhouse gas emissions we make are unavoidable, and sometimes we may just need to fly on holiday. If that is the case, and you want to mitigate the emissions you have made there is always the option of carbon offsetting. There has been a lot of well documented controversy around carbon offsetting, for a number of reasons, and there are particular concerns that it is being used as a vehicle for greenwashing by large corporations.
However, that doesn't mean that the concept cannot be used as a force for good. If one wants to avoid private carbon offsetting companies, I would recommend using the conservation charity the World Land Trust. While it is notoriously difficult to effectively calculate exact mitigation for emissions produced, the World Land Trust offers a tool for calculating your emissions, from flights, car travel and energy use, from which it then estimates a cost to protect the amount of land to mitigate against these emissions. At worst you would be putting money towards protecting land with valuable habitat and biodiverstiy.