Continental-scale temperature variability during the past two millennia

Continental-scale temperature variability during the past two millennia

21 April 2013 | PAGES 2k Network
The PAGES 2k Network reconstructed past temperatures for seven continental-scale regions over the past two millennia, revealing a long-term cooling trend that ended in the late 19th century. Multi-decadal to centennial temperature variability showed regional patterns, with more similarity within hemispheres than between them. No globally synchronous warm or cold intervals defined a Medieval Warm Period or Little Ice Age, but all reconstructions showed generally cold conditions between AD 1580 and 1880, with warm decades in some regions during the 18th century. The transition to colder conditions occurred earlier in the Arctic, Europe, and Asia than in North America or the Southern Hemisphere. Recent warming reversed the long-term cooling, with the area-weighted average temperature during 1971–2000 being higher than any other time in nearly 1,400 years. The PAGES 2k Network, coordinated with NOAA, provides a global dataset of proxy records and temperature reconstructions for seven continental-scale regions. The study highlights the importance of understanding past climate variability to distinguish anthropogenic impacts from natural variability. The reconstructions show regional differences in temperature trends, with significant cooling trends in most regions before the 20th century, except Antarctica. The cooling trend varied between 0.1 and 0.3°C per 1,000 years. The study also identified multi-centennial cooling, with higher temperatures in the early centuries of the first millennium compared to the late centuries of the second millennium. The cooling was attributed to factors such as solar irradiance, volcanic activity, land-cover changes, and orbital insolation. Multi-decadal to centennial variability showed regional differences, with a sustained warm interval from AD 830 to 1100 in the Northern Hemisphere. The transition to colder climates occurred earlier in the Arctic, Europe, and Asia than in North America or the Southern Hemisphere. The study found no globally synchronized multi-decadal shifts marking a Medieval Warm Period or Little Ice Age, but regional variations in temperature departures from a global cooling trend were observed. The twentieth century was the warmest or nearly the warmest century in all regions except Antarctica, where oceanic thermal inertia dampened warming. The study also found that the twentieth-century warming in the Northern Hemisphere was twice that of more ocean-dominated regions in Australasia and South America. The PAGES 2k reconstructions show clear regional expressions of temperature variability at multi-decadal to centennial scales, with a long-term cooling trend before the twentieth century. The study emphasizes the importance of understanding past climate variability to assess the impact of external and internal climate forcings on temperature fluctuations and trends at the continental scale. The reconstructions and proxy data will be useful for future studies, serving as a benchmark for comparisons with climate model simulations.The PAGES 2k Network reconstructed past temperatures for seven continental-scale regions over the past two millennia, revealing a long-term cooling trend that ended in the late 19th century. Multi-decadal to centennial temperature variability showed regional patterns, with more similarity within hemispheres than between them. No globally synchronous warm or cold intervals defined a Medieval Warm Period or Little Ice Age, but all reconstructions showed generally cold conditions between AD 1580 and 1880, with warm decades in some regions during the 18th century. The transition to colder conditions occurred earlier in the Arctic, Europe, and Asia than in North America or the Southern Hemisphere. Recent warming reversed the long-term cooling, with the area-weighted average temperature during 1971–2000 being higher than any other time in nearly 1,400 years. The PAGES 2k Network, coordinated with NOAA, provides a global dataset of proxy records and temperature reconstructions for seven continental-scale regions. The study highlights the importance of understanding past climate variability to distinguish anthropogenic impacts from natural variability. The reconstructions show regional differences in temperature trends, with significant cooling trends in most regions before the 20th century, except Antarctica. The cooling trend varied between 0.1 and 0.3°C per 1,000 years. The study also identified multi-centennial cooling, with higher temperatures in the early centuries of the first millennium compared to the late centuries of the second millennium. The cooling was attributed to factors such as solar irradiance, volcanic activity, land-cover changes, and orbital insolation. Multi-decadal to centennial variability showed regional differences, with a sustained warm interval from AD 830 to 1100 in the Northern Hemisphere. The transition to colder climates occurred earlier in the Arctic, Europe, and Asia than in North America or the Southern Hemisphere. The study found no globally synchronized multi-decadal shifts marking a Medieval Warm Period or Little Ice Age, but regional variations in temperature departures from a global cooling trend were observed. The twentieth century was the warmest or nearly the warmest century in all regions except Antarctica, where oceanic thermal inertia dampened warming. The study also found that the twentieth-century warming in the Northern Hemisphere was twice that of more ocean-dominated regions in Australasia and South America. The PAGES 2k reconstructions show clear regional expressions of temperature variability at multi-decadal to centennial scales, with a long-term cooling trend before the twentieth century. The study emphasizes the importance of understanding past climate variability to assess the impact of external and internal climate forcings on temperature fluctuations and trends at the continental scale. The reconstructions and proxy data will be useful for future studies, serving as a benchmark for comparisons with climate model simulations.
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