PubMed and CINAHL
1. exp greenhouse effect/
2. exp energy-generating resources/
3. 1 and 2
4. greenhouse gases.mp.
5. greenhouse gasses.mp.
6. carbon footprint.mp.
7. carbon emissions.mp.
8. 3 or 4 or 5 or 6 or 7
9. limit to English
ScienceDirect
1. TITLE-ABSTR-KEY
ambulance
or hospital
2. ALL
greenhouse gas*
or carbon footprint
or emissions
3. 1 and 2
Hand-searched tables of contents
Ecological Economics
Energy
Land Use Policy
Energy Economics
Energy Policy
Renewable Energy
Environmental Impact Assessment Review
Global Environmental Change
Journal of Cleaner Production
Journal of Environmental Economics and Management
Energy Conversion and Management

Note. ABSTR = abstract; exp = explode; mp = multiple parameters; * = truncated (includes gas, gases, gasses, etc.).