Quirks & Quarks·Bob McDonald's blog

A warning about warming from the past

Climate feedback loops have amplified and prolonged past periods of climate change.

Climate feedback loops have amplified and prolonged past periods of climate change

The volcano in southern Iceland's Eyjafjallajokull glacier sends ash into the air. Volcanoes also emit large amounts of CO2, and periods of massive vulcanism have changed the Earth's climate in the past (Brynjar Gauti/Associated Press)

A study by American researchers has shown that a warming event 56 million years ago was prolonged by a natural feedback loop that may have kept the Earth unusually warm for thousands of years.

The study looked at a climate  warming period called the Paleocene-Eocene Thermal Maximum, when global temperatures rose 5-8 C for about 100,000 years. The event could have been triggered by massive volcanic eruptions in the North Atlantic Region from Greenland to the Northern British Isles.

These eruptions would have released greenhouse gasses into the atmosphere both from the volcanoes themselves and possibly by releasing methane hydrates — methane trapped by pressure in a kind of icy slush deep in the ocean. The event had huge consequences, triggering extinctions on land and in the seas.

Sediment core containing multiple fossils from a site in Maryland (Rosie Oakes / Penn State)

But researchers found another factor that also contributed to the warming at that time and may have prolonged it. They examined sediments taken from coastlines along the US, the mid-Atlantic and Tanzania, and found unusual amounts of buried carbon from this time.

So where did it come from? They think this carbon must have been weathered out of carbon-bearing rocks on land and washed into the sea. Increased storminess and rainfall caused by the warming climate of the time would have also increased the rate of erosion of these rocks.

Some of the carbon eroded from these rocks would have been washed into the sea and buried — that's the carbon they found. But another portion would have escaped as carbon dioxide gas into the atmosphere. It then would have added to the already elevated levels of greenhouse gases in the atmosphere.

In other words, once climate change got going, one effect triggered another that then fed back onto the first. Warmer conditions increased erosion which made the climate spiral ever warmer. This is what's known as a feedback loop, and is analogous to what we hear when we put a microphone in front a speaker, and hear an ever-rising howl of noise.

Of course feedback isn't always a bad thing...

What's alarming is that the scientists warn that this warming event in the distant past could be be similar to what we face with our climate today.

Feedback loops are common in nature. At least two of them are currently operating in the Arctic, which is one of the fastest warming places on the planet. One loop involves sea ice, the other, melting permafrost.  

The Arctic Ocean has been losing more and more ice cover each summer, exposing more dark sea water to sunlight. White ice reflects sunlight back into space, keeping the climate cool, but dark water absorbs it, warming the Arctic Ocean, which melts more ice.

At the same time, the land surrounding the ocean is heating up, which is melting permafrost. Ancient organic matter such as grasses, moss and shrubs — even dead woolly mammoths and other extinct animals — are being released from the ice. This long frozen material is then decomposing, and releasing methane into the atmosphere. Methane is a potent greenhouse gas, so it traps more heat, and the feedback loop continues.

Melting sea ice is a significant arctic feedback loop, as it reduces reflection and increases absorbtion of solar energy (David Goldman/Associated Press)

Human activity has pushed our climate close to tipping points where these types of feedback loops can take over and perpetuate the warming for long periods of time. This new report has added yet another loop to the mix and there are probably others that have yet to be discovered. If we are to take lessons from past, we could be in for a hotter, stormier climate for millennia to come.

Of course, this is no reason to abandon efforts to cut our carbon emissions. On the contrary. The Paleocene temperatures shot up 8 C, we are trying to head off the warming at 2 C. While we don't know exactly where the tipping points for the feedback loops are, there is a chance we could prevent the worst case scenario.

These scientists are waving a red flag about the future, as scientists have been doing for decades. By taking action now, we still have a chance to pull the climate microphone away from the speaker before it gets too loud.

About the Author

Bob McDonald is the host of CBC Radio's award-winning weekly science program, Quirks & Quarks. He is also a science commentator for CBC News Network and CBC-TV's The National. He has received 12 honorary degrees and is an Officer of the Order of Canada.

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