“Our biggest national security threat is the environmental destruction of our planet and the arms race with ourselves.”

Source: "Space Lifeguard : An Interview with Gene Kranz" at Space.com (11 April 2000)
Context: In many ways we have the young people, we have the talent, we have the imagination, we have the technology. But I don't believe we have the leadership and the willingness to accept risk, to achieve great goals. I believe we need a long-term national commitment to explore the universe. And I believe this is an essential investment in the future of our nation — and our beautiful, but environmentally challenged planet.

Quoted in https://www.bbc.com/news/av/world-europe-50265870/mikhail-gorbachev-tells-the-bbc-world-in-colossal-danger Mikhail Gorbachev tells the BBC: World in ‘colossal danger’, BBC World News,(4 November 2019)
2000s

What I Didn't Find in Africa (2003)
Context: I was convinced before the war that the threat of weapons of mass destruction in the hands of Saddam Hussein required a vigorous and sustained international response to disarm him. Iraq possessed and had used chemical weapons; it had an active biological weapons program and quite possibly a nuclear research program — all of which were in violation of United Nations resolutions. Having encountered Mr. Hussein and his thugs in the run-up to the Persian Gulf war of 1991, I was only too aware of the dangers he posed.
But were these dangers the same ones the administration told us about? We have to find out. America's foreign policy depends on the sanctity of its information. For this reason, questioning the selective use of intelligence to justify the war in Iraq is neither idle sniping nor "revisionist history," as Mr. Bush has suggested. The act of war is the last option of a democracy, taken when there is a grave threat to our national security. More than 200 American soldiers have lost their lives in Iraq already. We have a duty to ensure that their sacrifice came for the right reasons.

Speech to the Michigan legislature, in Lansing, Michigan (15 May 1952), published in General MacArthur Speeches and Reports 1908-1964 (2000) by Edward T. Imparato, p. 206; part of this was also used in a speech in Boston, as quoted in TIME magazine (6 August 1951) http://www.time.com/time/magazine/article/0,9171,856843,00.html
Context: Talk of imminent threat to our national security through the application of external force is pure nonsense. Our threat is from the insidious forces working from within which have already so drastically altered the character of our free institutions — those institutions we proudly called the American way of life.

New York Times Op-Ed "Grounding a Pandemic" (6 June 2005) http://www.nytimes.com/2005/06/06/opinion/06obama.html?ex=1275710400&en=69f51e47097d5dd9&ei=5090&partner=rssuserland&emc=rss by Barack Obama and Richard Lugar
2005

Hugo Chávez speaking in October 2005 http://www.telegraph.co.uk/news/worldnews/1534596/The-wisdom-of-Chavez.html
2005

not just the extinction of species and animals and plants, that fifty years ago was the first signs of impending global disaster, but traffic congestion, oil prices, pressure on the health service , the growth of mega-cities, migration patterns, immigration policies, unemployment, the loss of arable land, desertification, famine, increasingly violent weather, the acidification of the oceans, the collapse of fish stocks, rising sea temperatures, the loss of rain forest. The list goes on and on. But they all share an underlying cause. Every one of these global problems, environmental as well as social becomes more difficult – and ultimately impossible - to solve with ever more people.
How Many People Can Live on Planet Earth? (BBC Horizon, 2009)

"Introduction: Thinkability"
Einstein's Monsters (1987)

Source: Never Have I Ever