New research suggests that sudden disruptions in Earth's climate thousands years ago, which caused extreme sea-level rise or mass ice caps melting, can be used as a warning system for the planet's tipping points today.Temperature tipping points that are unavoidable for centuries or more are thresholds beyond which rapid and large changes to the natural environment may occur.These include the possibility of catastrophic events such as the melting ice sheets atop Greenland or West Antarctica. They contain enough frozen water for oceans to lift more than a dozen metres (40 feet) high.They are difficult to predict because of the small or gradual changes in variables like atmospheric carbon concentrations, which trigger them.An international team of scientists reviewed past climate events and identified two major instabilities within the Earth system. These were caused by changes to ice, oceans and rainfall patterns.They examined the conditions that caused the BllingAllerd warming episode nearly 15,000 years back, when surface air temperatures rose up to 14 degrees Celsius above Greenland.The team also examined the end of the so called African humid period, around 6,000 to 5,000 years ago. This led to changes in ecosystems that led prehistoric human societies.The researchers discovered that several past climate systems such as ocean dynamics or rainfall patterns, had a tendency to slow down as they reached a tipping points, failing to recover from perturbations."Earth's past shows how abrupt changes to the Earth system have triggered cascading effects on ecosystems, and human societies as they struggled with adapt," stated Tim Lenton (review co-author, director of the University of Exeter’s Global Systems Institute).Lenton stated that "we face the risk of cascading tipsping points again now, but this time it's of our own making and the impacts of these will be global.""We could use some early warning systems to help us face that risk."Changes compoundCurrent atmospheric CO2 levels at 412 parts per Million have some precedent from at least 800,000. Years ago, but the rate of CO2 accumulation is not.Although scientists are split on the timing and if tipping points will occur, many scientists believe that carbon pollution has already caused ice-sheet melting.The review was published online on Thursday by the authors. It showed that past abrupt changes to Earth's system led to planet-wide disruption.At the beginning of the Bolling–Allerod warming, changes in ice levels and ocean currents can have cascading effects such as low ocean oxygen, reduced vegetation cover, atmospheric CO2 and methane levels.Victor Brovkin, lead author at the Max Planck Institute for Meteorology, said that although it sounds counterintuitive, in order to foresee the future, we might need to look back to the past.He said that the longer the observation period, "the chance of detecting abrupt changes or tipping points where small fluctuations lead to large impacts increases""This is why geological archives provide a rich resource for analysis of abrupt changes and their cascades."Agence France-Presse
