As direct measurements of climate were rare before the 1900s, anthropogenic climate change is generally viewed as a 20th century phenomenon. In a new international study led by The Australian National University (ANU), it has now been determined that global warming actually began as early as during the first stages of the Industrial Revolution.
Associate Professor Nerilie Abram, the lead researcher, noted that the first signs appeared in tropical oceans and the Arctic as early as the 1830s. This is much sooner than what scientists generally believed. 180 years of warming has already caused the average climate to rise above the range of changeability that was normal in the centuries before the Industrial Revolution.
The new findings will help scientists better understand how greenhouse gas emissions will in future impact on the climate. The extent with which humans have triggered the climate to move away from its pre-industrial state is still being assessed.
The study is extensive and involves studying comprehensive reconstructions of the climate covering the past 500 years. The team hopes to determine when the current sustained warming trend really began. Natural records of climate variations across the world’s continents and oceans are studied, including climate histories found in tree rings, cave decorations, ice cores and corals. To ascertain what caused the early warming, climate model simulations spanning thousands of years are also being looked at. This includes experiments performed for the most recent report by the UN’s Intergovernmental Panel on Climate Change (IPCC).
The early warming that started around the 1830s was ascribed to rising greenhouse gas levels. According to the University of Wollongong’s School of Earth and Environmental Sciences’ Dr Helen McGregor, a co-researcher in the study, humans were only responsible for small increases in the level of greenhouse gases in the atmosphere during the 1800s. In spite of this, the Earth’s climate responded rapidly in a measureable way to even the smallest escalation in carbon emissions during the start of the Industrial Age.
VIDEO: Century-scale temperature trends for the continents and tropical oceans over the last 500 years. Colours show the regional 100-year temperature trends, for every year since 1500CE. Indicator bar below the map shows the time-span of the 100-year trends. Non-significant trends are masked in grey. Video credit: Abram et al.
Major volcanic eruptions in the early 1800s were also looked at. These were however found to have had a minor impact on the early onset of climate warming. Abram notes that although the earliest signs of greenhouse induced warming developed in tropical oceans and the Arctic, it was soon followed by North America, Europe and Asia. Interestingly, the process was delayed in the Antarctic. This has been ascribed to the way the frozen continent’s ocean circulation pushes warming waters to the North and away from the continent.
The research was published in Nature journal.