Max Planck Institute for Meteorology news release.

The ongoing rapid retreat of Arctic sea ice is often interpreted as the canary in the mine for anthropogenic climate change. In a new study, scientists have now systematically examined the validity of this claim. They find that neither natural fluctuations nor self-acceleration can explain the observed Arctic sea-ice retreat. Instead, the recent evolution of Arctic sea ice shows a strong, physically plausible correlation with the increasing greenhouse gas concentration. For Antarctic sea ice, no such link is found – for a good reason.

When scientists try to attribute some observed climatic change to a specific forcing, they usually use complex climate models. The scientists at Germany’s Max Planck Institute for Meteorology (MPI-M), however, decided on a different strategy as they set out to identify the main driver for the observed sea-ice loss in the Arctic. Dirk Notz, lead author of the study that was now published in the journal Geophysical Research Letters [1], explains why: “Sea ice is so thin that it reacts very sensitive to the large natural fluctuations of weather and climate that prevail in the Arctic. Because these fluctuations are inherently chaotic, their specific timing cannot be reproduced by standard climate models. Such models therefore aren’t necessarily the best tool to examine if natural fluctuations did cause the observed sea-ice loss.”

The scientists instead used a historical record that described the natural variations of sea-ice extent between the early 1950s and late 1970s. These natural fluctuations were then compared to the magnitude of fluctuations of the Arctic sea-ice cover as measured from satellites since the late 1970s. From such comparison, the scientists found only a minute chance that the recently observed extreme sea-ice minima simply happened by chance – and they could exclude self acceleration as the main driver for the observed sea-ice retreat. “Whenever we had a strong sea-ice loss from one year to the next, the ice cover always recovered somewhat in the following year,” explains Dirk Notz. This would not be the case if the sea-ice retreat were indeed self-accelerating.

Jochem Marotzke, Director at MPI-M and co-author of the study, describes what the scientists did next: “Having excluded natural fluctuations and self acceleration as the main driver for the sea-ice retreat, it was clear to us that some external driver was responsible for the observed sea-ice decline. We therefore set out to find an external driver that showed a physically plausible relationship with the observed sea-ice retreat.” The scientists examined, for example, the strength of solar radiation. “Here, a physically plausible link to the observed sea-ice retreat can only be established if solar radiation had increased in recent years.” However, solar radiation has slightly decreased in the past decades. Its fluctuations are therefore very unlikely to be the main driver of the observed sea ice loss. The scientists could not find a plausible link to changes in prevailing wind patterns, volcanic eruptions, oceanic heat transport, or cosmic rays, either.

“In the end, only the increase in greenhouse gas concentration showed a physically plausible link with the observed sea-ice retreat. We expect a decreasing sea-ice cover for increasing greenhouse gas concentration, which is exactly what is observed,” Notz explains. The physical link between greenhouse gas concentration and sea ice is quite straightforward, he adds: “Greenhouse gases increase the downwelling thermal radiation. This radiation, in turn, is the major player in the heat budget of Arctic sea ice.”

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by Ben Holland, via the Rocky Mountain Institute

After little more than a year on the roads, the first mass-market electric vehicles have attracted tremendous scrutiny. On a monthly basis, commentators and automotive journalists proclaim their success or failure, based on sales fluctuations. At first glance, the equation seems simple: automobile companies build cars, and if they’re popular enough, they’ll sell.

But the EV market is arguably more complex than the traditional vehicle market. Sales result not only from automaker marketing but from a groundswell of support. Amounting to somewhat of a global movement, the EV market consists of an array of stakeholders—automakers, technology companies, governmental agencies, nonprofits, manufacturers, fleet owners, and consumers—all bringing unique motivations and perspectives on vehicle electrification. But they coalesce in one place—the city.

The challenges of transitioning to vehicle electrification are real. The internal combustion engine has been the established automotive technology for over a century. Switching out this familiar technology with the electric powertrain will not happen overnight. And it may not happen with any real scale without a concerted effort to support the industry. So stakeholders across the EV value chain are coming together in cities around the world, creating test beds and strongholds for the market. By fostering coordination among these entities, cities can create a localized movement and an adoptable model for others to follow. Replicating those efforts helps boost the electric vehicle industry’s chances for success.

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A penny for your cyber-thoughts.

By Mike Luckovich, From the Cartoonist Group

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