Human-induced climate change is older than you think

When do you think global warming first began to take effect? The 1990s? The 1950s? Surely not much earlier than the 1900s?

The truth is that this phenomenon is much older than you may think, with an international research project revealing a noticeable change in climate during the early stages of the Industrial Revolution. The study was published in the journal Nature and involved 25 scientists from across Australia, the United States, Europe and Asia.

As direct measurements of climate were rare before the 1900s, the team studied detailed reconstructions of climate spanning the past 500 years to identify when the current sustained warming trend really began. They examined natural records of climate variations across the world’s oceans and continents, including climate histories preserved in corals, cave decorations, tree rings and ice cores.

The study found that climate change was first detectable in the Arctic and tropical oceans around the 1830s — much earlier than expected — before proceeding to Europe, Asia and North America. The lead researcher on the project, Associate Professor Nerilie Abram from The Australian National University (ANU), described the result as “an extraordinary finding”.

“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.”

The researchers also analysed thousands of years of climate model simulations, including experiments used for the latest report by the UN’s Intergovernmental Panel on Climate Change (IPCC), to determine what caused this early warming. The result? Rising greenhouse gas levels.

Co-researcher Dr Helen McGregor, from the University of Wollongong, clarified that 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 measureable way to even the small increase in carbon emissions during the start of the Industrial Age,” she said.

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 findings will help scientists understand the future impact of greenhouse gas emissions on the climate.

Image caption: Associate Professor Nerilie Abram. Image credit: Stuart Hay, ANU.