July 24, 2019<\/p>\n\n\n\n
A team of\nclimate scientists at Northern Arizona University, along with their\ninternational collaborators, has completed new reconstructions of Earth\u2019s\ntemperature over the past 2,000 years, placing the exceptional 20th<\/sup>-century\nwarming into a longer-term context, as chronicled in a study published today in\nNature Geoscience<\/a><\/em>.<\/em><\/p>\n\n\n\n This\ninternational collaboration, part of the PAGES 2k Consortium, used a new,\nhighly curated set of paleoclimate data and compared seven different\nstatistical methods for reconstructing past global average temperature. Put\nsimply, they found these different ways of measuring climate change in the last\ntwo millennia all came back with similar results, especially when focusing on\ndecade-to-decade changes. This allowed the researchers to explore important\nquestions about how much of the past temperature changes can be ascribed to\ndifferent natural causes, including the randomness of the climate system, which\nis difficult to quantify without a long-term perspective. <\/p>\n\n\n\n Results showed\nthe most rapid, multi-decade-long global warming of the past 2,000 years occurred\nduring the second half of the 20th century, highlighting the extraordinary pace\nof current climate change, due mostly to human emissions of heat-trapping\ngases. The study also quantified changes in global temperature due to volcanic\neruptions and natural variability before the industrial revolution. These are\nimportant benchmarks for evaluating whether climate models accurately simulate\nchanging global climate.<\/p>\n\n\n\n \u201cReconstructions\nof the past help us place recent climate changes into an appropriate context,\u201d said\nMichael Erb<\/strong>, co-author and a postdoctoral scholar at NAU\u2019s School of\nEarth and Sustainability. \u201cThis study allowed us to estimate climate\nvariability over the past 2,000 years, showing just how large recent man-made\nwarming is compared to natural and volcano-forced climate variations over the\nrecent past. It also showed that climate models are doing a good job capturing\nthese sort of changes, which is helpful for model validation.\u201d<\/p>\n\n\n\n The PAGES\n2k Consortium includes Regents\u2019 Professor Darrell Kaufman<\/strong> and assistant professor\nNicholas McKay<\/strong>, also from NAU\u2019s School of Earth and Sustainability, and\na host of collaborators from around the nation and world, such as Costa Rica,\nChina, Switzerland, Germany and Australia. To generate the new temperature\nreconstructions, they first needed to gather together the PAGES 2k database, which\nconsists of biological and geological sources that provide information on\nhistorical temperatures and climate. These data sources include tree rings,\ncorals, glacier ice and sediments, providing information from all of the\nworld\u2019s continents and oceans. The collaboration is coordinated through the\nPast Global Changes (PAGES) project, which makes this valuable data available\nto other scientists for use in diverse paleoclimate research as well. <\/p>\n\n\n\n McKay and\nKaufman led the development of this database and are delighted to see that\neffort paying off. <\/p>\n\n\n\n \u201cPulling\ntogether such a diverse dataset is extremely challenging, but it\u2019s exciting to\nsee that work help us better understand the climate system,\u201d McKay said. \u201cThis\nis only the tip of the iceberg of what scientists can learn from these data.\u201d<\/p>\n\n\n\n \u201cThis\nstudy used the recently developed PAGES 2k database to improve on previous temperature\nreconstructions at the global scale,\u201d Kaufman said. \u201cThis is a major\naccomplishment that was completed in time for the results to be considered in\nthe upcoming climate assessment report from the Intergovernmental Panel on\nClimate Change.<\/p>\n\n\n\n A\ncompanion study, which used the same database to map how temperature over the\npast 2,000 years varied from place to place around the Earth, was published\nconcurrently in Nature<\/a><\/em>.<\/p>\n","protected":false},"excerpt":{"rendered":"