I am currently employed by the Department for the Environment, Food and Rural Affairs (Defra). I work in the science team responsible for all things to do with Greenhouse gas emissions estimates. What this means, in short, is that if someone in government (either a Minister, MP or another Civil Servant) has questions about what GHG emissions (either in the UK or elsewhere) are, were or will be at some point in future, we endeavor to answer this question to the fullest of our ability.
The work is a little broader than just pulling numbers out of a spreadsheet, fortunately. The main responsibility of the team is to produce the UK GHG Inventory, which is the dataset by which our progress towards our Kyoto target, as well as domestic targets, is measured. Developed countries that have joined the United Nations Framework Convention on Climate Change (UNFCCC) must submit annual estimates of their emissions, in the form of an inventory. The inventory is prepared externally by contractors, and we work with these contractors, managing the contract, ensuring that deadlines are met, and working to improve the way in which the inventory is prepared.
Colleagues in the team are also strongly involved in international negotiations on a diverse range of topics, including avoiding deforestation (which is a very significant source of GHG emissions), technology to mitigate climate change (such as low-carbon technologies that reduce the amount of GHGs we emit) and long term emissions reductions goals (like the Kyoto Protocol) where we support UK policy colleagues trying to secure international agreement on emissions reductions pathways.
I find the whole thing absolutely fascinating. I'm very lucky to be able to do a job I really enjoy.