We — all of us — now face a universal threat. Though it is not from outside this world, it is nevertheless cosmic in scale.

Consider this tale of two planets. Earth and Venus are almost exactly the same size, and have almost exactly the same amount of carbon. The difference is that most of the carbon on Earth is in the ground — having been deposited there by various forms of life over the last 600 million years — and most of the carbon on Venus is in the atmosphere.

As a result, while the average temperature on Earth is a pleasant 59 degrees, the average temperature on Venus is 867 degrees. True, Venus is closer to the Sun than we are, but the fault is not in our star; Venus is three times hotter on average than Mercury, which is right next to the Sun. It’s the carbon dioxide.

This threat also requires us, in Reagan’s phrase, to unite in recognition of our common bond.

Next Saturday, on all seven continents, the Live Earth concert will ask for the attention of humankind to begin a three-year campaign to make everyone on our planet aware of how we can solve the climate crisis in time to avoid catastrophe. Individuals must be a part of the solution. In the words of Buckminster Fuller, “If the success or failure of this planet, and of human beings, depended on how I am and what I do, how would I be? What would I do?”

Live Earth will offer an answer to this question by asking everyone who attends or listens to the concerts to sign a personal pledge to take specific steps to combat climate change. (More details about the pledge are available at algore.com.)

But individual action will also have to shape and drive government action. Here Americans have a special responsibility. Throughout most of our short history, the United States and the American people have provided moral leadership for the world. Establishing the Bill of Rights, framing democracy in the Constitution, defeating fascism in World War II, toppling Communism and landing on the moon — all were the result of American leadership.

Once again, Americans must come together and direct our government to take on a global challenge. American leadership is a precondition for success.