There’s an elephant in the room, but there is also one out in the garden and another in the shed. In fact I’m thinking of buying the field next door to accommodate more elephants. Very few people will notice them, because these are elephants we really don’t want to see, and want to tame even less.

The elephant is human population growth.

This spring I went to Cambodia, which suffered the most horrific conflict during the 1980s which killed up to a third of the population of six to seven million. A few decades later the figure has bounced up to 15 million. Tour guides proudly told us of the burgeoning industrialisation of an economy once almost entirely based on agriculture. Expecting to see the infamous jungle of ‘Nam movies, I mainly saw fields, fruit groves and rice paddies. Family size is falling with industrialisation, but the transition was stark. Farmers are cutting back the forest to create more land and I saw new roads leading to cleared wasteland and raised platforms designated for ‘new cities’ in flood-prone areas.

Moving on to Vietnam, the jungle was mainly absent too. Paddies and farms stretched along the banks of the Mekong. At over 90 million, ‘Nam has 2.5 times the population it had at the start of what they call ‘The American War’ despite the widespread slaughter and economic destruction. Whilst Cambodia still has a more traditional feel, Vietnam is on the path to looking like everywhere else: skyscrapers, billboards, traffic junctions, shopping malls and take-aways. At each major junction in Saigon (as most locals still call it), a phalanx of motorbikes eight wide and ten deep awaits the changing of the lights. They set off in a roar, weaving between each other in a great shoal. My thought was; ‘Whatever happens when all these people get cars?’

The tourist sites were heaving. Used to the ‘busy’ days in Guernsey when we were lucky to get 3 or 400 people turning up at the Castle I was in a whole different world. Hordes poured into the semi-abandoned jungle-clad ruin of Ta Prohm. Some 15,000 per day go into the Angkor Wat complex,  mostly Chinese, Koreans and a few Australians. Most will have flown.

Racking up my air miles, knowing I’m doing more damage to the climate than those motorcyclists, I looked out of my airliner window in the small hours, down into the darkness of the ‘stans from a few miles up. Or it should have been darkness, based on how blank all the atlases of that region look. Instead there were city lights, glittering as orange jewels, scattered in all directions. The world felt scarily full at that moment.

I came back to the interminable Brexit debate, and we know ‘Leave’ was in large part fuelled by fears over immigration. Those fears were bumped up by the exodus from Syria and Libya and other war-torn regions. We might imagine these wars are about one religious sect fighting another because they wear the wrong colour hat on Fridays, but like most wars resources are the root cause. Land is in short supply, fertile land is even scarcer and fresh water is at a premium across great swathes of the world. Bloody squabbles erupt over oil, diamonds, copper and so forth. Fuel is running out and shortages are likely to spark even more conflicts. ‘Rare earth’ metals on which much modern technology such as my smartphone relies are becoming rarer.

Millions are now living on mountains, volcano slopes, in swamps, in deserts, below sea-level, on tiny islands, in arctic regions and where jungle used to be. These areas could not naturally sustain more than a handful of human bands, yet we are building cities. Who is surprised when these areas are devastated by wildfires/ cyclones/ floods/ famine/ drought? Humans are not supposed to live there.

Nobody knows what the ‘carrying capacity’ of the Earth is but at 7.7 billion people and rising we may find out the hard way. It certainly cannot sustain 7.7 billion Americans, and who is to deny all those people the standard of consumption the Americans enjoy?

Environmentalists for the most part don’t want to talk about population. It smacks of poor-shaming and lets the resource-guzzling West off the hook. The UN doesn’t want to talk about it either; why should the West have it so good and not everyone else? Government control of population smacks of authoritarianism; it offends liberals, libertarians and ultra-conservatives alike, whilst the left would rather blame capitalism for the world’s problems. Birth control of any form also offends numerous religious groups.

Last year the world hosted an extra 82 million people, that’s an additional 160,000 more per day. It’s more than died in the whole Second World War and it would take a pandemic on the scale of the Spanish Flu or Black Death to significantly knock it back. Most growth is in the poorer regions of the world already groaning under the weight of numbers and environmental degradation. Their cities are choking with pollution.

It is not surprising millions want to move to Europe or America, and it is unsurprising that Europeans and people who have already made it to America don’t want their already overcrowded lands crowding even more. I saw a t-shirt on sale in South Dakota reading ‘Fuck off, We’re Full’. You can buy them on Amazon, car stickers too. Trump and his ilk use unpleasant language, but they articulate the fears of their electorate.

Migration is part of the human story, it has happened since the dawn of time. It has brought marriage and trade, the exchange of ideas and culture and it has brought prosperity to many. It has also brought war, exploitation, slavery, discrimination, disease, resource-raiding and extermination. Opposing migration is commonly decried as racist, a denial of human rights and a policy of the far right. Left-leaning Greens don’t have an anti-immigration/population control stance, yet population growth undermines efforts to consume less and preserve wild places. The net 270,000 people coming into the UK in 2018 is equivalent to a new city with the footprint of Newcastle, and even if they are poor when they arrive we can’t ban them from one day owning Range Rovers, flying to Florida or eating beef.

Across Europe we have seen the rise of ‘populist’ candidates with simplistic messages and ‘far right’ anti-immigration parties in a mood that smacks of the 1930s. A major problem is that Liberals and centre/right democrats have vacated the debate as too hot to handle. It is easier to attack the Alt-Right on the basis of their rhetoric than on the uncomfortable problems provoking it, so pragmatic discussion is almost non-existent.

We are in very scary, apocalyptic movie territory; No Blade of Grass and Interstellar both play on the results of global crop failures. The crazy world of Mad Max fights over water and oil. As a teenager I was chilled by the overpopulated world of Soylent Green and J G Ballard’s Billenium.

History has shown us that people under environmental stress do not sit still and die. The Migration Period saw peoples from the east moving west in successive waves; Huns, Goths, Vandals, Franks and Saxons. Even the names of these groups still carry echoes of the violence that followed. Illegal immigrants by definition are breaking laws, and criminal gangs are exploiting desperate people from the south prepared to risk their lives for a new home in the north.

The displacement of five million people from Syria is a new factor destabilising the European order, fuelling Brexit, which and in turn threatens the break-up of the United Kingdom. What if 50 million desperate people were on the move? If the climate change Cassandras are even close to being right, a billion could be displaced by rising seas and expanding deserts. No country is going to want them, but who is going to stop them? Unless rational people start to address the difficult issues, irrational people will be left to take the initiative.

We’re going to need a bigger shed.