3-minute story of 800,000 years of climate change with a sting in the tail

More than ever, we need strong and accountable leaders, to avoid the worst of climate change

There are those who say the climate has always changed, and that carbon dioxide levels have always fluctuated. That’s true. But it’s also true that since the industrial revolution, carbon dioxide(CO2) levels in the atmosphere have climbed to levels that are unprecedented over hundreds of millennia.

So here’s a short video we made, to put recent climate change and carbon dioxide emissions into the context of the past 800,000 years.

The temperature carbon dioxide connection

Earth has a natural greenhouse effect, and it is really important. Without it, the average temperature on the surface of the planet would be about -18 degrees Celsius and human life would not exist. CO2 is one of the gases in our atmosphere that traps heat and makes the planet habitable.

We have known about the greenhouse effect for well over a century. About 150 years ago, a physicist called John Tyndall used laboratory experiments to demonstrate the greenhouse properties of CO2 gas. Then, in the late 1800s, the Swedish chemist Svante Arrhenius first calculated the greenhouse effect of CO2 in our atmosphere and linked it to past ice ages on our planet.

Modern scientists and engineers have explored these links in intricate detail in recent decades, by drilling into the ice sheets that cover Antarctica and Greenland. Thousands of years of snow have compressed into thick slabs of ice. The resulting ice cores can be more than 3km long and extend back a staggering 800,000 years.

Scientists use the chemistry of the water molecules in the ice layers to see how the temperature has varied through the millennia. These ice layers also trap tiny bubbles from the ancient atmosphere, allowing us to measure prehistoric CO2 levels directly.

Temperature and CO2

The ice cores reveal an incredibly tight connection between temperature and greenhouse gas levels through the ice age cycles, thus proving the concepts put forward by Arrhenius more than a century ago.

In previous warm periods, it was not a CO2 spike that kickstarted the warming, but small and predictable wobbles in Earth’s rotation and orbit around the Sun. CO2 played a big role as a natural amplifier of the small climate shifts initiated by these wobbles. As the planet began to cool, more CO2 dissolved into the oceans, reducing the greenhouse effect and causing more cooling. Similarly, CO2 was released from the oceans to the atmosphere when the planet warmed, driving further warming.

But things are very different this time around. Humans are responsible for adding huge quantities of extra CO2 to the atmosphere – and fast.

The speed at which CO2 is rising has no comparison in the recorded past. The fastest natural shifts out of ice ages saw CO2 levels increase by around 35 parts per million (ppm) in 1,000 years. It might be hard to believe, but humans have emitted the equivalent amount in just the last 17 years.

How fast are CO2 levels rising? Ben Henley and Nerilie Abram

Before the industrial revolution, the natural level of atmospheric CO2 during warm interglacials was around 280 ppm. The frigid ice ages, which caused kilometre-thick ice sheets to build up over much of North America and Eurasia, had CO2 levels of around 180 ppm.

Burning fossil fuels, such as coal, oil and gas, takes ancient carbon that was locked within the Earth and puts it into the atmosphere as CO2. Since the industrial revolution, humans have burned an enormous amount of fossil fuel, causing atmospheric CO2 and other greenhouse gases to skyrocket.

In mid-2017, atmospheric CO? now stands at 409 ppm. This is completely unprecedented in the past 800,000 years.

Global Temperature and CO2 since 1850. Ben Henley and Nerilie Abram

The massive blast of CO2 is causing the climate to warm rapidly. The last IPCC report concluded that by the end of this century we will get to more than 4 degrees Celsius above pre-industrial levels (1850-99) if we continue on a high-emissions pathway.

If we work towards the goals of the Paris Agreement, by rapidly curbing our CO2 emissions and developing new technologies to remove excess CO2 from the atmosphere, then we stand a chance of limiting warming to around 2 degrees.

Observed and projected global temperature on high (RCP8.5) and low (RCP2.6) CO2 emission futures. Ben Henley and Nerilie Abram

The fundamental science is very well understood. The evidence that climate change is happening is abundant and clear. The difficult part is: what do we do next? More than ever, we need strong, cooperative and accountable leadership from politicians of all nations. Only then will we avoid the worst of climate change and adapt to the impacts we can’t halt.

The authors acknowledge the contributions of Wes Mountain (multimedia), Alicia Egan (editing) and Andrew King (model projection data).

Ben Henley, Research Fellow in Climate and Water Resources, University of Melbourne, University of Melbourne and Nerilie Abram, ARC Future Fellow, Research School of Earth Sciences; Chief Investigator for the ARC Centre of Excellence for Climate Extremes, Australian National University

This article was originally published on The Conversation. Read the original article.