Hank Green: Last week, 259 scientists from 39 countries came together to tell us about the state of the planet.  They were, and are, the Intergovernmental Panel on Climate Change, or IPCC, a group established by the United Nations 25 years ago for the express purpose of giving world leaders hard facts about global warming so that they can make informed decisions.  And on September 27th, they gave us more than 2200 pages of facts in their 2013 climate change report, the first report they've issued since 2007.  It's kind of a big deal, earth-wise.  And the media has covered it, but you know how they are, kind of like those people who keep cluttering up your Tumblr dash, they tend to put more thought into things like Miley Cyrus and Breaking Bad than the future of the planet.  But that's why we're here!  And if there's just five things you need to know about what 200+ scientists had to say about the climate, it'd be this.

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First things first, according to the IPCC, the warming of the planet is unequivocal.  That's their word.  In fact, they say, some of the changes that we're seeing now haven't occurred in hundreds or thousands, and, in some cases, hundreds of thousands of years.  For one thing, each of the last three decades has been warmer than any decade since 1850, and in the Northern hemisphere, it's been the warmest 30 year stretch of the last 14 centuries.  And we have a whole lot of changing planet around us to prove it.  Average temperatures have risen on land and at sea, the amounts of snow and ice have shrunk, and sea levels are higher.  

But this brings me to a little media malfunction I'd like to fix.  If you heard about the report at all in the past week, you probably heard about a pause that some corners of the media got their underwear in a bit of a bunch about.  A supposed period of about 15 years when global warming seemed to not be happening.  Well, internet, buddy, seriously, there was no pause.  What the report describes is the period from 1998 to 2011 when temperatures consistently rose, but only about a third to a half as much as during the decades before that.  So warming happened, but not as drastically or as fast.  But of course, you wouldn't know that by reading some of the headlines, which I won't bore you with.

Anyway, you already know the warming is real, another key point that the panel makes is that all of these climate trends coincide with, no surprise here, rises in greenhouse gases, gases that trap heat in the atmosphere, like carbon dioxide, methane, and nitrous oxide.  But brace yourself for this one, the report finds that these gases are now at levels that haven't existed in at least 800,000 years.  We're talking not since the earth's magnetic poles last reversed themselves, not since homo erectus had it goin' on.  To put things into more context, levels of CO2 are 40% higher than they were during the Industrial Revolution of the late 1700s, and methane levels are 150% higher.  This is mainly because of all of the fossil fuels that we're using to power all of our magnificent stuff, but the panel points out that a lot of these gas concentrations also stem from changes we're making to the land itself, with more carbon absorbing forests being cut down to make way for farms and settlements. 

Which leads us to the panel's next point which is, yes, global warming is all about us.  As the IPCC put it modestly themselves, it is extremely likely that human influence has been the dominant cause in the observed warming since the mid 20th century.  And since scientists like statistics, they've even expressed this in numbers.  In 2007, the panel put the likelihood that warming was caused by humans at 90%.  Now, they say that likelihood is 95-100%.  

Finally, in some of the report's strongest language, the IPCC says that it is virtually certain that there will be more frequent extremes of heat, fewer extremes of cold, as temperatures rise in the future.  Over the next 20-25 years, global average temperatures are expected to rise between 0.3 and 0.7 degrees Celsius.  And depending on what decisions we make by the end of this century, the world could be a very different place. Like, if we manage to substantially reduce the amount of greenhouse gases we're currently farting out, average surface temperatures by 2081 might be only 0.3 degrees higher, the report said.  But if the CO2 and methane keep getting more concentrated, we could be looking at a planet that's 4.8 degrees hotter, and that's just an average.  

Now, you'll notice that there's no scenario I've mentioned where the average temperatures are lower.  That's because the report says that literally no matter what we do, most aspects of climate change will persist for many centuries, even if emissions of CO2 were to stop today.  Now, I'm not here to lecture, and neither is the IPCC, I just hope that world leaders are taking a break from Breaking Bad and Wrecking Ball long enough to pay attention, but you know in America, the government is maybe still shut down, less likely.  *sigh*

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