Global warming, with its devastating impacts on coral reefs already being experienced, started earlier than previously thought, researchers have found. Credit:Morane Le Nohaic Helen McGregor, an ARC future fellow at the University of Wollongong and one of the paper's lead authors, said it was "quite a surprise" the international research teams of dozens of scientists had been able to detect a signal of climate change emerging in the tropical oceans and the Arctic from the 1830s. "Nailing down the timing in different regions was something we hadn't expected to be able to do," Dr McGregor told Fairfax Media. Interestingly, the change comes sooner to northern climes, with regions such as Australasia not experiencing a clear warming signal until the early 1900s (see chart). Nerilie Abram, another of the lead authors and an associate professor at the Australian National University's Research School of Earth Sciences, said greenhouse gas levels rose from about 280 parts per million in the 1830s to about 295 ppm by the end of that century. They now exceed 400 ppm.

Miner wearing a headlamp at the Lithgow Colliery, near Sydney, in December 1932. Understanding how humans were already altering the composition of the atmosphere through the 19th century means the warming is closer to the 1.5 to 2 degrees target agreed at last year's Paris climate summit than most people realise. "We are only talking about a small effect during the 19th century because the increases in greenhouse gases were small compared to the very rapid changes that we see today," Dr Abram said. Miners and their horses at the Balmain Colliery near Sydney, from the 1930s. Credit:Fairfax Media "But when you combine that with the fact we're already frighteningly close to that 1.5 degrees target [compared with pre-industrial levels], then even adding a little bit extra human contribution makes a difference."

Will Steffen, a member of the Australian Climate Council and an emeritus professor at ANU, said the paper shows an extra "couple of tenths of one degree" must be added to what are generally taken to be the baselines of warming since key instrumental records start from the 1880s. A chart from the Nature paper shows the onset times of warming depicted by the vertical bar in each region's plot. "For the first time we see really clearly what that warming was and when it started," Professor Steffen said. He said the authors' definition of a "time of emergence" when average temperatures exceeded the previous normal range of variability was also an important concept relevant to today's observations. "That is why we are seeing such extensive [coral] bleaching, why we're seeing burning of Tasmanian forests, and similarly dire ecological effects in other parts of the world," Professor Steffen said. "It's because these ecosystems are outside of their comfort zones, well and truly."

Dr Abram said more research is needed to understand what the lagging warming in the southern hemisphere means for nations such as Australia, as well as the rest of the world. The models and observations have a "really lovely agreement" for the northern hemisphere and tropical oceans, "but when we turn that around to look at the southern hemisphere, the models and the data aren't telling us the same story", she said. Dr McGregor said the oceans had been doing humans a big favour by absorbing most of the extra heat being trapped by greenhouse gases – more than 90 per cent – but much is still to be learnt about whether this phenomenon can continue. "What's going to change, when is this heat going to be released, and what are the thresholds for changing the climate?" she said. "I wonder – what climate surprises do we have ahead of us?" Malte Meinshausen, associate professor at the Climate & Energy College at the University of Melbourne, said greenhouse gas concentration began to turn upwards for carbon dioxide from about 1765 with the Industrial Revolution.

Loading Methane concentrations began ticking higher from about 1700 as agriculture became more intensive. Follow Peter Hannam on Twitter and Facebook.