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de Vries H.,Royal Netherlands Meteorological Institute | van de Wal R.S.W.,Institute for Marine and Atmospheric Research Utrecht
Climatic Change | Year: 2016

In a commentary paper, Bamber et al. (Nat Clim Change 3:424–427, 2016) respond to our recent assessment (De Vries and Van de Wal Clim Change 1–14, 2015) of their expert judgment based study on projections of future sea level rise due to the melting of the large ice sheets (Bamber and Aspinall Nat Clim Chang 3:424–427, 2013). In this response we comment on their remarks. © 2016, Springer Science+Business Media Dordrecht.

de Vries H.,Royal Netherlands Meteorological Institute | van de Wal R.S.W.,Institute for Marine and Atmospheric Research Utrecht
Climatic Change | Year: 2015

In a recent paper Bamber and Aspinall (Nat Clim Change 3:424–427, 2013) (BA13) investigated the sea-level rise that may result from the Greenland and Antarctic ice sheets during the 21st century. Using data from an expert judgment elicitation, they obtained a final high-end (P95) value of +84 cm integrated sea-level change from the ice sheets for the 2010–2100 period. However, one key message was left largely undiscussed: The experts had strongly diverging opinions about the ice-sheet contributions to sea-level rise. We argue that such (lack of) consensus should form an essential and integral part of the subsequent analysis of the data. By employing a method that keeps the level of consensus included, and that is also more robust to outliers and less dependent on the choice of the underlying distributions, we obtain on the basis of the same data a considerably lower high-end estimate for the ice-sheet contribution, +53 cm (+38-77 cm interquartile range of “expert consensus”). The method compares favourably with another recent study on expert judgement derived sea-level rise by Horton et al. (Q Sci Rev 84:1–6, 2014). Furthermore we show that the BA13 results are sensitive to a number of assumptions, such as the shape and minimum of the underlying distribution that were not part of the expert elicitation itself. Our analysis therefore demonstrates that one should be careful in considering high-end sea-level rise estimates as being well-determined and fixed numbers. © 2015, Springer Science+Business Media Dordrecht.

Hinssen Y.B.L.,Institute for Marine and Atmospheric Research Utrecht | Ambaum M.H.P.,University of Reading
Journal of the Atmospheric Sciences | Year: 2010

It is shown that a quantitative relation exists between the stratospheric polar cap potential vorticity and the 100-hPa eddy heat flux. A difference in potential vorticity between years is found to be linearly related to the flux difference integrated over time, taking into account a decrease in relaxation time scale with height in the atmosphere. This relation (the PV-flux relation) is then applied to the 100-hPa flux difference between 2008/09 and the climatology (1989-2008) to obtain a prediction of the polar cap potential vorticity difference between the 2008/09 winter and the climatology. A prediction of the 2008/09 polar cap potential vorticity is obtained by adding this potential vorticity difference to the climatological potential vorticity. The observed polar cap potential vorticity for 2008/09 shows a large and abrupt change in the potential vorticity in midwinter, related to the occurrence of a major sudden stratospheric warming in January 2009; this is also captured by the potential vorticity predicted from the 100-hPa flux and the PV-flux relation. The results of the mean PV-flux relation show that, on average, about 50% of the interannual variability in the state of the Northern Hemisphere stratosphere is determined by the variations in the 100-hPa heat flux. This explained variance can be as large as 80% for more severe events, as demonstrated for the 2009 major warming. © 2010 American Meteorological Society.

Holzinger R.,Institute for Marine and Atmospheric Research Utrecht | Williams J.,Max Planck Institute for Chemistry | Herrmann F.,Max Planck Institute for Chemistry | Lelieveld J.,Max Planck Institute for Chemistry | And 2 more authors.
Atmospheric Chemistry and Physics | Year: 2010

We present a novel analytical approach to measure the chemical composition of organic aerosol. The new instrument combines proton-transfer-reaction mass-spectrometry (PTR-MS) with a collection-thermal-desorption aerosol sampling technique. For secondary organic aerosol produced from the reaction of ozone with isoprenoids in a laboratory reactor, the TD-PTR-MS instrument detected typically 80% of the mass that was measured with a scanning mobility particle sizer (SMPS). The first field deployment of the instrument was the EUCAARI-IOP campaign at the CESAR tall tower site in the Netherlands. For masses with low background values (∼30% of all masses) the detection limit of aerosol compounds was below 0.2 ng/m3 which corresponds to a sampled compound mass of 35 pg. Comparison of thermograms from ambient samples and from chamber-derived secondary organic aerosol shows that, in general, organic compounds from ambient aerosol samples desorb at much higher temperatures than chamber samples. This suggests that chamber aerosol is not a good surrogate for ambient aerosol and therefore caution is advised when extrapolating results from chamber experiments to ambient conditions.

Oerlemans J.,Institute for Marine and Atmospheric Research Utrecht | Van Pelt W.J.J.,Norsk Polarinstitutt
Cryosphere | Year: 2015

The climate sensitivity of Abrahamsenbreen, a 20 km long surge-type glacier in northern Spitsbergen, is studied with a simple glacier model. A scheme to describe the surges is included, which makes it possible to account for the effect of surges on the total mass budget of the glacier. A climate reconstruction back to AD 1300, based on ice-core data from Lomonosovfonna and climate records from Longyearbyen, is used to drive the model. The model is calibrated by requesting that it produce the correct Little Ice Age maximum glacier length and simulate the observed magnitude of the 1978 surge. Abrahamsenbreen is strongly out of balance with the current climate. If climatic conditions remain as they were for the period 1989-2010, the glacier will ultimately shrink to a length of about 4 km (but this will take hundreds of years). For a climate change scenario involving a 2 m year-1 rise of the equilibrium line from now onwards, we predict that in the year 2100 Abrahamsenbreen will be about 12 km long. The main effect of a surge is to lower the mean surface elevation and thereby to increase the ablation area, causing a negative perturbation of the mass budget. We found that the occurrence of surges leads to a faster retreat of the glacier in a warming climate. Because of the very small bed slope, Abrahamsenbreen is sensitive to small perturbations in the equilibrium-line altitude. If the equilibrium line were lowered by only 160 m, the glacier would steadily grow into Woodfjorddalen until, after 2000 years, it would reach Woodfjord and calving would slow down the advance. The bed topography of Abrahamsenbreen is not known and was therefore inferred from the slope and length of the glacier. The value of the plasticity parameter needed to do this was varied by +20 and -20%. After recalibration the same climate change experiments were performed, showing that a thinner glacier (higher bedrock in this case) in a warming climate retreats somewhat faster. © Author(s) 2015.

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