Human activity has been driving climate change since the early stages of the Industrial Revolution almost two centuries ago – much earlier than previously thought, according to a groundbreaking new study.
An international team of scientists, led by Associate Professor Nerilie Abram from the Australian National University, have analysed detailed reconstructions of climate going back 500 years. To their surprise, they’ve found that the current global warming trend began in the 1830s, further confirming that it is an anthropogenic, or human-induced, phenomenon. The study was published today in Nature.
Co-researcher Dr Helen McGregor, an earth sciences expert from the University of Wollongong, tells SBS Science the findings have a major impact on our understanding of how climate change works.
“If we know when global warming started, we know what the actual rates of warming are and we know when our climate is emerging above natural variability,” McGregor explains.
“It helps us understand if we’re already in an extreme kind of climate or a global warming climate setup, and we can better forecast from there because we just have better baseline understanding.”
The researchers used data from climate model simulations and experiments, major volcanic eruptions and, most importantly, natural markers of climate variation found in places like corals, tree rings, and ice cores obtained from glaciers.
They then constructed new simulations of climate and found that instead of being a 20th century phenomenon as previously thought, climate change actually began in the 1830s, precisely coinciding with the historical period when carbon dioxide emissions began increasing due to human activity.
“One of the implications is that this early development of warming seems to imply that the climate system is able to respond quite quickly to increases in greenhouse gases,” says Abram. “That’s a problem if we’re increasing the level of greenhouse gases in the atmosphere.”
The researchers have also ruled out that the first signs of global warming occurred as recovery following some early 1800s major volcanic eruptions, which very briefly cooled the climate.
"Our initial response was [that] the climate is recovering from those volcanic eruptions and then at some point later we’ve got the effect of greenhouse gases coming in to continue the warming trend," says Abram.
"But if you look at climate model simulations that have only been forced with greenhouses gases and don’t have any of those other natural effects going on like volcanic eruptions, then we still produce the same result showing that the climate response to increasing greenhouse gases developed in the mid-19th century," she explains.
Dr McGregor says the study provides new, independent proof that climate change is indeed caused by human activity.
“One thing that our study provides is that it’s an alternative line of evidence,” she explains. “We’re not using thermometers and satellite records, we’re using natural archives of climate, so it’s a completely independent source of information that shows that climate change and warming is occurring.
"The central tenet of climate change, that the planet is warming, doesn’t change."
More sophisticated climate research
Professor Will Steffen, also from the ANU and the Climate Council, says the study is evidence of major improvements in climate change analysis.
“I think it shows that the climate system is sensitive to rather small changes, and changes at rather slower rates, compared to what’s going on now in the climate system,” he tells SBS Science.
“It also shows that our methods of interrogating the climate system as we are now are getting much more sophisticated as we go along.”
The researchers also found variations in natural markers of climate between the northern and southern hemispheres – the higher concentration of landmasses in the north, which warm at a faster rate than oceans, played a significant factor in the early emergence of climate change.
“We don’t have so many records from the southern hemisphere, but part of that could well be that we don’t have a complete understanding of how the southern hemisphere and the oceans in particular interact in this region in the climate system,” says McGregor.
“So understanding our region is actually, I think, maybe the major next step.”