Three senior Department of Homeland Security officials on Wednesday defended the agency's decision to spend money, time and personnel resources to study how climate change might affect U.S. national security.

Rep. Scott Perry, R-Pa., called a hearing in his Homeland Security subcommittee on Oversight and Management Efficiency after DHS requested $16 million in its 2016 budget on programs related to climate change. He also rejected the department's claim in its Quadrennial Homeland Security Review last year that climate change could be a significant factor in terrorist uprisings around the world.

That review said climate change poses "major areas" of homeland security risk. Among other things, it said water shortages could lead to more illegal immigration, and said the melting of ice on the oceans could increase smuggling and trafficking. It was criticized by Republicans for also saying climate change could lead militant groups to become active.

"I am outraged that the Department of Homeland Security continues to make climate change a top priority," he said in his prepared remarks. "Are the American people to believe that the increased operations by ISIS are due to hot weather or a shortage of water? Such assertions are ridiculous and, frankly, insulting."

But despite Perry's warning that DHS should focus on immigration, the Islamic State of Iraq and Syria and other threats, DHS officials said they were justified in examining how climate change affects security.

"To disregard natural disasters, pandemics, and climate change would be ignoring how these factors may indirectly act as 'threat multipliers'; and neglect our shared responsibility to strategically manage risk and build a more prepared, resilient nation," said Acting Assistant DHS Secretary Thomas Smith in his prepared statement. "It is through the thorough and candid assessment of these risks that that we will strengthen the security and resilience of the United States."

During the hearing, Smith stressed that the five core functions are DHS are all related to national security, but that DHS is examining climate change as a factor in its threat analysis.

Roy Wright, a deputy associate administrator at the Federal Emergency Management Agency, said climate change needs to be studied because weather events could create security conditions for people. FEMA is housed within DHS.

"Wherever possible, we bring data to bear and work with deference to state, local and tribal needs and priorities," he said. "By addressing future risks, state, local, tribal and territorial governments are best prepared for future extreme weather events and are able to bounce back faster at the individual and community level."

Robert Kolasky, a deputy assistant secretary at DHS, stressed that climate change will affect U.S. infrastructure, and that these impacts need to be measured.

"Working with the private sector and community leaders to plan for the impacts of climate change is essential," he said. "Long-term planning in the face of uncertainty is the cornerstone of risk management and we must address the risks of today while also preparing the country for the risks of the future."

The Quadrennial Homeland Security Review from 2014 said climate change poses "major areas" of homeland security risk. Among other things, it said water shortages could lead to more illegal immigration, and said the melting of ice on the oceans could increase smuggling and trafficking.