A new historic minimum in Arctic sea ice provides additional evidence of rapid acceleration of Arctic ice loss, propelled, beyond a reasonable doubt, by anthropogenic greenhouse gas emissions.
Norwegian scientists just announced that the extent of Arctic sea ice has reached a new minimum, below that reached in the (boreal) summer of 2007 when an unprecedented catastrophic decline was reported. The 2007 minimum has been exceeded at a time when there is still a good 10 days of additional ice melting in the Arctic to go, and following reports of unprecedented widespread surface ice melting of the Greenland ice sheet.
Meanwhile Europe is leaving behind the northern heat wave this boreal summer, the US continues to struggle with crop failure due to unusually high warm temperatures and extended drought, and the Caribbean and Asian nations prepare for an intense cyclone season.
I received a phone call from a journalist this week interested in my thoughts on the new minimum of Arctic ice sheet, since I published a paper earlier this year, arguing that the dynamics of the Arctic ice sheet is signaling at the proximity of a tipping point.
In our conversation he asked whether I was prepared to speculate on the possible causes of this new minimum. I found the question a little perplexing and conveying an intense sense of deja-vú, as this is a recurrent experience every month of August for at least the past 6 years.
In the 1993 movie Groundhog Day, Bill Murray is a TV weather reporter who finds himself locked onto the same day, waking up to same sequence of events repeating themselves over an over on a loop.
I too have the sense that I am locked onto a time loop, where journalists declare themselves perplexed to report that the Arctic is actually melting, and convey this sentiment of surprise to the public, despite a wealth of research that:
identifies the Arctic as the region most rapidly warming on Earth (e.g. ACIA 2004)
predicts the steepest warming rates for the Arctic as a consequence of anthropogenic green-house emissions (e.g. Meehl et al. 2007)
predicts an acceleration of ice loss in the Arctic (e.g. Holland et al. 2006, Velicogna and Whar 2006).
If this was a one-off event, I could understand the surprise and questions around the causes of Arctic ice loss and its prospects for the coming years. However, there has been a series of recurrent minima starting in 1996 to date.. Given the close match between predicted and realised trends, perplexity at a new record melting event either signals that the robust scientific understanding available on the response of Arctic ice to climate change is met with skepticism or that this knowledge is still confined within the scientific community and does not percolate to media or the public.
Either option is unsatisfactory, because the developments in the Arctic are not locked in the realm of Arctic ice experts, but every citizen can follow daily the status of Arctic ice, and even check this on a smart phone through an app. The changes in the Arctic are broadcasted as if this would be a remake of the movie Death Watch, but this time involving the opportunity for a global audience to watch the demise of Arctic ice in real time.
Possibly, we scientists are to be blamed, as we cherish uncertainty so much that we deliver messages to the media crowded with caveats and cautionary alerts to possible uncertainties. The consequences is the messages passed on are confusing, with uncertainties overplayed relative to robust understanding, supported by both evidence and validation of predictions by observed trends.
For instance, earlier this month NASA scientists reported a surprisingly rapid spread of surface melting from affecting 40 to 97 % of the ice-covered surface of Greenland in only four days. However, the press release included the statement by Lora Koenig, a Goddard glaciologist and a member of the research team analysing the satellite data, that:
Ice cores from Summit show that melting events of this type occur about once every 150 years on average. With the last one happening in 1889, this event is right on time. But if we continue to observe melting events like this in upcoming years, it will be worrisome.
This suggests that :
this event was not yet worrisome, and
that it was due to occur as expected from an apparent 150 year recurrence.
No connection was made in the note and associated statements to anthropogenic climate change, recent trends or predictions of climate models on the de-stabilisation of the Greenland ice sheet. So the notion conveyed was that this was a one-odd event that may be expected once every 150 years, unconnected to any previous trends or regional climate trends.
With so much evidence there, how can we continue to ponder on the possible ultimate causes of Arctic ice loss?
The noise on the climate change debate has reached such level that my colleagues in the US, particularly scientists within Federal agencies, tell me that they avoid taking a position on climate change in public conversations and news releases. The reluctance of the US public to agree with the wealth of scientific information pointing to an on-going and future warming of the climate due to anthropogenic green-house gas emissions seems to be curving now with the severe heat, drought and crop failure in the US this year. This curving NASA scientists now connect these heat waves to anthropogenic climate change (Hansen et al. 2012).
Nevertheless our predictions may turn to be wrong and our models can break in the future. Indeed, the statement “all swans are white” was almost a truism until black swans were discovered to the western world at the landing of Dutch navigators in the Swan River, WA.
We are certain to find “black swans”, now used as a synonym for the unexpected (Taleb, 2010), with ice trends in the Arctic, but, if anything these “black swans” are likely to consist on a yet faster acceleration of ice than expected, with the associated impacts on global climatic regulation.
The changes in the Arctic now meet the requirements to be considered “dangerous climate change” under the UN Climate Convention (Duarte et al. 2012a). The risk of ignoring these signals and taking serious action to mitigate climate change rests on the possibility that “dangerous climate change” will propagate, through existing tipping mechanisms in the Arctic, to the entire planet (Duarte et al. 2012a,b).
With all due consideration to uncertainty, policy makers need to accept the reality that ice loss in the Arctic is accelerating further, propelled, beyond a reasonable doubt, by anthropogenic greenhouse gas emission, and take due action.
Taking no action to mitigate climate change will eventually get us out of Groundhog Day to experience a new, unprecedented series of events.
But only to find a new reality of dangerous climate change spread, unchecked, throughout the planet.
ACIA. 2004. Impacts of a warming Arctic: Arctic climate impact and assessment, ed. S.J. Hassol.Cambridge:Cambridge University Press.
Duarte, C.M., T. M. Lenton, P. Wadhams and P. Wassmann. 2012. Abrupt climate change in the Arctic. Nature Climate Change 2: 60–62.
Duarte, C.M., S. Agustí, P. Wassmann, J. M. Arrieta, M. Alcaraz, A. Coello, N. Marbà, I. E. Hendriks, J. Holding, I. García-Zarandona, E. Kritzberg and D. Vaqué. 2012. Tipping elements in the Arctic marine ecosystem. AMBIO 41:44–55
Hansen, J., Sato, M. and Ruedy, R. 2012. Perception of climate change. Proc. Natl Acad. Sci. USA http://dx.doi.org/10.1073/pnas.1205276109 .
Holland, M.M., C.M. Bitz, and B. Tremblay. 2006. Future abrupt reductions in the summer Arctic sea ice. Geophysical Research Letters 33: L23503. doi:10.1029/2006GL028024.
Meehl, G.A., T.F. Stocker, W.D. Collins, P. Friedlingstein, A.T. Gaye, J.M. Gregory, A. Kitoh, R. Knutti, J.M. Murphy, A. Noda, S.C.B. Raper,I.G. Watterson, A.J. Weaver and Z.-C. Zhao, 2007. Global Climate Projections. In: Climate Change 2007: The Physical Science Basis. Contribution of Working Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change [Solomon, S.,D. Qin, M. Manning, Z. Chen, M. Marquis, K.B. Averyt, M. Tignor and H.L. Miller (eds.)]. Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA.
Taleb, N.N. (2010). The black swan: the impact of the highly improbable (Second ed.). Penguin.
Velicogna, I., and J. Whar. 2006. Acceleration of Greenland ice mass loss in spring 2004. Nature 443: 329–331.