1: With global warming, could the earth get warm enough for nearly all snow and ice to melt? If so, has anyone done a simulation that shows what the earth would look like?
2: If all countries started slugging it out with nukes in WW3, what would the earth look like?
3: Are there other anthropogenic ways thru which the earth could radically change?
Seas would rise 200 ft:
We can’t do it just yet, but soon we could redirect an asteroid into the earth.
Nuclear war would leave behind small round lakes where many [del]cities[/del] targets used to be. If any targets were dams, the areas downstream would be scrubbed clean for a ways. Depending on how much debris and soot is in the air to do the global cooling/nuclear winter thing, glaciers sooner or later will return to erase them, at least in the higher latitudes.
I highly doubt that. Most nukes used in war would be airburst for maximum effect, and won’t leave any crater (like the Hiroshima & Nagasaki bombs).
Yeah, you’ll get wreckage of buildings in cities (especially if people don’t return to the city to rebuild and maintain them), but not much earth moved around. Geologically, nuclear war would have very little direct impact.
Most of the indirect effects would be from undoing changes that humans have made, or preventing us (at least for a time) from making more changes. You might also see some other species going extinct, but mostly only ones that were already precarious.
The Earth has already done this at least once in the past. About 55 million years ago, the Earth got so warm that the polar ice caps melted. Trees grew all the way to the poles (at least as far as there was land) and many think that the area around the equator became almost uninhabitable due to the excessive temperatures. Unsurprisingly, a large extinction event is associated with this time period.
Google “Paleocene-Eocene Thermal Maximum” for more details. The exact cause and many of the details are debated, and different models have been proposed to explain exactly how it happened and what the conditions were actually like.
On the other extreme, somewhere around 600 to 800 million years ago, evidence of glacial ice scraping the surface on land that was near the equator at the time indicates that the entire Earth may have frozen solid. Many call this the snowball Earth theory.