This article is weak on logic, and , strong on strawmen.

As a first attempt to convert human consumption into land impacts EF is innovative and deserves credit for that alone. I continue to believe that it is pointing to about the right are in terms of scale when we look at how we should behave in terms of material consumption if we live in the numbers that we do, and there is no alternative single indicator.

The (definitely valid) criticism that EF is no more than a rough sketch on the back of an envelope simply does not justify the (also possibly true) conclusion that we need go back to the Drawing Board. Many fine buildings and valid scientific theories started life as a sketch on the back of an envelope or a wild apparently unprovable idea. That quality of uncertainty simply does not mean the design or underlying concept was fundamentally flawed. Nor does the demonstration of sensitivity in a model mean that the model does not work, it simply means that a better model and better data are required. It may be that the concept is fundamentally flawed but this has not been proven.

9 boundaries? Yes, more precise but less useful. Those boundaries too must be uncertain when we look into detail, and equally would be prey to denial by those with an interest in exceeding them – there is no alternative but to admit that any measure of sustainability is going to involve a lot of guessing. In the meantime all the indicators point in the same direction.

The statement that the EF is claiming a spurious level of accuracy is insulting to the intelligence of even the most dim-witted: The EF is a heuristic, highly synthetic model, and yes, potentially wildly inaccurate. But it is possibly somewhere near reality. The attitude of the Authors is like the passengers on a bus careering towards a perceived precipice shouting to the driver not to slow down because the danger may not in fact be real – indeed, it may be simply a bump in the road, an optical illusion or even a hallucination. Do the Authors seriously expect me as a fellow passenger to support their advice to ignore the warning signs on the basis that they may be wrong and may need re-evaluation?

Apart from quibbling about CO2 sequestration capacity, this “Perspective” contains no real critique of the EF method’s underlying thesis – that human consumption and emissions need to be supported by biophysical realities. To develop a perspective one needs distance - the article does not seem to me to come from a sufficiently detached position.

Yet there are many real questions about the EF approach which have been effectively ignored in the hurry to produce a hatchet job on the CO2 front – chemical pollution, the theoretical EF of a person completely integrated into the ecology (such as some tribals) the relationship of Agriculture to biodiversity, and the possibility of mass production of Ecological Space beyond a deliberately provocative tree planting example. Whether these should be seen as omissions from EF as it stands or as an indication that we need to go back to the drawing board (which I agree with) is not convincingly established in this article. .