When Will Arctic Sea Ice Disappear? Projections of Area, Extent, Thickness, and Volume

Abstract

Rapidly diminishing Arctic summer sea ice is a strong signal of the pace of global climate change. We provide point, interval, and density forecasts for four measures of Arctic sea ice: area, extent, thickness, and volume. Importantly, we enforce the joint constraint that these measures must simultaneously arrive at an ice-free Arctic. We apply this constrained joint forecast procedure to models relating sea ice to cumulative carbon dioxide emissions and models relating sea ice directly to time. The resulting "carbon-trend" and "time-trend" projections are mutually consistent and predict an effectively ice-free summer Arctic Ocean by the mid-2030s with an 80% probability. Moreover, the carbon-trend projections show that global adoption of a lower emissions path would likely delay the arrival of a seasonally ice-free Arctic by only a few years.

Probability assessments of an ice-free Arctic: Comparing statistical and climate model projections

“…Taken together, the results in Table 1 -assuming a standard extrapolation of future emissions -predict an essentially ice-free September Arctic Ocean will likely occur about a decade from now. This timing is broadly consistent with the statistical projections in Diebold and Rudebusch (2022), Diebold et al (2023), and other analyses. 11…”

“…Notz and Stroeve (2018) provide a similar benchmark for reaching NIFA. 11Diebold and Rudebusch (2022) found a slightly increasing rate of decline in Arctic sea ice over the past few decades, which is consistent with a linear relationship between sea ice and CO 2 , given the past increasing rate of change in emissions, as discussed inDiebold et al (2023).12 The confidence ellipses are not tilted with a demeaned carbon series. Since the independent variable is transformed to have zero mean, the sampling uncertainty in the estimation of the slope does not alter estimation of the intercept, and the lack of covariance between the slope and intercept estimate leads to non-tilted ellipses.…”

“…Also related isDiebold et al (2023), which continues with forecasting analyses as in Diebold and Rudebusch (2022), but which is not concerned with evaluation of dynamical climate models. Instead it develops and explores extensions, variations, and robustness checks for statistical forecasting models.…”

“…The definition of NIFA follows the usual convention in the literature as the appropriate definition of an effectively ice-free Arctic, reflecting the hypothesized persistence of residual sea ice clinging to northern coastlines despite an open Arctic ocean(Diebold et al, 2023).…”