This op-ed was originally posted on CNN.com.

Today, countless young people are flooding the streets of the world's major cities, demanding action to tackle climate change. The global movement stems from the stark reality that the window to addressing this emergency is closing. At the front of these demonstrations, there is frequently a banner warning that there are just "12 years to save the Earth."

If political leaders finally respond to the climate crisis, we may well have these youthful advocates to thank. But there is a problem with this timeline: We don't have 12 years to jump-start action on climate change — we have just one.

According to an article in the journal Nature, global greenhouse gas emissions must peak no later than next year and rapidly decline thereafter for us to have a good chance of preventing increasingly severe consequences from the climate crisis — everything from imperiled croplands, flooded communities and widespread disease. Delaying any longer will push us toward an ecological tipping point, with no way for humanity to claw its way back out.

Next year is also a critical point because it is when country leaders agreed to put forward new climate plans when they adopted the Paris Agreement in 2015. They knew that the climate action commitments in Paris would not be enough, and so they agreed to come back in five years to step up their efforts. We will soon find out if prime ministers and presidents will stand by their word. Collectively, these revised plans will point humanity to a future that is either bright or bleak...

Read the full op-ed on CNN.com.