Final answer:
Sources in the ecological footprint are processes emitting carbon, like burning fossil fuels, while sinks like oceans and vegetation absorb more carbon than they release.
Step-by-step explanation:
In the calculation of an ecological footprint, sources and sinks refer to different functions in the carbon cycle. Sources are processes that release carbon into the atmosphere. Two examples of this include burning fossil fuels and volcanic activity, both of which emit carbon dioxide, a greenhouse gas.
Conversely, sinks are processes or systems that absorb more carbon than they release, helping to remove carbon from the atmosphere. Two examples of carbon sinks are oceans and vegetation. Oceans absorb carbon dioxide from the atmosphere and use it in the process of carbonate sedimentation, whereas plants absorb carbon dioxide during photosynthesis to grow.