New research from last week 18/2012
Posted by Ari Jokimäki on May 7, 2012
Last week scientists moved the borders of unknown little further in following subjects (among others): astronomical climate forcing, NAO-snow cover relation, global temperature analysis, daily mean temperature, hurricane activity, ocean acidification, mass extinction, AMO, insect ice toleration, lake ice, sea ice, climate system annual cycle, growing season, 18th century meteorology, bark beetle outbreaks, summer monsoon, and iceberg distribution.
Astronomical forcing as a pacemaker of climate
Abstract: “There is evidence that ice age cycles are paced by astronomical forcing, suggesting some kind of synchronisation phenomenon. Here, we identify the type of such synchronisation and explore systematically its uniqueness and robustness using a simple paleoclimate model akin to the van der Pol relaxation oscillator and dynamical system theory. As the insolation is quite a complex quasiperiodic signal involving different frequencies, the traditional concepts used to define synchronisation to periodic forcing are no longer applicable. Instead, we explore a different concept of generalised synchronisation in terms of (coexisting) synchronised solutions for the forced system, their basins of attraction and instabilities. We propose a clustering technique to compute the number of synchronised solutions, each of which corresponds to a different paleoclimate history. In this way, we uncover multistable synchronisation (reminiscent of phase- or frequency-locking to individual periodic components of astronomical forcing) at low forcing strength, and monostable or unique synchronisation at stronger forcing. In the multistable regime, different initial conditions may lead to different paleoclimate histories. To study their robustness, we analyse Lyapunov exponents that quantify the rate of convergence towards each synchronised solution (local stability), and basins of attraction that indicate critical levels of external perturbations (global stability). We find that even though synchronised solutions are stable on a long term, there exist short episodes of desynchronisation where nearby climate trajectories diverge temporarily (for about 50 kyr). As the attracting trajectory can sometimes lie close to the boundary of its basin of attraction, a small perturbation could quite easily make climate to jump between different histories, reducing the predictability. Our study brings new insight into paleoclimate dynamics and reveals a possibility for the climate system to wander throughout different climatic histories related to preferential synchronisation regimes on obliquity, precession or combinations of both, all over the history of the Pleistocene.”
Citation: Bernard De Saedeleer, Michel Crucifix and Sebastian Wieczorek, Climate Dynamics, 2012, DOI: 10.1007/s00382-012-1316-1.
North Atlantic Oscillation is related to European snow cover, particularly in January and February
Abstract: “Annual snow cover in the Northern Hemisphere has decreased in the past two decades, an effect associated with global warming. The regional scale changes of snow cover during winter, however, vary significantly from one region to another. In the present study, snow cover variability over Europe and its connection to other atmospheric variables was investigated using Cyclostationary Empirical Orthogonal Function (CSEOF) analysis. The evolution of atmospheric variables related to each CSEOF mode of snow cover variability was derived via regression analysis in CSEOF space. CSEOF analysis clearly shows that the North Atlantic Oscillation (NAO) is related to European snow cover, particularly in January and February. A negative NAO phase tends to result in a snow cover increases, whereas a positive NAO phase results in snow cover decreases. The temporal changes in the connection between the NAO and European snow cover are explained by time-dependent NAO-related temperature anomalies. If the NAO phase is negative, the temperature is lower in Europe and snow cover increases; by contrast, when the NAO phase is positive, the temperature is higher and snow cover decreases. Temperature and snow cover variations in Europe are associated with the thermal advection by anomalous wind by NAO. CSEOF analysis also shows an abrupt increase of snow cover in December and January and a decrease in February and March since the year 2000, approximately. This abrupt change is associated with sub-seasonal variations of atmospheric circulation in the study region.”
Citation: Yoojin Kim, Kwang-Yul Kim and Baek-Min Kim, Climate Dynamics, 2012, DOI: 10.1007/s00382-012-1365-5.
NOAA introduces improvements to Merged Land-Ocean Surface Temperature analysis
Abstract: “This paper describes the new release of the Merged Land-Ocean Surface Temperature analysis (MLOST version 3.5), which is used in operational monitoring and climate assessment activities by the NOAA National Climatic Data Center. The primary motivation for the latest version is the inclusion of a new land dataset that has several major improvements, including a more elaborate approach for addressing changes in station location, instrumentation, and siting conditions. The new version is broadly consistent with previous global analyses, exhibiting a trend of 0.076 °C dec−1 since 1901, 0.162 °C dec−1 since 1979, and widespread warming in both time periods. In general, the new release exhibits only modest differences with its predecessor, the most obvious being very slightly more warming at the global scale (0.004 °C dec−1 since 1901) and slightly different trend patterns over the terrestrial surface.”
Citation: Russell S. Vose, Derek Arndt, Viva F. Banzon, David R. Easterling, Byron Gleason, Boyin Huang, Ed Kearns, Jay H. Lawrimore, Matthew J. Menne, Thomas C. Peterson, Richard W. Reynolds, Thomas M. Smith, Claude N. Williams, Jr., David L. Wuertz, Bulletin of the American Meteorological Society 2012, doi: http://dx.doi.org/10.1175/BAMS-D-11-00241.1.
So, how do we determine daily mean temperature then?
Abstract: “We compare some different approaches to estimating daily mean temperature (DMT). In many countries, the routine approach is to calculate the average of the directly measured minimum and maximum daily temperature. In some, the maximum and minimum are obtained from hourly measurements. In other countries, temperature readings at specific times throughout the day are taken into account. For example, the Swedish approach uses a linear combination of five temperature readings, including the minimum and the maximum, with coefficients that depend on longitude and month. We first look at data with very high temporal resolution, and compare some different approaches to estimating DMT. Then, we compare the Swedish formula to various averages of the daily minimum and maximum, finding the latter method being substantially less precise. We finally compare the Swedish formula to hourly averages, and find that a recalibrated linear combination improves estimation accuracy.”
Citation: Yuting Ma, Peter Guttorp, International Journal of Climatology, DOI: 10.1002/joc.3510.
Eastern North Pacific hurricane season 2010 was one of the least active seasons on record
Abstract: “The 2010 eastern North Pacific hurricane season was one of the least active seasons on record. Only seven named storms developed, which is the lowest number observed at least since routine satellite coverage of that basin began in 1966. Furthermore, only three of those storms reached hurricane status, which is also the lowest number of hurricanes ever observed in the satellite era season. However, two tropical storms made landfall – Agatha in Guatemala and Georgette in Mexico, with Agatha directly causing 190 deaths and moderate to severe property damage as a result of rain-induced floods and mud slides. On average, the National Hurricane Center track forecasts in the eastern North Pacific for 2010 were quite skillful.”
Citation: Stacy R. Stewart and John P. Cangialosi, Monthly Weather Review 2012, doi: http://dx.doi.org/10.1175/MWR-D-11-00152.1.
Expected ocean acidification from human actions seems to be unprecedented in the geologic past
Abstract: “Humans are continuing to add vast amounts of carbon dioxide (CO2) to the atmosphere through fossil fuel burning and other activities. A large fraction of the CO2 is taken up by the oceans in a process that lowers ocean pH and carbonate mineral saturation state. This effect has potentially serious consequences for marine life, which are, however, difficult to predict. One approach to address the issue is to study the geologic record, which may provide clues about what the future holds for ocean chemistry and marine organisms. This article reviews basic controls on ocean carbonate chemistry on different timescales and examines past ocean chemistry changes and ocean acidification events during various geologic eras. The results allow evaluation of the current anthropogenic perturbation in the context of Earth’s history. It appears that the ocean acidification event that humans are expected to cause is unprecedented in the geologic past, for which sufficiently well-preserved records are available.”
Citation: Richard E. Zeebe, Annual Review of Earth and Planetary Sciences, Vol. 40: 141-165 (Volume publication date May 2012), DOI: 10.1146/annurev-earth-042711-105521.
End-Permian mass extinction may be important ancient analog for 21st century oceans
Abstract: “The greatest loss of biodiversity in the history of animal life occurred at the end of the Permian Period (~252 million years ago). This biotic catastrophe coincided with an interval of widespread ocean anoxia and the eruption of one of Earth’s largest continental flood basalt provinces, the Siberian Traps. Volatile release from basaltic magma and sedimentary strata during emplacement of the Siberian Traps can account for most end-Permian paleontological and geochemical observations. Climate change and, perhaps, destruction of the ozone layer can explain extinctions on land, whereas changes in ocean oxygen levels, CO2, pH, and temperature can account for extinction selectivity across marine animals. These emerging insights from geology, geochemistry, and paleobiology suggest that the end-Permian extinction may serve as an important ancient analog for twenty-first century oceans.”
Citation: Jonathan L. Payne and Matthew E. Clapham, Annual Review of Earth and Planetary Sciences, Vol. 40: 89-111 (Volume publication date May 2012), DOI: 10.1146/annurev-earth-042711-105329.
Greenland ice cores show highly variable Atlantic Multidecadal Oscillation
Abstract: “The Greenland δ18O ice core record is used as a proxy for Greenland surface air temperatures and to interpret Atlantic Multidecadal Oscillation (AMO) variability. An analysis of annual δ18O data from six Arctic ice cores (five from Greenland and one from Canada’s Ellesmere Island) suggests a significant AMO spatial and temporal variability within a recent period of 660 years. A dominant AMO periodicity near 20 years is clearly observed in the southern (Dye3 site) and the central (GISP2, Crete and Milcent) regions of Greenland. This 20-year variability is, however, significantly reduced in the northern (Camp Century and Agassiz Ice Cap) region, likely due to a larger distance from the Atlantic Ocean, and a much lower snow accumulation. A longer time scale AMO component of 45–65 years, which has been seen clearly in the 20th century SST data, is detected only in central Greenland ice cores. We find a significant difference between the AMO cycles during the Little Ice Age (LIA) and the Medieval Warm Period (MWP). The LIA was dominated by a ∼20 year AMO cycle with no other decadal or multidecadal scale variability above the noise level. However, during the preceding MWP the 20 year cycle was replaced by a longer scale cycle centered near a period of 43 years with a further 11.5 year periodicity. An analysis of two coupled atmosphere-ocean general circulation models control runs (UK Met Office HadCM3 and NOAA GFDL CM2.1) agree with the shorter and longer time-scales of Atlantic Meridional Overturning Circulation (AMOC) and temperature fluctuations with periodicities close to those observed. However, the geographic variability of these periodicities indicated by ice core data is not captured in model simulations.”
Citation: Chylek, P., C. Folland, L. Frankcombe, H. Dijkstra, G. Lesins, and M. Dubey (2012), Greenland ice core evidence for spatial and temporal variability of the Atlantic Multidecadal Oscillation, Geophys. Res. Lett., 39, L09705, doi:10.1029/2012GL051241.
Did some insects survive in Greenland during last glacial stage?
Abstract: “Sediments from the last interglacial (Eemian) in Jameson Land, East Greenland, and the Thule area, NW Greenland, have revealed a number of insect fragments of both arctic and more or less warmth-demanding species. Altogether, the interglacial fauna of Coleoptera (beetles) indicates boreal conditions. Undoubtedly, a large fraction of the insect fauna succumbed when the mild Eemian climate cooled drastically during the last glacial stage. However, a group of hardy species now found far north into the High Arctic might be glacial survivors. It is, however, still puzzling why well-adapted arctic beetle species such as Amara alpina and Isochnus arcticus did not survive the last glacial stage in Greenland. Two factors that have not been sufficiently considered when discussing survival contra extinction are the importance of microclimate and the number of sun-hours during the Arctic summer. Even among the Coleoptera, which as a group fares quite badly in the Arctic, there might be survivors, at least among those found both during the interglacial and as fossils during the early Holocene. First of all, glacial survival applies to the seed bug Nysius groenlandicus, which was widespread during the Eemian, was found soon after the last deglaciation, and is now almost omnipresent in Greenland.”
Citation: Jens Böcher, Boreas, DOI: 10.1111/j.1502-3885.2012.00251.x.
Lakes in eastern North America already have up to 21 day longer ice free season
Abstract: “Ecosystems in biogeographical transition zones, or ecotones, tend to be highly sensitive to climate and can provide early indications of future change. To evaluate recent climatic changes and their impacts in a boreal-temperate ecotone in eastern North America, we analyzed ice phenology records (1975–2007) for five lakes in the Adirondack Mountains of northern New York State. We observed rapidly decreasing trends of up to 21 days less ice cover, mostly due to later freeze-up and partially due to earlier break-up. To evaluate the local drivers of these lake ice changes, we modeled ice phenology based on local climate data, derived climatic predictors from the models, and evaluated trends in those predictors to determine which were responsible for observed changes in lake ice. November and December temperature and snow depth consistently predicted ice-in, and recent trends of warming and decreasing snow during these months were consistent with later ice formation. March and April temperature and snow depth consistently predicted ice-out, but the absence of trends in snow depth during these months, despite concurrent warming, resulted in much weaker trends for ice-out. Recent rates of warming in the Adirondacks are among the highest regionally, although with a different seasonality of changes (early winter > late winter) that is consistent with other lake ice records in the surrounding area. Projected future declines in snow cover could create positive feedbacks and accelerate current rates of ice loss due to warming. Climate sensitivity was greatest for the larger lakes in our study, including Wolf Lake, considered one of the most ecologically intact ‘wilderness lakes’ in eastern North America. Our study provides further evidence of climate sensitivity of the boreal-temperate ecotone of eastern North America and points to emergent conservation challenges posed by climate change in legally protected yet vulnerable landscapes like the Adirondack Park.”
Citation: Colin M. Beier, John C. Stella, Martin Dovčiak and Stacy A. McNulty, Climatic Change, 2012, DOI: 10.1007/s10584-012-0455-z.
With 2007 wind, 2010 and 2011 would have reached record lows in Arctic summer sea ice extent
Abstract: “Strong summertime anticyclonic wind anomalies over the Arctic Ocean, with anomalous flow toward the Fram Strait, during summer months of 2007 contributed to the record-low the Arctic sea-ice extent observed in September of that year. Had the summer winds over the Arctic during the summers of 2010 and 2011 been the same as those in 2007, September sea ice extent would have reached new record lows in those years as well. By regulating the flow of ice toward and through the Fram Strait, variations in low-level winds over the Arctic have contributed to the month-to-month, year-to-year, and decade-to-decade variability of sea ice extent.”
Citation: Ogi, M. and J. M. Wallace (2012), The role of summer surface wind anomalies in the summer Arctic sea ice extent in 2010 and 2011, Geophys. Res. Lett., 39, L09704, doi:10.1029/2012GL051330.
Global warming is accompanied by amplification of the annual cycle of the climate system
Abstract: “The global summer monsoon precipitation (GSMP) provides a fundamental measure for changes in the annual cycle of the climate system and hydroclimate. We investigate mechanisms governing decadal-centennial variations of the GSMP over the past millennium with a coupled climate model’s (ECHO-G) simulation forced by solar-volcanic (SV) radiative forcing and greenhouse gases (GHG) forcing. We show that the leading mode of GSMP is a forced response to external forcing on centennial time scale with a globally uniform change of precipitation across all monsoon regions, whereas the second mode represents internal variability on multi-decadal time scale with regional characteristics. The total amount of GSMP varies in phase with the global mean temperature, indicating that global warming is accompanied by amplification of the annual cycle of the climate system. The northern hemisphere summer monsoon precipitation (NHSMP) responds to GHG forcing more sensitively, while the southern hemisphere summer monsoon precipitation (SHSMP) responds to the SV radiative forcing more sensitively. The NHSMP is enhanced by increased NH land–ocean thermal contrast and NH-minus-SH thermal contrast. On the other hand, the SHSMP is strengthened by enhanced SH subtropical highs and the east–west mass contrast between Southeast Pacific and tropical Indian Ocean. The strength of the GSMP is determined by the factors controlling both the NHSMP and SHSMP. Intensification of GSMP is associated with (a) increased global land–ocean thermal contrast, (b) reinforced east–west mass contrast between Southeast Pacific and tropical Indian Ocean, and (c) enhanced circumglobal SH subtropical highs. The physical mechanisms revealed here will add understanding of future change of the global monsoon.”
Citation: Jian Liu, Bin Wang, So-Young Yim, June-Yi Lee, Jong-Ghap Jhun and Kyung-Ja Ha, Climate Dynamics, 2012, DOI: 10.1007/s00382-012-1360-x.
Growing season and freeze-free period are getting longer in Colorado at high elevation
Abstract: “Most climate change studies on high elevation ecosystems identify changes in biota, while several report abiotic factors. However, very few report expansion of the freeze-free period, or discuss monthly changes of temperature and growing degree days (GDD) during the growing season. This study provides initial data on agriculturally-related aspects of climate change during the growing season (M-J-J-A-S) in the inter-montane desert of the San Luis Valley (SLV), Colorado. Temperature data were gathered from 7 climate stations within the SLV. Based on ordinal days, the last vernal freeze is occurring (p < 0.05) earlier at 3 stations than in prior years, ranging between 5.52 and 11.86 days during 1981–2007. Significantly-later autumnal freezes are occurring at 5 stations by 5.95–18.10 days, while expansion of the freeze-free period was significantly longer at all stations by 7.20–24.21 days. The freeze-free period averaged about 93 days prior to the 1980s, but now averages about 107 days. Increases (p < 0.05) in daily mean, maximum, minimum temperature occurred at nearly all stations for each month. Increases in GDD10, GDD4.4 (potato) and GDD5.5 (alfalfa) also occurred at nearly all stations for all months during 1994–2007. Higher temperatures increase the number of GDD, quickening crop growth and maturity, and potentially reducing yield and quality unless varieties are adapted to changes and water is available for the season extension and increased evapotranspiration.”
Citation: Ken Mix, Vicente L. Lopes and Walter Rast, Climatic Change, 2012, DOI: 10.1007/s10584-012-0448-y.
Meteorological observations from 18th century Brazil
Abstract: “Bento Sanches Dorta was an astronomer and geographer in the Portuguese colony of Rio de Janeiro in Brazil from 1781 to 1788. He recorded daily readings of meteorological and geomagnetic variables during that period. This dataset provides, to the best of our knowledge, the earliest known continuous 8-year-long instrumental meteorological observations for any South American site. His data show that the winters in this period were relatively cool, and that 1785 was the rainiest and hottest year, and 1787 the driest and coolest. The records display a distinct seasonal cycle and a variability that are comparable with the modern data.”
Citation: A. M. M. Farrona, R. M. Trigo, M. C. Gallego and J. M. Vaquero, Climatic Change, 2012, DOI: 10.1007/s10584-012-0467-8.
Spruce forest damaging bark beetle outbreaks are more severe in warmer climate
Abstract: “Temperature warming and the increased frequency of climatic anomalies are expected to trigger bark beetle outbreaks with potential severe consequences on forest ecosystems. We characterized the combined effects of climatic factors and density-dependent feedbacks on forest damage caused by Ips typographus (L.), one of the most destructive pests of European spruce forests, and tested whether climate modified the interannual variation in the altitudinal outbreak range of the species. We analyzed a 16-year time-series from the European Alps of timber loss in Picea abies Karsten forests due to I. typographus attacks and used a discrete population model and an information theoretic approach to compare multiple competing hypotheses. The occurrence of dry summers combined with warm temperatures appeared as the main abiotic triggers of severity of outbreaks. We also found an endogenous negative feedback with a 2-year lag suggesting a potential important role of natural enemies. Forest damage per hectare averaged 7-fold higher where spruce was planted in sites warmer than those within its historical climatic range. Dry summers, but not temperature, was related to upward shifts in the altitudinal outbreak range. Considering the potential increased susceptibility of spruce forests to insect outbreaks due to climate change, there is growing value in mitigating these effects through sustainable forest management, which includes avoiding the promotion of spruce outside its historical climatic range.”
Citation: Lorenzo Marini, Matthew P. Ayres, Andrea Battisti and Massimo Faccoli, Climatic Change, DOI: 10.1007/s10584-012-0463-z.
Global warming might be responsible for recent weakening of East Asian summer monsoon
Abstract: “We investigate the possible causes of the weakening of northern East Asian summer monsoon (EASM) from 1954 to 2010. We found that the decreased intensity of northern EASM as measured by a circulation index (EASMI) is significantly correlated with the increase of the surface air temperature (SAT) averaged over the Lake Baikal region (45°–65°N, 80°–130°E) defined as SATI. Corresponding to increasing SATI, an anomalous low-level anticyclone occurs with northeasterly prevailing over northern East Asia (30°–50°N,100°–130°E), resulting in a weakened southwesterly monsoon winds and drier climate in this region. Numerical experiments with the community atmosphere model version 3 (CAM3) show that the joint forcing induced by greenhouse gases (GHG), sea surface temperature (SST), solar radiance (SR), and volcano activity (VC) can replicate the observed trend of SATI and its related circulation anomalies, but without GHG forcing the model failed to simulate the warming trend of SATI after 1970s. This implies that the global warming is likely responsible for the local warming around the Lake Baikal, which in turn weakens the northern EASM in recent decades.”
Citation: Zhu, C., B. Wang, W. Qian, and B. Zhang (2012), Recent weakening of northern East Asian summer monsoon: A possible response to global warming, Geophys. Res. Lett., 39, L09701, doi:10.1029/2012GL051155.
Increased accuracy for mapping Antarctic iceberg distribution
Abstract: “Interest for icebergs and their possible impact on southern ocean circulation and biology has increased during the recent years. While large tabular icebergs are routinely tracked and monitored using scatterometer data, the distribution of smaller icebergs (less than some km) is still largely unknown as they are difficult to detect operationally using conventional satellite data. In a recent study, Tournadre et al. (2008) showed that small icebergs can be detected, at least in open water, using high resolution (20 Hz) altimeter waveforms. In the present paper, we present an improvement of their method that allows, assuming a constant iceberg freeboard elevation and constant ice backscatter coefficient, to estimate the top-down iceberg surface area and therefore the distribution of the volume of ice on a monthly basis. The complete Jason-1 reprocessed (version C) archive covering the 2002–2010 period has been processed using this method. The small iceberg data base for the southern ocean gives an unprecedented description of the small iceberg (100 m–2800 m) distribution at unprecedented time and space resolutions. The iceberg size, which follows a lognormal distribution with an overall mean length of 630 m, has a strong seasonal cycle reflecting the melting of icebergs during the austral summer estimated at 1.5 m/day. The total volume of ice in the southern ocean has an annual mean value of about 400 Gt, i.e., about 35% of the mean yearly volume of large tabular icebergs estimated from the National Ice Center database of 1979–2003 iceberg tracks and a model of iceberg thermodynamics. They can thus play a significant role in the injection of meltwater in the ocean. The distribution of ice volume which has strong seasonal cycle presents a very high spatial and temporal variability which is much contrasted in the three ocean basins (South Atlantic, Indian and Pacific oceans). The analysis of the relationship between small and large (>5 km) icebergs shows that a majority of small icebergs are directly associated with the large ones but that there are vast regions, such as the eastern branch of the Wedell Gyre, where the transport of ice is made only through the smaller ones.”
Citation: Tournadre, J., F. Girard-Ardhuin, and B. Legrésy (2012), Antarctic icebergs distributions, 2002–2010, J. Geophys. Res., 117, C05004, doi:10.1029/2011JC007441.
CLASSIC OF THE WEEK: Walker (1937)
Abstract: “The fluctuations of pressure, temperature, and rainfall in winter in the region of the North Atlantic had been studied as a connected system in the last paper of this series; and a similar system is now shown to hold in the spring, summer, and autumn. But the amount of persistence is small, so that the results are of little value for foreshadowing weather; nor does a consideration of the trade wind region lead to success in this respect. Similarly the Southern Oscillation which was found active in the summer and winter seasons over a large part of the globe is now shown to function in the two remaining seasons: and while that of March to May has little control over the following quarter, the Southern Oscillation of September to November has a correlation coefficient of .90 with the Oscillation of December to February. Thus there are a number of relationships of between .60 and .82 available for foreshadowing weather.”
Citation: Sir Gilbert T. Walker, 1937, Memoirs of the Royal Meteorological Society, Vol. IV, No. 39.
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