[MUSIC] July 2016 was the hottest July ever recorded.

Same with June.

And also May.

April, though .

In fact, every month going back to October 2015 has been the hottest since 1880.

Cue the Nelly.

Its hard to argue Earth isnt heating up.

Because unless you have a neck problem it IS.

But whats REALLY warming the Earth?

The climates a complex system, influenced by everything from our orbit to gases in our atmosphere to volcanoes.

And when we say warmer warmer compared to WHAT?

For most of history, temperature records looked something like this “Hot today.

Hotter ‘nyesterday.

” But with the development of accurate thermometers and standardized temperature scales in the 1700s, we could finally get some real data, from ships crossing the ocean, weather stations around the world, hashtag colonialism.

But weather isnt climate, and a few temperature records do NOT a complete global climate history make.

at we were collecting enough data in enough places to figure out an average temperature for the whole world, which is why US climate graphs start here while the UK goes back to here.

Should we believe what Ben Franklin or Thomas Jefferson wrote in their weather journal?

Can we really trust all those old records?

These are good questions, but climate scientists have looked at the data through many different lenses, and every time they do the math, they get the same answer.

Earth is warming up, fast.

But none of this explains the cause.

It could be human activity, but it could also be so many other things.

Earths orbit is pretty wobbly.

Our elliptical path around the sun spins like a hula hoop.

Earths axis draws a circle every 21,000 years, and wobbles back and forth every 41,000, and all these affect Earths climate.

But scientists understand these changes really well, and when they use them to predict climate change?

They dont see any.

s heat, and it also changes in cycles, dimming and brightening sorta like a light bulb.

For most of the last thousand years, when the sun turned up, temperatures rose on Earth, and when the sun dimmed, temperatures fell.

But in the past few decades, the suns been cooling slightly, yet Earth keeps getting hotter.

lar activity cant explain todays climate change.

We know carbon dioxide traps heat in the atmosphere, and the last time Earths CO2 levels were this high, Homo sapiens didnt exist.

But maybe all this CO2 is Earths fault?

When volcanoes erupt, they release tons of the stuff, like little magma powered Earth burps.

urns out humans release about a hundred times more CO2.

Volcanic activity cant explain climate change.

Some things actually cool the Earth.

Cutting down more trees makes Earths surface lighter, it reflects more light back into space.

phere do the same thing, they make our atmosphere reflective, so less radiation gets in.

Yet even with these cooling effects getting stronger, Earths getting warmer.

But we know that greenhouse gases like CO2 and methane have skyrocketed, and when we calculate how temperatures should change based based on those levels, we finally see a rise.

Subtract the cooling from trees and clouds and pollution, and it matches more than a century of data.

This isnt magic, its math.

These climate graphs dont show absolute temperatures, because absolute temperatures, the number on a thermometer, can be misleading.

The top of a mountain will always be colder than the valley below, but if they are both a degree above normal, it gives us a hint that the larger climate might be different.

This is why we look at the “anomaly ” how different todays average temperature is from the average temperature somewhere in the past, the degrees above “normal.

” But what IS normal?

The last month Earths temperature was below the 20th century average was December 1984.

Many of you havent seen below-average temperatures in your lifetime.

July 2016 was the 379th consecutive month, and the 40th July in a row, of above average temperatures.

ut breaking Olympic records than climate records.

Are we really just used to this?

Maybe ed the idea of “shifting baselines ”, the idea that we evaluate change very differently depending on what were comparing to.

Today, about half a million bison live in North America, a remarkable recovery from 9t h centurBuy.t compared to the 20 to 30 million that roamed the plains before 1600, our bison baseline suddenly paints a very different picture.

We know how hot Earth has been over the past century and a half.

We have the data.

Scientists understand that Earths climate is a complex puzzle, whose pieces affect one ot he r in mWhaneny twaheysy .pu t those pieces together, to recreate that history, the picture is clear.

Lets take a long hard look at it.

Stay curious.