August 25, 2016

Humans have caused climate change for 180 years

International consortium, including UOW expert, finds climate change started in early stages of industrial revolution. 

An international research project has found human activity has been causing global warming for almost two centuries, proving human-induced climate change is not just a 20th century phenomenon.

The study, published today (25 August) in Nature, found global warming began during the early stages of the Industrial Revolution and is first detectable in the Arctic and tropical oceans around the 1830s, much earlier than scientists had expected.

Climate change expert Dr Helen McGregor, from UOW's School of Earth and Environmental Sciences, co-authored the report. She said the finding was unexpected and extraordinary.

The new findings have 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 warming climate.

“In the tropical oceans and the Arctic in particular, 180 years of warming has already caused the climate to move above the range of variability that was normal in the centuries prior to the Industrial Revolution,” Lead author Associate Professor Nerilie Abram from The Australian National University (ANU) said.

Associate Professor Abram said anthropogenic climate change was generally talked about as a 20th century phenomenon because direct measurements of climate are rare before the 1900s.

However, the team studied detailed reconstructions of climate spanning the past 500 years to identify when the current sustained warming trend really began.

Scientists examined hundreds of natural records of climate variations across the world’s oceans and continents. These included natural histories preserved in corals, sediment layers, cave decorations, tree rings and ice cores.

The research team also analysed many 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 the early warming.

The data and simulations together pinpointed the early onset of warming to around the 1830s, and found the early warming was attributed to rising greenhouse gas levels.

Dr McGregor, an ARC Future Fellow who is among UOW’s 2016 Women of Impact, said 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 at in the start of the Industrial Age,” Dr McGregor said.

Recovery of the climate following major volcanic eruptions in the early 1800s was found to be only a minor factor in defining the early onset of climate warming.

Associate Professor Abram said the earliest signs of greenhouse-induced warming developed during the 1830s in the Arctic and in tropical oceans, followed soon after by 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 research team involved 25 scientists from across Australia, the United States, Europe and Asia, working together as part of the international Past Global Changes 2000 year (PAGES 2K) consortium.

A collaborator on the study, Associate Professor Michael Evans (pictured above with Dr McGregor) from the University of Maryland, USA, recently visited UOW as part of the UOW Visiting International Scholar Awards. While in Wollongong, Professor Evans gave a masterclass in quantitative data analysis to help research students understanding atmospheric, oceanographic, and long-term climate interactions.

Applications for the next round of Visiting International Scholar Awards are now open. For more information, visit www.uow.edu.au/research/researchgrants.

For more information about UOW researchers, visit scholars.uow.edu.au.