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Here's something to consider this Earth Day: If the world doesn't completely bring to a halt its greenhouse gas emissions within 35 years, we could be set adrift "into completely uncharted waters" of dangerous sea level rise, heat waves and persistent drought, floods, food insecurity, and vicious disease outbreaks, which will most immediately impact the poor and vulnerable.
That's the assessment of the Earth League, a 17-member panel of leading international scientists.
Diplomats will meet in Paris later this year at the annual UN climate summit. They have pledged to agree on steps to keep global temperature rise to within 2 degrees Celsius (3.4 degrees Fahrenheit) compared to pre-Industrial Age levels.
Johan Rockström, chair of the Earth League and Executive Director of the Stockholm Resilience Centre, urged bold, rapid action on climate change.
"The window of opportunity is closing fast. We are on a trajectory that will leave our world irrevocably changed," he said. "We would never consider this level of risk in any other walk of life, yet we seem prepared to take this risk with our planet. Conversely, the scientific evidence shows that we can create a positive future but only with bold action now."
In their statement, the Earth League outlines "essential elements" for an international climate deal. Among them, rich nations must provide financing and technological know-how to poor countries in order to help them transition to clean energy economies. Rather than degrading grasslands and forests, nations should work to strengthen these natural carbon sinks. And, in order to remain within 2 degrees Celsius of warming, at least 75 percent of known fossil fuel reserves around the world must remain in the ground.
Jeffrey Sachs, Director of the Earth Institute at Columbia University and an author of the statement, said the upcoming Paris meeting is "the moment of truth."
"The key to success is deep decarbonisation by mid-century," he said. "Our studies show that this can be accomplished, at modest cost, and with a significant improvement in the quality of life. Success will require a shared global vision, strong national commitments, and global cooperation on technology pathways.