Issuing an appeal for a new citizen activism in the free world, President Barack Obama renewed his call Wednesday to reduce U.S. and Russian nuclear stockpiles and to confront climate change, a danger he called “the global threat of our time.”

In a wide-ranging speech that enumerated a litany of challenges facing the world, Obama said he wanted to reignite the spirit that Berlin displayed when it fought to reunite itself during the Cold War.

“Today’s threats are not as stark as they were half a century ago, but the struggle for freedom and security and human dignity, that struggle goes on,” Obama said at the city’s historic Brandenburg Gate under a bright, hot sun. “And I come here to this city of hope because the test of our time demands the same fighting spirit that defined Berlin a half-century ago.”

The president called for a one-third reduction of U.S. and Russian nuclear stockpiles, saying it is possible to ensure American security and a strong deterrent while also limiting nuclear weapons.

Obama’s address comes nearly 50 years after John F. Kennedy’s famous Cold War speech in this once-divided city. Shedding his jacket and at times wiping away beads of sweat, the president stood behind a bullet-proof pane and read his remarks from text before a crowd of about 6,000.

It was a stark contrast to the speech he delivered in the city in 2008, when he summoned a crowd of 200,000 to embrace his vision for American leadership. Whereas that speech soared with his ambition, this time Obama came to caution his audience not to fall into self-satisfaction.

“We must acknowledge that there can at times be a complacency among our Western democracies,” he said. “Today people often come together in places like this to remember history, not to make it. Today we face no concrete walls or barbed wire.”

The speech came just one week shy of the anniversary of Kennedy’s famous Cold War speech in which he denounced communism with his declaration “Ich bin ein Berliner” (I am a Berliner). Obama, clearly aware that he was in Kennedy’s historic shadow, asked his audience to heed the former president’s message.

“If we lift our eyes as President Kennedy calls us to do, then we’ll recognize that our work is not yet done,” he said. “So we are not only citizens of America or Germany, we are also citizens of the world.”

The president has previously called for reductions to nuclear stockpiles. But by addressing the issue in a major foreign policy speech, Obama signaled a desire to rekindle an issue that was a centerpiece of his early first-term national security agenda.

The president discussed non-proliferation with Russian President Vladimir Putin when they met Monday on the sidelines of the Group of 8 summit in Northern Ireland. During Obama’s first term, the U.S. and Russia agreed to limit their stockpiles to 1,550 as part of the New START Treaty.

In Moscow, Russian foreign policy aide Yuri Ushakov said that plans for any further arms reduction would have to involve countries beyond Russia and the United States.

“The situation is now far from what it was in the ’60s and ’70s, when only the U.S.A. and the Soviet Union discussed arms reduction,” Ushakov said.

Obama’s calls for cooperation with Moscow come at a time of tension between the U.S. and Russia, which are supporting opposite sides in Syria’s civil war. Russia also remains wary of U.S. missile defense plans in Europe, despite U.S. assurances that the shield is not aimed at Moscow.

Germany’s foreign minister, Guido Westerwelle, is a strong advocate of nuclear disarmament and has long called for the removal of the last U.S. nuclear weapons from German territory, a legacy of the Cold War. The Buechel Air Base in western Germany is one of a few remaining sites in Europe where they are based.

Under an agreement drawn up when they formed a coalition government in 2009, German Chancellor Angela Merkel’s conservatives and Westerwelle’s Free Democratic Party agreed to press NATO and Washington for the nuclear weapons to be withdrawn, but did not set any timeframe.

Nuclear stockpile numbers are closely guarded secrets in most nations that possess them, but private nuclear policy experts say no countries other than the U.S. and Russia are thought to have more than 300. The Federation of American Scientists estimates that France has about 300, China about 240, Britain about 225, and Israel, India and Pakistan roughly 100 each.

(AP)