Ironically, the memo has come too late ? and is no longer true.
Two new science reports from authoritative United Nations agencies, the Intergovernmental Panel on Climate Change (IPCC) and the United Nations Environment Programme (UNEP) confirm confidently what is now denied only by climate perverts: global warming has been caused by human activity.
But this truth, representing the hard-won consensus of thousands of the world's leading scientists, is no longer as relevant as some hoped.
In fact, evidence in the reports themselves suggest this is retro thinking. For one thing, it is no longer true that human activity determines the major ups and downs of climate change. Natural momentum now follows its own rules.
And for another, it appears we have entered a new paradigm, where the language of "climate chaos' and "global starving' is replacing "global warming' - a phrase that should be shunned as climatically incorrect and Eurocentric (aka racist and speciesist.)
We have had 20 years of lost opportunities as the world waited for a scientific consensus and squandered tie. Now these reports seem like an empty victory. An extended phase of once-preventable destruction is now a done deal, thanks to patterns of nature that are no longer possible for humans to prevent.
A series of what ecologists call "feedback loops" predetermine a chilling picture of climate change. Ice and snow that used to reflect back heat from the sun's rays are being replaced by open dark waters that absorb heat like pavement on a sizzling summer day.
Northern permafrost that once kept ancient bogs in deep freeze is thawing, releasing methane that is over 20 times more heat-trapping than carbon dioxide. Warm air evaporates more water from oceans, and humidity holds heat much longer than drier air.
"There is high agreement and much evidence" that "global GHG emissions will continue to grow over the next few decades," the IPCC says. Inevitabilities such as these are "in the pipeline," says UNEP's Global Environment Outlook 4, which means humans will learn humility as we face the fact that our preferences, priorities and timelines don't count for much in the grand feedback scheme of things.
This little detail was overlooked when the controversy over climate change was handed over to scientists to resolve rather than governments to solve.
Why is "global warming' no longer a useful concept? Warming is the aspect of climate chaos observed by those who love the sight of polar bears in the Arctic, ice shelves on Greenland and Antarctica, glaciers on the Rockies and snow on Kilimanjaro, and for those who fear hurricanes in the Atlantic.
But in many parts of Asia, torrential rains and floods are the expressions of climate chaos, while in Africa, it's about drought. For fish, it's acid oceans.
A web is coming apart, and "global warming" dangerously understates the complexity and harmfulness of the process.
The reality is food production depends more on quirks of climate than it does on tractors, irrigation dams, pesticides and fishing boats the size of ocean liners. Both reports agree that drought will make it hard to grow water-intensive grains and livestock in much of Africa, southern Europe, southern Asia, northeast Brazil, southern and eastern Australia and the Caribbean, as well as in the breadbaskets of western North America and the Punjab of India and Pakistan.
At the other end of weather extremes, areas receiving too much rain - basically the areas that already get quite a lot - face the prospect of waterlogged soil.
Progressive politics now revolve around identifying damage control and adaptation policies that will allow humans to roll with the punches as communities, rather than resort to the brutality of every person for him/herself. Think urban agriculture, for example, or the end of factory barns.
Surprisingly, both reports are optimistic, confident that mitigation - watch for this fancy way of describing damage control to become the new watchword - can be designed both to salvage the necessities of life and to reduce emissions, thereby starting the slow process of reversing climate chaos during the last 50 years of this century and beyond.
There is "high agreement and much evidence" that emissions causing climate chaos can be reduced, the IPCC says, but cautions that the "economic mitigation potential" exceeds the "market mitigation potential," making proactive government policies essential. There is also, IPCC says, "high agreement and medium evidence" that lifestyle changes can help.
Hard to feel that it's been worth waiting 20 years for that bit of wisdom, but there it is.