That's very vague. Collapse how? According to other comments we have already remove 60% of species, why wasn't that enough to cause a collapse. Other species take up the slack left by those removed.
Let's look at it from a different perspective though. If thousands of scientists are wrong and we improve the environment but there was never any danger of human extinction then we still end up with a more enjoyable planet. If thousands of scientists are right and we don't improve the environment then we all die.
This doesn't really explain human extinction. Our food supply doesn't come from a natural ecosystem.
- Commercial bee populations aren't declining. (There has been an increase in Colony Collapse Disorder, but lost colonies are replaced and total bee population hasn't declined.)
> The most essential staple food crops on the planet, like corn, wheat, rice, soybeans and sorghum, need no insect help at all; they are wind-pollinated or self-pollinating. Other staple food crops, like bananas and plantains, are sterile and propagated from cuttings, requiring no pollination of any form, ever.
- None of the crops that require pollination from insects are essential to human survival. It's hard to see how their loss could lead to our extinction.
- Crops can be pollinated by hand or machine.
- Crops can be propagated without seeds.
- Crops can be grown in all kinds of unbelievable conditions. Crops can be grown without soil. They can be grown in space stations, completely isolated from Earth's ecosystems.
- Extinction is a very strong claim. To support it, it wouldn't be enough, for example, to show that 90% of the population would die off, leaving 750 million people. They need to propose a mechanism by which all humans would die.
If you think that the human food supply will not be affected by a planet-wide ecosystem collapse, you might want to think again.
Fertile soil is not just dirt. Talk to a soil expert and you'll find out very quickly how difficult it is to keep soil healthy, especially if you punish it every day with pesticides and herbicides. See you long you can maintain production if you don't have a support system of insects, arachnids, worms, fungi and so on. You'll end up with just dirt. Nothing grows in just dirt. You can try to keep up production by downing it in fertilizer, but in the end you'll just prolong the inevitable; loss of crop and collaps of production.
See how many humans you can feed by growing crops in space stations. See how long you can maintain a closed ecosystem in space.
To your last point; if you lose more than 30% to 30% of the productive workforce, you can kiss human civilization goodbye; our manufacturing is highly de-centralized, but heavily interdependent and without safety buffer.. Our infrastructure is wide-spread and needs tons of maintenance. Lose enough people and it all comes crashing down, leaving the survivors with broken machinery for which they don't have energy, don't have the knowledge to operate let alone repair if (not when) they stop working. They will also have to deal with all the poison and radioactive fallout from all the fission reactors that experience core-meltdown because nobody's around anymore to power them down over the period of ten years.
Don't kid yourself; saving what's left of this earth's ecosystem is the only shot we have. There's not techo-utopia down the road to carry us to eternity and the heat-death of the universe. Its you and me and the rest of us puny humans that will have to do the saving.
I am not an expert on anything but I can give the answer a stab. Let us make many assumptions:
Say plankton dies off, say animals eating plankton die, say humans eating those animals now have less food. Say all the fish die and we are reduced to land-based food. Now we have more space competing for farm land, we have to clear forest. Clearing adds to CO2 emissions, construction, more emissions, less CO2 being taken out. It's clear how this is all one giant feedback loop. Less biodiversity, more overabundance of something else, which leads to less consumption of something else which leads to collapse of ecosystems which leads to use trying to patch things up and doing even more harm.
Just zoom out and think about things that consume things and how that loops back directly to humans, environment, overproduction, overuse and eventually unsustainable usage of resources until there are none left.
My go to example is if we lose insects which pollinate plants we would have a very very hard time growing certain foods. There is a certain unforeseeable complexity to these things.
Just a speculatory example, losing migratory birds could weaken the soil microbiome and seed biodiversity in the places they migrate to, from, and over. There could be a crop-critical organism in their path that relies on the regular influx of new bacteria or seeds from a certain place.
On what we have already removed: a building likely still stands if you remove 60% of the contents of the building, the last 40% is what is really holding it up.
In addition to collapse, climate change, etc which would be relatively predictable, there would also likely be a potent feed back mechanism in the form of global war bringing the extinction tipping point closer much more quickly than we are prepared to cope with.
