anorlunda said: The question is a value judgement, not a question of science.

jackwhirl said: A thought occurred to me. Deserts have a relatively high albedo: https://en.wikipedia.org/wiki/Albedo#Terrestrial_albedo

phinds said: Based on almost total ignorance, I look at it like this: If you look at the Earth as a system, I think natural deserts are just part of the order of things and that asking if they are "good or bad" is trying to apply a man-made standard to a system we didn't create and probably should mess with (although we do, of course).

Here's where the "you know what I mean" factor should have kicked in. My question is pretty obviously anthropocentric. "Good" and "bad" are human value judgements, so, yes, I'm concerned about the earth as a 'vessel' for human life most of all.To the extent we have screwed up the Amazon it's because we sacrificed a long term human benefit for a very short term one. I'm really not concerned about the welfare of monkeys except to the extent a healthy monkey population means a healthy human population, if it does. I would be kind of happy if all bees died out because I don't like being stung, but it turns out bees have a huge benefit to people in that they pollinate the plants we eat.So, were we to reforest the Sahara, would we just be doing the same thing somehow? This is where I would assume science has something to say: there must be people who study the effect of desert on the global weather system.The question is asked with the assumption humans are to be the ultimate winners, long term.This is the kind of thing I'm wondering about. What happens if the earth's albedo comes to be outside certain parameters? You don't have to answer that, I'm just saying it's the sort of thing that would have to be closely looked at before undertaking to reforest some huge desert.We're not exactly in a position to not mess with it to some degree if we want to survive: even woods-dwelling tribesmen have to cut trees down and kill animals. The role of science in this is to provide the best information about what alterations to nature we can get away with.