We've known about the idea of the greenhouse effect since the 1820s,
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...