Congress doesn't believe global warming is a security threat
Climate change will shift the equation of global power and craziness, and the intelligence community is trying to place for those situations. But Congress isn't interested in that. Mother Jones' Kate Sheppard gives this example:
In 2008, [Thomas] Fingar, [former chairman of the National Intelligence Council] now a fellow at Stanford University, took the lead in drafting the first national intelligence assessment on the security challenges presented by climate change. It found that global warming will further destabilize already-volatile parts of the world and should be considered in national security planning. But congressional Republicans dismissed the report as "a waste of resources."
Global warming is enough of a security concern that the Navy has a climate change task force, and the CIA has offices devoted to addressing climate-related threats to national security. So some members of Congress (cough GOP cough) want to shut those down.
I guess if you believe that climate change doesn't exist, then thinking about its impacts does seem like a waste of time. But we’re talking about a government that is armored against an effort to blow up planes using two-ounce shampoo bottles and souvenir snow globes. Even if global warming were merely plausible, it would probably be worth looking into.