The Limits to Growth, published in 1972, delivered a depressing message to humanity: even with modern technology, the Earth’s resources are limited, and current rates of population and economic growth are unlikely to be sustained through the end of the 21st century.

It turns out that the message still merits our attention 50 years after it was mocked by economists at the time.

Thomas Murphy, a professor of physics at the University of California, San Diego, asserts that, notwithstanding the lack of absolute confidence over whether or not the world will experience an unavoidable catastrophe by the end of this century, our current course cannot be maintained for much longer.

His findings can be found in a recent comment paper from Nature Physics.

Murphy, an astronomer by training, became interested in planetary limitations while teaching a seminar on energy and the environment. Students investigated the mechanics of energy, how to assess energy demand and resources, and the environmental consequences. Murphy understood that the problems with resource and energy consumption were more serious than most people thought.

“This is something not enough people are paying attention to,” says Murphy. “What does life look like after resource depletion? What actions can we take now to mitigate the worst outcomes—and how do we get people to take this seriously?”

When considering fossil fuels, mined minerals, or land, it is obvious that the Earth has finite resources, but it can be challenging to envision a time when humankind will have to modify its way of life to account for these limitations.

The author of the book Energy and Human Ambitions on a Finite Planet, Murphy, argues that in the past, the Earth was able to support our growing resource demands. 

“But remember, the Earth has never hosted 8 billion humans before, all of us pursuing increased consumption demands. We cannot base projections for future resources on the past. This is uncharted territory.”

Murphy used our historical growth rate of a factor of ten each century to project future energy usage. If people consume 18 TW (terrawatts) of energy globally now, that amount will increase to 100 TW by 2100, 1,000 TW by 2200, and so on. In 400 years, we would use more energy than the Sun gives off on Earth, and in 1,300 years, we would use more energy than the Sun gives off in all directions.

Using the same growth rate to estimate future levels of waste heat (the end product of all our energy use, which is ultimately radiated into space) similarly presents a bleak outlook: the quantity of waste heat produced would accelerate, leading to a rise in global temperatures. The Earth’s surface will reach the boiling point of water in about 400 years.

Murphy says that this extrapolation of energy use and wasted heat is not realistic and is not a prediction. It was designed to demonstrate how our previous, unrestricted growth cannot last into the future indefinitely. In fact, if the progression shows anything, it’s that the time when people on Earth can use energy without limits will be short compared to how long civilization has been around.

Even the most pessimistic economists will admit that the Earth’s physical resources have a finite amount. However, many argue that this won’t have an impact on economic growth because once money is “decoupled” from physical resources, it will be able to grow unrestricted by the depletion of fossil fuels or minerals.

Some people would argue that money is not subject to the laws of physics or that we can maintain economic development by innovating, according to Murphy. But those things are not exempt from constraints. Even if you consider the virtual world, the resources needed to create and maintain those machines are tangible. That is evident in the enormous amounts of energy that bitcoin mining uses.

Murphy acknowledges that many economic activities don’t necessitate the intensive use of physical resources. For instance, jobs in the legal and financial sectors essentially involve the use of computers, lighting, and heating, rather than the fabrication of concrete and steel. And it may be simple to believe that the fraction of disconnected activities will continue to increase while resource needs continue to drop indefinitely, the demand for physical resources will eventually reach a threshold where it cannot fall any further. As Murphy points out, there will always be a demand for food among humans.

“We don’t see the economic growth we’re currently experiencing for what it is: a phase,” adds the researcher. “And one reason we don’t see it is because we don’t want to and have never had to. Continued growth spares us from having to address the issue of reallocating present resources more equitably.”

He observes that the alleged advantages of economic expansion have two sides. People may be lifted out of poverty and given improved access to food, water, and healthcare as the economy expands. As their populations increase and their living standards rise, the increased resource demands put an undue strain on the planet’s ability to provide these same advantages.

Long-term planning, according to Murphy, is the actual solution and necessitates a fundamental change in the way we view ourselves as a species. 

“We need to change our relationship with the planet. We need the humility to accept that we do not own the Earth,” says the author.

“But how do you convince somebody of something that’s never happened before, lies in the future and requires sacrifice?

“I hope that we can plant some seeds soon that will lead to wiser decisions down the road.”

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