Archive for August, 2012

High late August 2012 Greenland ice temperature maintains low ice sheet reflectivity and melting

Friday, August 24th, 2012

Daily surface temperatures in June-August 2012 have peaked more than 5 C (~9 F) warmer for the whole ice sheet than the 2000-2009 daily averages according to my analysis of ice surface temperatures from  daily NASA MODIS MOD11 satellite derived Land Surface Temperature (LST) retrievals. Over the highest elevations, surface temperatures were nearly 10 C (~18 F) warmer than in the 2000′s decade, leading to an area of ice sheet surface melting, unprecedented in the satellite observational record beginning in 1978.

Fig. 1. Greenland clear sky ice surface temperature anomaly relative to the 2000-2009 baseline.

To a first approximation, when ice sheet temperature increases, its reflectivity decreases (Box et al. 2012). After a low temperatures 10-13 August, 2012 the surface reflectivity of sunlight (a.k.a. albedo) increased from the accumulation of fresh bright snow (Fig. 2). Then as surface temperatures rose again, above one standard deviation of the 2000-2009 average, the ice sheet albedo again dropped 18-23 August, 2012 below previous observations (since 2000), especially at the intermediate elevations of 1000-1500 m where melting in all likelihood remains active this year. As reported by Marco Tedesco, 2012 melting is already setting the record since the late 1950s, and with this late melt season albedo drop and high surface temperature anomaly, this “Goliath” melt has got to be growing.

Fig. 2. Daily Greenland ice sheet reflectivity (a.k.a. albedo) values spanning nearly 13 years; 2000-2012.

The daily albedo anomaly map (Fig. 3) indicates widespread low reflectivity, especially at the ice sheet periphery where surface elevations are lower, the atmosphere is warmer, and melting persists. Positive reflectivity anomalies over the northwest ice sheet suggest the return and persistence of fresh snow.

Fig. 3. Daily albedo anomaly map.

About the surface temperature data

Land surface temperature MODIS thermal infrared observations enable retrieval of land surface temperature (LST) under cloud-free conditions at 1 km horizontal resolution. The MODIS MOD11A1 data product is based on daily averaged LST retrievals from swath data and a split-window algorithm using MODIS thermal bands 31 (11 μm) and 32 (12 μm) (Wan et al., 2002). These data have a RMS error 1 deg. C in comparison with independent in-situ observations (Wan et al., 2008), with higher RMS errors found over Greenland (Hall et al., 2008a; Hall et al., 2008b; Koenig and Hall, 2010).

Works Cited

  • Box, J. E., Fettweis, X., Stroeve, J. C., Tedesco, M., Hall, D. K., and Steffen, K.: Greenland ice sheet albedo feedback: thermodynamics and atmospheric drivers, The Cryosphere, 6, 821-839, doi:10.5194/tc-6-821-2012, 2012. open access
  • Hall, D. K., Williams Jr., R. S., Luthcke, S. B., and Digirolamo, N. E.: Greenland ice sheet surface temperature, melt and mass loss: 2000–2006, J. Glaciol., 54, 81–93, doi:10.3189/002214308784409170, 2008a.
  • Hall, D. K. J. E. Box, K. Casey, S. J. Hook, C. A. Shuman, K. Steffen, Comparison of satellite-derived and in-situ observations of ice and snow surface temperatures over Greenland, Remote Sensing of Environment, 2008b
  • Koenig, L. S., and D. K. Hall, 2010: Comparison of satellite, thermochron and station temperatures at Summit, Greenland, during the winter of 2008/09. J. Glaciol., 56, 735–741.

See also:

Byrd Polar Research Center Near Real-time Greenland Ice:

  1. Surface Temperature Monitoring  
  2. Ice Albedo Monitoring

@climate_ice on Twitter

Jason Box homepage

2012 summer Greenland ice reflectivity, lowest since year 1150?

Wednesday, August 15th, 2012

After a weeklong delay in data availability from a 61st satellite maneuver in 13 years to makeup low earth orbit drag, we find Greenland ice reflectivity (a.k.a. albedo) returning toward higher values, evidence of fresh snowfall accumulation and accompanying lower temperatures now as the melt season approaches its end. The latest average Greenland ice reflectivity (69.2%) from 13 August is at a level still below 1 standard deviation from the 2000-2009 10 year ‘climatology’. 2012 values are right on track with the previous record low year 2011.

larger and more numerous albedo dips

Apparently distinct from previous years in number and intensity of low albedo (evidence of melt) episodes, the 2012 melt season is characterized by 4 anomalous lows, centered on: 2 June (71.4%); 27 June (67.4%); 16 July (64.0%); and 1 August (65.2%).

The albedo lows are punctuated by the brightening effect of snowfall events. There could be a late season melt episode as in 2004 or 2003.

Below, a similar pattern is evident at the highest (coldest) 700 m (2000 ft) of the ice sheet.

lowest albedo since year 1150?

The 16 July low was the lowest in the satellite observational record and coincided with 97% of the ice sheet surface area melting. Previous maximum melt extent values since 1978 (when satellite obseravations begin, this is what NASA meant by “unprecedented”) are under 60% of the ice sheet area. Because the 2012 summer temperature was warmer than previous years (as I tweeted 5 August: June 2012, warmest on record for Greenland’s capital Nuuk since at least 1866 when continuous record keeping began, +7.2 C vs +4.3 C average), warmer than 1929 by at least 0.5 deg. C, and if the near surface air temperature records, continuous since 1840, are any indication (Box et al. 2009) this albedo anomaly and accompanying melt extent is probably without precedent since the Medieval Warm Period when the Norse settled Greenland.  Greenland temperature variability is high and there is evidence during the late Medieval Warm Period of a warm period in year 1150, that is 862 years before present (Kobashi et al. 2011). Other factors than warming that could have temporarily lowered Greenland ice reflectivity include the effect of major volcanic eruptions or wild fires. The latter I speculated here. The former has a noteworthy cooling effect but could conceivably still blanket the ice sheet with low reflectivity soot.

Kobashi et al. 2011 Fig. 1.

The albedo work is based largely on:

  • Box, J. E., Fettweis, X., Stroeve, J. C., Tedesco, M., Hall, D. K., and Steffen, K.: Greenland ice sheet albedo feedback: thermodynamics and atmospheric drivers, The Cryosphere, 6, 821-839, doi:10.5194/tc-6-821-2012, 2012. open access

Works Cited

  • Box, J.E., L. Yang, D.H. Browmich, L-S. Bai, 2009: Greenland ice sheet surface air temperature variability: 1840-2007, J. Climate, 22(14), 4029-4049, doi:10.1175/2009jcli2816.1. PDF
  • Kobashi, T., K. Kawamura, J. P. Severinghaus, J.‐M. Barnola, T. Nakaegawa, B. M. Vinther, S. J. Johnsen, and J. E. Box (2011), High variability of Greenland surface temperature over the past 4000 years estimated from trapped air in an ice core, Geophys. Res. Lett., 38, L21501, doi:10.1029/2011GL049444.

See also:

Byrd Polar Research Center Greenland Ice Albedo Monitoring

@climate_ice on Twitter

Jason Box homepage

 

Greenland ice sheet albedo feedback: mass balance implications

Tuesday, August 7th, 2012

Here’s a preview of my American Geophysical Union presentation abstract…

Greenland ice sheet albedo feedback: mass balance implications

Jason E Box1, Marco Tedesco2, Xavier Fettweis3, Dorothy K Hall4, Konrad Steffen5, Julienne Christine Stroeve6

  1. Byrd Polar Rsch Ctr Scott Hall, The Ohio State University, Columbus, OH, United States.
  2. The City University of New York, New York City, NY, United States.
  3. Department of Geography, University of Liege, Liege, Belgium.
  4. NASA Goddard Space Flight Center, Greenbelt, MD, United States.
  5. Swiss Federal Institute for Forest, Snow and Landscape Research ( WSL) , Birmensdorf, Switzerland.
  6. National Snow and Ice Data Center, Boulder, CO, United States.
 Greenland ice sheet mass loss has accelerated responding to combined glacier discharge and surface melt water runoff increases. During summer, absorbed solar energy, modulated at the surface primarily by albedo, is the dominant factor governing surface melt variability in the ablation area. NASA MODIS data spanning 13 summers (2000 – 2012), indicate that mid-summer (July) ice sheet albedo declined by 0.064 from a value of 0.752 in the early 2000s. The ice sheet accordingly absorbed 100 EJ more solar energy for the month of July in 2012 than in the early 2000s. This additional energy flux during summer doubled melt rates in the ice sheet ablation area during the observation period.

Abnormally strong anticyclonic circulation, associated with a persistent summer North Atlantic Oscillation extreme 2007-2012, enabled 3 amplifying mechanisms to maximize the albedo feedback: 1) increased warm (south) air advection along the western ice sheet increased surface sensible heating that in turn enhanced snow grain metamorphic rates, further reducing albedo; 2) increased surface downward shortwave flux, leading to more surface heating and further albedo reduction; and 3) reduced snowfall rates sustained low albedo, maximizing surface solar heating, progressively lowering albedo over multiple years. The summer net infrared and solar radiation for the high elevation accumulation area reached positive values during this period, contributing to an abrupt melt area increase in 2012.

A number of factors make it reasonable to expect more melt episodes covering 100% of the ice sheet area in coming years: 1) the past 13 y of increasing surface air temperatures have eroded snowpack ‘cold content’, preconditioning the ice sheet for earlier melt onset. Less heat is required to bring the surface to melting; 2) Greenland temperatures, have lagged the N Hemisphere average in the 2000s, need to increase further for Greenland to be in phase with the N Hemisphere average. 3) Arctic amplification of enhanced greenhouse warming is driven by albedo feedback over sea ice, terrestrial environments, and through autumn-winter heat release from open water areas. Likely melt area increases is despite a second order negative feedback operating in the accumulation area identified statistically from more summer snowfall (brightening effect) in anomalously warm summers. Without this negative feedback, the accumulation area complete surface melting may have happened sooner than in 2012.

While it has been shown that the ice sheet dynamics can adjust rapidly to ice flow perturbations, a negative feedback responsivity, the mass imbalance of the ice sheet in the coming decades is likely to be increasingly negative because of the positive feedback from surface albedo with air temperature. Surface melting may therefore increasingly dominate ice sheet mass loss, as glaciers retreat from a marine termini and the area of low albedo expands over the gradually sloping ice sheet. The albedo feedback ensures an increasing solar energy absorption. What could shut the positive feedback down would be a combination of an anomalously cold winter and anomalously thick snowpack. This scenario is possible given the cooling effect of a major N Hemisphere volcanic eruption or some other event to reduce surface heating.

http://bprc.osu.edu/wiki/Greenland_Ice_Albedo_Monitoring

KEYWORDS: [0726] CRYOSPHERE / Ice sheets, [0758] CRYOSPHERE / Remote sensing, [0740] CRYOSPHERE / Snowmelt, [0776] CRYOSPHERE / Glaciology.

 

 

 

 

 

 

 

 

 

early-August 2012 Greenland ice reflectivity dips again below 2 standard deviations

Monday, August 6th, 2012

As in the mid-July case, the early August ice sheet albedo has declined to an average more than 5% (or 2 standard deviations) below the average of the previous 12 years (2000-2011). A “2-sigma” event has a probability of occurrence under 5% in a random climate.

 

The decline is again concentrated in the accumulation area above 1500 m elevation where melting is less common as it is in the lower elevations.

The thermodynamic impact of widespread reflectivity decline is:

  1. more ice sheet solar energy absorption
  2. more erosion of snowpack heat content
  3. more preconditioning of future early melt onset cases
  4. more melting in 2012

…all in a self-reinforcing feedback loop that amplifies melting (see Box et al. 2012, link below).

The early August decline is similar to August declines in 2008, 2004, and 2001. What is different is that the decline is from a lower point.

The 4 August 2012 albedo is not as low as the lowpoint reached on 15 July, 2012.

Work Cited

  • Box, J. E., Fettweis, X., Stroeve, J. C., Tedesco, M., Hall, D. K., and Steffen, K.: Greenland ice sheet albedo feedback: thermodynamics and atmospheric drivers, The Cryosphere, 6, 821-839, doi:10.5194/tc-6-821-2012, 2012. open access

My climate-cryosphere updates on Twitter

My Byrd Polar Research Center homepage

Greenland ice sheet summer surface air temperatures: 1840-2011

Saturday, August 4th, 2012

Developing a new manuscript (Box et al. submitted), I’ve managed to update the Box et al. (2009) near-surface air temperature reconstruction and am struck after incorporating 4 more years, it seems little doubt that recent summer air temperatures for Greenland ice are the highest in at least 172 years. Summer temperatures in the late 2000s are roughly 0.5 C warmer than in the 1930s and even warmer than at any time since at least 1840s. Because the reconstruction captures the end of the Little Ice Age, it is further reasonable to think that Greenland probably hasn’t been as warm in summer than since the time the Norse colonized Greenland beginning in 982. Implications for the recent warmth are of course grabbing headlines. I’ll be adding 2012 data soon.

Temperature anomalies relative to the 1951-1980 average.

While earlier studies (e.g. Chylek et al. 2006) ascribe significance to the fact that 1920s temperature increases were greater in magnitude since those after the early 1990s, this point lacks relevance because 1.) the 1920s trend was measured from the depth of an (unexplained) decadal cool period while the recent trend, i.e., measured beginning in 1994, after the 1991-1993 Mt. Pinatubo volcanic cooling and especially because 2.) the recent summer temperatures are ~0.5 C higher in absolute magnitude than those in the 20th century.

 20th Century cooling period

During the ~63 year period (1930 to 1992) cooling prevailed that can be attributed partially to an increases in atmospheric aerosols that reduce surface insolation. Liepert et al (2002) estimated that there a global reduction of about 4% in solar radiation reaching the ground between 1961 and 1990. West Greenland is a focus of sulfate aerosol-induced cooling (Rozanov et al. 2002, Box et al. 2009). Cold episodes in 1983-84 and 1991-92 enhance this cooling trend and are caused by major volcanic eruptions (Box, 2002; Box et al. 2009). The cooling phase has also been attributed to the Atlantic Multidecadal Oscillation (AMO) (e.g. Schesinger et al. 1994). Though, it remains unclear whether AMO is a recurrent harmonic oscillation or just a hiatus of warming caused by sulphate cooling. The post-1994 warming, is attributable to: 1.) a growing absence of sulfate cooling because there has not been a major volcanic eruption since at Mount Pintubo in 1991; 2) a reversal of the global dimming trend (Wild et al. 2009); and 3) ongoing and intensifying anthropogenic global warming (AWG) owing to a dominance of enhanced greenhouse effect despite various anthropogenic cooling factors such as aerosols and contrails (IPCC, 2007). Year 2010 annual surface air temperature observations around west and south Greenland exceeding 3 standard deviations from the 1901-2000 century baseline.

Works Cited

  • Box, J.E., L. Yang, D.H. Browmich, L-S. Bai, 2009: Greenland ice sheet surface air temperature variability: 1840-2007, J. Climate, 22(14), 4029-4049, doi:10.1175/2009jcli2816.1.
  • Box, J..E., Greenland ice sheet mass balance reconstruction. Part II: Surface mass balance (1840-2010), J. Climate, submitted 30 July, 2012.
  • Chylek, P., M. K. Dubey, and G. Lesins, 2006: Greenland warming of 1920–1930 and 1995–2005, Geophys. Res. Lett., 33, L11707, doi:10.1029/2006GL026510.
  • Liepert, B. G. (2002), Observed reductions of surface solar radiation at sites in the United States and worldwide from 1961 to 1990, Geophys. Res. Lett., 29(10), 1421, doi:10.1029/2002GL014910.
  • Rozanov, E. V., and Coauthors, 2002: Climate/chemistry effects of the Pinatubo volcanic eruption simulated by the UIUC stratosphere/troposphere GCM with interactive photochemistry. J. Geophys. Res., 107, 4594, doi:10.1029/2001JD000974.
  • Schlesinger, M. E., 1994: An oscillation in the global climate system of period 65-70 years. Nature 367 (6465): 723–726
  • Wild, M., B. Trüssel, A. Ohmura, C. N. Long, G. König‐Langlo, E. G. Dutton, and A. Tsvetkov, 2009: Global dimming and brightening: An update beyond 2000. J. Geophys. Res., 114, D00D13, doi:10.1029/2008JD011382.

My climate-cryosphere updates on Twitter

My Byrd Polar Research Center homepage

Greenland albedo rebounds from snowfall but is again followed widespread high air temperatures

Wednesday, August 1st, 2012

In the latest update of daily Greenland reflectivity (a.k.a., albedo) observed by the NASA MODIS sensors, we see the effect of fresh snow brightening the ice sheet surface after the extreme low albedo in mid July, 2012. Late July’s reflectivity remains below other years in the observational record since 2000 and the values are trending lower again because of the darkening effect of near-surface air temperatures reported for 24-31 July being near or above the melting point, according to ground observations maintained by Konrad Steffen, director of the Swiss Federal Institute for Forest, Snow and Landscape Research. The earlier high melt area episode was 11-15 July, 2012.

Daily ice sheet averaged reflectivity values for 13 individual years beginning in 2000. 0-3200 m refers to the elevation range of the whole ice sheet.

If the 24-31 July high temperatures are on par with those from 11-15 July, 2012 and if there is not another summer snowfall at the higher elevations of the ice sheet, I’d expect the albedos to decline further, reaching say 65.5% in the coming days.

These results are after the externally-reviewed publication Box et al. (2012), citation below.

Work Cited

  • Box, J. E., Fettweis, X., Stroeve, J. C., Tedesco, M., Hall, D. K., and Steffen, K.: Greenland ice sheet albedo feedback: thermodynamics and atmospheric drivers, The Cryosphere, 6, 821-839, doi:10.5194/tc-6-821-2012, 2012. open access

My climate-cryosphere updates on Twitter

My Byrd Polar Research Center homepage

Reflectivity (a.k.a. albedo) anomaly computed as the July average albedo for 5 km grid cells for the 12 year period (2000-2011) minus July 2012 values. Negative anomaly values mean the ice sheet is darker than average.