I read Damian Carrington’s interview with Paul Ehrlich and found Paul’s analysis to ring frighteningly true (Scientist stands by warning that collapse of civilisation is coming, 23 March). His book The Population Bomb predicted starvation in the 1970s, something that was avoided by the “green revolution” in intensive agriculture. The green revolution was the point at which farmers turned away from natural techniques (eg mixed farms and crop rotation) and instead started using chemical fertilisers and pesticides along with hybrid plants whose seeds could often not be harvested for re-use. This led to higher yields at first, but then to exhausted and polluted soil and increasing debt to suppliers.

The role of the green revolution was to “delay the calamity”. But at a great cost to nature. So what was humankind’s reaction to these developments? Instead of stopping to take stock, we became addicted to the consumerist traits of “cheap and abundant” with no thought for the real cost and inherent risk.

The world is now moving into further “revolutions” involving GM crops, the establishment of mega-farms and digitalisation. For me these are newer, more aggressive techniques for “overdrawing our account” with the natural world. And everyone knows that a surefire way to ultimate calamity is to try to pay a debt by taking on more debt.

Hats off to Paul Ehrlich but shame on the human race.

Alan Mitcham

Cologne, Germany

• It is depressing to see the Guardian recycling Paul Ehrlich’s discredited views. The key fact of contemporary population trends is that the birth rate in the developing world is now lower than it was in rich countries a few decades ago. There are no good estimates of the population-carrying capacity of our planet, but it is almost certainly well above the likely peak of population that will be reached in the second half of this century. Reducing the vast global inequalities in energy consumption will do far more for the environment than the ultimately racist idea that the poor have too many children.

Prof John MacInnes

Centre for Population Change, University of Edinburgh

• Paul Ehrlich’s prediction of half a century ago – of the end of civilisation in a decade or two – may be the most obvious aspect of his theory, but it is not the most fundamental. Far more important is his failure to recognise that what he calls the “perpetual growth of human enterprise” is linked not to human activities as such, but to the economic system of capitalism whose raison d’etre is profit making. Every time goods or services are sold, profit is made which is then reinvested to start another cycle of profit making.

This process takes place regardless of whether the profit is directly reinvested to make more commodities, or indirectly by passing it on to others to invest by purchasing their goods or services or by depositing it into a bank which lends it to others to invest. It follows that economic growth and its complementary growth in consumption, what he calls overconsumption, are byproducts of profit making and if they are to be unnecessary, then we have to do away with profit making altogether.

Fawzi Ibrahim

Author, Capitalism Versus Planet Earth

• Paul Ehrlich’s views on population are understandable although such concerns go back millennia. The elephant in the room is that human numbers will only fall if deaths exceed births; we can all complain about other people’s kids but contemplating our own obituary is less popular.

A further concern is squeezing the same population into less space. Climate change is now being fuelled by emissions from melting ice sheets and their knock-on effects; these could easily outweigh reductions from human emissions. Huge numbers of climate refugees may need rehousing in decades to come, to say nothing of food, clothing and the jobs required to afford decent lifestyles. Given the current attitudes to migrants, how keen will richer countries be to take people or to fund moving them to less populous but still habitable areas?

Iain Climie

Whitchurch, Shropshire

• The issue of overstretched cities is an important one (The 100 million city: is 21st century urbanisation out of control? on 1, 19 March). But it is vital not to take “extreme scenarios” as fact or as a call to drastically limit urban growth. Cities do not simply continue to grow along the lines predicted by past trends, but are affected by economic, development and ecological pressures. Urban growth can also help manage total population growth. The evidence shows that as people move into cities they have fewer children because of economic and social pressures.

The implication that African cities are exploding can have damaging consequences for the poorest and most vulnerable people. It can result in governments clearing or cracking down on shanty towns and slums as an excuse to curb population growth. If Africa’s governments see urban growth as an opportunity to provide decent housing and livelihoods for their current populations, rather than panicking about what these may be in the years to come, then an urban future can be created that benefits all and ensures that no one will be left behind as cities grow.

Andrew Norton

Director, International Institute for Environment and Development (IIED)

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