Detection and attribution of past changes in cyclone activity is hampered by biased cyclone records due to changes in observational capabilities. Here we relate a new homogeneous record of Atlantic tropical cyclone activity based on storm surge statistics from tide gauges to changes in global temperature patterns. We examine 10 competing hypotheses using non-stationary generalized extreme value analysis with different predictors (North Atlantic Oscillation, Southern Oscillation, Pacific Decadal Oscillation, Sahel rainfall, Quasi-Biennial Oscillation, Radiative Forcing, Main Development Region temperatures and its anomaly, global temperatures, and gridded temperatures). We find that gridded temperatures, Main Development Region, and global average temperature explain the observations best. The most extreme events are especially sensitive to temperature changes, and we estimate a doubling of Katrina magnitude events associated with the warming over the 20th century. The increased risk depends on the spatial distribution of the temperature rise with highest sensitivity from tropical Atlantic, Central America and the Indian Ocean. Statistically downscaling 21st century warming patterns from 6 climate models results in a 2-7 fold increase in the frequency of Katrina magnitude events for a 1°C rise in global temperature (using BNU-ESM; BCC-CSM-1-1; CanESM2; HadGEM2-ES; INM-CM4; NorESM1-M).

Citation: Grinsted, A. (2013): An estimate of global glacier volume, The Cryosphere, 7, 141–151, doi:10.5194/tc-7-141-2013

[link]

We present here surface water vapor isotopic measurements conducted from June to August~2010 at the NEEM camp, NW-Greenland (77.45° N 51.05° W, 2484 m a.s.l.). Measurements were conducted at 9 different heights from 0.1 m to 13.5 m above the snow surface using two different types of cavity-enhanced near infrared absorption spectroscopy analyzers. For each instrument specific protocols were developed for calibration and drift corrections. The inter-comparison of corrected results from different instruments reveals excellent reproducibility, stability, and precision with a standard deviation of ~ 0.23‰ for δ18O and ~ 1.4‰ for δD. Diurnal and intra-seasonal variations show strong relationships between changes in local surface humidity and water vapor isotopic composition, and with local and synoptic weather conditions. This variability probably results from the interplay between local moisture fluxes, linked with firn-air exchanges, boundary layer dynamics, and large-scale moisture advection. Particularly remarkable are several episodes characterized by high (> 40‰) surface water vapor deuterium excess. Air mass back-trajectory calculations from atmospheric analyses and water tagging in the LMDZiso atmospheric model reveal that these events are associated with predominant Arctic air mass origin. The analysis suggests that high deuterium excess levels are a result of strong kinetic fractionation during evaporation at the sea ice margin.

Citation: Steen-Larsen, H. C., Johnsen, S. J., Masson-Delmotte, V., Stenni, B., Risi, C., Sodemann, H., Balslev-Clausen, D., Blunier, T., Dahl-Jensen, D., Ellehøj, M. D., Falourd, S., Gkinis, V., Grindsted, A., Jouzel, J., Popp, T., Sheldon, S., Simonsen, S. B., Sjolte, J., Steffensen, J. P., Sperlich, P., Sveinbjörnsdóttir, A. E., Vinther, B. M., and White, J. W. C.: Continuous monitoring of summer surface water vapour isotopic composition above the Greenland Ice Sheet, Atmos. Chem. Phys. Discuss., 13, 1399-1433, doi:10.5194/acpd-13-1399-2013, 2013.in discussion here.. status: accepted

UPDATE: 

In one of the tests we calibrate against LeClercq's historical contribution from small glaciers and compare the resulting projections to Radic and Hock. Since then Marzeion et al. has projected much greater contributions, which are more in line with what we obtain with the semi-empirical model.  

Efforts to extract a Greenland ice core with a complete record of the Eemian interglacial (130,000 to 115,000 years ago) have until now been unsuccessful. The response of the Greenland ice sheet to the warmer-than-present climate of the Eemian has thus remained unclear. Here we present the new North Greenland Eemian Ice Drilling (‘NEEM’) ice core and show only a modest ice-sheet response to the strong warming in the early Eemian. We reconstructed the Eemian record from folded ice using globally homogeneous parameters known from dated Greenland and Antarctic ice-core records. On the basis of water stable isotopes, NEEM surface temperatures after the onset of the Eemian (126,000 years ago) peaked at 8 ± 4 degrees Celsius above the mean of the past millennium, followed by a gradual cooling that was probably driven by the decreasing summer insolation. Between 128,000 and 122,000 years ago, the thickness of the northwest Greenland ice sheet decreased by 400 ± 250 metres, reaching surface elevations 122,000 years ago of 130 ± 300 metres lower than the present. Extensive surface melt occurred at the NEEM site during the Eemian, a phenomenon witnessed when melt layers formed again at NEEM during the exceptional heat of July 2012. With additional warming, surface melt might become more common in the future.


NEEM Community Members, 2012, Eemian interglacial reconstructed from a Greenland folded ice core. Nature, 493, 489–494, doi:10.1038/nature11789

This will be a challenge to reproduce by ice sheet models. Current generation models show a terminal decline at much lower temperatures than what is indicated here. I have a feeling the ice sheet geometry feedback on atmospheric flow is a key to explaining this. It will also be good to see studies investigating how much of the large isotope signal can be explained by isotope enabled circulation models using different ice sheet geometries. 

Detection and attribution of past changes in cyclone activity are hampered by biased cyclone records due to changes in observational capabilities. Here we construct an independent record of Atlantic tropical cyclone activity on the basis of storm surge statistics from tide gauges. We demonstrate that the major events in our surge index record can be attributed to landfalling tropical cyclones; these events also correspond with the most economically damaging Atlantic cyclones. We find that warm years in general were more active in all cyclone size ranges than cold years. The largest cyclones are most affected by warmer conditions and we detect a statistically significant trend in the frequency of large surge events (roughly corresponding to tropical storm size) since 1923. In particular, we estimate that Katrina-magnitude events have been twice as frequent in warm years compared with cold years (P < 0.02).Aslak Grinsted, John C. Moore, and Svetlana Jevrejeva (2012), Homogeneous record of Atlantic hurricane surge threat since 1923, PNAS, doi:10.1073/pnas.1209542109 [pdf]

[Suppl info.]

Macias-Fauria, Grinsted, Helama, Holopainen (2012), Persistence matters: Estimation of the statistical significance of paleoclimatic reconstruction statistics from autocorrelated time series. Dendrochronologia, 30 (2), doi:10.1016/j.dendro.2011.08.003 [pdf]

This paper is an advancement because the conventional wisdom in dendroclimatology is that "... there is no significance test for CE, any value greater than zero indicates some degree of model skill (Cook et al., 1994)". (e.g. p272 from this 2009 book). - Well we provide such a test now, and we show that you commonly need to be more than just positive to beat p=0.05. 

Kemp et al. obtained a really nice proxy of relative sea level from North Carolina. North Carolina is subsiding and they therefore apply a 'GIA' correction to obtain a sea level record free of this particular local effect. In our comment we argue that the uncertainty they use in the subsidence correction is too small. The important point is not that we have a better estimate than theirs, but that there is a range of different estimates, and that their uncertainty does not bracket them all. Further the particular estimate they have chosen is an outlier, and cannot explain tide gauge observations (see right column). The effect of a greater subsidence correction and greater uncertainty is shown in this figure (click to zoom):

In their paper they then proceed to calibrate a semi-empirical model of global sea level, to this local sea level record. I believe this is not a suitable calibration target precisely because it is local. Further, our key point is that the uncertainties are too low, and that the proxy record as a consequence should not provide as strong constraints to the fitting procedure (therefore the model confidence intervals are artificially too tight). In my personal opinion the NCRSL record is much better suited as a validation for sea level models (in contrast to a calibration target). 

Links to paper, comment and reply:

Their response deals almost exclusively with what is the best value to choose as the GIA. This is exemplified in their final conclusive paragraph: "Regional geological data remain the most robust means to estimate late Holocene GIA ...". However, this response does not at all address the key problem we are highlighting: They have an overly optimistic uncertainty interval. We believe that the uncertainty interval should be several times greater than their stated value, and we base this on the work of Engelhart et al. [Disclaimer: Kemp et al. use the Engelhart paper to support the 'optimistic' uncertainty interval. The authors therefore feel that we misrepresent Engelhart. I would argue that we represent Engelhart's data exactly as it is and make our own conclusions. Can that really be called a misrepresentation?]

The figure and text in the column on the right shows that a 1mm/yr subsidence rate cannot explain the regional tide gauge trends. 

Detailed response to their 4 points: 

Engelhart et al: http://geology.gsapubs.org/content/37/12/1115.full

The figure below is from the supplementary info to Engelhart et al. The important thing here is that each tide gauge (red dot) has been chosen, so that it should be unaffected by confounding factors like ground water pumping. The distance between Tump Point, NC and Churchill, Canada is ~2950 km. For comparison the Global average rate of rise over the 20th century is 2mm/yr. We can subtract the global rate from the local relative rate of sea level rise to estimate the subsidence. That gives a subsidence of atleast 2 mm/yr.   

 

It seems clear that before this issue is resolved, it is dangerous to assume global=local and that it therefore is premature to use the record as a calibration target. 

We analyze the global sea-level budget since 1850. Good estimates of sea-level contributions from glaciers and small ice caps, the Greenland ice sheet and thermosteric sea level are available over this period, though considerable scope for controversy remains in all. Attempting to close the sea-level budget by adding the components results in a residual displaying a likely significant trend of .0.37 mm/a from 1955 to 2005, which can, however, be reasonably closed using estimated melting from unsurveyed high-latitude small glaciers and ice caps. The sea-level budget from 1850 is estimated using modeled thermosteric sea level and inferences from a small number of mountain glaciers. This longer-term budget has a residual component that displays a rising trend likely associated with the end of the Little Ice Age, with much decadal-scale variability that is probably associated with variability in the global water cycle, ENSO and long-term volcanic impacts.

Moore, Jevrejeva, and Grinsted, The Historical Sea Level Budget, Ann. Glac., 52, (59) , 2011, [link] [pdf]