By Tony Ryan, University of Sheffield

For almost all of our species’ 200,000-year history, man’s relationship with the Earth was no different to that of any other animal. All their energy was provided directly by the sun. Sunlight captured by plants using photosynthesis was converted into food and fuel. They ate roots, fruits and grains (and animals that also ate roots, fruits and grains) to provide their bodies with energy. They burned wood to keep themselves warm and fat to provide light at night.

It was a successful strategy for survival and over tens of thousands of years the human population spread across six continents.

However, locked in to this natural solar cycle, there was a limit to how many people their lifestyle could support, and the total number of inhabitants fluctuated below 500m depending on disease, wars and food supply.

Then, 350 years ago, everything changed. We began to supplement our energy needs with coal and oil (humans had been using coal since pre-historic times but not on a large scale). This was still energy from sunshine, but this time millions of years old. In less than two centuries the human population exploded, doubling in size to 1 billion people. It has continued to grow ever since, but the rate of change has increased significantly. It took 100,000 years to reach the first billion people: today we are adding a further billion every 12 years. The result is a huge squeeze on all natural resources. Over the next two decades we will witness huge increases in demand for energy, food and water – a perfect storm.

This is our fourth century of exponential population growth. In the past, humans coped by burning more fossilised sunshine in the form of coal, oil and gas, and expanding the amount of land under cultivation or using more artificially-produced fertiliser. But those solutions simply won’t work any more, not least because of anthropomorphic climate change caused by the release of carbon dioxide from the combustion of those fossil fuels. Our remaining stocks of fossilised sunshine are harder to get at and we are running out of fresh water and new places we can farm. A new study by colleagues of mine found that one-third of the world’s arable land has been lost to pollution and erosion over the past 40 years.

Looking to the future, the key question is not simply: “How many people are there going to be?” but rather: “How are they all going to live?”

In 2012, the Royal Society sought to address this issue in a publication called People and the Planet. This report’s frank conclusion was that in the developed and emerging economies, consumption has reached unsustainable levels and must be reduced immediately. It claims that the increase in population will “entail scaling back or radical transformation of damaging material consumption and emissions and the adoption of sustainable technologies. This change is critical to ensuring a sustainable future for all.”

We have been here many times before. The whole of human history is essentially the story – albeit usually on a local scale – of population growth and increasing competition for resources. Since ancient times wars have been fought over land, water, food, fuel, metals and other natural capital, while many civilisations have also faced destruction as a result of disease, famine and shortages.

Where we have overcome these challenges in the past it is invariably ingenuity and innovation that have provided the solution. And we will require those same qualities in abundance, because we have never had to tackle problems of this magnitude before, nor on a global scale.

Achieving this goal is possible and realistic, but it will not be easy.

It will not happen by accident and it will bring changes for all of us, both in the way that we live and in what we consume. It is without doubt the biggest challenge of our age.

This statement is not intended to belittle the impact of climate change, but the repercussions of global warming will play out over decades; we have some time to adapt and respond to the consequences. In contrast we are already living with the results of explosive population growth: rising fuel and food prices, wars, immigration, famine, energy shortages and economic uncertainty.

These issues affect us all today and all are a direct consequence of adding one million people to the population of the world every five days.

Big problems usually require radical solutions, but there are genuine grounds for optimism. Fundamentally, we need to reconnect the global economy with the sun and live within our means, just as we did in the past. Capturing a single hour of the sunlight that reaches the Earth – a tiny fraction of our star’s output – would meet our global energy needs for a whole year.

Harnessing the power of the sun will allow us to meet the increasing food and energy needs of the world’s population in the context of an uncertain climate and global environment change.

Sustainable routes to food and energy security can be found, but time is of the essence and the clock is ticking.

Tony Ryan, Pro-vice Chancellor for Science and Director of the Grantham Centre for Sustainable Futures, University of Sheffield

This article was originally published on The Conversation. Read the original article.