Study: ‘Virtually’ Certain Impact Of Manmade ‘Climate Change Is Observable In Arctic Sea Ice Already Today’

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.”

In the Antarctic, the situation is different. Here, the sea-ice cover is slightly increasing. This increase is clearly incompatible with greenhouse gas concentration being the main driver for the sea-ice evolution down South. The major reason for this discrepancy lies in the different land-mass distributions, the scientists find. In the Arctic Ocean, the ice is virtually locked by the surrounding land masses, and its extent is primarily governed by its melting and freezing. Therefore, greenhouse gases play such an important role up in the high North. In the Antarctic, by contrast, the sea ice is free to drift around in the open Southern Ocean. Hence, the ice extent there is primarily governed by the prevailing wind patterns. “Our results show that greenhouse gas concentration is currently not a major driver for sea-ice extent in the Southern Ocean, where winds and currents clearly are more important,” explains Marotzke. “In the land-locked Arctic Ocean, however, greenhouse gas concentration appears to play the dominating role for the observed sea-ice evolution”.

[1] The original manuscript is freely accessible at: Opens external link in current window

Notz, D. and J. Marotzke (2012), Observational record reveals external driver for Arctic sea-ice retreat, Geophys. Res. Lett., VOL. 39, L08502, 6 PP., 2012, doi:10.1029/2012GL051094.

Max Planck Institute for Meteorology news release. Paper available here. Abstract concludes:

We find that the available observations are sufficient to virtually exclude internal variability and self-acceleration as an explanation for the observed long-term trend, clustering, and magnitude of recent sea-ice minima. Instead, the recent retreat is well described by the superposition of an externally forced linear trend and internal variability. For the externally forced trend, we find a physically plausible strong correlation only with increasing atmospheric CO2 concentration. Our results hence show that the observed evolution of Arctic sea-ice extent is consistent with the claim that virtually certainly the impact of an anthropogenic climate change is observable in Arctic sea ice already today.

8 Responses to Study: ‘Virtually’ Certain Impact Of Manmade ‘Climate Change Is Observable In Arctic Sea Ice Already Today’

  1. Dan Galpern says:

    The operative phrase gives one pause for its formulation. With virtual certainty I can say that it is virtually certain that the Max Plank Institute meant to say something less abstruse.

  2. Leif says:

    Science will not say it is “certain” you will die if you fall out of a plane at 10,000 feet without a parachute. They will say “it is virtually certain” however and chances are that they will be correct. If you “believe” otherwise please prove it. Don’t force me to try, I will stick with science.

  3. Joe Bickner says:

    “No, of course not! Global Warming isn’t caused by mankind! That’s just a liberal conspiracy theory!”

  4. Mulga Mumblebrain says:

    Ignoring probabilities in the high 90%s is insane.

  5. From Peru says:

    Jumpimg from a plane without a parachute IS a 100% (probability=1)certain death. The energy released in the collision with the surface is simply HUGE!

    There are some examples of 100% certainties in science:

    The Earth is not flat, but almost (but not quite) a sphere.

    You are reading this comment in this moment, and I am writing this in Lima, Peru.

    CO2 is a triatomic molecule made from two oxygen atoms and and one carbon atom.

    Helium is heavier than hydrogen (whith heavy I mean the magnitude of mass at the rest frame)


    Denying that is denying reality.

    On the other hand, when we are talking about very harmful, dangerous and deadly possibilities, even a few % probability is alarming.

    That is, climate change would be alarming even if the probability were 1%, because the danger is huge. Compare it with a pandemic of a highly infectious desease: even a few % of case fatality ratio will kill more people than World War 2 (like in 1918-1919)

  6. Todd says:

    Soot transport to sea ice and the resulting change in albedo is a factor that makes the isolation of GHG effects on sea ice changes more challenging. Any mention of how this was accomplished by the researchers?

  7. Leif says:

    Good points Peru. However I have read of a WWII bomber crew man that fell from an attacked bomber and lived. Presumably he was a light person with a flight suit that would limit his terminal velocity and he landed in a large hay stack. Beginning altitude is questionable but high enough to reach terminal velocity none the less. So while your points are well taken, I would put them in a tautology class, never the less, “near certain” keeps me in the “fail safe” quadrant.

  8. NJP1 says:

    sorry Peru, if you were an economist you would know perfectly well that the earth was flat