Oh Harry, it’s all a bit complicated isn’t it? From extracts released of a Vogue interview you have done with the great primatologist Jane Goodall, you imply that you plan to have just one more child because of your concerns about the environment.

Well, compared with your parents and grandparents, that’s a good start. But the planet is not responding well to your jet-setting lifestyle, and two more little Sussexes adopting Dad and Mum’s ways won’t help.

To make any difference to planet Earth, you and your family really must stop taking those private jets to Jamaica, the luxury safaris in Botswana, the weddings in Montego Bay, the impromptu winter getaways in Tromsø, the “babymoons” in Australia and New York, the downtime on Mediterranean islands and the quick flights to Fiji. Not to mention the ecological cost of living in all those grand houses and palaces or going on the royal tours.

But you are right to link the fate of the planet with human population increase. It would be a dereliction of responsibility these days not to protect the planet, and many of the great conservationists, like Jane Goodall, David Attenborough and Chris Packham, recognise that the near tripling of human numbers in the past 70 years, along with the huge increase in the consumption of resources by the wealthy, have been responsible for the collapsing ecosystems, the climate crisis and pollution.

So, of all the lifestyle choices you could make, having one less child is by far the best option. Research from Lund University in Sweden found that by choosing to have one less child, a parent would reduce their CO2 emissions by 58.6 tonnes a year during their lifetime; over 25 times more than from any other action. Getting rid of the car, avoiding long-haul flights and going vegetarian are all well and good, but these actions, say the researchers, save very small amounts of CO2 in comparison with having one less child.

And, Harry, you are no ordinary parent. In ecological terms you and your family are a herd of elephants trashing the forest. Over a lifetime, the average British-born babe will emit up to 150 times more CO2 than one born in Ethiopia. You are only 34, and you have probably already emitted more CO2 and other greenhouse gases than most of the 18 million people living in Malawi will do in their lifetimes.

But it’s good that you spoke to Goodall, because very few people want to admit the inconvenient truth that population is a primary driver of global ecological crisis. Most political parties and environment groups are afraid to talk about it because it smacks of prejudice against countries with higher birth rates. How much easier to close the debate and blame all biodiversity loss and climate change on the rich for their profligate lifestyles.

Consumption matters, of course, but so do sheer numbers. World population, which currently stands at 7.5 billion, is increasing by 82 million people a year and looks likely to reach 11 billion within the lifetime of Prince Harry’s children. Sustaining another 3.5 billion people, or an extra India and China, will inevitably impact on climate, oceans and forests, and deplete natural resources. Many in areas of high growth want fewer children but cannot access contraception.

However, population growth, resource consumption and environmental impact are closely linked, and there is little chance that the great extinction of species the world is seeing and the climate emergency can be turned round unless they are addressed together.

As David Attenborough says: “It’s not just climate change; it’s sheer space, places to grow food for this enormous horde. Either we limit our population growth or the natural world will do it for us. The natural world is doing it for us right now.”