The long-awaited signal that the next Ice Age is already on its way may have been seen. If so, our civilization’s doom will be inevitable, for all our efforts to reduce global warming will have been futile. Who knows? Within a century, humans may be gladly burning whatever carbon they can to produce greenhouse gases. We don’t know because this has never happened before.

Recent data shows that the only place in the Northern Hemisphere that is cooling down is in the North Atlantic. Despite — or perhaps because of — another record of high summer heat — the ocean around Greenland has been cooling for a while. In fact, it’s dropped over 1° Celsius since 1900. While that doesn’t seem like much, where it is happening is critical to the temperature distribution of the planet. For as the warm Gulf Stream flows past the Greenland icecap to make Europe a temperate and pleasant region, it is diluted by the waters from the melting ice. Which makes this “cold blob” disturbing. Too much freezing water pouring in from all that global warming could stop the Atlantic Meridional Overturning Circulation, or AMOC, cold, as it were. Since that current is a vital part of the way heat is constantly distributed from the tropics to the poles, this could in effect be like turning down the thermostat for the whole planet. Would this be enough to prevent human-driven climate change? Or would that just make the situation more unstable? It’s too soon to tell, but it may be already too late to stop. But it is cosmically ironic that the real danger from global warming might not be from the Earth burning up, but from triggering the Big Chill.

An AMOC shutdown would be a global catastrophe, causing accelerated sea level rise on the US East Coast, plunging Europe into a winter deep freeze and shifting the monsoon in Africa, driving prolonged droughts.

And that could be just the beginning. However, scientists claim that more data is needed before they can tell for sure.

So enjoy the summer, but remember, just as spring follows summer, “winter is coming.”