The human extinction argument is more or less a strawman. People are instead arguing that our advanced civilization will collapse. Which is pretty plausible if

The human extinction argument is more or less a strawman. People are instead arguing that our advanced civilization will collapse. Which is pretty plausible if food shortages lead to famines, war, nuclear exchanges etc. As for monarchs, this is just a number we can see well because people track it. They're nice in and of themselves, but also a marker of wider changes. For example, insect populations seem to be collapsing even in nature reserves, and with them, birds. This causes both short run and near run problems. Short run is that our own food systems may not survive a mass extinction well. Crop yields are expected to decline markedly with increasing temperatures, and necessary pollinators may vanish. Likewise, the oceans may stop producing fish for us to eat in the quantities we do now. It also presages trouble for humans. For example, sugarcane workers in the tropics are now suffering acute kidney failure due to chronic dehydration despite drinking water. The operating temperatures are too hot for outdoor work that used to be possible. With more heat, more areas will pose risks for human habitation. In the longer run, each species loss is irreplaceable. Imagine we make it through this and in 100 years we are exploring the universe and have sustainable energy sources. But we destroyed as much of our species as past comet and extinctions did. I think our descendants will be rather mad at us. In those species will be much lost potential for scientific and medical uses. To say nothing of the joy of nature or anything else. Gone forever so that 1-2 generations could live a certain way. More than half of all human co2 has been emitted in the past 30 years. We're destroying the work of millions of years of evolution for a brief spurt.