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Hello I'm Hank Green, and welcome back for SciShow Breaking News. If you're like me and you're marking your days until December 21st, 2012, you'll know that it is just six weeks until the amazing celestial odometer that is the Mayan calender will click over, kicking off a whole new 394 year unit that the Maya referred to as the B'akt'un.

And if you've been suckered into believing that the world is going to end because an ancient people ran out of stone to carve their calender on, well, here's where you can get your mind right.

But more important, and interesting, than debunking a dumb conspiracy theory is solving the mystery of what caused the actual collapse of the Maya civilization.

The Maya still thrive today throughout Central America, thank you very much. But the region once supported a vast network of city-states that made all kinds of mind blowing achievements, from, like, inventing rubber to developing the concept of zero.

Then, about a thousand years ago, the Maya world spiralled into chaos, causing its people to disperse and much of its culture to be lost. So, why?

Today, in the Journal Science, a team of anthropologists and climate scientists, says that it's discovered a factor that couldn't be more relevant today - drought.

The team studied ancient rainfall patterns by analyzing levels of oxygen isotopes they found in underground rock formations. Particularly in the tropics, rainwater contains high concentrations of the heavy isotope Oxygen-18 because it condenses more quickly than its lighter isotopic cousins.

This rainwater then percolates through the ground and is captured in cave deposits. So, by studying the layers of Oxygen-18 found in a cave in Belize, the team was able to measure the region's history of rainfall, pretty cool.

And they discovered that rainfall patterns correspond almost exactly with the civilization's highs and lows. For instance, the rise in expansion of complex Maya society from about 450 - 660 AD coincided with the period of unusually heavy rain, which likely allowed for more food production, and thus a bigger, more stable population.

But then, between about 660 - 1000 AD, the research shows that the rain began to taper off, and this is when the empire began to decline as well. Maya monuments from this time document growing political insecurity and more warfare among city-states, just as rain was becoming more scarce.

Finally, the team found that the driest period in the isotope record, an extended drought from 1020 - 1100 AD correlated closely with what's known today as the Mayan collapse.

This is when populations began to plummet, cities began to be abandoned, and the construction of temples, tombs, and monuments stopped completely.

So, why is this relevant? Well, for one thing, another study in the exact same journal suggests that we should prepare today for even more hot, dry conditions than we ever expected. 

You may remember when I interviewed Dr. Kevin Trenberth, senior scientist at the National Center for Atmospheric Research, about the connection between extreme weather and climate change.

Well since then, Trenberth has been studying the dozens of different climate models that scientists have been using over the years to see which have been the most accurate by comparing what they've each predicted with what's actually happened.

And today, he reports that the most accurate climate models turn out to be the same ones that predict much higher global temperatures than many of us expected. While most scientists have been saying that average temperatures will rise about 2.8 degrees Celsius by 2100, the most accurate models actually put it 40% higher, at 3.9 degrees Celsius.

This is important, Trenberth says, because higher temperatures will mean even more extreme heat waves and severe droughts, among many other weather consequences.

So, no, the world is not going to end in six weeks, I can guarantee you that, and it's not going to end just because it's been a long, dry summer. But the news we are getting today from the ancient Maya sounds a lot like the news we're getting from modern climate science, and we ignore this news at our own risk.

Thank you for watching this episode of SciShow Breaking News. If you want to keep up-to-date on the latest advances in science you can go to youtube.com/scishow and subscribe. And if you have any questions or comments or ideas for us we're on Facebook and Twitter, and of course, down in the comments below.

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