It creates us much angst worrying about the possibilty of planet earth ending 
as we know it.
To refer to it as "sentimentality" can trivialises it
yet it is in our interest to know we can think of any new world
in a positive manner.
What is worrying is THE ATTITUDE that is destroying the planet.
If the planet was changing of its own accord
(ie without the disproportional humn influence)
then any fretting could well be called sentimentality.
The reality is that selfish individuals and corporations
are undeniably responsible so that
fighting against the powers that are changing our planet
is as profound as praying or performing a spiritual ritual.

Arthur C Clarke ended his book "2001 - A Space Oddysey" with an
environmentalist *attitude* that addresses the issue. 
The (short) final chapter is reproduced on this site.