Loss of Arctic’s Reflective Sea Ice Will Advance 2°C Guardrail 25 Years

Fast mitigation may still avoid complete loss of sea ice

12 June 2019 — Losing the remaining Arctic sea ice and its reflective power to send incoming solar energy safely back to space is equivalent to adding one trillion tons of CO2 to the atmosphere, on top of the 2.4 trillion emitted since the Industrial Age. This roughly equates to adding 25 years of additional global CO2 emissions. These are the conclusions of a new study formally published in Geophysical Research Letters this week.

Radiative Heating of an Ice-Free Arctic Ocean, by K. Pistone, I. Eisenman, and V. Ramanathan used direct satellite observations to assess the impact of ice-free Arctic Ocean. The authors conclude the loss of sea ice will add 21 W/m2 of solar heating to the region, relative to the 1979 baseline, which averaged over the globe amounts to 0.71 W/m2. (For context, forcing from CO2 from pre-industrial to 2011 was 1.83 W/m2.)  This forcing is equivalent to an increase in CO2 concentration from 400 to 456.7 ppm.

“Losing the reflective power of Arctic sea ice will lead to warming equivalent to one trillion tons of CO2 and advance the 2ºC guardrail by 25 years. Any rational policy would make preventing this a top climate priority for world leaders,” said author V. Ramanathan, Professor of atmospheric and climate sciences at Scripps Institution of Oceanography, University of California, San Diego.

While the paper presents a worst-case scenario, observation-based research shows the Arctic is rapidly destabilizing, and models are systematically underestimating this. The authors note that “there is a striking bias between the modeled Arctic sea ice changes and the observations [and that] the observed Arctic sea ice retreat per degree of global warming is 2.1 times larger than” relevant model results, “with no model … simulating a value as extreme as the observations”, suggesting “substantial systematic biases in the model projections of the level of global warming at which the Arctic becomes annually ice-free.”

An earlier study by the same team calculated that the ice lost in the Arctic between 1979 and 2011 added 6.4 W/m2 to the Arctic- which averaged globally - is equivalent to 25% as much as forcing as from CO2 during the same time period. Additional research shows that strong, multi-year ice is down to 1% of the existing ice. There is great uncertainty about the timing of when the Arctic could become ice-free, with some research suggesting that recent trends could lead to an ice-free Arctic as early as the 2020s and others suggesting 2030 or later depending on future warming and natural variability.

For the baseline calculations, the authors assumed that cloud cover would remain constant. However, they calculate that if the loss of the Arctic ice is accompanied by a complete loss of cloud cover, the total added warming could be three times greater. Conversely, if the Arctic experienced complete cloud cover, the total warming could be half as much. Under all scenarios considered, the study concludes that “the radiative heating of complete Arctic sea ice loss could substantially accelerate the rate of future global warming, advancing global warming," and "drastically shorten the time available to adapt to climate changes and the time for achieving carbon neutrality.”

“It’s increasingly clear that we can’t keep the climate safe without saving the Arctic. Adding 21 W/m2 will kick off a wicked cascade of impacts that will reverberate throughout the world,” said Durwood Zaelke, President of the Institute for Governance & Sustainable Development. “Because the Arctic’s role in regulating the global climate is a critical link in the chain of climate protection it should be the focus of an all-out effort to keep it strong and safe, including strategies to rebuild strong multi-year ice.”

Zaelke continued, “this requires cutting emissions of short-lived pollutants, which can cut Arctic warming by more than half, and speeding up strategies to remove carbon dioxide we’ve already emitted, including natural processes that use photosynthesis to pull carbon dioxide from the atmosphere and store it in trees, grasslands, wetlands, and other biomass, and soils. We also need a crash program to speed mechanical means of direct air capture of carbon dioxide, to remove up to a trillion tons of carbon dioxide over the century. And we need to expedite the study of solar radiation management.”

The study is here (behind paywall).

IGSD’s plain language summary of the study is here.