Earth in Human Hands, David Grinspoon – a review

Planetary scientist and astrobiologist David Grinspoon examines Earth and makes the case for humanity’s role in shaping it in a new book, “Earth in Human Hands” (published in 2016).

Throughout the history of Earth, there have been an incredible number of critical moments that determined what direction our planet would take next. Just a few tens of millions of years after the Solar System first formed, a catastrophic collision with a Mars-sized planet wreaked havoc on the entire planet, and created the Moon from its debris. Two billion years later, life almost went extinct as anaerobic organisms, producing oxygen as a waste product, almost poisoned the planet and caused it to freeze over entirely. And every few hundred million years or so, a mass extinction wipes out about half the species living on the globe, including 65 million years ago, with a massive asteroid causing the demise of the dinosaurs.

But these events weren’t simply catastrophes for life across-the-board, but also opportunities for the survivors. For the first time, a single, sentient species – humanity – has their hands on the controls while it’s happening.

Quite literally, shaping our planet’s future is something we’re actively doing right now.

Over three billion years ago our solar system had three habitable planets – Venus, Earth, and Mars that had very similar beginnings.  All three had substantial amount of water on their surface, had the raw ingredients for life and all three had active geologies, volcanoes, atmosphere and weather. There were multiple chances for life to evolve and thrive there as it has here on Earth. Yet today only Earth still has life.

All three worlds saw their climates change naturally, due to a few processes that we know of and a few others that are uncertain. Grinspoon lays out clearly what we know about Venus and its runaway greenhouse effect, what we know about Mars and how it lost its magnetic field and had its atmosphere stripped away, and what we know about Earth, and how our world survived, sometimes only barely, our early challenges.

These studies of Venus and Mars have contributed to our improved understanding of Earth and its complex systems.  Models of Martian atmosphere developed to understand dust storms there later helped scientists understand how an asteroid impact could have wiped out the dinosaurs 65 million years ago and also lead to the coming together of scientists to put forward their now famous TTAPS report in1983.  It is a report named after the last names of the four leading scientists, Richard P Turco, Owen Toon and Thomas P. Ackerman, three planetary scientists, James B Pollack, an astrophysicist and Carl Sagan, an astronomer, cosmologist, astrophysicist, author and science populariser.

In this report the scientists made the case for “nuclear winter,” (a term coined in this report) and its ominous hypotheses about the environmental effects of a nuclear war. The basic cause of nuclear winter as hypothesised by researchers, would be the numerous and immense fireballs caused by exploding nuclear warheads. These fireballs would ignite huge uncontrolled fires (firestorms) over any and all cities and forests that were within range of them. Great plumes of smoke, soot, and dust would be sent aloft from these fires, lifted by their own heating to high altitudes where they could drift for weeks before dropping back or being washed out of the atmosphere onto the ground. Several hundred million tons of this smoke and soot would be shepherded by strong west-to-east winds until they would form a uniform belt of particles encircling the Northern Hemisphere from 30° to 60° latitude. These thick black clouds could block out all but a fraction of the Sun’s light for a period as long as several weeks. Surface temperatures would plunge for a few weeks as a consequence, perhaps by as much as 11° to 22° C (20° to 40° F). The conditions of semidarkness, killing frosts, and subfreezing temperatures, combined with high doses of radiation from nuclear fallout, would interrupt plant photosynthesis and could thus destroy much of the Earth’s vegetation and animal life. The extreme cold, high radiation levels, and the widespread destruction of industrial, medical, and transportation infrastructure along with food supplies and crops would trigger a massive death toll from starvation, exposure, and disease. A nuclear war could thus reduce the Earth’s human population to a fraction of its previous numbers.

This report came under intensive study by both the American and Soviet scientific communities. 

There’s also a long discussion about the search for extraterrestrial intelligence (SETI) in the book. Could the lack of detections of alien civilisations say something about the difficulty in dealing with planetary change bought on by technological development? Or, could that silence mean that they respond in a different way, taking a more sustainable approach versus exponential growth?

“We find ourselves running a planet, without knowing how it should be done,” writes the author. He goes onto describes the human struggle for organisation, the quest for operating a planet, for searching for a workable system of operating the world and taking care of it in our relatively young civilisation.

Grinspoon argues in the book that it is not unreasonable to think that life can reshape a planet: life has altered the Earth since the first lifeforms emerged, from the creation of minerals that would not be produced by physical processes to the “snowball Earth” of two billion years ago when the rapid influx of oxygen into the atmosphere from cyanobacteria wrecked the methane-based greenhouse effect keeping the planet warm. Grinspoon calls those effects planetary change of the second kind, with the first kind reserved for random events, like volcanic eruptions and asteroid impacts.

That humans can alter the planet is thus not surprising; what is unprecedented, though, is the rate of change, such as the surge of carbon dioxide levels in the atmosphere. This is what he calls planetary change of the third kind, or “inadvertent change”: humans didn’t intend to reshape the planet and alter its climate as part of industrialisation, but rather this was a byproduct. This ultimately, he argues, will require planetary change of the fourth kind: intentional action to mitigate the damage the inadvertent change has caused. Such changes have already taken place. He notes the international accords to end the use of chlorofluorocarbons (CFCs) that were damaging the ozone layer; the ozone layer, in danger of being depleted a few decades ago, is now on the rebound.

“We should regard ourselves as apprentice planetary engineers,” he writes, “easing up on those behaviours that have been throwing the system out of balance, taking those steps we know are safe, and learning all that we can about how the system works so that by the time we need to call upon more intensive interventions, we will be ready to do so safely and wisely.”  He touches upon planetary defence from asteroid and comet impacts (planetary changes of the first kind); while not an imminent threat, it’s something that we will be able to manage once we become planetary engineers of the fourth kind.

Although our current behaviour threatens not only our own future but that of countless other creatures, our species has dealt with the threat of extinction before, thanks to our innate inventiveness and ability to adapt. Our challenge now is to awaken to our role as a force of planetary change, and to grow into this task. We must become graceful planetary engineers, conscious shapers of our environment and caretakers of Earth’s biosphere. This is a perspective that begs us to ask not just what future do we want to avoid, but what do we seek to build? What kind of world do we want? Are humans the worst thing or the best thing to ever happen to our planet? Today we stand at a pivotal juncture, and the answer will depend on the choices we make.