Abstract
The ongoing retreat of glaciers globally is one of the clearest manifestations of recent global warming associated with rising greenhouse gas concentrations. By comparison, the importance of greenhouse gases in driving glacier retreat during the most recent deglaciation, the last major interval of global warming, is unclear due to uncertainties in the timing of retreat around the world. Here we use recently improved cosmogenic-nuclide production-rate calibrations to recalculate the ages of 1,116 glacial boulders from 195 moraines that provide broad coverage of retreat in mid-to-low-latitude regions. This revised history, in conjunction with transient climate model simulations, suggests that while several regional-scale forcings, including insolation, ice sheets and ocean circulation, modulated glacier responses regionally, they are unable to account for global-scale retreat, which is most likely related to increasing greenhouse gas concentrations.
Highlights
The ongoing retreat of glaciers globally is one of the clearest manifestations of recent global warming associated with rising greenhouse gas concentrations
Transient simulations with a coupled global climate model show that modulation by other forcings can explain regional variability in the glacier retreat chronology, with insolation explaining early deglaciation in the western United States, and seesaw responses to the AMOC explaining millennial variability in the Southern Hemisphere
Onset of glacier retreat in the tropics is generally consistent with CO2 forcing, but the existing chronology cannot exclude earlier retreat, possibly identifying the influence of El Nino-Southern Oscillation (ENSO) variability on glacier surface mass balance, or some other as yet unidentified regional forcing
Summary
The ongoing retreat of glaciers globally is one of the clearest manifestations of recent global warming associated with rising greenhouse gas concentrations. The importance of greenhouse gases in driving glacier retreat during the most recent deglaciation, the last major interval of global warming, is unclear due to uncertainties in the timing of retreat around the world. We use recently improved cosmogenic-nuclide production-rate calibrations to recalculate the ages of 1,116 glacial boulders from 195 moraines that provide broad coverage of retreat in mid-to-low-latitude regions. This revised history, in conjunction with transient climate model simulations, suggests that while several regional-scale forcings, including insolation, ice sheets and ocean circulation, modulated glacier responses regionally, they are unable to account for global-scale retreat, which is most likely related to increasing greenhouse gas concentrations. Together with transient model simulations, our results suggest that greenhouse gases were the major driver of globalscale glacier retreat, while other factors modulated glacier responses regionally
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