How'd you get in here? I'm the Internet, I never left. Now why'd

you change the name? Global warming wasn't happening so you had to call it "Climate Change"?

The overall average temperature of the planet is increasing so Global Warming is technically

correct, but that doesn't mean it's going to be warmer everywhere all the time.

And that leads to some confusion, like on a cold winter's day, you might say...

So much for global warming! Exactly.

So the term climate change indicates that the problem is more intense storms, droughts

and floods, ocean acidification, not just that the globe is warming.

But it's not. What?

The globe's not warming. Since when?

1995 Um, that's not how you draw a trendline through

data. If the slope is nil, the climate's chill.

Y'know thirteen of the fourteen hottest years occurred this century and the graph you're

using is old, it doesn't include satellite data. If you take that into account, the trend

is obviously continuing upwards. Oh, so now you say it's warming. In the past

scientists told us it was cooling. Why can't they just admit that they have no idea what's

going on? It's true in the 1970's there were some papers

published predicting cooling, but over that same time period there were six times as many

papers predicting warming. So scientists really haven't changed their tune.

Well just judging by temperatures, I say they're wrong. The Earth is cooling.

But you don't just have to go by temperatures. There are plenty of other signs that the globe

is warming, like sea levels are rising three millimetres a year. That's an indication that

the oceans are getting warmer and so are expanding. Ice on Antarctica and Greenland is melting

at unprecedented rates and arctic sea ice continues to decline.

Nuh-uh. Arctic sea ice increased forty percent in the last two years.

That last little uptick? That's what you focus on? What about the general downward trend?

It could mean anything. You know if the Earth is warming the most likely source of the problem

is the sun. The sun is getting brighter. Did you ever think of that?

The sun was getting brighter, in the 1930's, and it probably contributed to some warming

then. But since the 50's the sun has been getting dimmer and temperatures continue to

rise. Oh, so you automatically assume it's man-made

CO2. You know humans only emit a tiny fraction

of the CO2 released into the atmosphere every year.

That's true. People emit about 30 gigatonnes compared with 780 gigatonnes from natural

land and ocean processes. So you admit it, humans aren't the problem.

No! Before us the system was in balance with the land and oceans absorbing that same amount

- 780 gigatonnes a year. This balance kept the carbon dioxide levels

in the atmosphere between 180 and 280 part per million for 800,000 years. Now it's at

400 parts per million and still rising. But our small contribution couldn't have caused

that. Well the amount of CO2 in the atmosphere is

increasing by about fifteen gigatonnes or two parts per million every year.

But how do you know that's man-made CO2? Because the isotope carbon-13 is less common

in fossil fuels than it is naturally in the atmosphere. And over time we're seeing the

concentrations of carbon-13 are decreasing. But volcanoes emit way more CO2 than humans.

No they don't. They emit about 0.25 gigatonnes annually. That's less than one percent as

much as humans. OK, well even if we are responsible for the

rise in CO2, it doesn't matter because water is by far the most potent greenhouse gas.

Yes it is. I win.

No you don't! Water in the atmosphere is increasing as well.

But that can't be due to human activity. The only way for the atmosphere to hold more

water vapour is if it gets warmer. So... Hang on, you're not saying...

Yes! It all comes back to CO2. A doubling of CO2 on its own would increase the temperature

of the globe by one degree Celsius. But that warming means there will be more water vapour

in the atmosphere and ice will melt reducing the reflectivity of Earth's surface. So it's

a positive feedback loop, which a bunch of different sources of evidence all indicate

will lead to about a 3 degree Celsius rise in temperature.

But if this is true, why have all the predictions failed. In actuality most of the predictions

show remarkable agreement with observations. But you're probably thinking of the model

from 1988, back when we thought climate sensitivity was higher. If you re-run that model with

3 degrees of warming for every doubling of CO2, the predictions match exactly the warming

that we've observed. But the Earth has warmed and cooled in the

past. So who was releasing CO2 then, aliens? We understand that past changes in the climate

were triggered at regular intervals by Milankovitch cycles, that is the periodic oscillation of

the Earth's tilt, precession of the tilt, and stretching and squishing of Earth's elliptical

orbit. During every warming cycle, CO2 and temperature

rise together. Ah, but if you look closely at that graph,

you'll see that CO2 lags behind the temperature rise, so it can't be causing the warming.

The CO2 doesn't cause the first warming. The Milankovitch cycles change the way the sunlight

hits the Earth and that causes a little bit of warming decreasing the solubility of CO2

in the oceans. So some of that CO2 is released and that is a positive feedback loop, which

amplifies the warming. In fact over 90% of the increase happens after the CO2 starts

to rise. Let's say you're right, and the CO2 we're

releasing is warming the planet. What's so bad about that? The planet gets a little warmer,

big deal. I'm not claiming it's going to be some sort

of crazy catastrophe, but we are going to get more intense storms, more droughts and

floods, the oceans will become more acidic, sea levels will rise and my point is it would

be better for all species on this planet and probably cheaper for us if we just started

reducing emissions now than if we wait and pay the consequences later.

No thanks. Why are you wearing sunglasses?

Global warming. This episode of Veritasium was supported by

Audible.com a leading provider of audiobooks with over 150,000 titles in all areas of literature

including fiction, non-fiction, and periodicals. This week I wanted to recommend the book Merchants

of Doubt, which is about scientists who have spread misinformation about certain topics

like how cigarettes cause lung cancer, or how CFC's cause the ozone hole, or now how

CO2 is causing the planet to warm. So if you want to find out more about that you can download

this book by going to audible.com/veritasium or you can pick any other book of your choosing

for a one month free trial. So I want to thank Audible for supporting me, and I want to thank

you for watching.