And one of the things that we have to realize, or to demonstrate with climate change, is that there was a significant climate change at the end of the Pleistocene during the time of extinction.
(the things; to realize; we) (one of the things; is; that there was a significant climate change at the end of the Pleistocene during the time of extinction)
the things one of the things
to realize is
we
that there was a significant climate change at the end of the Pleistocene during the time of extinction