13.6 Threats to Life on Earth
Life on Earth rests on a delicate balance of living and non-living systems. Just a little less oxygen, a slightly warmer planet, or a thinner ozone layer could endanger life — and human actions are now disturbing that balance.
The Triple Planetary Crisis The three biggest environmental challenges, together called the triple planetary crisis, are:
- Climate change — long-term shifts in temperature, rainfall and weather;
- Biodiversity loss — the disappearance of plants and animals;
- Pollution — of air, water and soil.
They are connected, and each makes the others worse.
Climate change
The Greenhouse Effect, Pushed Too Far Burning fossil fuels (coal, oil) releases greenhouse gases like carbon dioxide and methane, which trap extra heat — causing global warming. Normally, trees, plants and ocean plankton absorb CO₂ and keep the balance. But burning fossil fuels releases carbon locked underground for millions of years, faster than the Earth can absorb it, so heat builds up. Even a small temperature rise can melt ice caps, raise sea levels (flooding coastal cities), cause extreme weather, and make many species vanish.
Biodiversity loss and pollution
When the Web Frays When habitats are destroyed, species disappear and ecosystems unravel (Chapter 12): lose the grass, and deer and grasshoppers struggle — and the tigers and foxes that eat them lose food too. Every species has a role, and losing even a few weakens nature’s ability to support life. Pollution adds to the harm: air pollution causes breathing problems, smog and acid rain; water and soil pollution from factory, farm and plastic waste poison aquatic life and spread harmful substances through the food chain.
Ever Heard Of… The World Working Together Countries have made global agreements to protect the environment: the Montreal Protocol (1987) cut ozone-destroying CFCs, helping the ozone layer slowly recover; the Earth Summit (1992) launched action on climate and biodiversity; and the Kyoto Protocol (2005) and Paris Agreement (2015) committed nations to cut greenhouse gases. The Paris Agreement aims to limit warming to below 1.5 °C — but as of 2025 the world is not on track, and much more action is needed.
What we can do
Everyone Can Help Earth’s four spheres are all connected, so protecting one protects the rest. We can cut greenhouse gases with renewable energy (solar, wind), use energy wisely, and travel cleaner. We can preserve biodiversity (diverse ecosystems are stronger) and use resources sustainably. And small daily actions add up — reuse, repair, recycle, save energy and water, and share what you learn. Sustaining life on Earth needs all of us, from local communities to global leaders.