"Do we really have to change the energy and transportation and agriculture and forestry systems in the world and shift to a low-carbon pattern?" the former US vice president asked in a speech.
"The answer is 'Yes'... Because now the answer is coming from nature itself," he said.
Gore pointed to a string of extreme droughts, record-breaking downpours and high tides, along with melting Arctic ice as evidence of climate change.
He added that the scientific community is "virtually unanimous" on the existence of man-made climate change and the evidence is "just as clear as it is for the existence of gravity."
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"One hundred and fifty heads of state, the largest number ever gathered in history, are in the same place on the same day, and not a single word of climate denial."
Gore also sounded a hopeful note about humanity's ability to end its reliance on fossil fuels and shift to green energy sources. He said the amount of electricity provided by wind has grown exponentially and the cost of solar power has plummeted.
"Business community, investors... And others have brought the technologies of solar photovoltaics, wind power and efficiency... To the point where these new approaches are extremely competitive," he said.
Negotiators in Paris will aim to strike a bargain that limits global temperature rise to two degrees Celsius (3.6 degrees Fahrenheit) over pre-industrial times by limiting greenhouse gas emissions from burning fossil fuels.