but it was Eunice Foote - a women's rights activist -

who first showed how it could actually work.

In 1856, she used an air pump to fill glass cylinders with different gases

and then tested the effect of sunlight on them.

One was carbon dioxide, CO2.

"The receiver containing the gas became itself much heated...

and on being removed, it was many times as long in cooling..."

Foote's experiment suggested that CO2 and water vapour

trap heat more than other gases do

and the potential effects on our climate began to emerge.

"An atmosphere of that gas

would give to our Earth a high temperature."

That year she submitted her findings

to an American scientific society.

At their conference she wasn't able to take questions directly

because someone else presented her work for her

and it wasn't published in the proceedings of the society.

Another journal did end up publishing her paper,

but it went largely unnoticed.

Three years later, Irish physicist John Tyndall

did more complex experiments,

finding other greenhouse gases that trap heat.

He went on to become one of the founding figures of climate science.

Nobody knows if he'd read Eunice Foote's paper,

but his own didn't mention her or her glass cylinders at all.

No pictures of Foote have survived,

and her contribution remained buried for 150 years -

only coming to light by chance in 2010,

when a retired geologist discovered a citation of her work

in an antique science annual.

Guy Stewart Callendar was a steam engineer by day

and an avid collector of climate data in his spare time.

By the 1930s, he was collecting temperature readings

from 147 weather stations around the world.

No-one had ever collated the data like this before,

and when he compared his temperature readings

to historic measurements of CO2, he discovered a clear pattern.

Callendar saw that not only was climate change happening,

it was at least partly down to the burning of fossil fuels.

In 1938, Callendar presented his findings to a scientific body

but the idea that we humans could influence

something as huge as the Earth's climate

was still, for many, too hard to believe.

It wasn't until after the Second World War

that the effect of human activity on global warming -

the "Callendar Effect" - was proved right.

In 1958, chemist Charles Keeling's colleagues

were studying the relationship between

ocean acidity and carbon dioxide.

Until then, it had been thought that the oceans quickly absorb most CO2,

taking it out of the atmosphere,

but that didn't appear to be true.

Keeling had a hunch that scientists had been underestimating

how much of the gas was actually over our heads.

I was telling these people that the whole field was

pretty badly screwed up.

Atmospheric CO2 readings had been taken for decades,

but the data was unreliable.

Keeling was convinced he could do better, and looked for a spot

that was as far as possible from the pollution of cities and industry.

He went to the middle of the North Pacific,

4,000 metres above sea level,

to the huge, active volcano of Mauna Loa, in Hawaii.

If you had to have picked a spot anywhere,

which would have given

a representation of the whole world with one single site,

Mauna Loa Observatory is probably about the best choice.

His new data proved two things.

Firstly, it showed that CO2 goes up and down with the seasons.

But if you zoom out from these "saw's teeth"

you can see the second thing that Keeling proved -

atmospheric CO2 was increasing year on year.

Keeling began plotting his readings on a graph,

and the ominously upward-curving line - the "Keeling Curve" - was born.

But the Mauna Loa project faced challenges.

Equipment broke down, and it struggled to secure funding.

It was only through sheer perseverance

that the observatory kept taking its readings.

Keeling was eventually awarded

a National Medal of Science for his work,

and today, Mauna Loa is still the world's benchmark site

for measuring CO2.

It's now more than 160 years

since Eunice Foote suggested the cause of global warming,

more than 80 years since Guy Callendar demonstrated

the planet was warming because of human activity,

and more than 60 years since Charles Keeling showed

CO2 was rising at an alarming rate.

And here we are...