Short term (low single-digit decades): rapid sealevel rise. When (not "if") the Thwaites Glacier goes and the West Antartic Ice Sheet floats (not melts, just gets seawater underneath it) then we're looking at circa 5 metres, stabilising globally in about 12 days.

Goodbye every single coastal city, air or sea port, industrial area, power plant, transport infrastructure in the world.

Medium term (high single-digit decades): rapid global warming pushing the habitable zones to the poles and sub-polar regions. Note, critically, that means agriculture, as there are no established ecosystems to hunt/gather from at the poles.

We are heading for ~7º C by the end of the 21st century. Never mind 4º, double it.

Long term (millennia): another mass extinction event, much as the previous ones. We're 75-80% of the way through already, though.

Geological terms...

Hundreds of thousands of years: if humans go extinct, the planet will recover in 100K years or so, with plentiful but severely species-impoverished ecosystems.

Tens of millions of years: lots of new species, new rich ecosystems form.

Hundreds: if another sentient species evolves, it will have a hard time bootstrapping an technological civilisation, as we've extracted most of the the easy-to-access resources.