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Planet Earth's nine lives:
Our planet's limits

Planet Earth's nine 'lives': what are they?

If you've looked at some of my other guides, you'll already know something about what humans are doing which affects our planet. Most of the nine planetary 'lives' are still okay but three of them are not. Bad news, you might think. But the good news is that you people can fix them if you have the will. You and your fellow humans, acting together, have so much power if you choose to use it wisely. It may take you some time but you can do it!

The scientists now know there are nine planetary boundaries ('lives'). Think of the white line which marks out a tennis courtInformationThanks!It was Johan Rockström who thought up this metaphor. He was the lead scientist in this planetary boundaries work. You'll see and hear him at the end of this guide in a video. If you hit a ball which lands outside the boundary, you lose a point. Everyone can see where boundary lines are so the game works. But what if you didn't know where the boundaries were? How could you know if the ball was 'in' or 'out'? Humans have been 'playing' with our planet's resources without even thinking that there might be boundaries. But now, thanks to science, the boundary lines are clear. No-one will now be able to claim that they didn't know about these limits, though some people will be sure to ignore them and claim they don't believe the evidence.

Here's another way of looking at this. Imagine you're driving a car about in the desertInformationThanks!This metaphor - which I've modified slightly - comes from Jon Foley, University of Minnesota, and one of the original planetary boundaries team. You can see him in a great, very short video at the end of this guide.. It's dark and the headlights go out and you know there are cliffs which plunge down to a canyon somewhere nearby. Do you carry on driving and hope for the best? Or do you wait till daybreak so you can see clearly where those cliffs (boundaries) are? I think I'd wait till daybreak, wouldn't you?

The nine planetary boundaries:

1. Climate change: the planet is heating up and could soon do so much faster
2. Acid oceans: the seas are becoming hostile to animals with shells
3. Ozone depletion: the ozone layer which protects us is damaged
4. AerosolInformationWhat in the world are aerosols?Aerosols are tiny particles which are so light that they're supported by the air and loft high into the atmosphere to spread around the planet loading: soot and smoke from burning fuels and forests
5. NitrogenInformationAbout NitrogenNitrogen, chemical symbol N, is vital for plant growth. It makes up most of the air we breathe but is non-reactive unless combined with other elements. It is the reactive forms of N which are the problem and phosphorusInformationWhat is phosphorus?Phosphorus, chemical symbol P, is also vital for plant growth cycles: nature can't cope with all the fertilisers used by farmers
6. Fresh water: most fresh water on or under the landInformationAquifersNatural underground water stores, which can be vast, are called aquifers is now being used by humans. Many rivers don't even reach the sea any more
7. Land use: there's a limit to how much land humans can farm
8. Biodiversity loss: life itself is in danger as extinction looms for many animals and plants. Whole ecosystemsInformationWhat are ecosystems?An ecosystem is an interconnected web of living things. Damage one part of it and the whole system may collapse are threatened and yet people depend on them utterly
9. Chemical pollution: artificial chemicals used around the world harm humans and wildlife

Sounds boring? Or too complicated? Big sciency words can be off-putting, I know. That's why I've written this guide for you: to explain the scientists' new understanding of how our planet works; a basic book of rules for running planet Earth safely. Because now, you people with your powerful technologies, are almost like gods. You have the power to change the planet for good or for ill. Use your power wisely... and soon!

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