One of the most important developments in economics is something in which economists had no hand: the identification of the environmental limits which humans, busily producing and consuming, cross at their peril.

Earth has existed for about 4 billion years and humans have lived on Earth for about 200,000 years. For almost all of that time we were hunters and gatherers, but 10,000 to 12,000 years ago we settled down, to farm and create civilisation.

Its probably no coincidence that, for about that time, Earth has enjoyed a stable climate, with no more ice ages nor period of great heat, in which palms grew in Antarctica. This is the geological epoch called the Holocene, in which we live although it may be ruled that weve moved to the Anthropocene, a new epoch in which the human species has made major alterations to the planet.

In its modern form, economics can be dated to 1776, when Adam Smith publishedThe Wealth of Nations. Beliefs about how the economy works were well-defined by the time Alfred Marshall publishedPrinciples of Economicsin 1890.

The point is that all economic activity all the efforts of humans to earn a living both depends on the natural environment and adversely affects it. By 1900, there were only about 1.6 billion humans on the planet, not enough to do much damage.

If we wrecked some area, we could just move to somewhere that hadnt been wrecked, while the first bit gradually recovered.

So, at the time conventional economics was established, it was perfectly sensible to assume that the environments role in economic activity could be taken for granted. It was just there and it always would be. It was, as economists say, a free good.

When, from the 1700s, we started burning fossil fuel coal, oil and gas for heat, light and energy, we had no reason to worry that one day it might run out. It certainly never occurred to us that this might end up having an effect on the climate.

It took many decades before scientists began telling us that all the things we were doing to improve our lives cutting down forests, damming rivers, drilling for water, ploughing, fertilising crops, fishing with nets were damaging the soil, causing erosion, killing species, lowering the water table, and damaging the environment in other ways.

However, in just the past century or so, the worlds population has gone from 1.6 billion to 8 billion. Every extra human does a bit more damage to the environment. But thats not the main thing. The main thing thats changed is our use of advances in technology to hugely increase our standard of living and, in the process, massively increase the damage were doing to the environment.

Which brings us to planetary boundaries. In 2009, the Swedish scientist Johan Rockstrom and a scientist from the Australian National University, the late Will Steffen, with many helpers, established a framework listing the key categories of environmental damage, and estimating the amount of damage that could be done to each before the risk increased that the Earth system could no longer recover.

A second update of these estimates, led by an American oceanographer based in Copenhagen, Katherine Richardson, was released last month. With the ANUs Professor Xuemei Bai, Richardson has written an article explaining the planetary boundaries.

There are nine boundaries. Three of them cover what wetakefrom the ecological system: loss of biodiversity (extinction of species), loss of fresh water (pumping too much water from rivers and aquifers) and land use (deforestation).

Something economists didnt know or didnt realise affected them is that the laws of physics say we can never truly get rid of anything that exists on Earth.

All we or the ecosystem can do is change the form of the thing.

Water can evaporate, but its still up in the clouds, for instance. We can cut down a tree, but as it slowly sinks into the dirt, it releases the carbon dioxide it had previously taken up.

This means that all our economic activity leaves in its wake a lot of waste. Not just landfill, but in many other forms.

So, the remaining six boundaries concern the waste our activity greatly adds to what would have occurred naturally. They are: greenhouse gases which cause climate change; ocean acidification (carbon absorbed by the sea); emission of chemicals that deplete the Earths ozone layer; novel entities (synthetic chemicals such as plastics, DDT and concrete); aerosols; and nutrient overload (nitrogen and phosphorus from fertilisers that wash into rivers and the sea, causing algae blooms, killing fish and coral).

Crossing any of these boundaries doesnt trigger immediate disaster. But it does mean weve moved from the safe zone into dangerous territory. And the nine boundaries are interrelated and interacting, in ways we dont yet fully understand.

In 2009, the scientists found wed already crossed three boundaries: biodiversity, climate change and nutrient overload. By the 2015 update, a fourth boundary had been crossed: land use.

And by this years update, only three boundarieshadntbeen crossed: ocean acidification (but only just), aerosol pollution, and stratospheric ozone depletion where an international agreement banning CFCs is slowly reducing the ozone hole we created.

Richardson and Bai say were now well into the danger zone, where we as well as every other species are now at risk. We are eating away at our own life support systems, they say.

One thing to be said for economists is that, unlike some, they dont try to tell scientists how to do their job. Very few economists dispute the scientists evidence that climate change has been caused by human activities.

It was economists who developed the best means to reduce carbon emissions emission trading schemes which other countries have adopted, but Australia rejected.

When our governments decide to act on the other planetary boundaries, it will be economists who work out the best way to do it.

First published in The Sydney Morning Herald October 6, 2023