New research from last week 38/2012
Posted on 25 September 2012 by Ari Jokimäki
This time we have papers relating to oceans: acidification, temperatures in past oceans, AMOC variability, and intermediate Atlantic water in Arctic Ocean. Other studies are about temperatures in Canada, clouds and precipitation of North America, small mammal ranges, nitrogen compounds, Arctic climate change, and there's a separate section on other other studies.
Amount of ocean acidification and climate sensitivity don't go hand in hand
Abstract: "It is now well understood that the global surface ocean, whose pH has been reduced by ~0.1 in response to rising atmospheric CO2 since industrialization, will continue to become more acidic as fossil fuel CO2 emissions escalate. However, it is unclear how uncertainties in climate sensitivity to future CO2 emissions will alter the manifestation of ocean acidification. Using an earth system model of intermediate complexity, we perform a set of simulations that varies equilibrium climate sensitivity by 1.0 to 4.5°C for a given CO2 emissions scenario and find two unexpected and decoupled responses. Firstly, the greater the climate sensitivity, the larger the surface mixed layer acidification signal but the smaller the subsurface acidification. However, taken throughout the ocean, highest climate sensitivity will paradoxically cause greater global warming while buffering whole-ocean pH by up to 24% on centennial time-scales. Secondly, we find a large decoupling between pH and carbonate ion concentration in surface waters whereby these chemical properties show opposite effects under variable climate sensitivity. For every 1°C increase in climate sensitivity, the surface ocean pH reduction grows by 4%, while surface ocean carbonate ion reduction shrinks by 2%. The chemical and spatial decoupling found here highlights the importance of distinguishing the biological impacts of pH and aragonite saturation and understanding the spatial extent of important calcifying biomes so as to truly understand the long-term impacts of ocean acidification."
Citation: Katsumi Matsumoto, Ben McNeil, Journal of Climate 2012, doi: http://dx.doi.org/10.1175/JCLI-D-12-00290.1.
Canada is getting warmer
Abstract: "This study presents a second generation of homogenized monthly mean surface air temperature data set for Canadian climate trend analysis. Monthly means of daily maximum and of daily minimum temperatures were examined at 338 Canadian locations. Data from co-located observing sites were sometimes combined to create longer time series for use in trend analysis. Time series of observations were then adjusted to account for nation-wide change in observing time in July 1961, affecting daily minimum temperatures recorded at 120 synoptic stations; these were adjusted using hourly temperatures at the same sites. Next, homogeneity testing was performed to detect and adjust for other discontinuities. Two techniques were used to detect non-climatic shifts in de-seasonalized monthly mean temperatures: a multiple linear regression based test and a penalized maximal t test. These discontinuities were adjusted using a recently developed quantile-matching algorithm: the adjustments were estimated with the use of a reference series. Based on this new homogenized temperature data set, annual and seasonal temperature trends were estimated for Canada for 1950–2010 and Southern Canada for 1900–2010. Overall, temperature has increased at most locations. For 1950–2010, the annual mean temperature averaged over the country shows a positive trend of 1.5°C for the past 61 years. This warming is slightly more pronounced in the minimum temperature than in the maximum temperature; seasonally, the greatest warming occurs in winter and spring. The results are similar for Southern Canada although the warming is considerably greater in the minimum temperature compared to the maximum temperature over the period 1900–2010."
Citation: Vincent, L. A., X. L. Wang, E. J. Milewska, H. Wan, F. Yang, and V. Swail (2012), A second generation of homogenized Canadian monthly surface air temperature for climate trend analysis, J. Geophys. Res., 117, D18110, doi:10.1029/2012JD017859.
Reconstruction of vertical temperature gradients in past oceans
Abstract: "A total of 25 mudstone samples from two sections in northwest Germany and northeast England (palaeolatitude ~ 40°N), respectively, of Hauterivian and early Barremian age were analyzed using TEX86 palaeothermometry. In addition, the stable isotope ratio (δ18O, δ13C) and trace element content (Mg, Sr, Fe, and Mn) of 138 belemnite guards from the same two outcrops were determined to reconstruct past sea water temperatures. The TEX86 based sea surface temperatures were constantly warm (24–26 °C) throughout the entire Hauterivian for both sections and even warmer for the early Barremian (27-30 °C). Stable water temperatures prevailed over a period of ~ 6.4 Ma in the southernmost part of the Boreal Realm. These findings clearly support the view of warm equable conditions for the Hauterivian at least for mid latitudinal settings. A constant off-set between higher TEX86-derived temperatures and lower δ18OBel-derived temperatures was observed. This may be explained by either increased sea water salinities, a deep dwelling habitat of belemnites or a combination of both. A by 3‰ higher salinity of the sea water below the thermocline, which would at least partly explain the by ~ 2‰ too positive δ18OBel values, can not be ruled out in these epicontinental settings. A habitat of the belemnites below the thermocline in perhaps 50 – 100 m water depth may have contributed to the positive δ18OBel data as well. The temperature difference between the TEX86 and the δ18OBel findings might therefore reflect a vertical temperature gradient of the water column of 4-5 °C and a salinity of the subsurface waters of 38‰."
Citation: Jörg Mutterlose, Matthias Malkoc, Stefan Schouten, Jaap S. Sinninghe Damsté, Palaeogeography, Palaeoclimatology, Palaeoecology, http://dx.doi.org/10.1016/j.palaeo.2012.09.006.
Volcanic eruptions might be a pacemaker for variability of Atlantic Meridional Overturning Circulation
Abstract: "The mechanisms involved in Atlantic meridional overturning circulation (AMOC) decadal variability and predictability over the last 50 years are analysed in the IPSL–CM5A–LR model using historical and initialised simulations. The initialisation procedure only uses nudging towards sea surface temperature anomalies with a physically based restoring coefficient. When compared to two independent AMOC reconstructions, both the historical and nudged ensemble simulations exhibit skill at reproducing AMOC variations from 1977 onwards, and in particular two maxima occurring respectively around 1978 and 1997. We argue that one source of skill is related to the large Mount Agung volcanic eruption starting in 1963, which reset an internal 20-year variability cycle in the North Atlantic in the model. This cycle involves the East Greenland Current intensity, and advection of active tracers along the subpolar gyre, which leads to an AMOC maximum around 15 years after the Mount Agung eruption. The 1997 maximum occurs approximately 20 years after the former one. The nudged simulations better reproduce this second maximum than the historical simulations. This is due to the initialisation of a cooling of the convection sites in the 1980s under the effect of a persistent North Atlantic oscillation (NAO) positive phase, a feature not captured in the historical simulations. Hence we argue that the 20-year cycle excited by the 1963 Mount Agung eruption together with the NAO forcing both contributed to the 1990s AMOC maximum. These results support the existence of a 20-year cycle in the North Atlantic in the observations. Hindcasts following the CMIP5 protocol are launched from a nudged simulation every 5 years for the 1960–2005 period. They exhibit significant correlation skill score as compared to an independent reconstruction of the AMOC from 4-year lead-time average. This encouraging result is accompanied by increased correlation skills in reproducing the observed 2-m air temperature in the bordering regions of the North Atlantic as compared to non-initialized simulations. To a lesser extent, predicted precipitation tends to correlate with the nudged simulation in the tropical Atlantic. We argue that this skill is due to the initialisation and predictability of the AMOC in the present prediction system. The mechanisms evidenced here support the idea of volcanic eruptions as a pacemaker for internal variability of the AMOC. Together with the existence of a 20-year cycle in the North Atlantic they propose a novel and complementary explanation for the AMOC variations over the last 50 years."
Citation: Didier Swingedouw, Juliette Mignot, Sonia Labetoulle, Eric Guilyardi and Gurvan Madec, Climate Dynamics, 2012, DOI: 10.1007/s00382-012-1516-8.
Identifying uncertainties in Arctic climate change projections
Abstract:"Wide ranging climate changes are expected in the Arctic by the end of the 21st century, but projections of the size of these changes vary widely across current global climate models. This variation represents a large source of uncertainty in our understanding of the evolution of Arctic climate. Here we systematically quantify and assess the model uncertainty in Arctic climate changes in two CO2 doubling experiments: a multimodel ensemble (CMIP3) and an ensemble constructed using a single model (HadCM3) with multiple parameter perturbations (THC-QUMP). These two ensembles allow us to assess the contribution that both structural and parameter variations across models make to the total uncertainty and to begin to attribute sources of uncertainty in projected changes. We find that parameter uncertainty is an major source of uncertainty in certain aspects of Arctic climate. But also that uncertainties in the mean climate state in the 20th century, most notably in the northward Atlantic ocean heat transport and Arctic sea ice volume, are a significant source of uncertainty for projections of future Arctic change. We suggest that better observational constraints on these quantities will lead to significant improvements in the precision of projections of future Arctic climate change."
Citation: Daniel L. R. Hodson, Sarah P. E. Keeley, Alex West, Jeff Ridley, Ed Hawkins and Helene T. Hewitt, Climate Dynamics, 2012, DOI: 10.1007/s00382-012-1512-z.
Variation of NO2 and NOx concentrations between and within 36 European study areas
Abstract:"The ESCAPE study (European Study of Cohorts for Air Pollution Effects) investigates long-term effects of exposure to air pollution on human health in Europe. This paper documents the spatial variation of measured NO2 and NOx concentrations between and within 36 ESCAPE study areas across Europe. In all study areas NO2 and NOx were measured using standardized methods between October 2008 and April 2011. On average, 41 sites were selected per study area, including regional and urban background as well as street sites. The measurements were conducted in three different seasons, using Ogawa badges. Average concentrations for each site were calculated after adjustment for temporal variation using data obtained from a routine monitor background site. Substantial spatial variability was found in NO2 and NOx concentrations between and within study areas; 40% of the overall NO2 variance was attributable to the variability between study areas and 60% to variability within study areas. The corresponding values for NOx were 30% and 70%. The within-area spatial variability was mostly determined by differences between street and urban background concentrations. The street/urban background concentration ratio for NO2 varied between 1.09 and 3.16 across areas. The highest median concentrations were observed in Southern Europe, the lowest in Northern Europe. In conclusion, we found significant contrasts in annual average NO2 and NOx concentrations between and especially within 36 study areas across Europe. Epidemiological long-term studies should therefore consider different approaches for better characterization of the intra-urban contrasts, either by increasing of the number of monitors or by modelling."
Citation: Josef Cyrys et al., Atmospheric Environment Volume 62, December 2012, Pages 374–390, http://dx.doi.org/10.1016/j.atmosenv.2012.07.080.
Ranges of small mammals extended northwards during Paleocene-Eocene Thermal Maximum
Abstract: "An abrupt global warming event marks the Paleocene-Eocene boundary, known as the Paleocene-Eocene Thermal Maximum (PETM). The event is distinguished in the strata globally by a significant negative excursion of δ13C ratio values. The response of the terrestrial biota to the abrupt climatic change has been well studied in northern Wyoming in the Bighorn Basin, where it has been observed that the mammalian fauna during the global warming event is represented by smaller, but morphologically similar species to those found later in the Eocene. Various hypotheses have been proposed to explain the observation smaller body sizes during the global warming event. In this article, evidence is presented to support the hypothesis that the observed body size decrease during the PETM was influenced by the appearance of smaller southern species who extended their geographic range northward during the abnormal global warming event. Using disperse organic carbon isotopic ratios of bulk sediment, the negative excursion of δ13C was located in the Piceance Creek Basin of western Colorado, 400 kilometers to the south of the Bighorn Basin. Below the stratigraphic level marking the negative carbon excursion in the Piceance Creek Basin are five specimens of the phenacodontid mammal (Ectocion parvus), a diminutive species of the genus Ectocion restricted to the basal Eocene (Wa-0 Biozone) in northern Wyoming. The five specimens of Ectocion parvus are associated with a late Paleocene (Clarkforkian) mammalian fauna in Colorado, implying that the diminutive species extended its geographic range northward during the global warming event. This evidence supports biogeographic models that assume poleward biogeographic shifts during global warming events, and will have modern day implications for the conservation of species as global temperatures rise in the near future."
Citation: Benjamin John Burger, Palaeogeography, Palaeoclimatology, Palaeoecology, http://dx.doi.org/10.1016/j.palaeo.2012.09.008.
Intermediate Atlantic water in Arctic Ocean was exceptionally warm during 2000s
Abstract: "This analysis evaluates the thermal state of the intermediate (depth range: 150–900m) Atlantic Water (AW) of the Arctic Ocean, beginning in the 1950s and with particular focus on the transition from the 1990s to the 2000s and on changes during the 2000s. Using an extensive array of observations, we document AW warming trends across various time scales and demonstrate that the 2000s were exceptionally warm, with no analogy since the 1950s nor probably in the history of instrumental observations in the Arctic Ocean. Warming in the recent decade was dominated by a warm AW pulse in addition to the underlying trend. Since 1997, the Canadian Basin experienced faster warming rate compared with the Eurasian Basin. The relative role of the AW warmth in setting the net energy flux to, and mass balance of the Arctic sea ice is still under debate. Additional carefully orchestrated field experiments are required in order to address this question of on-going Arctic climate change."
Citation: Igor V. Polyakov, Andrey V. Pnyushkov, and Leonid A. Timokhov, Journal of Climate 2012, doi: http://dx.doi.org/10.1175/JCLI-D-12-00266.1.
How clouds and precipitation affect North America summer temperature?
Abstract: "In North America (NA), trends in summer surface air temperatures vary on decadal time scales, and some regions have temperature trends that exhibit a lack of warming in 1982-2009. From a surface energy balance perspective, the summer mean daily maximum temperature change can be affected by changes in solar heating that is associated with cloud cover change, and changes in surface evaporative cooling due to different precipitation and land surface wetness, but little is known about regional cloud cover and precipitation feedbacks to decadal temperature trends. Changes in cloudiness and precipitation and their connections with summer mean daily maximum temperature variations in NA were investigated using observation-based products of temperature and precipitation and satellite-derived cloud cover and radiation products. Results show that summer mean daily maximum temperature variance is largely explained by changes in cloud cover and precipitation. Cloud cover effect dominates at the high and middle latitudes of NA and precipitation is a more dominant factor in the southern United States. The results indicate that cloud cover is either the major indicator of the summer mean daily maximum temperature changes (the effect) or the important local factor influencing the changes (the cause). Cloud cover is negatively correlated with mean daily maximum temperature variation in spring and autumn at the middle latitudes of NA, but not at the high latitudes."
Citation: Qiuhong Tang, Guoyong Leng, Journal of Climate 2012, doi: http://dx.doi.org/10.1175/JCLI-D-12-00225.1.
Some other studies from last week
CLASSIC OF THE WEEK: Langley & Abbot (1900)
Abstract: No abstract. Among other things, gives historical view on solar spectrum research.
Citation: Langley, S., Abbot, C., Annals of the Astrophysical Observatory of the Smithsonian Institution, vol. 1, pp.7-21.
This is a cross-post from AGW Observer. When each paper is published, it is notified in AGW Observer Facebook page and Twitter page. At least some of these are also retweeted in Skeptical Science 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.