Okay, Kids. Here's Your Inheritance. You Owe $535 Trillion Dollars.

Imagine if your older generations had handed you a tab of $535 trillion.

That's the estimated cost of "negative emissions" technologies those who follow us will have to implement if they want to survive climate change.

These are the main findings of new research published in Earth System Dynamics, conducted by an international team led by US climate scientist James Hansen, previously the director of NASA’s Goddard Institute for Space Studies.

The most promising negative emissions technology is BECCS – bioenergy with carbon capture and sequestration. It involves growing crops which are then burnt in power stations to generate electricity. The carbon dioxide produced is captured from the power station chimneys, compressed, and piped deep down into the Earth’s crust where it will be stored for many thousands of years. This scheme would allow us to both generate electricity and reduce the amount of CO2 in the Earth’s atmosphere.

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Humans have pumped over 1.5 trillion tonnes of CO2 into the atmosphere since 1750. It is not just the amount, but the rate at which this CO2 has been added. The oceans can absorb extra CO2 but not fast enough to remove all human inputs and so it has been progressively building up in the atmosphere. This extra CO2 traps more heat than would otherwise escape out into space. More energy is therefore entering the climate system than leaving it.

Over decades and centuries the climate will move back into balance with the same amount of energy leaving as entering. But this will be at a higher temperature with among other things less ice, higher sea levels, more heatwaves, and more floods. The last time the Earth’s climate experienced such an energy imbalance was the Eemian interglacial period some 115,000 years ago. At that time global sea levels were six to nine metres higher than today.

The Hansen team argues that even maintaining the current energy imbalance risks locking in several metres of sea level rise. That is because slow processes such as melting ice sheets still haven’t “caught up”. The longer the climate is held out of balance, the greater their effect will be.

Whatever assumptions you make about economic growth, or however much you discount future costs, it’s unimaginable that US$535 trillion could be afforded. While these costs will be spread over 80 years, this will also be a period in which the global population will increase from seven billion to perhaps 11 billion and beyond. Humanity will need to grow enough crops to feed these billions while fuelling BECCS schemes at a time when climate change will already be impacting food production. There are also no guarantees that BECCS or any other negative emission technologies will actually work. If they fail then large amounts of CO2 could be released very rapidly with disastrous consequences.

If we are at or are heading to this point, remedies such as BECCS are fanciful nonsense and not just because of the out of this world cost. The amount of energy that would be required to plant, grow, harvest and transport this biofuel feedstock would be massive and the emissions associated with those processes also be massive. Also, we're fast depleting our remaining stocks of high quality, arable farmland. A third of our global stocks of arable land have been lost in just the past 40 years. The U.N. Food and Agriculture Organization estimates that, at the rate we're degrading our productive farmland, we have about 60-years of crop production left. In 2012 the UN FAO announced the world had entered a state of permanent food insecurity. BECCS will only worsen these problems by taking cropland out of food production for intensive biomass production. You can't square that circle.

What we have to find is a way to slash emissions from fossil fuels and, yes, biofuels which are energy from the "surface carbon cycle" will be needed. However it's all for naught if we fail to resolve two other man-made existential threats - overpopulation and over-consumption. We can't go to nine billion. We have to shed more than half of our existing population until we're at or below the three billion mark. Even then we will have to slash our demands on the the Earth's resources, renewable and non-renewable until the economy returns to the safety zone as a subset of the environment.

There are ways but we won't find them with our current political leadership both within our country and globally.