Your Life as Planet Earth

A new way to understand the story of the Earth, its climate and our origins

Climate changes in Earth's past - a warning for our future

Ice ages and orbital wobbles...

Variations in our orbit around the sun have caused a drumbeat of climate oscillations throughout Earth's history, most recently driving the last ice ages. But they are not the cause of modern climate change.

Your Life as Planet Earth shows readers how the orbital pulse affected the planet through hothouse climates and ice ages, operating at timescales slow-enough that oceans and the atmosphere remained in balance. The book also shows how the oscillations between glacial periods and interglacials during the last ice age helped to drive human evolution and dispersal.

Orbital wobbles controlling climate in the Eocene

Click image to enlarge. Orbital cycles of climate and landscape in Wyoming during the Eocene. Simplified from Smith et al EPSL 2014. Currently it isn’t clear if either A or C coincide withinsolation maxima: salt pans may have coincided with the higher evaporation associated with summer insolation maxima, or alternatively enhancement of themonsoon over the western US due to insolation maxima could have led to high lake levels. A fuller account can be found here.

We are in the tail-end of an interglacial period now. The Earth was cooling over the last 6,000 years as it headed into the next glacial phase, scheduled for about the year 3500 AD (based on Earth’s orbit). But all that changed when we got to the industrial era. Global temperatures departed from that cooling trend in parallel with our greenhouse gas emissions.

Palm-fringed Arctic and balmy dinos

It’s true the Earth has been as warm before as temperatures that scientists project for the end of this century. Your Life as Planet Earth highlights that, aside from some warm interglacials, the average climate was last as warm as we expect in the year 2100 during the Pliocene epoch – before the emergence of the genus Homo which includes you and me. That was a time when rain-drenched forests fringed the Arctic Ocean, summer Arctic temperatures were 3°C (5°F) warmer than today, and sea levels were 15-25m (50-82ft) higher than today. With today's CO2 levels similar to Pliocene levels, we have already 'baked-in' at least a Pliocene-like climate for our future, unless corrective action is taken.

Going further back in time to the Eocene, the world then was very warm and humid – on average 10°C (18°F) warmer than today. The Arctic was inhabited by turtles, alligators, primates, tapirs, and the hippo-like Coryphodon. Lowland Antarctica was warm and covered in near-tropical vegetation, and London was a mangrove swamp as monsoonal jungle covered much of the planet.

Going back even further to the age of the dinosaurs, life flourished in a time of high CO2 levels and balmy global temperatures with high sea levels. Even Antarctica was forested and supported a healthy population of dinosaurs.

So what’s there to worry about?

lots... read on...


The deadly record of abrupt climate changes

Life flourished in the Eocene, the Cretaceous and other times of high CO2 in the atmosphere because they were (mostly) times of nearly constant, mildly oscillating climate. Greenhouse gasses had millions of years to adjust to be in balance with the carbon in the oceans and the weathering of rocks, even at high CO2 levels.

But there were a number of times in Earth’s past when greenhouse gasses jumped rapidly. These almost always were highly destructive episodes, sometimes causing mass extinctions such as at the end of the Permian and Triassic periods. Those catastrophes have been tied to greenhouse gas emissions from unusually massive volcanic eruptions known as “Large Igneous Provinces” (LIPs).

Large Igneous Province

Large Igneous Province - click to enlarge

The symptoms from those events (huge and rapid carbon emissions, a big jump in global temperatures, rising sea levels, ocean acidification, ocean oxygen starvation) are all happening today.

But we can't blame volcanoes for modern global warming. The last LIP was 16 million years ago, and  today’s volcanoes don’t even come close to emitting the levels of greenhouse gasses that humans do.

The Siberian Traps LIP triggered the end-Permian extinction, which saw around 90% of species go extinct, and it left tropical regions on the planet lethally hot, too hot for complex life to survive. The Central Atlantic LIP triggered the Triassic mass extinction, another one of the 5 biggest mass extinctions in the geological record. Even in the end-Cretaceous extinction, in which dinosaurs were finally wiped out by an asteroid impact, a major global-warming extinction event was already underway 150,000 years before the impact due to massive eruptions in India, which emitted a pulse of CO2 that sent global temperatures soaring by 7°C (13°F).

Modern climate change is extremely abrupt by the standards of past climate changes. This puts us in the territory of the kinds of catastrophic climate changes that our planet has experienced before, and offers no comfort at all for the likely outcome from today’s climate change.

The power of billions of individuals together

Your Life as Planet Earth reveals how life has changed our planet several times before. Where one isolated individual's effect may be insignificant, billions of individuals can change the planet forever.

One example was the evolution of cyanobacteria, whose emissions of oxygen fundamentally changed the planet around 2.5 billion years ago, plunging the world into a deep freeze, but enabling the evolution of oxygen-breathing animals like you and me.

The book also recounts several other occasions when life had dramatic effects on the planet  (like the first burrowing worms, or the invention of wood).

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