In explaining climate change, for people who are truly interested in learning about it, I always like to start with an easy experiment: you can take two glass containers -- one with room air and one with more CO2 added, and put it in the sun, seeing which one heats up the fastest. Easy, simple. In fact, Eunice Foote did exactly this experiment in 1856:



Then we can ask: How much CO2 is in our atmosphere? Since trees take in CO2 and most living organisms let off CO2, there's always fluctuations. So the next thing would be to look at the CO2 concentrations in the atmosphere, measured all over the Earth -- starting in the Mauna Loa Volcanic Observatory in 1958 and expanding from there.

What do we see? Concentrations go up and down a little, naturally, every year, because there are more leaves on trees in summer in the Northern Hemisphere than in winter. Yet the average rises every year, leading to the famous Keeling Curve:



That's just from 1958 to the present. When you look at the concentrations over the last 800 thousand years, an even more interesting trend emerges:

https://climate.nasa.gov/climate_resources/24/graphic-the-relentless-rise-of-carbon-dioxide/

That's 412 parts per million currently, and the last highest level was about 350 thousand years ago at 300 ppm, before modern humans were even around.

So we know (1) that CO2 is a greenhouse gas and (2) that there is a lot more CO2 in the atmosphere now than in the last 800,000 years.

One would think the planet would be warming, giving these two facts. So now we'd have to look to see how temperatures have fluctuated over time, and if increases in temperature correlates in any way with increases in CO2. Is there a correlation?

Turns out there is.

Over 100 years:



And over 800 thousand years:



Then the question becomes: why is this happening? Where is all of this extra CO2 coming from -- and in such a relatively short period of time?

The answer to that question is because of human activity, especially since the industrial revolution. As world population increases, and more trees are cut down (for fuel, houses, and to make room for raising livestock), there is less of a carbon "sponge."

But on top of this, we're also burning things. Burning wood puts CO2 into the atmosphere. Cows and other livestock also release a lot of methane, another greenhouse gas.

But of course it's not only wood and not only livestock. The main culprit, it turns out -- and why the industrial revolution was mentioned -- is fossil fuel: coal, oil, and natural gas. These are carbon-dense objects, and when burned release a huge amount of CO2. Multiply this burning by an increasing population, year after year for over 150 years, and it becomes very clear where the excess CO2 is coming from.

So human activity is the driver of rapid global warming.

Lastly, so what? What's the big deal about increasing the global temperature by just a few degrees?

I think the answer to this is obvious once you realize how only a few fractions of a degrees has large effects over time, which we're already beginning to see. The melting of the ice caps, sea level rise, an increase in draughts and wildfires -- all happening before our eyes, as every year we break more heat records.

In my opinion, I think it's undeniable that this is the issue of our time and those of us who aren't in denial should at least put it in their top 3 political priorities and act accordingly.