Wordspy defines Green Accounting as:

n. A system in which economic measurements take into account the effects of production and consumption on the environment.

My own concept of green accounting is a bit more practical insofar as I see it as a future sub-specialty of the accounting profession that equips people with the concepts, math, science, simulation, and financial skills to account for the "external" costs of producing a product or service. External costs are the ecosystem costs that are usually not accounted for in the costs of producing a good or service. A good starting point would be to know how to account for the amount of green house gases, water, and waste are required to produce, distribute, and consume any particular good or service. We now have an emerging global awareness where these particular environmental costs are becoming increasingly important to account for and the concepts and software to do that accounting are starting to build into a discipline that might be called "Green Accounting".

I don't really view "Green Accounting" as something that should be done by economists from a 100 mile high perspective and in broad strokes. I think it should be something that all companies should start to think about at an operational level and consequently "Green Accounting" might be a specialized type of accountant companies would hire to, for example, do some green accounting to figure out how many offsets the company should consider buying; or else "Green Accounting" is just another type of skill that all accountants need to become familiar with in order to be deemed a professional in that field. The future probably includes both scenarios.

Consider the problem of hosting an event like the Olympics and trying to assess the costs of hosting the event in terms of the green house gases emitted, the freshwater resource impacts, and the amount of waste produced? What type of professional should be called in to a full accounting of the "external" costs of hosting the Olympics, in addition to other costs and benefits?