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08/14/2009 05:12 am ET | Updated May 25, 2011

# Understanding Why Climate Change is Human-Induced: A Day in the Life of the Earth

Note to reader: click on the links in the text for the real data. This is not a work of fiction.

About a month ago, I was driving my son to school on a sunny day. So he started asking me lots of questions about the Sun. "How old is it? How long will it live? What will happen to Earth when the Sun dies?" I started explaining, and in the middle of it he shut me down with this one: "Daddy, how long is a billion years?" It's why I wrote this post.

It's actually such an important question, and I thought about it all the way home. It's at the heart of a key recurring problem in science education in that the vast majority of humans truly don't understand lengths of time that are far longer than our lifetimes. No wonder that folks don't understand global warming as due to human intervention, and think it reasonable to interpret the data as explained by natural variation in the environment over long timescales. No wonder that folks don't understand the timescales for evolution of species.

So here now is a novel way to look at it.

Humans and Time
We humans now live on average about 75 years (in the developed world; in Africa the life expectancy is frighteningly low at 32 to 55). I'll assume that 75 years is the life expectancy of a human in the absence of devastating diseases like AIDS, and with availability to modern medicine.

We humans also like to perceive the passage of time in units of seconds, minutes, hours, days, weeks, months, and years. We've created these units because they are comfortable, connected to the rhythms in the sky and in our bodies, and each is used to make sense of events both short and long.

Now here's the critical point for the rest of the story:

One of our average humans sees 75 years x 365.25 days/year =
27,394 days in their life

That's amazing. That's 27,394 days of getting up in the morning, eating, working, playing, relaxing, and going to bed. Put this way, the length of a single day is absolutely inconsequential relative to a human lifetime. Agreed?

A Really Cool Diary
So let's say I had this really cool diary with one page for every day of our average human's life. It's a single book with 27,394 pages. I could give it to you at birth and ask you to record your life one page -- one day -- at a time (with some help from a friend in your early and possibly later years). Like I said, one cool diary.

A Day in the Life of the Earth
Let's say planet Earth was this large cosmic creature. She's got a life expectancy of about 10 billion years, from her birth with the Sun nearly 5 billion years ago, to her ultimate fate when the Sun is in its waning years some 5 billion years from now.

Earth obviously has a lot to say, and she's been keeping a diary since she was born. But she's got it in far too many volumes, since each didn't come with many pages, and they're all old and worn out. Hey, I think a new diary is a perfect gift for her! I'll give her one of my really cool diaries with 27,394 pages. I'll help her move all her old diary entries into the new one so it will truly record her 10 billion year life. Why don't we call each page .... a Geologic Day. And every Geologic Day is absolutely inconsequential relative to Earth's lifetime. After all, Earth has 27,394 of them.

Every Geologic Day, Earth will write in her diary the comings and goings for that day. Here's the next important point:

Every one of the 27,394 pages in Earth's diary -- each Geologic Day -- is 365,000 years long enough time for 14,600 human generations.

How come? Easy: 10 billion years divided by 27,394.

Take a minute to process that.

This might give you a new perspective for spans of time for Earth -- called geologic time -- relative to the time span for our fleeting lives.

So I give my friend the Earth one of my cool diaries. She likes it -- her life all in one book. I also happen to be very close with Earth, and she's letting me look at her diary. So here we are in the middle of her life and she just now finished her entry for day 13,697. She's already written the first 13,696 pages (I helped her transfer the entries from her old diary with Apple Time Capsule.) Here now is her page 13,697.

Dear diary-
Today, as always, I'm going to keep a watchful eye across my surface. It's an important responsibility being an oasis of life in a vast space. I'm painfully aware that all the countless forms of life that live on me depend on a very delicate balance of surface conditions. Every Geologic Day, I try to avoid those asteroids and comets and super volcanoes that have wreaked havoc with my sphere of life -- my biosphere.

Today started out as always, pretty routine with lots of new things to see. I'm still watching those bipedal creatures I first noticed about 6 Geologic Days ago. Over the last few days, it looked like there were a few different species of them. But by the middle of the day today, I'm pretty sure there's only one dominant species left. I'm fascinated with them. They're intelligent. They make tools.

Well, time to stop writing it's just about the next Geologic Day. There's only 35 Geologic Seconds left in this one (150 years to us humans). Wait ... did you see that?! Carbon dioxide levels in my atmosphere just spiked! This just can't be right! All of a sudden carbon dioxide is at the highest level it's been in at least 2 Geologic Days ... maybe even 50 Geologic Days (800,000 to 20 million years)!

This is serious. Carbon dioxide might seem innocent enough -- my diversity of life creates and uses it. But my neighbor Venus has an atmosphere that is 96% carbon dioxide, and while her surface should be about 125 deg F (50 deg C) at her distance from the Sun, the actual temperature is 880 deg F (470 deg C) -- hot enough to melt lead. Carbon dioxide is a gas that helps induce a greenhouse effect on a planet, causing elevated surface temperatures, and in the case of Venus the effect is absolutely extreme. In my case, my biosphere is in a delicate balance, and even though carbon dioxide is a trace gas, a substantial percentage increase can cause dramatic imbalance.

So all of a sudden -- in almost an imperceptibly small amount of time -- carbon dioxide in my atmosphere has skyrocketed. It's increase is nothing short of -- stunning. This is not due to natural cycles. No natural variation would happen this fast. This is the definition of cataclysmic. Some global scale, very short event that should be obvious. But I see no obvious crater, no super volcano ... let me keep looking.

Wait. What's happening now?! The temperature just spiked! Temperature variation over the recent past shows "little ice ages" and warming trends, but what I'm seeing now is a spike -- a very quick change -- and to a far higher temperature than seen in the recent past. And it spiked at the same time as did the carbon dioxide.

This is very bad. Warnings are now coming in from everywhere -- rapidly decreasing sea ice, rapid glacial melt. There has to be a cause. Something's happened. Something's different. This looks like the start of a planet-wide catastrophic event -- an irreversible change in the global environment. I've got to find out what's happening before it's too late for countless species on my surface. Let me keep looking and see if I can find something big that's happened in this instant in time ... a trigger ... something obvious.

Wait .... it's ... it's the bipeds! Oh no ... they're everywhere! Their technology is everywhere -- just in the last 35 Geologic Seconds! It's ... it's an infestation!

They have got to be stopped. They're supposed to be intelligent -- maybe not. But I've got to try reasoning with them.

Hey you!! Look at the data!! Look at the data!! Quick! Quick!

What are you doing!! Stop!! Are you crazy? Do you think you can load my atmosphere with those levels of emissions from your technology -- in a blinding instant of time -- and not impact me? Do you think my systems are capable of scrubbing the atmosphere that fast? My systems don't work on timescales of 35 geologic seconds!!

...Not enough of them are listening..

They're too busy, too pre-occupied ... with themselves.

They don't seem to care if they are committing suicide. Fine. Their choice. But they do not have the right to take countless other life forms with them. I've got to put in an emergency call to Interplanetary Pest Control, or ... tomorrow will be a very bad day.

A note from Dr. James Hansen, Director of the NASA Goddard Institute for Space Studies
Public understanding of climate change depends on an understanding of time scales. Goldstein does a brilliant job of making clear the rapidity of the human-made intervention in the climate system, and the correlation of global warming with the appearance of technology powered by fossil fuels.

Teachers and parents:

This is cross-posted at Blog on the Universe, which includes how to make this a visual lesson in the classroom and at home.