Tag Archives: Global Warming

August 17, 1771 (a Saturday)

Alone in a sealed jar, a mouse would die from exhaled CO2. But as scientist Joseph Priestley observed in 1771, adding a mint plant allows the mouse to thrive. In this proof of photosynthesis, the mint absorbed CO2, retained carbon for growth, and released oxygen. Two centuries later humans tried—and failed—to survive in a sealed environment in Arizona's Biosphere 2.

On this date, Joseph Priestley began an experiment in which he discovered photosynthesis, although he did not give it that name. He described his experiment in 1772 in a paper entitled “Observations on Different Kinds of Air”:

…I flatter myself that I have accidentally hit upon a method of restoring air which has been injured by the burning of candles, and that I have discovered at least one of the restoratives which nature employs for this purpose. It is vegetation. In what manner this process in nature operates, to produce so remarkable an effect, I do not pretend to have discovered; but a number of facts declare in favour of this hypothesis…

One might have imagined that, since common air is necessary to vegetable, as well as to animal life, both plants and animal had affected it in the same manner, and I own that I had that expectation, when I first put a sprig of mint into a glass-jar, standing inverted in a vessel of water; but when it had continued growing there for some months, I found that the air would neither extinguish a candle, nor was it at all inconvenient to a mouse, which I put into it.

…Accordingly, on the 17th of August 1771, I put a sprig of mint into a quantity of air, in which a wax candle had burned out, and found that, on the 27th of the same month, another candle burned perfectly well in it. This experiment I repeated, without least variation in the event, not less than eight or ten times in the remainder of the summer.

Priestley’s experiment also demonstrated the key processes of the natural carbon cycle. Although Priestley could not name the gases responsible, the fire and respiration used up oxygen and gave off carbon dioxide. The mint reversed both processes. Photosynthesis took up the carbon dioxide, converted it into plant tissue, and gave off oxygen as a by-product.

Priestley’s experiment thus has ecological implications for today, since the world is just a bigger jar. Tens of billions of tons of carbon a year pass between land and the atmosphere: given off by living things as they breathe and decay and taken up by green plants, which produce oxygen. A similar traffic in carbon, between marine plants and animals, takes place within the waters of the ocean. And nearly a hundred billion tons of carbon diffuse back and forth between ocean and atmosphere.

1917 image of Athbasca Glacier, Jasper National Park, Canada, courtesy National Archives of Canada, from the Wheeler Survey; 2005 image by Gary Braasch. Receding glaciers are visible evidence of global warming.

Compared with these vast natural exchanges, the few billion tons of carbon that humans contribute to the atmosphere each year seem paltry. Yet like a finger on a balance, our steady contributions are throwing the natural cycle out of whack. The coal, oil, and natural gas that drive the industrial world’s economy all contain carbon inhaled by plants hundreds of millions of years ago — carbon that now is returning to the atmosphere through smokestacks and exhaust pipes, joining emissions from forests burned to clear land in poorer countries. The atmosphere’s carbon dioxide level has risen by some 30 percent since Priestley’s time. It may now be higher than it has been in at least 20 million years.

Carbon dioxide is foremost in an array of gases from human activity that increase the atmosphere’s ability to trap heat, resulting in ongoing global warming.


  • Allen, J.F. and W. Martin, “Evolutionary biology: Out of thin air,” Nature 445: 610-612 (8 February 2007)
  • Appenzeller, Tim, “The case of the missing carbon”, National Geographic Magazine (Feb 2004) , vol 205, number 2, p 88.

The Anthropocene Begins: April 28, 1784

Figure from Watt's 1784 patent for a steam locomotive.

Figures from Watt’s 1784 patent for a steam locomotive.

On this date, James Watt’s patent for a steam locomotive was granted. What is especially noteworthy is that this date therefore can be considered as the beginning of the Anthropocene, a new geologic epoch defined by the massive impact of humankind on the planet, according to Dutch chemist and Nobel laureate Paul Crutzen, who coined the term. That impact will endure in the geologic record long after our cities have crumbled.

In 2000, in IGBP Newsletter 41, Crutzen and Eugene F. Stoermer, to emphasize the central role of mankind in geology and ecology, proposed using the term “anthropocene” for the current geological epoch. In regard to its start, they said:

To assign a more specific date to the onset of the “anthropocene” seems somewhat arbitrary, but we propose the latter part of the 18th century, although we are aware that alternative proposals can be made (some may even want to include the entire holocene). However, we choose this date because, during the past two centuries, the global effects of human activities have become clearly noticeable. This is the period when data retrieved from glacial ice cores show the beginning of a growth in the atmospheric concentrations of several “greenhouse gases”, in particular CO2 and CH4. Such a starting date also coincides with James Watt’s invention of the steam engine in 1784.


Welcome to the Anthropocene

April 28, 1975 (a Monday)

On this date, Peter Gwynne, at the time the science editor of Newsweek, pulled together some interviews from scientists and wrote a nine-paragraph story, entitled “The Cooling World“, about how the planet was getting cooler. Ever since, Gwynne’s “global cooling” story – and a similar Time Magazine piece – have been brandished gleefully by those who say it shows global warming is not happening, or at least that scientists – and often journalists – don’t know what they are talking about.

Fox News loves to cite it. So does Rush Limbaugh. Sen. James Inhofe, R-Okla., has quoted the story on the Senate floor. That one article in 1975 was so brilliant, that it has managed to disprove over 33,000 scientifically researched papers written since.

His piece has been used by Forbes as evidence of what the magazine called “The Fiction of Climate Science.” It has been set to music on a YouTube video. It has popped up in a slew of finger-wagging blogs and websites dedicated to climate denial.

But, revisionist lore aside, it was hardly a cover story. It was a one-page article on page 64. It was, Gwynne concedes, written with a bit of hyperbole that sometimes marked the magazine’s prose: “There are ominous signs the earth’s weather patterns have begun to change dramatically…” the piece begins, and warns of a possible “dramatic decline in food production.”

Although the story observed – accurately – that there had been a gradual decrease in global average temperatures from about 1940, by about 1980 it was clear that Earth’s average temperature was headed upward.

Even today, “there is some degree of uncertainty about natural variability,” acknowledged Mark McCaffrey, programs and policy director of the National Center for Science Education based in Oakland, California. “If it weren’t for the fact that humans had become a force of nature, we would be slipping back into an ice age, according to orbital cycles.”

But earth’s glacial rhythms are “being overridden by human activities, especially burning fossil fuels,” McCaffrey noted. The stories about global cooling “are convenient for people to trot out and wave around,” he said, but they miss the point:

What’s clear is we are a force of nature. Human activity – the burning of fossil fuels and land change – is having a massive influence. We are in the midst of this giant geoengineering experiment.