Is Earth heading for extinction?

*From full-blown collapse to gradual die off, math models reveal three possible fates for planet
*Innovative zero-emissions power plant begins tests on new approach to capturing carbon

Scientists have modelled the three possible fates for our planet as Earth’s population grows and the effects of climate change worsen.Mathematicians modelled how advanced civilisations on ancient exoplanets might have survived or perished when faced with a similar changing environment.

They showed that humanity could go through a soft landing, a gradual die off, or full-blown collapse.Experts said a die-off, in which, as much as seven in ten of a planet’s inhabitants were wiped out before stabilising, was by far the most common outcome.A soft landing was the most positive outcome, and occurred when a civilisation adapted to its changing planet without a mass extinction.

During a full-blown collapse, the planet was too sensitive to recover from damage caused by its inhabitants, leading to a rapid annihilation of all intelligent life.There is bad news for Earth. Even when planets switched to renewable fuels to save themselves from extinction, the damage done was sometimes still enough to wipe out the inhabitants, according to the models.

Scientists said the simulations reveal “a radical truth about the challenge we face as we push the Earth into its human-dominated era.”The team, led by scientists at the University of Rochester in New York, used models for population growth on Earth to mark out how alien planets may have grown.Using statistical models they mapped out possible histories of alien worlds, the civilisations they grew, and the climate change that followed.

They called these societies “Exo-civilizations” and say that learning from their mistakes could help us prepare for the effects of climate change.Writing in the Atlantic, coauthor Professor Adam Frank said: “Given that more than 10 billion trillion planets likely exist in the cosmos, unless nature is perversely biased against civilisations like ours, we’re not the first one to appear.

“That means each exo-civilization that evolved from its planet’s biosphere had a history: A story of emergence, rising capacities, and then maybe a slow fade or rapid collapse.“And just as most species that have ever lived on Earth are now extinct, so too most civilizations that emerged (if they emerged) may have long since ended.“So we’re exploring what may have happened to others to gain insights into what might happen to us.”

Also, a team of engineers in La Porte, Texas, has spent the past several weeks running tests on a prototype power plant that uses a stream of pure carbon dioxide (CO2) — not air — to drive a turbine. If the zero-emission technology developed by NET Power in Durham, North Carolina, succeeds, it could help to usher in an era of clean power from fossil fuels.

The company broke ground on the roughly 25-megawatt plant in March 2016, after raising US$140 million for the project, and completed construction last year. It is now running a battery of tests on the combustor that powers the plant, a one-of-a-kind device built by the Japanese industrial giant Toshiba. If the tests go as planned, NET Power will hook up the turbine and begin generating electricity later this year.

Officials say everything is running smoothly so far. “We’re still smiling,” says chemical engineer Rodney Allam, the facility’s lead designer. Allam is now a partner with 8 Rivers, a technology company in Durham that co-owns NET Power with Exelon, a major electricity provider in Chicago, Illinois, and McDermott International, an energy-services company in Houston, Texas.

Meanwhile, the University of Rochester in New York team’s calculations combined population statistics from Earth’s species with generic physics and chemistry that make up climates on other planets.They applied the laws of these climates to scenarios in which an industrial civilisation arrived on a planet and began consuming its resources.

As the society used up resources for energy, it grew because its capacity to feed more people expanded, allowing it consumes more resources.Eventually this loop had feedback effects on the planet that damaged it and began to make it uninhabitable.This mirrors humanity’s relationship with Earth following the industrial revolution, during which we began to burn fossil fuels for energy, Professor Frank said.

As part of the simulations, researchers imagined the civilisation had two types of energy source: One with a high impact on the planet, like fossil fuels, and one with a low impact, like solar power.In some of the models the researchers allowed the civilisation to switch to low-impact resources as the health of the planet plummeted.

The models revealed three distinct types of civilisational histories that showed what could happen on Earth if population and climate trends continue.Unfortunately, of the three fates observed, none were positive.The most common outcome observed by the team was known as the die off.As the civilisation on the simulated planets used energy, its population exploded, but its use of resources pushed the planet away from the conditions the society had become accustomed to.

As the population continued to expand the planet became uninhabitable, forcing a devastating drop in the number of civilians until a sustainable planetary civilisation was achieved once more.In many of the models, researchers observed that as much as 70 per cent of the population perished before a steady state was reached again.The second outcome viewed by the team was the soft landing – the most positive outcome of the three observed.

This time, the growing population and the planet maintained a smooth transition to a new, balanced equilibrium, partly through low-impact resources.Although the civilisation changed the planet, it did so without triggering a mass extinction, like those observed in the first outcome.Outcome number three was a full-blown collapse, which also started with a skyrocketing population.

However, these worlds were too sensitive to change and were unable to cope with a rapidly expanding, resource-hungry civilisation. As conditions on the worlds collapsed around them, the civilisations in these scenarios were rapidly wiped out.Researchers programmed some civilisations to switch from high-impact energy sources to low-impact ones, to find out whether this would change their fate.While populations that relied solely on high-impact resources were immediately wiped-out, those that made the switch to low-impact alternatives would fall, then stabilise.

Unfortunately, it was not always enough to stop an extinction event, with some simulated civilisations still rushing downward to extinction eventually.Professor Frank said the models showed that switching to renewable sources might not help Earth if humanity irreparably damages it before shifting to green energy.He said: “The collapses that occurred even when the civilisation did the smart thing demonstrated an essential point about the modelling process.“Because the equations capture some of the real world’s complexity, they can surprise you.

“In some of the “delayed collapse” histories, the planet’s own internal machinery was the culprit. Push a planet too hard, and it won’t return to where it began.”Meanwhile, what separates the La Porte facility from a standard power plant is the CO2 cycle at its core. A conventional power plant burns fossil fuels to generate steam that drives a turbine — and it also emits CO2 as a byproduct.By contrast,  NET Power will drive its turbine with a loop of hot pressurized CO2. The first step is to fill the system with CO2, which must then be heated in order to drive the turbine — much like a conventional power plant heats water to create steam.

The combustor then ignites a mixture of natural gas and oxygen, which is extracted from the atmosphere in a separate facility. This heats up the CO2 in the loop that drives the turbine, but it also produces additional CO2 that must be siphoned off to keep the system in balance.The result is a stream of pure CO2 that can be buried or put into a pipeline – rather than the atmosphere – at virtually no cost. That gives it an edge over existing technologies for stripping CO2 out of a conventional power plant’s exhaust; these drive up costs while sapping around 20 per cent of the plant’s power.

Allam says that, if all goes well, NET Power’s technology will produce electricity as cheaply and efficiently as a conventional, modern gas-fired power plant — and earn additional revenue by other means. For instance, oil companies might buy the plant’s excess CO2 and pump it into their wells to boost oil production. NET Power could also sell nitrogen and argon produced by the plant’s air separator.

A coal-fired power plant in Houston that is equipped with a competing CO2-capture technology is already delivering the gas it collects to a nearby oil field. The $1-billion Petra Nova project came online in January 2017. It uses an amine-based solvent to capture about one-third of the emissions from a single power-generating unit — up to 1.6 million tonnes of CO2 annually.

But the project — a joint venture between NRG Energy in Princeton, New Jersey, and JX Nippon Oil and Gas Exploration in Tokyo — depended on both a $190 million grant from the US Department of Energy and additional oilfield revenue to turn a profit, says Daniel Cohan, an atmospheric scientist at Rice University in Houston. By contrast, he notes NET Power’s claim that its power plant will turn a profit even before it begins selling CO2. “If the plant does everything they say, it’s hard to imagine why you would want to build a traditional power plant,” Cohan says. “But there are still a lot of ifs ahead.”

One major challenge will be ensuring proper combustion of oxygen and methane in the presence of CO2, which normally acts as a fire extinguisher. NET Power is several months behind schedule on this task, but project officials say that was the result of Toshiba’s decision to test the plant’s combustor on site rather than sending it to an independent test facility; that meant installing and reconfiguring equipment at the otherwise complete plant.

Once the project begins producing electricity, NET Power engineers must also show that the plant operates as efficiently as advertised, says Howard Herzog, who studies carbon capture and sequestration at the Massachusetts Institute of Technology in Cambridge. The challenge, he says, will be to address the inevitable problems that arise when engineers are building the first-of-a-kind facility without sacrificing energy efficiency or driving up costs.

NET Power officials say they are ready to take advantage of recently expanded US-government tax credits for carbon capture and sequestration projects — beginning with a proposed 300-megawatt plant that could be operational by 2021. But the company’s chief executive, Bill Brown, says the company isn’t reliant on subsidies, and is already seeking customers and manufacturing partners abroad. It is also looking at potential markets for CO2, which could soon become a cheap chemical feedstock.”We don’t like to rely on policy around here,” Brown says. “We like to rely on science.”