Three decades ago, astronomer Carl Sagan was already warning about climate change.
What follows comes from his famous book Cosmos (1980). Few were listening.
“The global temperature of the Earth would be below the freezing point of water if not for the greenhouse effect. It keeps the oceans liquid and life possible. A little greenhouse is a good thing. Like Venus, the Earth also has about 90 atmospheres of carbon dioxide; but it resides in the crust as limestone and other carbonates, not in the atmosphere. If the Earth were moved only a little closer to the Sun, the temperature would increase slightly. This would drive some of the CO2 out of the surface rocks, generating a stronger greenhouse effect, which would in turn incrementally heat the surface further. A hotter surface would vaporize still more carbonates into CO2, and there would be the possibility of a runaway greenhouse effect to very high temperatures. This is just what we think happened in the early history of Venus, because of Venus’s proximity to the Sun. The surface environment of Venus is a warning: something disastrous can happen to a planet rather like our own.
The principal energy sources of our present industrial civilization are the so-called fossil fuels. We burn wood and oil, coal and natural gas, and, in the process, release waste gases, principally CO2, into the air. Consequently, the carbon dioxide content of the Earth’s atmosphere is increasing dramatically. The possibility of a runaway greenhouse effect suggests that we have to be careful: Even a one- or two-degree rise in the global temperature can have catastrophic consequences…
A few million years ago, when human beings first evolved on Earth, it was already a middle-aged world, 4.6 billion years along from the catastrophes and impetuosities of its youth. But we humans now represent a new and perhaps decisive factor. Our intelligence and our technology have given us the power to affect the climate. How will we use this power? Are we willing to tolerate ignorance and complacency in matters that affect the entire human family? Do we value short-term advantages above the welfare of the Earth? Or will we think on longer time scales, with concern for our children and our grandchildren, to understand and protect the complex life-support systems of our planet? The Earth is a tiny and fragile world. It needs to be cherished.”
Today, millions of people are aware of the climate crisis and are campaigning to phase out fossil fuels, to reduce waste, and to protect the environment. Together, they are taking personal, communal, and national responsibility for their own and the planet’s future. It will be a roller-coaster of a struggle.
Carl Sagan was Professor of Astronomy and Space Sciences at Cornell University. He received the Joseph Priestley Award “for his contributions to the exploration of the universe through radioastronomy” and a Pulitzer Prize for his book The Dragons of Eden: Speculations on the Evolution of Human Intelligence. He died in 1996.