Over its history, Earth has fluctuated between two climate states: Icehouses, with ice caps at at least one of the poles, and Hothouses, when there is no ice at the poles.
How Earth’s Climate Changed Over the Past 500 Million Years
Published: February 11, 2020
Isabel Montañez: The Earth over its history has fluctuated broadly over two climate states: Icehouses and Greenhouses.
Onscreen: Also known as hothouses.
Montañez: What is key is that greenhouses are the much more common climate state.
Onscreen: During Greenhouses, the poles had no ice.
Marshall Shepherd: I think people are familiar with the fact that dinosaurs once roamed the planet, but they may not be familiar with the fact that the climate was really warm then. There’s not much ice at the poles, so there’s not much difference between temperature at the poles and the equator.
People may be surprised to know that we live in an Icehouse planet right now.
Montañez: Humans evolved in an Icehouse. The one that we are in started about 34 million years ago.
Onscreen: What defines an Icehouse are ice caps at one or both of the poles.
The fluctuations between Hothouse and Icehouse periods go along with changes in carbon dioxide levels in the atmosphere. More CO2 means a warmer Earth.
Montañez: With no exception when CO2 goes up, the temperatures do too and when CO2 declines, the temperatures also decline.
During ice houses CO2 varies over a narrow range between about 200 parts per million and 300 parts per million. We are now over 407 parts per million.
Shepherd: One of the things that we’re seeing for the first time is the human footprint.
Since the industrial revolution, we started injecting more CO2 and other greenhouse gases into the atmosphere. The rate of change of CO2 now is quite rapid.
Montañez: We are headed out of what is typical for this glacial state.
Shepherd: That is starting to impact our climate in ways that we understand in some regards, and in some regards we don’t.
When we change the climate, we are also changing other aspects of the Earth’s system. We’re changing the oceans, we’re changing the ice sheets, we’re changing where mosquitoes can live, we’re changing sea level...
Montañez: Ocean circulation, land temperatures, atmosphere circulation, and the weather patterns.
Shepherd: There are so many impacts on the Earth’s system from climate change that it’s going to affect your life, no matter where you live.
It’s really tempting to say: "The climate has changed in the past and the Earth has always survived. Why are we worried about this?" Well, here’s the big difference: us. Are we going to survive? The planet will likely adjust, it will be resilient, but we are living in this rapidly changing climate system for the first time.
Onscreen: About 300 million years ago, the planet shifted from an Icehouse to a Hothouse.
Montañez: Once the Earth transitioned out of that Icehouse and permanently into a Greenhouse, it was in that Greenhouse state for 200 plus million years.
The question is: How high does CO2 have to get to push us potentially fully into a Greenhouse?
Shepherd: It’s important to understand that at the end of the day there’s no Plan B planet. This is it for us
I have a healthy dose of fear about the future. But I also have a healthy dose of optimism. If we focus on the problem we can find solutions.
Director: Lucy Haken
Assistant Producer: Sacha Thorpe
Digital Producer: Ana Aceves
Unit TV & Film
PhanTASTIC (Phanerozoic Technique-Averaged Surface Temperature Integrated Curve) courtesy of NMNH, Smithsonian
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