When to use or not use a definite article

I am still confused when to use and when to omit the definite article.  I end up guessing, which is sometimes right and often wrong.  Example 1: "En lo que se refiere a incendios forestales." We're talking about forest fires in general and there is no definite article "los".  Example 2: "Es importante que no nos olvidemos del cambio climatico."  The English statement is that we must not forget about climate change in general.  This time there is the definite article "el" or "del".  Is there a rule or guideline that might clear this up for me?  Thanks.