Cosmos Editorial
Human-induced climate change has been kicking along for nearly two centuries, a new study shows.
Nerilie Abram from the Australian National University and an international crew of colleagues traced Earth’s climate over the past 500 years and found warming of the northern hemisphere began in the 1830s, with the southern hemisphere following suit around 50 years later.
The work, published in Nature, “really surprised” the researchers, says Abram: “It was an extraordinary finding.”
While the Industrial Revolution saw a rush of technological advances from the mid-1700s to mid-1800s, it also spelled the start of humanity’s penchance for burning fossil fuels to power it all – and start pumping carbon dioxide and other gases into the atmosphere.
In the 1830s, atmospheric carbon dioxide levels were around 280 parts per million. But by the end of the century, levels reached 295 parts per million (and today, they’re at 403 parts per million and still rising).
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So were those carbon dioxide levels back in the 1830s high enough to change the climate? This is what Abrams and colleagues set out to find.
They trawled through a natural archive of the planet’s climate history, including ice cores drilled deep from polar ice, tree rings, corals and cave stalactites from the northern and southern hemispheres.
They found signs of warming in the 1830s.
To determine what caused this extra heat – was it carbon emissions from burning fossil fuels or simply natural variation? – they also analysed climate simulations.
That data showed only greenhouse gases could produce the pattern of climate change evident in the Earthly archive.
So why did the northern hemisphere warm sooner than the southern?
The researchers aren’t sure, but they suspect it has something to do with the south’s continents and vast oceans. Oceans have soaked up around 90% of the total global energy imbalance since 1950, and in the mid to late 1800s may have helped regulate the climate better.
But knowing that the planet responds to changes in atmospheric carbon so quickly is important for climate scientists in future mitigation efforts.
Reducing or reversing atmospheric carbon could mean rapid payoffs, too.
