AGW Observer

Observations of anthropogenic global warming

New research from last week 41/2012

Posted by Ari Jokimäki on October 15, 2012

It seems that this week I felt nostalgic as there are plenty of papers on past climate in this week’s batch. Perhaps I just miss the good old days when climate was all nice.


Large contribution of Canada’s glaciers to sea level rise

Accelerated contributions of Canada’s Baffin and Bylot Island glaciers to sea level rise over the past half century – Gardner et al. (2012) [FULL TEXT]

Abstract: “Canadian Arctic glaciers have recently contributed large volumes of meltwater to the world’s oceans. To place recently observed glacier wastage into a historical perspective and to determine the region’s longer-term (~50 years) contribution to sea level, we estimate mass and volume changes for the glaciers of Baffin and Bylot Islands using digital elevation models generated from airborne and satellite stereoscopic imagery and elevation postings from repeat airborne and satellite laser altimetry. In addition, we update existing glacier mass change records from GRACE satellite gravimetry to cover the period from 2003 to 2011. Using this integrated approach, we find that the rate of mass loss from the region’s glaciers increased from 11.1 ± 3.4 Gt a−1 (271 ± 84 kg m−2 a−1) for the period 1963–2006 to 23.8 ± 6.1 Gt a−1(581 ± 149 kg m−2 a−1) for the period 2003–2011. The doubling of the rate of mass loss is attributed to higher temperatures in summer with little change in annual precipitation. Through both direct and indirect effects, changes in summer temperatures accounted for 70–98% of the variance in the rate of mass loss, to which the Barnes Ice Cap was found to be 1.7 times more sensitive than either the Penny Ice Cap or the region’s glaciers as a whole. This heightened sensitivity is the result of a glacier hypsometry that is skewed to lower elevations, which are shown to have a higher mass change sensitive to temperature compared to glacier surfaces at higher elevations. Between 2003 and 2011 the glaciers of Baffin and Bylot Islands contributed 0.07 ± 0.02 mm a−1 to sea level rise accounting for 16% of the total contribution from glaciers outside of Greenland and Antarctica, a rate much higher than the longer-term average of 0.03 ± 0.01 mm a−1 (1963 to 2006).”

Citation: Gardner, A., Moholdt, G., Arendt, A., and Wouters, B.: Accelerated contributions of Canada’s Baffin and Bylot Island glaciers to sea level rise over the past half century, The Cryosphere, 6, 1103-1125, doi:10.5194/tc-6-1103-2012, 2012.


Observed interannual variability of the Atlantic meridional overturning circulation

Observed interannual variability of the Atlantic meridional overturning circulation at 26.5°N – McCarthy et al. (2012) [FULL TEXT]

Abstract: “The Atlantic meridional overturning circulation (MOC) plays a critical role in the climate system and is responsible for much of the heat transported by the ocean. A mooring array, nominally at 26°N between the Bahamas and the Canary Islands, deployed in Apr 2004 provides continuous measurements of the strength and variability of this circulation. With seven full years of measurements, we now examine the interannual variability of the MOC. While earlier results highlighted substantial seasonal and shorter timescale variability, there had not been significant interannual variability. The mean MOC from 1 Apr 2004 to the 31 March 2009 was 18.5 Sv with the annual means having a standard deviation of only 1.0 Sv. From 1 April 2009 to 31 March 2010, the annually averaged MOC strength was just 12.8 Sv, representing a 30% decline. This downturn persisted from early 2009 to mid-2010. We show that the cause of the decline was not only an anomalous wind-driven event from Dec 2009–Mar 2010 but also a strengthening of the geostrophic flow. In particular, the southward flow in the top 1100 m intensified, while the deep southward return transport—particularly in the deepest layer from 3000–5000 m—weakened. This rebalancing of the transport from the deep overturning to the upper gyre has implications for the heat transported by the Atlantic.”

Citation: McCarthy, G., E. Frajka-Williams, W. E. Johns, M. O. Baringer, C. S. Meinen, H. L. Bryden, D. Rayner, A. Duchez, C. Roberts, and S. A. Cunningham (2012), Observed interannual variability of the Atlantic meridional overturning circulation at 26.5°N, Geophys. Res. Lett., 39, L19609, doi:10.1029/2012GL052933.


Climate change threatens Lake Tahoe’s most highly valued characteristics

The response of Lake Tahoe to climate change – Sahoo et al. (2012) [FULL TEXT]

Abstract: “Meteorology is the driving force for lake internal heating, cooling, mixing, and circulation. Thus continued global warming will affect the lake thermal properties, water level, internal nutrient loading, nutrient cycling, food-web characteristics, fish-habitat, aquatic ecosystem, and other important features of lake limnology. Using a 1-D numerical model—the Lake Clarity Model (LCM) —together with the down-scaled climatic data of the two emissions scenarios (B1 and A2) of the Geophysical Fluid Dynamics Laboratory (GFDL) Global Circulation Model, we found that Lake Tahoe will likely cease to mix to the bottom after about 2060 for A2 scenario, with an annual mixing depth of less than 200 m as the most common value. Deep mixing, which currently occurs on average every 3–4 years, will (under the GFDL B1 scenario) occur only four times during 2061 to 2098. When the lake fails to completely mix, the bottom waters are not replenished with dissolved oxygen and eventually dissolved oxygen at these depths will be depleted to zero. When this occurs, soluble reactive phosphorus (SRP) and ammonium-nitrogen (both biostimulatory) are released from the deep sediments and contribute approximately 51 % and 14 % of the total SRP and dissolved inorganic nitrogen load, respectively. The lake model suggests that climate change will drive the lake surface level down below the natural rim after 2085 for the GFDL A2 but not the GFDL B1 scenario. The results indicate that continued climate changes could pose serious threats to the characteristics of the Lake that are most highly valued. Future water quality planning must take these results into account.”

Citation: G. B. Sahoo, S. G. Schladow, J. E. Reuter, R. Coats, M. Dettinger, J. Riverson, B. Wolfe and M. Costa-Cabral, Climatic Change, 2012, DOI: 10.1007/s10584-012-0600-8.


Using old weather observations to validate past climate reconstructions

Constraining the temperature history of the past millennium using early instrumental observations – Brohan et al. (2012) [FULL TEXT]

Abstract: “The current assessment that twentieth-century global temperature change is unusual in the context of the last thousand years relies on estimates of temperature changes from natural proxies (tree-rings, ice-cores, etc.) and climate model simulations. Confidence in such estimates is limited by difficulties in calibrating the proxies and systematic differences between proxy reconstructions and model simulations. As the difference between the estimates extends into the relatively recent period of the early nineteenth century it is possible to compare them with a reliable instrumental estimate of the temperature change over that period, provided that enough early thermometer observations, covering a wide enough expanse of the world, can be collected. One organisation which systematically made observations and collected the results was the English East India Company (EEIC), and their archives have been preserved in the British Library. Inspection of those archives revealed 900 log-books of EEIC ships containing daily instrumental measurements of temperature and pressure, and subjective estimates of wind speed and direction, from voyages across the Atlantic and Indian Oceans between 1789 and 1834. Those records have been extracted and digitised, providing 273 000 new weather records offering an unprecedentedly detailed view of the weather and climate of the late eighteenth and early nineteenth centuries. The new thermometer observations demonstrate that the large-scale temperature response to the Tambora eruption and the 1809 eruption was modest (perhaps 0.5 °C). This provides an out-of-sample validation for the proxy reconstructions – supporting their use for longer-term climate reconstructions. However, some of the climate model simulations in the CMIP5 ensemble show much larger volcanic effects than this – such simulations are unlikely to be accurate in this respect.”

Citation: Brohan, P., Allan, R., Freeman, E., Wheeler, D., Wilkinson, C., and Williamson, F.: Constraining the temperature history of the past millennium using early instrumental observations, Clim. Past, 8, 1551-1563, doi:10.5194/cp-8-1551-2012, 2012.


How ice sheets and climate affect each other

Modelling large-scale ice-sheet–climate interactions following glacial inception – Gregory et al. (2012) [FULL TEXT]

Abstract: “We have coupled the FAMOUS global AOGCM (atmosphere-ocean general circulation model) to the Glimmer thermomechanical ice-sheet model in order to study the development of ice-sheets in north-east America (Laurentia) and north-west Europe (Fennoscandia) following glacial inception. This first use of a coupled AOGCM–ice-sheet model for a study of change on long palæoclimate timescales is made possible by the low computational cost of FAMOUS, despite its inclusion of physical parameterisations similar in complexity to higher-resolution AOGCMs. With the orbital forcing of 115 ka BP, FAMOUS–Glimmer produces ice caps on the Canadian Arctic islands, on the north-west coast of Hudson Bay and in southern Scandinavia, which grow to occupy the Keewatin region of the Canadian mainland and all of Fennoscandia over 50 ka. Their growth is eventually halted by increasing coastal ice discharge. The expansion of the ice-sheets influences the regional climate, which becomes cooler, reducing the ablation, and ice accumulates in places that initially do not have positive surface mass balance. The results suggest the possibility that the glaciation of north-east America could have begun on the Canadian Arctic islands, producing a regional climate change that caused or enhanced the growth of ice on the mainland. The increase in albedo (due to snow and ice cover) is the dominant feedback on the area of the ice-sheets and acts rapidly, whereas the feedback of topography on SMB does not become significant for several centuries, but eventually has a large effect on the thickening of the ice-sheets. These two positive feedbacks are mutually reinforcing. In addition, the change in topography perturbs the tropospheric circulation, producing some reduction of cloud, and mitigating the local cooling along the margin of the Laurentide ice-sheet. Our experiments demonstrate the importance and complexity of the interactions between ice-sheets and local climate.”

Citation: Gregory, J. M., Browne, O. J. H., Payne, A. J., Ridley, J. K., and Rutt, I. C.: Modelling large-scale ice-sheet–climate interactions following glacial inception, Clim. Past, 8, 1565-1580, doi:10.5194/cp-8-1565-2012, 2012.


Planetary fertility reconstruction of the past 400,000 years

Planetary fertility during the past 400 ka based on the triple isotope composition of O2 in trapped gases from the Vostok ice core – Blunier et al. (2012) [FULL TEXT]

Abstract: “The productivity of the biosphere leaves its imprint on the isotopic composition of atmospheric oxygen. Ultimately, atmospheric oxygen, through photosynthesis, originates from seawater. Fractionations during the passage from seawater to atmospheric O2 and during respiration affect δ17O approximately half as much as δ18O. An “anomalous” (also termed mass independent) fractionation process changes δ17O about 1.7 times as much as δ18O during isotope exchange between O2 and CO2 in the stratosphere. The relative rates of biological O2 production and stratospheric processing determine the relationship between δ17O and δ18O of O2 in the atmosphere. Variations of this relationship thus allow us to estimate changes in the rate of O2 production by photosynthesis versus the rate of O2–CO2 isotope exchange in the stratosphere. However, the analysis of the 17O anomaly is complicated because each hydrological and biological process fractionates δ17O and δ18O in slightly different proportions. In this study we present O2 isotope data covering the last 400 ka (thousand years) from the Vostok ice core. We reconstruct oxygen productivities from the triple isotope composition of atmospheric oxygen with a box model. Our steady state model for the oxygen cycle takes into account fractionation during photosynthesis and respiration by the land and ocean biosphere, fractionation during the hydrologic cycle, and fractionation when oxygen passes through the stratosphere. We consider changes of fractionation factors linked to climate variations, taking into account the span of estimates of the main factors affecting our calculations. We find that ocean oxygen productivity was within 20% of the modern value throughout the last 400 ka. Given the presumed reduction in terrestrial oxygen productivity, the total oxygen production during glacials was likely reduced.”

Citation: Blunier, T., Bender, M. L., Barnett, B., and von Fischer, J. C.: Planetary fertility during the past 400 ka based on the triple isotope composition of O2 in trapped gases from the Vostok ice core, Clim. Past, 8, 1509-1526, doi:10.5194/cp-8-1509-2012, 2012.


Northern Hemisphere June snow cover extent decreases faster than Arctic sea ice

Spring snow cover extent reductions in the 2008–2012 period exceeding climate model projections – Derksen & Brown (2012)

Abstract: “Analysis of Northern Hemisphere spring terrestrial snow cover extent (SCE) from the NOAA snow chart Climate Data Record (CDR) for the April to June period (when snow cover is mainly located over the Arctic) has revealed statistically significant reductions in May and June SCE. Successive records for the lowest June SCE have been set each year for Eurasia since 2008, and in 3 of the past 5 years for North America. The rate of loss of June snow cover extent between 1979 and 2011 (−17.8% decade−1) is greater than the loss of September sea ice extent (−10.6% decade−1) over the same period. Analysis of Coupled Model Intercomparison Project Phase 5 (CMIP5) model output shows the marked reductions in June SCE observed since 2005 fall below the zone of model consensus defined by +/−1 standard deviation from the multi-model ensemble mean.”

Citation: Derksen, C. and R. Brown (2012), Spring snow cover extent reductions in the 2008–2012 period exceeding climate model projections, Geophys. Res. Lett., 39, L19504, doi:10.1029/2012GL053387.


Antarctic Peninsula glacier surfaces are lowering

Multi-decadal glacier surface lowering in the Antarctic Peninsula – Kunz et al. (2012)

Abstract: “From approximately 400 glaciers of the western Antarctic Peninsula, no in situ records of mass balance exist and their recent contribution to sea level is consequently poorly constrained. We seek to address this shortcoming by using surface elevations from USGS and BAS airborne (1948–2005) and ASTER spaceborne (2001–2010) stereo imagery, combined by using a rigorous semi-automated registration approach, to determine multi-decadal glacier surface elevation changes in the western Antarctic Peninsula for 12 glaciers. All observed glaciers show near-frontal surface lowering and an annual mean lowering rate of 0.28 ± 0.03 m/yr at the lower portion of the glaciers during the ∼4 decades following the mid-1960s, with higher rates for the glaciers in the north-west parts of the Antarctic Peninsula. Increased lowering of up to 0.6 m/yr can be observed since the 1990s, in close correspondence to increased atmospheric positive degree days. In all cases, surface lowering reduces to zero within 5 km of the glacier front at around 400 m altitude. This lowering may have been at least partially compensated for by increased high-altitude accumulation.”

Citation: Kunz, M., M. A. King, J. P. Mills, P. E. Miller, A. J. Fox, D. G. Vaughan, and S. H. Marsh (2012), Multi-decadal glacier surface lowering in the Antarctic Peninsula, Geophys. Res. Lett., 39, L19502, doi:10.1029/2012GL052823.


Freshwater flux from Greenland increasing faster than expected

Recent large increases in freshwater fluxes from Greenland into the North Atlantic – Bamber et al. (2012)

Abstract: “Freshwater (FW) fluxes from river runoff and precipitation minus evaporation for the pan Arctic seas are relatively well documented and prescribed in ocean GCMs. Fluxes from Greenland on the other hand are generally ignored altogether, despite their potential impacts on ocean circulation and marine biology. Here, we present a reconstruction of the spatially distributed FW flux from Greenland for 1958-2010. We find a modest increase into the Arctic Ocean during this period. Fluxes into the Irminger Basin, however, have increased by fifty percent (6.3{plus minus}0.5 km3 yr-2) in less than twenty years. This greatly exceeds previous estimates. For the ice sheet as a whole the rate of increase since 1992 is 16.9{plus minus}1.8 km3 yr-2. The cumulative FW anomaly since 1995 is 3200{plus minus}358 km3, which is about a third of the magnitude of the Great Salinity Anomaly (GSA) of the 1970s. If this trend continues into the future, the anomaly will exceed that of the GSA by about 2025.”

Citation: Bamber, J. L., M. R. van den Broeke, J. Ettema, J. T. M. Lenaerts, and E. Rignot (2012), Recent large increases in freshwater fluxes from Greenland into the North Atlantic, Geophys. Res. Lett., doi:10.1029/2012GL052552.


Hadley Cell might contract rapidly when CO2 reaches 1000 ppm

New thoughts about the cretaceous climate and oceans – Hay & Floegel (2012)

Abstract: “Several new discoveries suggest that the climate of the Cretaceous may have been more different from that of today than has been previously supposed. Detailed maps of climate sensitive fossils and sediments compiled by Nicolai Chumakov and his colleagues in Russia indicate widespread aridity in the equatorial region during the Early Cretaceous. The very warm ocean temperatures postulated for the Mid-Cretaceous by some authors would likely have resulted in unacceptable heat stress for land plants at those latitudes, however, and may be flawed. Seasonal reversals of the atmospheric pressure systems in the Polar Regions are an oversimplification. However, seasonal pressure difference between 30° and 60° latitude become quite pronounced, being more than 25 hPa in winter and less than 10 hPa in summer. This results in inconstant winds, affecting the development of the gyre-limiting frontal systems that control modern ocean circulation. The idea of Hasegawa et al. (2011) who suggest a drastic reduction in the size of the Hadley cells during the warm Cretaceous greenhouse is supported by several numerical climate simulations. Rapid contraction of the Hadley cell such that its sinking dry air occurs at 15° N latitude rather than 30° N is proposed to occur at a threshold of 1,000 ppmv CO2 in the atmosphere. This change will probably be reached in the next century.”

Citation: William W. Hay, Sascha Floegel, Earth-Science Reviews, http://dx.doi.org/10.1016/j.earscirev.2012.09.008.


Other studies from last week

Vegetation and climatic changes of SW China in response to the uplift of Tibetan Plateau – Zhang et al. (2012)

Paleo-climate of the central European uplands during the last glacial maximum based on glacier mass-balance modeling – Heyman et al. (2012)

Relationship between the expansion of drylands and the intensification of Hadley circulation during the late twentieth century – Shin et al. (2012)

Urban heat island in a coastal urban area in northern Spain – Acero et al. (2012)

Mixed nonlinear regression for modelling historical temperatures in Central–Southern Italy – Diodato et al. (2012)

The global signature of the ENSO and SST-like fields – Varotsos (2012)

Phenological changes of oceanic phytoplankton in the 1980s and 2000s as revealed by remotely sensed ocean-color observations – D’Ortenzio et al. (2012)

How warming and steric sea level rise relate to cumulative carbon emissions – Williams et al. (2012)

Sensitivity to Glacial Forcing in the CCSM4 – Brady et al. (2012)

Temporal scales of tropospheric CO2, precipitation, and ecosystem responses in the central Great Plains – Cochran & Brunsell (2012)

Isotopic and lithologic variations of one precisely-dated stalagmite across the Medieval/LIA period from Heilong Cave, central China – Cui et al. (2012) [FULL TEXT]

Sea surface temperature variability in the Pacific sector of the Southern Ocean over the past 700 kyr – Ho et al. (2012)

Optimal temperature for malaria transmission is dramatically lower than previously predicted – Mordecai et al. (2012)

Improving spatial temperature estimates by resort to time autoregressive processes – Joly et al. (2012)

Extreme ozone depletion in the 2010–2011 Arctic winter stratosphere as observed by MIPAS/ENVISAT using a 2-D tomographic approach – Arnone et al. (2012) [FULL TEXT]

The recent shift in early summer Arctic atmospheric circulation – Overland et al. (2012)

How should we grow cities to minimise their biodiversity impacts? – Sushisnky et al. (2012)

A longer climate memory carried by soil freeze–thaw processes in Siberia – Matsumura & Yamazaki (2012) [FULL TEXT]

CO2 fertilization and enhanced drought resistance in Greek firs from Cephalonia Island, Greece – Koutavas (2012)

Sensitivity and response of Bhutanese glaciers to atmospheric warming – Rupper et al. (2012)


CLASSIC OF THE WEEK: Shapley (1921)

Note on a Possible Factor in Changes of Geological Climate – Shapley (1921) [FULL TEXT]

Abstract: No abstract.

Citation: Harlow Shapley, The Journal of Geology, Vol. 29, No. 6 (Sep. – Oct., 1921) (pp. 502-504).


When each paper is published, it is notified in AGW Observer Facebook page and Twitter page. Here’s the archive for the research papers of previous weeks. If this sort of thing interests you, be sure to check out A Few Things Illconsidered. They also have a weekly posting containing lots of links to new research and other climate related news.

One Response to “New research from last week 41/2012”

  1. [...] 2012/10/15: AGWObserver: New research from last week 41/2012 [...]

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