Refuting means criticising, condemning or denouncing the previous position of natural world being subservient to humans. The ecological economics reverses the position by making the human economy subservient to the natural world. The reversing may also be considered a form of refutation
but there is no explicit refutation of the earlier position.

Hello, Could someone please clarify why it cannot be "a", i.e. circumscribing/limiting the environmental economist's subordination?

The sentence is setting up a contrast between two fields: Environmental Economics and Ecological Economics.
1. Environmental Economics (Older field): Focuses on the "monetary valuation" (putting a dollar value on) of natural resources. This implies the subordination of the natural world to the human economy.
2. Ecological Economics (Emergent field): Positions the human economy as a subsystem of natural ecologies (meaning nature is primary).

The action of Ecological Economics must be to oppose or overturn the perspective of Environmental Economics. Therefore, the blank must mean contradicting, opposing, or overturning.
- circumscribing: Restricting something within limits. (Too weak; it's a fundamental shift in perspective, not just a restriction.)
- corroborating: Confirming or giving support to. (Opposite meaning.)
- ameliorating: Making something better. (Doesn't capture the idea of reversing the hierarchy.)
- refuting: Proving a statement or theory to be wrong or false; contradicting. (Fits the idea of rejecting the core assumption of the older field.)
- reversing: Changing to the contrary, opposite, or inverse. (Fits perfectly, as the new field reverses the hierarchy: nature is dominant, not subordinate.)

Both refuting and reversing strongly indicate the rejection and fundamental change in perspective necessary for this contrast. However, since the new field places the economy within nature, this is a clear reversal of the older field's hierarchy (economy over nature). Refuting is a good synonym here, but typically, single-blank questions require finding the single best fit from the list. If we must choose one:

The most precise word for changing the order of hierarchy ("subordination") is reversing. If the prompt implies selecting one best word, reversing is the strongest fit for the structural shift described. If this were a Select-Two format, both refuting and reversing would likely be correct.

Assuming this is a single-choice question, the best fit is reversing.