it is

The word it’s, with an apostrophe, is not a possessive, but contraction of the phrase it is.

It’s possible that if global warming continues, malaria could reoccur in Sweden.

NP-Complete problems are intractable, but it’s possible to find a tractable subproblem.

[The word its, without an apostrophe, is the possessive form of it. The word its is therefore is an exception to the rule that singular possessives are formed adding ‘-s (as in “Emma‘s car”).

Headline language, with its many omitted words, complicates syntactic classification.]