I was born in 2100.
A long time ago, long before I was born, people used to smoke. The very concept of smoking is unknown to many these days, so let me explain. It's as stupid as eating small rocks, or wood maybe. But it's not that. It was dried tobacco leaves. It would hurt a little the first time people would do it, and even make them caugh. But then, as they kept trying, the pain would eventually fade away. After some time, they might even start to feel some joy when doing it. Or maybe they pretended to and forced themselves to believe it. Or maybe it's the social pressure, people did't really why know but they kind of liked it. Or maybe it was the ads in the 70's and 80's. People used to "go on a cigarette break". Except that smoking does your body no good whatsoever. Quite the opposite to be honest. Smoking was killing people so slowly that most people would not even acknowledge it. They would doubt it, refute it.
People were stupid.
A long time ago, long before I was born, people used to move around in big boxes made of steel. They called it a car. Not only did a car take up a lot of space, it also was powered with gasoline (refined crude oil, something that's long gone now). Gas cars used to cause a lot of pollution, especially in big cities. That was bad. Real bad you know. In the 20th century, in less than a few decades, all cities changed and turned into car-centric cities: everything was designed around and for cars, not for humans. People were forced to walk on narrow sidewalks. They also had to endure noise, mostly from passing cars. If that wasn't enough, the only air they could breathe was extremely polluted, causing over 400,000 premature deaths in Europe in 2015.
A long time ago, long before I was born, people used to eat animals. You read it right, A-N-I-fucking-M-A-L-S. Not only wild ones. Actually, most of the eaten animals were raised in farms and fed with antibiotics. Some of them never saw the sunlight. People were slaughtering them: over 60,000,000,000 land animals were killed EVERY SINGLE YEAR in the 2000's. When it comes to sea animals, the figures were much worse... There were the hunters too, pretending to protect the environment and restoring some kind of balance. As if nature needed us for that...
A long time ago, long before I was born, people used to cut down trees (mostly forests) to make room for crop fields... to feed animals which would in turn... feed humans. What a stupidity. No wonder CO2 levels rose exponentially.
A long time ago, long before I was born, people used to worship plastic. Plastic was everywhere, all the time. Single-use plastic was a thing for sure. Plastic bottles, plastic spoons, plastic cups, plastic toys. A shit ton of plastic ended its course in oceans. It played a major role in the decline of sea animals.
A long time ago, long before I was born, people used to care more about jobs than they cared about the environment. Transitioning the car industry from oil to electricity? Too many people said "it's gonna destroy jobs cause electric engines require much less parts and workforce". It's exactly like keeping your job and then the day you retire your house gets burned down versus giving up your job and starting looking for another one but knowning that the day you retire your house will still be there. Jobs vs the Environment.
But all of that is gone now, people don't do that no more. Everyone's fucking dead. Humans. Animals. Forests. Everything is gone. The planet is barely fit to live. Our unsustainable way of life killed us all. Those who remain live harsh lifes. Every day is a fight for survival, for food, for clean water, for power. Most lands people inhabited are underwater now, as the sea level is much higher than in the early 2000's.
It all changed at the end of the last century. The global population was reaching its peak: 10,500,000,000. In less than 20 years, the global average temperature rose by 1.5 Celsius degrees, by far exceeding the worst projections made in the beginning of the century. The Great Global Warming (GGW as they call it these days) was true after all.