Joel Cohen
Mathematical Biologist, Rockefeller University

You Are 25 100-Watt Light Bulbs, Burning All Day

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Each of us consumes energy at a rate roughly equivalent to a 100-watt bulb. But, given the amount of energy that goes into maintaining domestic farm animals, and the inanimate energy we produce, “you should think of each person you see as a parade of 25 people.”

Joel Cohen

Joel E. Cohen is a mathematical biologist and Professor of Populations at Rockefeller and Columbia Universities. His research deals with the demography, ecology, epidemiology and social organization of human and non-human populations and with mathematical concepts useful in these fields. The author of 14 books, he has been honored with numerous awards, including the Sheps Award from the Population Association of America, the Distinguished Statistical Ecologist Award, the Tyler Prize for Environmental Achievement in 1999 and the Mayor's Award for Excellence in Science and Technology from the Mayor of the City of New York, Michael R. Bloomberg in 2002. Professor Cohen has been elected to the National Academy of Sciences, the American Academy of Arts and Sciences and the American Philosophical Society. He lives in New York. 
QuestionHow much energy do humans consume

Joel Cohen: Well, the average number of calories that we eat per day is about 2,100 kilocalories per day. Okay? And that's energy per unit time, kilocalories per day. So energy per unit time is what we call power in physics. Not the Washington DC kind of power, but power for physicist is how much energy are you burning up per unit time? And if you calculate how much that works out to, it's the same thing as a 100 watt bulb. So a watt is a joule per second and if you calculate how many joules your burn up in a day at 100 watts, that works out to be 2100 kilocalories per day. So if you have, like if there are three people in the room and it gets warm, it's because they're generating 300 watts of heat, it's like having a 300 watt bulb going on. So if you multiply 100 watts by 6.8 billion, which is the number of people on the planet, you find out that the whole power generation of the human species is about .68 terawatts, okay? A terawatt is a lot of watts. Let's see, there's kilowatts, megawatts, gigabytes, gigawatts, and then terawatts, so it's a lot. 

So our domestic, just to finish the thought, our domestic animals, if we are .68 terawatts, our domestic animals are about twice that. So that makes it about 1.4 terawatts. And then if you look at all of the domestic, all of the inanimate energy that people produce, it's about 15 terawatts. So you should think of each person you see as a parade of 25 people. First there's the person and that person's energetic consumption, immediately behind are two people who represent the domestic animals on average that that person is responsible for. And after that, there are 22 more people who represent the inanimate energy, okay? So 1 plus 2 plus 22 is 25, so why are we transforming the earth? Because we have 7 billion people, but each of them has 25 shadows, energetic shadows, so it's the same as if were covered with 175 billion people. That's how we are transforming the earth. And the animals are a part of that, they're the equivalent of two of those people