President Barack Obama walks in after being introduced at the U.S. Coast Guard Academy graduation in New London, Conn., May 20, 2015. (AP Photo/Pablo Martinez Monsivais)

GROTON-NEW LONDON, Conn.  -- President Obama warned Wednesday that climate change is a growing and "serious threat" to national security, tying severe weather to the rise of the extremist group Boko Haram in Nigeria and the civil war in Syria.

In his latest bid to turn up political pressure on Republicans over the environment, Obama challenged 218 newly commissioned officers at the U.S. Coast Guard Academy to take the threats of climate as seriously as they would a cutter in peril on the seas.

"You don’t sit back; you take steps to protect your ship," Obama said. "Anything less is a dereliction of duty. The same is true for climate change."

Alluding to usual robust GOP support for U.S. troops, Obama said: “Politicians who say they care about military readiness ought to care about this as well.”

"Climate change constitutes a serious threat to global security, an immediate risk to our national security," he told the graduates in their dress white uniforms at the campus football stadium, "and, make no mistake, it will impact how our military defends our country.  And so we need to act— and we need to act now.”

Here are key moments from President Obama's commencement address to the Coast Guard Academy class of 2015, in which he told the graduates climate change would affect "everything that you do in your careers." (WhiteHouse.gov)

Obama's focus on the environment is part of a continuing effort by his administration to ramp up public attention to the issue even as the president's legislative agenda on the matter is stalled by opposition from congressional Republicans. Many in the GOP have expressed skepticism about the effects of global warming and called the concerns inflated.

[Obama’s most at-risk legacy isn’t Obamacare. It’s climate change.]

In his remarks here, Obama tied droughts and crop damage from severe weather to the rise of Boko Haram, which has terrorized civilians in Nigeria, and to the bloody civil war in Syria. He cast controlling climate change as a "key pillar of American global leadership" and called it "a core element of our diplomacy."

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Last month, Obama visited the Everglades to highlight steps his administration is taking on the environment, announcing new small-scale federal initiatives to protect national parks. Last fall, the administration struck a major climate deal with China to reduce emissions.

To win more support, the president has begun to tie concerns to the nation's security in the face of potentially large-scale natural disasters and the impact of reckoning with damage caused by global warming to the economy.

The issue has been raised on the campaign trail with most Republican candidates for the White House expressing doubts about climate change.

"In Miami and Charleston, streets now flood at high tide.  Along our coasts, thousands of miles of highways, roads, railways and energy facilities are vulnerable," Obama said. "It’s estimated that a further increase in sea level of one foot — just one foot — by the end of this century could cost our nation $200 billion.”

Other administration officials also are touching on the topic. Secretary of State John F. Kerry, who returned to Washington after several days in Asia, said he discussed climate change during meetings that also focused on the nuclear threat of North Korea and the problems of violent extremism across the globe.

[Kerry, in Seoul, slams North Korea]

"So now it's time to put aside discredited scientific arguments and partisan politics and to focus on the facts," Kerry said, "not just for our health and the health of our children but for our planet's security as well."

As part of his commencement address to the Coast Guard Academy class of 2015, President Obama recognized 100-year-old Olivia Hooker, who lived through a racial attack in 1921 and became the first African American woman to enlist in the U.S. Coast Guard. (WhiteHouse.gov)