GOOD morning. I would like to start by saying how pleased I am to see so
many of you at the Edinburgh Science Festival in this first year of the 22nd
century. My role today is to discuss the Great Depopulation that took place
last century, leaving us with today's global total of around two billion
people - about what we had back in 1950.

It was Thomas Malthus who, in the 18th century, first suggested that a
growing population might outstrip its food supply. It didn't happen in
Malthus's day, of course, or for the next two centuries. Even when the rate
of growth of the world population hit its peak in the 1960s and 1970s,
scientists kept crop yields ahead of demand, thanks to the "Green
Revolution", which eventually introduced high-yielding crops, chemical
fertilisers and mechanised agriculture to every region capable of using
them. There were sporadic famines, but they were triggered by uneven
distribution of wealth.

By the 1990s it was apparent that population growth had slowed, and in 1994
demographers predicted that numbers would stabilise at 9 billion by 2050.
Many people stopped worrying about a population crisis.
As we all now know, the demographers were half right. The population did
reach 9 billion. But it didn't stay there long. By the 2050s, food
production was declining sharply, and in many places, high-yield agriculture
collapsed completely. This led to the great famines. Meanwhile, population
density triggered two other agents of decline: the great migrations and the
plagues. World population plummeted.

What happened to turn the sunny forecasts of the 1990s into the horror that
followed? In retrospect, it seems obvious: the Earth could feed 9 billion
people - but only for a short time. The environmental cost was too high to
be sustainable. To put it simply, we ran out of soil and we ran out of
water.

We destroyed the soil by using harmful farming technologies to wring more
crops out of the land. Chemical fertilisers could replace the mineral
nutrients taken by the plants, but couldn't restore the soil's fine
microstructure. Excessive ploughing, and compaction by heavy farm machinery
left the soil prone to erosion. It simply blew and washed away.
This process was well under way by the late 20th century. Indeed, in 2001 a
report by the World Resources Institute, an American environmental think
tank, found that soil and water degradation were already decreasing yields
on 16 per cent of the world's agricultural land.

We knew the danger, but in many places little was done to slow soil
degradation. This was partly because research on soil structure dropped to
almost nothing when most agricultural research was privatised at the turn of
the century. But it was mainly because demand for food was increasing, and
it proved hard to move away from the old technology while maintaining
yields.

Eventually, soil degradation helped to halve yields across Australia,
eastern Asia and Europe. The great dust storms of the 2050s whipped millions
of tonnes of irreplaceable topsoil off the land and brought famine even to
wealthy nations.

North America was spared this problem. Ploughing had always served mainly to
control weeds, and North American farmers replaced it with weedkiller after
the introduction of genetically engineered, herbicide-tolerant crops. Europe
rejected genetically engineered crops until 2035, but by then it was too
late - crop varieties engineered for North America could not thrive in its
degraded soils.

But North America had other problems, primarily water shortages. Many
irrigated regions were using up ancient, underground deposits of water,
while others drained rain-fed aquifers faster than they were being
replenished. Many parts of the world faced the same problem. Even in 2000,
the fertile Punjab was pumping irrigation water from aquifers twice as fast
as rainfall could replace it. By 2020, these had nearly run dry, as had
those beneath the breadbasket region of northern China. The Ogallala aquifer
in western North America collapsed soon after. In these regions, farmers had
to go back to relying on rainfall, just when climate change began to make
that less predictable.

Even where water supplies did not depend on aquifers, the swelling
population pushed demand for drinking and irrigation water beyond supply. In
2001, the populations of what were then Egypt, Sudan and Ethiopia were on
course to double within 50 years. Ethiopia had used irrigation to intensify
its highland agriculture, but it needed a more reliable supply of water. So
in 2026, it began damming the Blue Nile.

Egypt, which received 80 per cent of its water from the river, reacted by
destroying the dam that year and, after a bloody war, annexed the entire
Blue Nile catchment. Similar pressures, and the exhaustion of the Negev
aquifer, led Israel to take control of the Jordan in 2029, while Iraq bombed
Turkey's Ataturk Dam on the Euphrates two years later. These are generally
considered the first of the continuing water wars.

Food from the oceans plummeted, too. Astonishing as it seems, a hundred
years ago wild fish from the seas provided protein for billions of people.
But we took fish out of the sea faster than they could reproduce, and by
2020 many major stocks had collapsed. A global ban on fishing might have
allowed some to recover even then, but the demand for protein was so great
that no one could muster the political will. Those once rich ocean areas are
now dominated by species that provide little protein. In most cases this
change is expected to be permanent.

Even as the fish harvest dwindled, urban prosperity increased, notably in
East Asia. This led to skyrocketing demand for milk and meat. Thirsty farm
animals increased the demand for water. But their major impact was on grain
reserves: it takes 3 kilograms of grain to produce 1 kilogram of meat. So
long as meat eaters could pay, the huge Chinese pig conglomerates, for
instance, could easily outbid poor people for grain on the global market.
Prices trebled in the 2020s, starting a wave of famine.

What were the scientists doing all this time? After all, by the turn of the
millennium many of the threats to the global food supply had been predicted.
Some fields were already nearing the limit of what they could grow. The high
yields achieved by the Green Revolution came from crop varieties that put
more of the carbon they fixed through photosynthesis into grain, and less
into stalks and leaves. By 2000 we had pushed the plants to their limits.
And in places such as the rice fields of Japan, we were already pouring on
as much nitrogen fertiliser as the plants could handle.

Still, there was room to improve yields in much of the world, and optimists
proposed numerous technical fixes, such as better crop varieties and farming
technologies. In many cases people did develop fixes. But often by the time
these were ready, the problem itself had changed. What defeated us, I think,
was the complexity of the problems and the speed at which they changed. The
goalposts kept moving.

The greatest challenge, of course, has been climate change. As we know, it
is now too warm or wet or dry to grow wheat in most places where it thrived
a century ago. Where there is still enough soil and water, varieties of
maize and sorghum deliver substantial yields - but it took a while to
develop them.

Likewise, many of us would not be here without the genetically engineered
high-yield barley the Russians and Canadians now grow in the Arctic. But it
took two decades of research to develop varieties that could thrive on
melted permafrost.

Changing climates also meant changing pests. After the north Chinese aquifer
ran dry, plant breeders engineered a dry-land variety of wheat. But as the
region warmed up, exotic insect pests and diseases moved north. The new
wheat, designed to cope with the old pests, proved susceptible to the
newcomers. Breeders introduced variety after variety to respond to each new
problem, but never quite kept up.

This frenzy of crop development brought its own problems, as breeders tried
to work a few high-yielding characteristics into all regional varieties. By
the time fulminating wheat bunt broke out in 2047, almost every strain of
wheat in the world carried the same set of genes involved in photosynthesis.
Unfortunately, the bunt fungus attacked the very characteristics coded for
by those genes. In 2053, the disease wiped out nearly all the world's wheat
crop. Global wheat production still hasn't recovered.

The increasing globalisation of trade cushioned the initial regional food
shortages. The Rio Plus Ten global conference of 2002 famously predicted
that all famine would cease, as production shortfalls could be met by
imports. But this missed the point that increasing global trade was already
spreading invasive, alien insects, plants and microbes throughout the world.
No longer held in check by natural predators, these visitors turned into
pests. Worse, these new pests, like the old ones, quickly became resistant
to the chemicals farmers used to control them. The big corporations had a
hard time finding new pesticides.

In the face of all this, many farmers joined a worldwide exodus and sold
their land to the expanding cities. They swelled the numbers of unemployed
in these conurbations, a process that was already under way in the 1990s in
megacities such as Shanghai. The hungry, out-of-work urban hordes caused
political upheaval nearly everywhere, which in turn triggered huge
migrations of people seeking a living or escaping violence. The struggle for
costly food, clean water and healthcare increased tensions between rich and
poor - especially as TV and the Internet constantly reminded the poor of
what they did not have.

The sheer size of some cities created its own problems. Getting massive
quantities of food in, and waste out, became harder and harder. When either
process faltered, even briefly, people died because of violence, efforts to
flee or plain starvation.

Worst of all, as the megacities mushroomed, the densely packed masses of
hungry people became a perfect breeding ground for epidemics. Simple
overcrowding spread diseases such as leprosy, which re-established itself in
Europe in the 2030s. As cities outgrew their sewerage and drinking-water
systems, the decline in hygiene ushered in killers such as dysentery.
Warming, trash-strewn cities helped launch the bubonic plague pandemic of
2047. Typhus returned worldwide in 2056. Overburdened medical services
couldn't deal properly with any of the diseases, especially after the
widespread emergence of drug-resistant bacteria made antibiotics redundant.
The vast numbers of displaced people were also a factor in the spread of
disease, including the re-invasion of North America by malaria - a process
aided by warmer winters. In Africa and South America, ever-expanding human
settlements invaded new territories, notably deserts and tropical forests.
This led to novel encounters with local fauna, and the emergence of at least
two dozen new diseases, including monkeypox and the haemorrhagic virus that
caused Europe's worst disease mortality since the Middle Ages.
Agriculture gave us yet more plagues. Animal diseases that attack humans
flourished - the Flanders flu, which emerged from pigs in 2018, was the
first of five flu pandemics last century. But new ones also emerged in
giant, crowded livestock barns, helped by the global movement of animal
produce. Human-adapted foot and mouth virus (HAFMV) emerged in Taiwan in
2065, and spread uncontrollably.

Safety precautions could have prevented the emergence of these infections.
But as both demand and the cost of food and water soared, hard-pressed
farmers could not afford them. At the time of the first prion disease, for
instance, Europe could afford to incinerate more than a million cattle that
were mainly infected only in their brains. The thought is shocking today.
Famine, war and pestilence have always figured in human history, but their
fury has redoubled over much of the past century. The breakdown in our
natural support systems of soil, water, climate and crops happened too fast
for us to cope.

Could we have avoided any of this misery? I think so, if we had acted early.
We did once have the technology - or the ability to develop it - that would
have fed 9 billion, kept them free from disease and perhaps living in peace.
But we never stayed organised socially, politically or economically for long
enough to deliver the solutions when and where they were needed.
Sometimes I wonder whether it would have been different if, when industry
globalised at the start of the millennium, political power had globalised
too. I know the idea of global government is a heresy. But so many of our
crises were outside the realm of corporate concern, and beyond the power of
national and regional governments. A global authority might have been able
to monitor and perhaps stem the spread of human, animal and crop diseases.
It might have launched earlier research into foreseeable dangers, such as a
wheat crop that depended on only a few proprietary genes. It might have
provided jobs in time to prevent some of the mass migrations. We who remain
can only wonder what would have happened if it had.