In recent years, there has been an increased focus on the human influence over climate change, with research pointing to our activity as the cause of global warming. Although the data might seem to suggest the human connection to climate change as a relatively recent occurrence – with a global temperature spike of 0.8° C (1.4° F) over the last 100 years – a new study by researchers from the Australian National University reveals that we have been behind the warming of the Earth for 180 years, suggesting that it's not simply a 20th-century phenomenon.
One of the main reasons for the perception of climate change as a 20th-century event is the lack of direct climate measurements prior to the 1900s. In order to fill in this gap, lead researcher Nerilie Abram and her team reconstructed climate patterns over the past 500 years in order to get a better picture of when global warming began.
In order to reconstruct these climate patterns, Abram's team examined temperature reconstructions from natural archives including ice cores, tree rings and corals, and integrated this data with the temperatures they obtained through the analysis of climate-model simulations spanning thousands of years, some of which were used by the UN's Intergovernmental Panel on Climate Change's (IPCC) latest report.
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To remove the effects of year-to-year variability, they used a statistical approach in order to pinpoint the time period when the most recent long-term warming trends began to surface. The results revealed that the many global-warming trends seen today stem, in many places around the world (in particular the Arctic and tropical oceans), from around the 1830s. This time period marks the beginning of the Industrial Revolution when greenhouse gases began to rise.
"It was an extraordinary finding," says Abram. "It was one of those moments where science really surprised us. But the results were clear. The climate warming we are witnessing today started about 180 years ago."
Although it is clear from the data that humans indeed caused increases in greenhouse gas levels in the atmosphere during the 1800s, these increases were only minor. Yet the researchers suggest that even these small increases led to a cascade of effects on the Earth's climate, with the carbon emissions essentially marking the onset of the global warming that we are observing today.
Ultimately, understanding how humans have affected global warming over the years and the nature of the Earth's climate shift since the pre-industrial period is important in order to help scientists predict the continued effects of greenhouse gas emissions on the climate, devise solutions to minimize their damages, and better grasp the Earth's sensitivity to such emissions.
The findings were published in the journal Nature.
Source: Australian National University