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Since this series' maiden voyage, the impossible has come to pass: Mighty walls that maintained insuperable ideological differences have come tumbling down; deadly enemies have embraced and begun to work together. The imperative to cherish the Earth and protect the global environment that sustains all of us has become widely accepted, and we've begun, finally, the process of reducing the obscene number of weapons of mass destruction. Perhaps we have, after all, decided to choose life. But we still have light years to go to ensure that choice. Even after the summits and the ceremonies and the treaties, there are still some 50,000 nuclear weapons in the world — and it would require the detonation of only a tiny fraction of them to produce a nuclear winter, the predicted global climatic catastrophe that would result from the smoke and the dust lifted into the atmosphere by burning cities and petroleum facilities.
The world scientific community has begun to sound the alarm about the grave dangers posed by depleting the protective ozone shield and by greenhouse warming, and again we're taking some mitigating steps, but again those steps are too small and too slow. The discovery that such a thing as nuclear winter was really possible evolved out of the studies of Martian dust storms. The surface of Mars, fried by ultraviolet light, is also a reminder of why it's important to keep our ozone layer intact. The runaway greenhouse effect on Venus is a valuable reminder that we must take the increasing greenhouse effect on Earth seriously.
Important lessons about our environment have come from spacecraft missions to the planets. By exploring other worlds we safeguard this one. By itself, I think this fact more than justifies the money our species has spent in sending ships to other worlds. It is our fate to live during one of the most perilous and, at the same time, one of the most hopeful chapters in human history.
Our science and our technology have posed us a profound question. Will we learn to use these tools with wisdom and foresight before it's too late? Will we see our species safely through this difficult passage so that our children and grandchildren will continue the great journey of discovery still deeper into the mysteries of the Cosmos? That same rocket and nuclear and computer technology that sends our ships past the farthest known planet can also be used to destroy our global civilization. Exactly the same technology can be used for good and for evil. It is as if there were a God who said to us, “I set before you two ways: You can use your technology to destroy yourselves or to carry you to the planets and the stars. It's up to you.”
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55 min 20 sec

 

Carl Sagan

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Those who are skeptical about carbon dioxide greenhouse warming might profitably note the massive greenhouse effect on Venus. No one proposes that Venus's greenhouse effect derives from imprudent Venusians who burned too much coal, drove fuel-inefficient autos, and cut down their forests. My point is different. The climatological history of our planetary neighbor, an otherwise Earthlike planet on which the surface became hot enough to melt tin or lead, is worth considering — especially by those who say that the increasing greenhouse effect on Earth will be self-correcting, that we don't really have to worry about it, or (you can see this in the publications of some groups that call themselves conservative) that the greenhouse effect is a "hoax".

 

Carl Sagan

 

Without doubt, terrorist groups are trying to buy, build or steal a bomb. Furthermore, there is enough highly-enriched uranium (HEU) in the world to build more than 100,000 weapons, and rogue individuals are selling technology on the black market. If terrorists get hold of HEU, they could not be prevented from smuggling it into a targeted city, building a bomb and exploding it.
To my mind, the only realistic solution to this danger is to lock down all nuclear materials and eliminate all nuclear weapons in all countries: Global Zero. I am now dedicated to achieving this goal as a leader of the Global Zero movement. This movement was launched in December 2008 in Paris by an international group of 100 current and former heads-of-state, national security officials, military commanders and business, civic and faith leaders — and in just two years has grown to 300 leaders and 400,000 citizens worldwide.
The group believes that whatever deterrent value nuclear weapons had in the Cold War is now outweighed by the dangers of proliferation and nuclear terrorism. Our international Global Zero Commission has developed a practical, step-by-step plan to eliminate all nuclear weapons through phased and verified reductions.
To build on the progress made to date, we need a worldwide public movement to make Global Zero an urgent global imperative — and to bring all nuclear weapons countries to the table to negotiate multilateral nuclear arms reductions for the first time in history.

 

Valerie Plame

 

As long as some of us choose to rely on nuclear weapons, we continue to risk that these same weapons will become increasingly attractive to others.
I have no doubt that, if we hope to escape self-destruction, then nuclear weapons should have no place in our collective conscience, and no role in our security.
To that end, we must ensure — absolutely — that no more countries acquire these deadly weapons.
We must see to it that nuclear-weapon states take concrete steps towards nuclear disarmament.
And we must put in place a security system that does not rely on nuclear deterrence.

 

Mohamed ElBaradei

 

I'll be philosophical. Until about two billion years ago, it was impossible to have any life on earth; that is, there was so much radiation on earth you couldn't have any life — fish or anything. Gradually, about two billion years ago, the amount of radiation on this planet—and probably in the entire system—reduced and made it possible for some form of life to begin... Now when we go back to using nuclear power, we are creating something which nature tried to destroy to make life possible... Every time you produce radiation, you produce something that has a certain half-life, in some cases for billions of years. I think the human race is going to wreck itself, and it is important that we get control of this horrible force and try to eliminate it... I do not believe that nuclear power is worth it if it creates radiation. Then you might ask me why do I have nuclear powered ships. That is a necessary evil. I would sink them all. Have I given you an answer to your question?

 

Hyman G. Rickover

 

One thing I try to point out to people, and Dick Lindzen has pointed this out in the past, too, is that, as most of you probably know, about ninety percent of the earth’s greenhouse effect is water vapor, then carbon dioxide, methane and some trace gases. The water vapor con-centration in the atmosphere goes up and down quite a bit, but it is self-regulating. Things don’t get too warm before precipitation systems suck the water vapor out again. I don’t understand how we can know how much warming there will be with global warming until we understand how precipitation systems change with warming. We don’t under-stand that, and I have papers from modelers who have said the same thing. Modelers don’t like to talk about what they don’t know. So until we understand these natural proc-esses that remove the earth’s primary greenhouse gas, water vapor, from the atmosphere – which is a self-regulating part of the earth keeping a constant temperature – I don’t think we can predict how much warming there will be due to increasing CO2. It is a mat-ter of faith again, I think. We are not saying that we don’t believe that there can be sig-nificant global warming. As John said, if you add CO2, something has to change. But things are changing all the time anyway. The big question is: So what? How much is it going to change, compared to other things? And what can you do about it?

 

Roy Spencer