Earth is heading for another mass extinction ā and human activity is to blame. The worldās gaze may be focused on COVID-19 right now. But the risks to nature from human-made global warming ā and the imperative to act ā remain clear.
At several points in the history of our planet, increasing amounts of carbon dioxide in the atmosphere have caused extreme global warming, promptingĀ the majority of speciesĀ on Earth to die out.
In the past, these events were triggered by a hugeĀ volcanic eruptionĀ or asteroid impact. Now, Earth is heading for another mass extinction ā and human activity is to blame.
I am an Earth and Paleo-climate scientist andĀ have researchedĀ the relationships between asteroid impacts, volcanism, climate changes and mass extinctions of species.
My research suggests the current growth rate of carbon dioxide emissions is faster than those which triggered two previous mass extinctions, including the event that wiped out the dinosaurs.
The worldās gaze may be focused on COVID-19 right now. But the risks to nature from human-made global warming ā and the imperative to act ā remain clear.
The current rate of CO2 emissions is a major event in the recorded history of Earth. EPA
Past mass extinctions
Many species can adapt to slow, or even moderate, environmental changes. But Earthās history shows that extreme shifts in the climate can cause many species toĀ become extinct.
For example, about 66 million years ago an asteroid hit Earth. The subsequent smashed rocks and widespread fires released massive amounts of carbon dioxide overĀ about 10,000 years. Global temperatures soared, sea levels rose and oceans became acidic. AboutĀ 80% of species, including the dinosaurs, were wiped out.
And about 55 million years ago, global temperatures spiked again, overĀ 100,000 years or so. The cause of this event, known as theĀ Paleocene-Eocene Thermal Maximum, is not entirely clear. One theory, known as theĀ āmethane burpā hypothesis, posits that a massive volcanic eruption triggered the sudden release of methane from ocean sediments, making oceans more acidic and killing off many species.
So is life on Earth now headed for the same fate?
Comparing greenhouse gas levels
Before industrial times began at the end of the 18th century, carbon dioxide in the atmosphere sat at aroundĀ 300 parts per million. This means that for every one million molecules of gas in the atmosphere, 300 were carbon dioxide.
In February this year, atmospheric carbon dioxide reachedĀ 414.1 parts per million. Total greenhouse gas level ā carbon dioxide, methane and nitrous oxide combined ā reached almostĀ 500 parts per million of carbon dioxide-equivalent
Author provided
Carbon dioxide is now pouring into the atmosphere at a rate ofĀ two to three parts per million each year.
Using carbon records stored in fossils and organic matter, I have determined that current carbon emissions constitute an extreme event in the recorded history of Earth.
My researchĀ has demonstrated that annual carbon dioxide emissions are now faster than after both the asteroid impact that eradicated the dinosaurs (about 0.18 parts per million CO2 per year), and the thermal maximum 55 million years ago (about 0.11 parts per million CO2 per year).
The next mass extinction has begun
Current atmospheric concentrations of carbon dioxide are not yet at the levels seen 55 million and 65 million years ago. But the massive influx of carbon dioxide means the climate is changing faster than many plant and animal speciesĀ can adapt.
A major United Nations reportĀ released last year warned around one million animal and plant species were threatened with extinction. Climate change was listed as one of five key drivers.
The report said the distributions of 47% of land-based flightless mammals, and almost 25% of threatened birds, may already have been negatively affected by climate change.
Many researchers fear the climate system is approaching aĀ tipping pointĀ - a threshold beyond which rapid and irreversible changes will occur. This will create a cascade ofĀ devastating effects.
There are already signs tipping points have been reached. For example,Ā rising Arctic temperaturesĀ have led toĀ major ice melt, and weakened theĀ Arctic jet streamĀ ā a powerful band of westerly winds.
A diagram showing the weakening Arctic jet stream, and subsequent movements of warm and cold air. NASA
This allows north-moving warm air to cross the polar boundary, and cold fronts emanating from the poles toĀ intrude south into Siberia, Europe and Canada.
A shift in climate zones is also causing the tropics to expand and migrate toward the poles, at a rate of aboutĀ 56 to 111 kilometres per decade. The tracks of tropical and extra-tropical cyclones are likewise shifting toward the poles. Australia is highly vulnerable to this shift.
Uncharted future climate territory
ResearchĀ released in 2016 showed just what a massive impact humans are having on the planet. It said while the Earth might naturally have entered the next ice age in about 20,000 yearsā time, the heating produced by carbon dioxide would result in a period of super-tropical conditions, delaying the next ice age to about 50,000 years from now.
During this period, chaoticĀ high-energy stormy conditionsĀ would prevail over much of the Earth.Ā My research suggestsĀ humans are likely to survive best in sub-polar regions and sheltered mountain valleys, where cooler conditions would allow flora and fauna to persist.
Earthās next mass extinction is avoidable ā if carbon dioxide emissions are dramatically curbed and we develop and deploy technologies toĀ remove carbon dioxide from the atmosphere. But on the current trajectory, human activity threatens to make large parts of the EarthĀ uninhabitableĀ - a planetary tragedy of our own making.
Main image:Ā Ā Shutterstock
Andrew Glikson, Earth and paleo-climate scientist, Australian National University
This article is republished from The Conversation under a Creative Commons license. Read the original article.
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