Human activity has been causing global warming for almost two centuries, says new research, proving that human-induced climate change is not just a 20th century phenomenon.
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The study showed that warming began during the early stages of the industrial revolution and was first detected in the Arctic and tropical oceans around the 1830s, which was later spread to Europe, Asia and North America.
However, climate warming appears to have been delayed in the Antarctic, possibly due to the way ocean circulation is pushing warming waters to the North and away from the frozen continent, the researchers said.
"The climate warming we are witnessing today started about 180 years ago," said lead researcher Nerilie Abram Associate Professor at The Australian National University (ANU) in Canberra, Australia.
"In the tropical oceans and the Arctic in particular, 180 years of warming has already caused the average climate to emerge above the range of variability that was normal in the centuries prior to the Industrial Revolution," Abram added.
Abram also found that the early warming was attributed to rising greenhouse gas levels.
Humans only caused small increases in the level of greenhouse gases in the atmosphere during the 1800s.
"But, the early onset of warming detected in this study indicates the Earth's climate did respond in a rapid and measurable way to even the small increase in carbon emissions during the start of the industrial age," explained Helen McGregor from the University of Wollongong in New South Wales, Australia.
In addition, the researchers also studied major volcanic eruptions in the early 1800s and found they were only a minor factor in the early onset of climate warming.
The study has important implications for assessing the extent that humans have caused the climate to move away from its pre-industrial state, and will help scientists understand the future impact of greenhouse gas emissions on the climate.
For the study, published in the journal Nature, an international team of scientists examined natural records of climate variations across the world's oceans and continents.
These included climate histories preserved in corals, cave decorations, tree rings and ice cores. They also analysed thousands of years of climate model simulations to determine what caused the early warming.