Earth Day: The Facts

You probably figured out that yesterday was Earth Day. (Is this only a U.S. thing?)


Anyhow, in honor of Earth Day, I thought I would share some facts about, well, the Earth.

The Earth is about 4 billion years old.


Which means life on Earth has had 4 billion years to evolve into what it is today.

Earth is habitable in large part due to the way our atmosphere has evolved and we have greenhouse gases to thank for this!


The Greenhouse Effect — when gases like carbon dioxide, methane, and water vapor trap heat in the atmosphere — is a good thing. Without it, the Earth would be too cold for us to survive. The gases essentially act like a blanket around the Earth, trapping heat. They are the insulation we need to keep Earth at a good temperature for life.


It turns out that CO2 is the greenhouse gas that tells us most about global temperature, where higher levels of CO2 correspond to higher global average temperature.

Since 1958, the Scripps CO2 Program has measured the amount of CO2 in the atmosphere from an observatory on Mauna Loa, a Hawaiian volcano. These measurements indicate CO2 levels for the global atmosphere, thanks to the short timescale of atmospheric mixing.

Atmospheric CO2 has been rising dramatically since the record began. In May 2013, CO2 reached an average 400 parts per million (ppm) for the first time since recording began.


Since then, atmospheric CO2 has continued to rise. During April 2014, there were only 11 hours when CO2 levels dropped below 400 ppm.


But levels of CO2 in the atmosphere are cyclical! If you fill in the data for the last 800,000 years (with some help from ice core records) we see that large fluctuations in CO2 have been going on for a while.

But nothing like what we see today.


It used to be that even the CO2 maximums were down around 300 ppm. Now we’re barely dipping below 400 ppm.

But this has happened before! Atmospheric CO2 was at 400 ppm as recent as about 3 million years ago. This period of Earth’s history is known as the Pliocene. And guess what, the Earth survived it!


…but we didn’t.


3 million years ago, during the Pliocene, there were no humans on Earth.


Global temperatures were 3.5 to 5.5 degrees F (2 to 3 degrees C) higher.


Sea level was 25 meters higher.


These are the things we have in store for our new 400 ppm world. We’re not there yet, but Earth’s climate is rapidly playing catchup to balance itself in 400 ppm conditions. And for the first time in history, humans are having to face the consequences.

It’s true: the Earth will survive this, as it has before. But humans have not. For society, the timescale of this balancing is important. How long will it take for all of these changes to take effect? How long do we have to mitigate and adapt to the mounting impacts before it’s too late?

Questions like these are why it’s so important to understand the climate system and how it changes, so that we can make good decisions about how we’re taking care of the planet. Not because we’re treehuggers, but because we’re survivalists.

3 thoughts on “Earth Day: The Facts

  1. Very informative (and a bit dismaying). Thanks for a clear explanation and the helpful charts and pictures. Happy Earth Day to you too. Hang in there, Earth….


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