Global, Arctic, and Antarctic sea ice volume predictions using score-driven threshold climate models

Abstract

The literature on sea ice predictions uses a variety of general circulation models (GCMs), which suggest diverse predictions of the date of ice-free or almost ice-free oceans, and focus mainly on the Arctic. GCMs are not sensitive enough to tipping points in the Atlantic meridional overturning circulation (AMOC), and they underestimate the sensitivity of Arctic sea ice to carbon emissions. We contribute to the literature in two ways: First, we use a novel time series model, named the score-driven threshold climate (SDTC) model, and we report global, Arctic, and Antarctic sea ice predictions. For the SDTC model, the estimations are computationally less demanding than those of the GCMs. Second, we combine long-run 1,000-year frequency climate data from 798,000 to 1,000 years ago, and short-run annual data from year 850 to year 2014. We present the evolution of long-run and short-run climate data with descriptive statistics. We estimate the SDTC model using annual data from 850 to 2014 for Arctic and Antarctic sea ice volume Icet and Antarctic land surface temperature Tempt. We use the atmospheric CO2,t concentration as a clustering variable to define periods of climate change. Hence, CO2,t concentration drives the regime-switching dynamics of parameters in the SDTC model. We report in-sample interval forecasts of global, Arctic, and Antarctic sea ice from 1980 to 2014. Observed global and Arctic sea ice volumes are below the forecasted interval from 2003. The observed Antarctic sea ice volume is below the forecasted interval from 2011. We report out-of-sample interval forecasts of sea ice from 2015 to 2314. The out-of-sample forecasts, μ[μ±2σ], indicate that if the current trend of climate change continues, then Arctic sea ice will disappear around 2058[2049,2068], and global and Antarctic sea ice will disappear around 2174[2123,2270].