Pollution is an obvious example - we do not have the option of growing food, or finding enough water, on a squeaky-clean planet, but on one increasingly tarnished and trashed by the way we have used it so far.
Cutting waste and clearing up pollution costs money. Yet time and again it is the quest for wealth that generates much of the mess in the first place.
Living in a way that is less damaging to the Earth is not easy, but it is vital, because pollution is pervasive and often life-threatening.
Soil: Contaminated land is a problem in industrialised countries, where former factories and power stations can leave waste like heavy metals in the soil. It can also occur in developing countries, sometimes used for dumping pesticides. Agriculture can pollute land with pesticides, nitrate-rich fertilisers and slurry from livestock. And when the contamination reaches rivers it damages life there, and can even create dead zones off the coast, as in the Gulf of Mexico.
Chemicals are a frequent pollutant. When we think of chemical contamination it is often images of events like Bhopal that come to mind.
But the problem is widespread. One study says 7-20% of cancers are attributable to poor air and pollution in homes and workplaces.
The WHO, concerned about chemicals that persist and build up in the body, especially in the young, says we may "be conducting a large-scale experiment with children's health".
Some man-made chemicals, endocrine disruptors like phthalates and nonylphenol - a breakdown product of spermicides, cosmetics and detergents - are blamed for causing changes in the genitals of some animals.
Affected species include polar bears - so not even the Arctic is immune. And the chemicals climb the food chain, from fish to mammals - and to us.
About 70,000 chemicals are on the market, with around 1,500 new ones appearing annually. At least 30,000 are thought never to have been comprehensively tested for their possible risks to people.
But the snag is that modern society demands many of them, and some are essential for survival.
So while we invoke the precautionary principle, which always recommends erring on the side of caution, we have to recognise there will be trade-offs to be made.
The pesticide DDT does great damage to wildlife and can affect the human nervous system, but can also be effective against malaria. Where does the priority lie?
Chemical pollution was blamed for killing fish in Kankaria Lake in Ahmadabad, India
The industrialised world has not yet cleaned up the mess it created, but it is reaping the benefits of the pollution it has caused. It can hardly tell the developing countries that they have no right to follow suit.
Another complication in tackling pollution is that it does not respect political frontiers. There is a UN convention on transboundary air pollution, but that cannot cover every problem that can arise between neighbours, or between states which do not share a border.
Perhaps the best example is climate change - the countries of the world share one atmosphere, and what one does can affect everyone.
For one and all
One of the principles that is supposed to apply here is simple - the polluter pays.
Sometimes it is obvious who is to blame and who must pay the price. But it is not always straightforward to work out just who is the polluter, or whether the rest of us would be happy to pay the price of stopping the pollution.
A recent study detailed the plastic litter that pollutes the marine environment
One way of cleaning up after ourselves would be to throw less away, designing products to be recycled or even just to last longer.
Previous generations worked on the assumption that discarding our waste was a proper way to be rid of it, so we used to dump nuclear materials and other potential hazards at sea, confident they would be dispersed in the depths.
We now think that is too risky because, as one author wrote, "there's no such place as 'away' - and there's no such person as the 'other'".
Ask not for whom the bell tolls - it tolls for thee, and for me.