Over the past several decades, numerous target dates or time frames have been put forward as the point where we MUST start reducing or already have reduced fossil fuel emissions by X amount or face irreversible, possibly cataclysmic consequences. "By the year 2000, by 2020, by 2030, by 2050," etc. Many of these target dates have come and gone, and those who proposed them may have just shifted the target further into the future, perhaps similar to the way apocalyptic cult leaders have proposed dates for the end of the world.
From Martin Luther King, Jr.'s "Beyond Vietnam" speech at the Riverside Church in New York one year before he was assassinated:
We are now faced with the fact, my friends, that tomorrow is today. We are confronted with the fierce urgency of now. In this unfolding conundrum of life and history, there is such a thing as being too late. Procrastination is still the thief of time. Life often leaves us standing bare, naked, and dejected with a lost opportunity. The tide in the affairs of men does not remain at flood — it ebbs. We may cry out desperately for time to pause in her passage, but time is adamant to every plea and rushes on. Over the bleached bones and jumbled residues of numerous civilizations are written the pathetic words, “Too late.” There is an invisible book of life that faithfully records our vigilance or our neglect. Omar Khayyam is right: “The moving finger writes, and having writ moves on.”