Renewable resources

Renewable resources are the ones that show restoration and regeneration over time.

Most of India gets plenty of sunshine. Rivers are filled again and again by rain and melting glaciers. Forests renew themselves. Soil builds itself up again through natural processes.

So solar energy, wind energy, energy from flowing water and timber from forests are all renewable. But the book adds a condition, and the condition is the whole point.

"For them to remain renewable there is a condition — the natural rhythm of restoration and regeneration must not be disturbed." If we cut timber faster than the forest can grow trees, we will in the end use the forest up.

Think of a cut finger. It takes about a week to heal. If you cut it again every two days, it never heals. 'Renewable' is about speed: take more slowly than Nature replaces, and the resource renews; take faster, and it does not.

The Himalayas show this on a huge scale. Industry that runs on fossil fuels, and the cutting of forests, have (among other causes) led to rising temperatures. In some places glaciers now melt faster than snow and rain can replace them, and the plains below depend on this 'water tower' for their water.

Fishing shows the same pattern. Fishing communities traditionally did not fish during the spawning season (when fish lay eggs), which kept fish numbers up. Fishing as a big business brought over-fishing, and tuna (a fish that keeps the ocean in balance by eating smaller fish and shrimps) is still declining despite agreements to protect it.

Two terms worth keeping:

• Ecosystem functions are what Nature does anyway: a forest filters water, stops soil being washed away, and gives animals a home. Trees naturally produce oxygen.
• Ecosystem services are what we get from those functions: clean water, protected farmland, pollinated crops.

And one number to remember: a mature tree produces about 275 litres of oxygen a day, while a person needs about 350 litres.