Let’s talk about the science of climate change.
Don’t you mean Global Warming? 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 a count, 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
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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
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Audible for supporting me, and I want to thank you for watching.