AGW Observer

Observations of anthropogenic global warming

New research from last week 12/2011

Posted by Ari Jokimäki on March 28, 2011

Here is the new research published last week. I’m not including everything that was published but just some papers that got my attention. Those who follow my Facebook page (and/or Twitter) have already seen most of these, as I post these there as soon as they are published. Here, I’ll just put them out in one batch. Sometimes I might also point out to some other news as well, but the new research will be the focus here. Here’s the archive for the news of previous weeks. By the way, if this sort of thing interests you, be sure to check out A Few Things Illconsidered, they have a weekly posting containing lots of links to new research and other climate related news. Planet 3.0 also reports new research.

Published last week:

Alpine aquatic species threatened by glacier loss

Climate change links fate of glaciers and an endemic alpine invertebrate – Muhlfeld et al. (2011) “Climate warming in the mid- to high-latitudes and high-elevation mountainous regions is occurring more rapidly than anywhere else on Earth, causing extensive loss of glaciers and snowpack. However, little is known about the effects of climate change on alpine stream biota, especially invertebrates. Here, we show a strong linkage between regional climate change and the fundamental niche of a rare aquatic invertebrate—the meltwater stonefly Lednia tumana—endemic to Waterton-Glacier International Peace Park, Canada and USA. L. tumana has been petitioned for listing under the U.S. Endangered Species Act due to climate-change-induced glacier loss, yet little is known on specifically how climate impacts may threaten this rare species and many other enigmatic alpine aquatic species worldwide. During 14 years of research, we documented that L. tumana inhabits a narrow distribution, restricted to short sections (~500 m) of cold, alpine streams directly below glaciers, permanent snowfields, and springs. Our simulation models suggest that climate change threatens the potential future distribution of these sensitive habitats and the persistence of L. tumana through the loss of glaciers and snowfields. Mountaintop aquatic invertebrates are ideal early warning indicators of climate warming in mountain ecosystems. Research on alpine invertebrates is urgently needed to avoid extinctions and ecosystem change.” Clint C. Muhlfeld, J. Joseph Giersch, F. Richard Hauer, Gregory T. Pederson, Gordon Luikart, Douglas P. Peterson, Christopher C. Downs and Daniel B. Fagre, Climatic Change, DOI: 10.1007/s10584-011-0057-1.

Geoengineering proposals are problematic – a review

A review of climate geoengineering proposals – Vaughan & Lenton (2011) “Climate geoengineering proposals seek to rectify the current radiative imbalance via either (1) reducing incoming solar radiation (solar radiation management) or (2) removing CO2 from the atmosphere and transferring it to long-lived reservoirs (carbon dioxide removal). For each option, we discuss its effectiveness and potential side effects, also considering lifetime of effect, development and deployment timescale, reversibility, and failure risks. We present a detailed review that builds on earlier work by including the most recent literature, and is more extensive than previous comparative frameworks. Solar radiation management propsals are most effective but short-lived, whilst carbon dioxide removal measures gain effectiveness the longer they are pursued. Solar radiation management could restore the global radiative balance, but must be maintained to avoid abrupt warming, meanwhile ocean acidification and residual regional climate changes would still occur. Carbon dioxide removal involves less risk, and offers a way to return to a pre-industrial CO2 level and climate on a millennial timescale, but is potentially limited by the CO2 storage capacity of geological reservoirs. Geoengineering could complement mitigation, but it is not an alternative to it. We expand on the possible combinations of mitigation, carbon dioxide removal and solar radiation management that might be used to avoid dangerous climate change.” Naomi E. Vaughan and Timothy M. Lenton, Climatic Change, DOI: 10.1007/s10584-011-0027-7.

Primate reproduction decreases with global warming

Birth seasonality and offspring production in threatened neotropical primates related to climate – Wiederholt & Post (2011) “Given the threatened status of many primate species, the impacts of global warming on primate reproduction and, consequently, population growth should be of concern. We examined relations between climatic variability and birth seasonality, offspring production, and infant sex ratios in two ateline primates, northern muriquis and woolly monkeys. In both species, the annual birth season was delayed by dry conditions and El Niño years, and delayed birth seasons were linked to lower birth rates. Additionally, increased mean annual temperatures were associated with lower birth rates for northern muriquis. Offspring sex ratios varied with climatic conditions in both species, but in different ways: directly in woolly monkeys, and indirectly in northern muriquis. Woolly monkeys displayed an increase in the proportion of males among offspring in association with El Niño events, whereas in northern muriquis, increases in the proportion of males among offspring were associated with delayed onset of the birth season, which itself was related, although weakly, to warm, dry conditions. These results illustrate that global warming, increased drought frequency, and changes in the frequency of El Niño events could limit primate reproductive output, threatening the persistence and recovery of ateline primate populations.” Ruscena Wiederholt, Eric Post, Global Change Biology, DOI: 10.1111/j.1365-2486.2011.02427.x.

Danish forest has increased its carbon uptake

Increasing net CO2 uptake by a Danish beech forest during the period from 1996 to 2009 – Pilegaard et al. (2011) “The exchange of CO2 between the atmosphere and a beech forest near Sorø, Denmark, was measured continuously over 14 years (1996–2009). The simultaneous measurement of many parameters that influence CO2 uptake makes it possible to relate the CO2 exchange to recent changes in e.g. temperature and atmospheric CO2 concentration. The net CO2 exchange (NEE) was measured by the eddy covariance method. Ecosystem respiration (RE) was estimated from nighttime values and gross ecosystem exchange (GEE) was calculated as the sum of RE and NEE. Over the years the beech forest acted as a sink of on average of 157 g C m−2 yr−1. In one of the years only, the forest acted as a small source. During 1996–2009 a significant increase in annual NEE was observed. A significant increase in GEE and a smaller and not significant increase in RE was also found. Thus the increased NEE was mainly attributed to an increase in GEE. The overall trend in NEE was significant with an average increase in uptake of 23 g C m−2 yr−2. The carbon uptake period (i.e. the period with daily net CO2 gain) increased by 1.9 days per year, whereas there was a non significant tendency of increase of the leafed period. This means that the leaves stayed active longer. The analysis of CO2 uptake by the forest by use of light response curves, revealed that the maximum rate of photosynthetic assimilation increased by 15% during the 14-year period. We conclude that the increase in the overall CO2 uptake of the forest is due to a combination of increased growing season length and increased uptake capacity. We also conclude that long time series of flux measurements are necessary to reveal trends in the data because of the substantial inter-annual variation in the flux.” Kim Pilegaard, Andreas Ibrom, Michael S. Courtney, Poul Hummelshøj and Niels Otto Jensen, Agricultural and Forest Meteorology, doi:10.1016/j.agrformet.2011.02.013.

Younger Dryas onset is still a mystery

The Mysterious Onset Of The Younger Dryas – Fiedel (2011) “The 1300-year-long Younger Dryas cold reversal (12,900-11,600 cal BP) is seen most clearly in Greenland ice cores. Contemporaneous changes of climate and environment in more southerly regions were variably expressed. The precise timing of the abrupt Younger Dryas onset is still uncertain. It was linked to a sudden increase in 14C manifest as a “cliff” where 14C dates drop from 11,000 to 10,600 radiocarbon years BP within a century of real time, followed by a long plateau. Changes in ocean and/or atmospheric circulation or solar radiation, and even a comet impact have been proposed as triggers, but the abruptness and severity of YD onset still elude explanation.” S J Fiedel, Quaternary International, doi:10.1016/j.quaint.2011.02.044.

Mixture of divergence and climatic signals in trees of Tibet

Dynamic relationships between Picea crassifolia growth and climate at upper treeline in the Qilian Mts., Northeast Tibetan Plateau, China – Zhang et al. (2011) “Knowledge of the spatial pattern and temporal relationships between tree-growth and climatic factors are important not only for the projection of forest growth under varying climate but for dendroclimatology in general. Here, we systematically investigated tree-growth climate relationships of Picea crassifolia at upper treeline in the Qilian Mts., northwestern China. 297 trees from eleven sites, covering a large part of the natural range of this species, show increasing and partly divergent correlations with temperature in the most recent decades. The dominant signal at all sites was a strengthening of negative correlations of annual radial growth with summer temperature. In a subset of trees at six sites, a strengthening positive correlation with summer temperatures existed as well. Wetter and high altitude sites tended to show a higher percentage of trees that are positively correlated with warming temperatures, indicating that some individuals there may take advantage of warmer conditions. Divergent responses between the two sub-populations clustered by their response to climate factor were significantly stronger in the last 30 years compared to earlier time slices. In the same time frame, hydrothermal conditions of the investigation area changed to a drier and warmer combination. Drought conditions, most likely affecting the radial growth of most P. crassifolia, have been intensifying over time and expanding spatially from the middle Qilian Mts. to most of our study area during the last half century. While explanations such as methodological effects due to trend removal or human disturbance at the sampling sites might be able to explain the result at single sites, the spatial and temporal co-occurrence of large scale changes in climate and tree growth suggests a causal link between them.” Yongxiang Zhang, Xuemei Shao and Martin Wilmking, Dendrochronologia, 2011, doi:10.1016/j.dendro.2010.11.001.

Winter warming events cause damage to Arctic plants

Impacts of multiple extreme winter warming events on sub-Arctic heathland: phenology, reproduction, growth, and CO2 flux responses – Bokhorst et al. (2011) “Extreme weather events can have strong negative impacts on species survival and community structure when surpassing lethal thresholds. Extreme, short-lived, winter warming events in the Arctic rapidly melt snow and expose ecosystems to unseasonably warm air (for instance, 2–10°C for 2–14 days) but upon return to normal winter climate exposes the ecosystem to much colder temperatures due to the loss of insulating snow. Single events have been shown to reduce plant reproduction and increase shoot mortality, but impacts of multiple events are little understood as are the broader impacts on community structure, growth, carbon balance and nutrient cycling. To address these issues, we simulated week-long extreme winter warming events -using infrared heating lamps and soil warming cables- for three consecutive years in a sub-arctic heathland dominated by the dwarf shrubs Empetrum hermaphroditum, Vaccinium vitis-idaea (both evergreen) and V. myrtillus (deciduous). During the growing seasons after the 2nd and 3rd winter event, spring bud burst was delayed by up to a week for E. hermaphroditum and V. myrtillus, and berry production reduced by 11–75% and 52–95% for E. hermaphroditum and V. myrtillus respectively. Greater shoot mortality occurred in E. hermaphroditum (up to 52%), V. vitis-idaea (51%), and V. myrtillus (80%). Root growth was reduced by more than 25% but soil nutrient availability remained unaffected. Gross primary productivity was reduced by more than 50% in the summer following the 3rd simulation. Overall, the extent of damage was considerable, and critically plant responses were opposite in direction to the increased growth seen in long-term summer warming simulations and the ‘greening’ seen for some arctic regions. Given the Arctic is warming more in winter than summer, and extreme events are predicted to become more frequent, this generates large uncertainty in our current understanding of arctic ecosystem responses to climate change.” S. Bokhorst, J. W. Bjerke, L. E. Street, T. V. Callaghan, G. K. Phoenix, Global Change Biology, 2011, DOI: 10.1111/j.1365-2486.2011.02424.x.

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