Society is vulnerable to extreme weather events and, by extension, to the human impact on future events. As climate changes weather patterns will change. The search is on for more effective methodologies to aid decision-makers both in mitigation to avoid climate change and in adaptation to changes. The traditional approach employs ensembles of climate model simulations, statistical bias correction, downscaling to the spatial and temporal scales relevant to decision-makers, and then translation into quantities of interest. The veracity of this approach cannot be tested, and it faces in-principle challenges. Alternatively, numerical weather prediction models in an altered climate setting can provide tailored naritives of high-resolution simulations of high-impact weather in a future climate. This Tales of Future Weather approach will aid in the interpretation of lower resolution simulations. Arguably, it potentially provides a complementary and more realistic and more physically consistent pictures of what future weather might look like.
Projections of future changes in weather extremes on the regional and local scale depend on a realistic representation of trends in extremes in regional climate models (RCMs). We have tested this assumption for moderate high temperature extremes (the annual maximum of the daily maximum 2 m temperature, T ann.max ). Linear trends in T ann.max from historical runs of 14 RCMs driven by atmospheric reanalysis data are compared with trends in gridded station data. The ensemble of RCMs significantly underestimates the observed trends over most of the north-western European land surface. Individual models do not fare much better, with even the best performing models underestimating observed trends over large areas. We argue that the inability of RCMs to reproduce observed trends is probably not due to errors in large-scale circulation. There is also no significant correlation between the RCM T ann.max trends and trends in radiation or Bowen ratio. We conclude that care should be taken when using RCM data for adaptation decisions.
In arctic tundra, large and small mammalian herbivores have substantial impacts on the vegetation community and consequently can affect the magnitude of carbon cycling. However, herbivores are often absent from modern carbon cycle models, partly because relatively few field studies focus on herbivore impacts on carbon cycling. Our objectives were to quantify the impact of 21 years of large herbivore and large and small herbivore exclusion on carbon cycling during peak growing season in a dry heath tundra community. When herbivores were excluded, we observed a significantly greater leaf area index as well as greater vascular plant abundance. While we did not observe significant differences in deciduous dwarf shrub abundance across treatments, evergreen dwarf shrub abundance was greater where large and small herbivores were excluded. Both foliose and fruticose lichen abundance were higher in the large herbivore, but not the small and large herbivore exclosures. Net ecosystem exchange (NEE) likewise indicated the highest carbon uptake in the exclosure treatments and lowest uptake in the control (CT), suggesting that herbivory decreased the capacity of dry heath tundra to take up carbon. Moreover, our calculated NEE for average light and temperature conditions for July 2017, when our measurements were taken, indicated that the tundra was a carbon source in CT, but was a carbon sink in both exclosure treatments, indicating removal of grazing pressure can change the carbon balance of dry heath tundra. Collectively, these findings suggest that herbivore absence can lead to changes in plant community structure of dry heath tundra that in turn can increase its capacity to take up carbon.
Symbiotic nitrogen fixation (SNF) by higher plants and their bacterial symbionts is a globally important input of nitrogen. Our understanding of the mechanisms that control SNF and the time‐scales over which they operate has been constrained by the limitations of the existing methods for measuring SNF. One method, Acetylene Reduction Assays by Cavity ring‐down laser Absorption Spectroscopy (ARACAS), seems promising, as it is highly sensitive and gives rapid, continuous, repeatable and real‐time measurements of nitrogenase activity. ARACAS has been used to study nitrogen fixation in lichens, mosses and asymbiotic bacteria, but adapting it to higher plants poses challenges because acetylene and ethylene can influence plant function. Here, we report modifications to ARACAS that allow it to be used on higher plants in an environmentally controlled incubation chamber. The modifications include lower concentrations of acetylene (2%) and ethylene and concurrent measurements of whole‐chamber CO2 exchange, H2O exchange and nitrogenase activity, linking nitrogenase activity to whole‐plant rates of photosynthesis and respiration. After propagating the error terms from all sources, we establish the following parameters of the method: (a) The detection limit of our method was 2–3 ppbv C2H4 per hour, although it rose substantially when we used tank‐derived acetylene, which has much higher ethylene contamination; (b) Repeated measures at a frequency of 3 days or longer did not diminish nitrogenase activity or photosynthesis, although daily measurements diminished nitrogenase activity; (c) This method can detect changes at time‐scales as short as seconds; (d) Continuous measurement of nitrogenase activity is maintained above 90% of the maximum rate for 7.0 ± 1.3 (M ± SD) hours. This method has the potential to improve our understanding of the controls over SNF, and therefore, how SNF and global nitrogen and carbon cycling are likely to be affected by global change.
The intensity and occurrence of extreme weather events are expected to change with climate change. This change necessitates adaptive responses to extreme events, which need to take into account different societal perspectives, in order to be robust. In this paper, we explore the perspectives of different social actors in the Netherlands with respect to extreme weather events and ways to adapt to these events. The paper reports on a set of 41 interviews, using the repertory grid technique. The results were analyzed, to identify (a) the perspectives that stakeholders hold as most important for adaptation to extreme weather events; (b) the determinants of differences in perspectives. We find six different perspectives, all of which prioritize different adaptive actions. Producing robust adaptive responses which include different perspectives is therefore not a straightforward matter and is likely to result in win-lose situations. Further, differences in perspectives were not closely related to different sectors the interviewees belonged to. Thus, the traditional approach of involving different sectors to discuss and produce adaptation measures may be too limiting and needs to be supplemented to involving actors with different perspectives. The level of concern and level of information influenced the ways interviewees perceive adaptation priorities for extreme weather events. Participation in information events does not always result in perceived need to prepare for extreme events, something that adaptation communication needs to take into account.
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