On Monday, nearly 150 world leaders will gather in Paris in a global show of solidarity for the fight against climate change, which threatens to wreak havoc on economies and food production.
The leaders will launch two weeks of intense negotiations involving nearly 200 nations aimed at sealing the world's first truly global pact to curb the pace at which the planet is heating up. If the Paris deal is clinched, it will mark the culmination of more than two decades of bitter negotiations between rich and poor nations over the sharing of responsibility for greenhouse gas emission cuts, and how to pay for them.
Ahead of Paris, over 170 nations submitted their climate action plans to the United Nations. These plans will form the foundation of the new agreement.
The French government has staked its international reputation on getting an agreement and has spared no expense in hosting the conference on the north-eastern edge of the city, with security beefed up further after this month's terror attacks. About 40,000 people are expected to attend what will be one of the largest environmental gatherings.
Paris is important because it is expected to launch a new process for all nations to combat climate change. A Paris agreement is not meant to be a one-shot deal. Instead, it is the start of a decades-long effort in which rich and poor nations progressively strengthen their climate actions to try to ensure the globe doesn't heat up beyond 2 deg C. This is the level that scientists say we cannot bust - doing so would put us at risk of more extreme storms, droughts, floods and a faster sea-level rise.
An analysis of the current pledges puts the world on a path to a warming of 2.7 deg C, meaning nations will have to ratchet up their climate plans quickly.
The test for Paris is to agree on a mechanism to quickly deepen emission cuts. Another test is agreement on enough cash for poorer nations to invest in cleaner energy and adapt to climate impact.