….we’ll end up with abjectly nonsensical policy, won’t we?

Take this from The Guardian:

Agriculture is the world’s largest industry. Pasture and cropland occupy around 50% of the planet’s habitable land and uses about 70% of fresh water supplies.

Agriculture doesn’t use 70% of fresh water supplies. Nothing like, it’s an ingloriously silly thing to say. Having said it of course leads to very silly indeed proposals for doing something about it.

The Guardian’s own link to the FAO to back up the assertion contains this:

On average, agriculture accounts for 70 percent of global freshwater withdrawals.

Which is something wildly different from the first assertion. Of the fresh water that humanity diverts in the system 70% is used by agriculture. Something - as we really do insist - very different from the claim that agriculture uses 70% of fresh water supplies.

We can approach these numbers from the other side. Total rainfall is some 500,000 cubic km a year. 70% of that is over the oceans of course so we might or might not say that’s part of the available supply. River discharge of the 107,000 km3 that falls on land seems to be 37,000 km3. 35% of rain runs into the sea, therefore nothing at all can be abstracting 70% of all (land based) rain from the system.

We can go further too. That oft quoted insistence that it takes two or three tonnes of water to grow a kilo of wheat. Well, OK. Much of that falls from the sky onto the field. That which doesn’t run off into the rivers (see above) returns to the atmosphere through some combination of evaporation, transpiration and, for all we know, perspiration. Whether we’re growing wheat or thistles in that field there’s not much difference in that water cycle. Equally with that 15 tonnes of water to grow a kg of beef. Cows do not turn up at the slaughterhouse as 1 tonne of bovine and 15,000 tonnes of water in a big trailing bag (as a loaf of bread does not have a 3 tonne reservoir attached). That 15,000 tonnes is respirated, transpired, perspired or even pissed out again, back into the cycle. Which would be much the same if we grew bunnies we didn’t eat in that field instead of cows.

Agriculture does use 70% of the water than humans use, that’s the actual truth. It’s also entirely true that some of that is used horrendously inefficiently - irrigation of alfalfa in Southern California being an obvious example. The alfalfa produced is worth less than the alternative uses of the same supplied water. Sure we should do something about that - having an actual and real market in water would solve that particular problem by teatime.

But 70% of water used by humans is an entirely different number from 70% of all water, or all freshwater, or all freshwater supplies, or all freshwater annual availability or any other such construction we’d like to think up. Further, not having agriculture would change the abstraction from the overall system only by a tiny amount at the margin - for whatever plant and animal life replaced agriculture would also use water to something close to the same extent. As also evaporation would still happen.

If we start believing abjectly stupid claims then we’re going to end up with stupidly abject policies. Farming doesn’t use 70% of the world’s freshwater, nothing like. So, stop believing that it does.