Example: some GMO crops are more tolerant of compacted soil and weed competition, reducing the need to till the soil. Tilling the soil requires enormous amounts of diesel fuel, with obvious bad environmental implications. By reducing the use of diesel, the GMO crops help the environment.

Oh, you don't even have to accept global warming to see how using diesel to till the soil can cause harm. Particulate matter in the air is really harmful. (both the diesel exhaust and the soil getting churned up into the air) Disturbed soil runs off into streams, leading to dead zones. Competition for crude oil seems to support war, which has lots of bad effects on the environment.

So... eat GMO to save the environment.

Tilling the soil is not needed if you practice organic permaculture farming.

That way we get reduced productivity, meaning we need to devote more land to crops and less to wilderness or whatever. Also, what you can do in a labor-intensive garden is not going to produce affordable food for billions.

From the source I have given:

> A recent study compared the effectiveness of a rotenone-pyrethrin mixture versus a synthetic pesticide, imidan. Rotenone and pyrethrin are two common organic pesticides; imidan is considered a "soft" synthetic pesticide (i.e., designed to have a brief lifetime after application, and other traits that minimize unwanted effects). It was found that up to 7 applications of the rotenone- pyrethrin mixture were required to obtain the level of protection provided by 2 applications of imidan.

> It seems unlikely that 7 applications of rotenone and pyrethrin are really better for the environment than 2 applications of imidan, especially when rotenone is extremely toxic to fish and other aquatic life.

I know it is anecdotal evidence, but organic farmers would not care if the fertilizer/pesticide made from mined minerals are better/worse for the environment or not as long as it passes the "organic" criteria. A rather more useful criteria IMO would be "relatively harmless to the environment"

> Can you explain how focus on a local supply chain, say, as one element of Organic farming practice is detrimental to either of those things, [human] health or environment?

http://freakonomics.com/2011/11/14/the-inefficiency-of-local...

"Forsaking comparative advantage in agriculture by localizing means it will take more inputs to grow a given quantity of food, including more land and more chemicals—all of which come at a cost of carbon emissions."