Quirks & Quarks·Analysis

66 Million years of climate history give present day perspective

Bob McDonald's blog: We're in the midst of an unprecedented rate of climate change

Bob McDonald's blog: We're in the midst of an unprecedented rate of climate change

A firefighter watches the Bobcat Fire burning on hillsides near Monrovia Canyon Park in Monrovia, California on September 15, 2020. (Ringo Chiu/AFP via Getty Images)

Two studies of ocean floor sediments, correlated with astronomical observations have charted the Earth's climate into the distant past showing warm and cold periods lasting millions of years. Our present rate of climate change exceeds them all.

Scientists at the University of California Santa Cruz worked with international colleagues to study core samples taken from ocean floors around the world. 

Using isotopes of oxygen preserved in the cores, they were able — for the first time — to produce a high fidelity record showing four major climatic periods dubbed the "warmhouse," "hothouse," "coldhouse" and "icehouse." These periods lasted millions of years with temperatures either significantly above or below what we are experiencing today.

During the warm-hothouse phase, between 57 and 35 million years ago, the average temperature was 5 to 8 degrees higher than today. There were no polar ice caps. Then the planet began to cool, ultimately to the "icehouse" cycle that included ice ages and warmer periods that we've been in over the last three million years or so. 

This pattern has been influenced partly by changes in the tilt of the Earth's axis and our orbit around the sun, known as Milankovitch cycles.

Greenhouse gases triggering a hothouse Earth

Today we are in an interglacial (between glaciations) warm period, but the extra warming we're seeing cannot be explained by those cycles.

The long historical changes from hot to cold took millions of years, but over the past 150 years, human activity has put our foot on the temperature accelerator. The researchers point out that if the "business as usual" greenhouse gas emissions scenario modelled by the United Nations Intergovernmental Panel on Climate Change (IPCC) continues unabated, the Earth will be back in a hothouse condition by the year 2300, a condition the planet hasn't seen in 50 million years. 

A man walks his bicycle through a street flooded by Hurricane Sally in Pensacola, Florida, on September 16, 2020. (Chandan Khanna/AFP via Getty Images)

Another study at Columbia University's Lamont -Doherty Earth Observatory used isotopes of carbon found in fossilized sea shells to determine what made that hothouse time so hot. It turns out that 55.6 million years ago, intense volcanism spewed huge amounts of carbon dioxide into the atmosphere for thousands of years, with most of it absorbed by the oceans. This made the oceans very acidic, which would have been hard for marine life. 

But once again, the study found that the rate of carbon emitted by all those ancient volcanoes was less than what we humans are spewing out today. They calculate we're releasing carbon anywhere from three to eight times faster than was occurring during that planet-transforming period of extreme volcanic activity.

A man stands near some of the destruction caused by the Almeda Fire in Phoenix, Oregon, September 15, 2020. Infernos across California, Oregon and Washington state have burned millions of acres this year, killed dozens of people and forced hundreds of thousands from their homes. (ROBYN BECK/AFP via Getty Images)

Biggest concern is the rate of climate change

These studies underline how dramatically swift our impact on the environment really is. The concern of the scientists is not just the amount of heating our carbon emissions are causing, because the planet has been much warmer and much cooler in the past. What is most worrying them is the rate of change. 

We are seeing increases in average global temperatures happening in decades or centuries that historically took millennia. And rapid change is difficult for ecosystems and species to adapt to. Over the past half billion years or so, there have been five global mass extinctions, and rapid climatic transformation is thought to have been a major factor in most of them. Many researchers are now calling our current era the "sixth extinction."

These images showing several tropical cyclones in the Atlantic Ocean were taken in a two hour period on September 18, 2020. (CIRA/NOAA)

Now, with the largest wildfires in their history sweeping through California and the Western U.S., as well as significant fire seasons in Siberia and Brazil, severe tropical storms and droughts becoming more frequent, the winds of change are upon us.

Will we take our foot off the accelerator and avoid plunging the planet into another hothouse world?

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.