Peter Anderson points out that human metabolism produces huge amounts of CO 2 , Jonathan Cockburn says massive population growth is causing climate change, while Richard Vernon says educating women is the key to population control

As you say, the cement component of concrete generates much CO 2 (Concrete: the most destructive material on Earth, 26 February). Roughly 1 tonne of CO 2 per tonne of cement. Or 1 million tonnes per year of CO 2 for a small-sized plant. Cement consumption per capita is between 50kg and 2,000kg per person per year, depending on the phase of development of the country and the availability of alternative building materials. Taking an unholy average, each member of the human population is responsible, through their fondness for a built environment, for roughly 500kg per year of CO 2 from cement. What you forgot to point out is that human metabolism contributes roughly 300kg per person per year of CO 2 through exhaled breath. Perhaps more in Westminster, the offices of newspapers and the vicinity of sports grounds. The annual US dollar turnover of the worldwide cement industry, by the by, is only 60% of that of Walmart.

Suffice to say that the most destructive material on Earth is not concrete. It’s not oil or coal either. The most destructive material on Earth is human flesh. The clue is in the anthropo part of anthropogenic climate change. If you really want to save the planet a radical cull is required, but if you’re too tender for that, worry not. The Verhulst model for population growth suggests that the adjustment will happen of itself.

Peter Anderson

(Consulting engineer to the cement industry), Barwick-in-Elmet, West Yorkshire

• In George Monbiot’s manifesto for climate strikers (Opinion, 20 February), he suggests: “The world has been thrown into climate chaos, caused by fossil fuel companies, the billionaires who profit from them and the politicians they have bought.” And he proposes the restoration of the “benign conditions in which humans and other species can thrive”.

Unfortunately, he’s completely missed one of the main issues driving climate change, namely the huge increase in the number of people living on this planet. When he was born in 1963 the world population was 3.2 billion. Today, just 56 years later, it’s around 7.7 billion. It’s precisely the success of our thriving human population that is causing untold damage around the world to the “other species” he mentions. We’re adding around 81 million people a year to the world’s population, and climate change is just one of the consequences of massive population growth. It’s no good just reducing carbon emissions; we also need to have fewer children. This will be the fastest way to save our planet.

And politicians, economists and businesspeople must stop talking about “growth” being a good thing. We urgently need to start planning to decrease our population growth and our economies and world travel, and put a halt to flagrant spending on throwaway goods etc. Only then will our (far fewer) grandchildren have a better life.

Jonathan Cockburn

Hewelsfield, Gloucestershire

• Jonathan Watts does us an important service (Decline in biodiversity ‘threatens food crisis’, 22 February) in bringing to our attention the comprehensive UN report on the state of the world’s biodiversity with respect to our need for food, and the many factors threatening food production.

Too often, particular threats to humanity are identified, attracting justified concern and attention, when they themselves have a more fundamental upstream cause. Climate change is driven by climate changers, all 7.7 billion of us, increasing at more than 80 million annually. Each new soul will need additional food, energy, housing, education and health services, and clean water and air in an increasingly polluted world.

We have to talk about population. Charities such as Population Matters, for whom Sir David Attenborough and several other scientists are patrons, show how entirely non-coercive and proven ways are available for the reduction and reversal of population growth urgently required. When women have access to education and contraception, they will not choose to have more children than they can support. Population decline follows.

Richard Vernon

Iffley, Oxfordshire

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