First, you might notice that the book was published (copyrighted) in 1998.
Global warming has been a hot topic for a number of years. So, it may not be crucial that books on this be brand new. But for some topics, the currency of the book is critical.
For example, if you were doing research on school violence,
you might really want recent books or articles that might include discussion
of the rash of school shootings that took place in the last few years.