Al Gore has addressed the Democratic National Convention in Denver, Colorado. He was Bill Clinton's vice-president and narrowly lost the 2000 election to George W Bush.
Below are some key excerpts from his speech.
ON WHY ELECTIONS MATTER
The question facing us is, simply put, will we seize this opportunity for change? That's why I came here tonight: to tell you why I feel so strongly that we must seize this opportunity to elect Barack Obama President of the United States.
Eight years ago, some said there was not much difference between the nominees of the two major parties and it didn't really matter who became president. Our nation was enjoying peace and prosperity. Some assumed we would continue both, no matter the outcome. But here we all are in 2008, and I doubt anyone would argue now that election didn't matter.
Take it from me, if it had ended differently, we would not be bogged down in Iraq, we would have pursued bin Laden until we captured him. We would not be facing a self-inflicted economic crisis; we would be fighting for middle-income families.
ON THE CHOICE IN 2008
Today, we face essentially the same choice we faced in 2000, though it may be even more obvious now, because John McCain, a man who has earned our respect on many levels, is now openly endorsing the policies of the Bush-Cheney White House and promising to actually continue them. The same policies all over again?
If you like the Bush-Cheney approach, John McCain's your man. If you want change, then vote for Barack Obama and Joe Biden.
ON WHAT OBAMA WILL DO
Barack Obama is telling us exactly what he will do: launch a bold new economic plan to restore America's greatness; fight for smarter government that trusts the market, but protects us against its excesses; enact policies that are pro-choice, pro-education and pro-family, establish a foreign policy that is smart as well as strong; provide health care for all and solutions for the climate crisis.
ON CLIMATE CHANGE
As I have said for many years throughout this land, we're borrowing money from China to buy oil from the Persian Gulf to burn it in ways that destroy the future of human civilization. Every bit of that has to change.
Many scientists predict that the entire north polar ice cap may be completely gone during summer months in the first term of the next president. Sea levels are rising, fires are raging, storms are stronger.
Military experts warn us our national security is threatened by massive waves of climate refugees destabilizing countries around the world, and scientists tell us the very web of life is endangered by unprecedented extinctions.
ON BARACK OBAMA
His experience has also given him genuine respect for different views and humility, in the face of complex realities that cannot be squeezed into the narrow compartments of ideology.
His experience has taught him something that career politicians often overlook: that inconvenient truths must be acknowledged if we are to have wise governance.
The extraordinary strength of his personal character - and that of his wonderful wife, Michelle - is grounded in the strengths of the American community. His vision and his voice represent the best of America. His life experience embodies the essence of our motto - e pluribus unum - out of many, one.