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Understanding the causes of past atmospheric methane (CH4) variability is important for characterizing the relationship between CH4, global climate and terrestrial biogeochemical cycling. Ice core records of atmospheric CH4 contain rapid variations linked to abrupt climate changes of the last glacial period known as Dansgaard-Oeschger (DO) events and Heinrich events (HE)1,2. The drivers of these CH4 variations remain unknown but can be constrained with ice core measurements of the stable isotopic composition of atmospheric CH4, which is sensitive to the strength of different isotopically distinguishable emission categories (microbial, pyrogenic and geologic)3-5. Here we present multi-decadal-scale measurements of δ13C-CH4 and δD-CH4 from the WAIS Divide and Talos Dome ice cores and identify abrupt 1‰ enrichments in δ13C-CH4 synchronous with HE CH4 pulses and 0.5‰ δ13C-CH4 enrichments synchronous with DO CH4 increases. δD-CH4 varied little across the abrupt CH4 changes. Using box models to interpret these isotopic shifts6 and assuming a constant δ13C-CH4 of microbial emissions, we propose that abrupt shifts in tropical rainfall associated with HEs and DO events enhanced 13C-enriched pyrogenic CH4 emissions, and by extension global wildfire extent, by 90-150%. Carbon cycle box modelling experiments7 suggest that the resulting released terrestrial carbon could have caused from one-third to all of the abrupt CO2 increases associated with HEs. These findings suggest that fire regimes and the terrestrial carbon cycle varied contemporaneously and substantially with past abrupt climate changes of the last glacial period.

Climate change is driving compositional shifts in ecological communities directly by affecting species and indirectly through changes in species interactions. For example, competitive hierarchies can be inversed when competitive dominants are more susceptible to climate change. The brown seaweed Fucus vesiculosus is a foundation species in the Baltic Sea, experiencing novel interactions with the invasive red seaweed Gracilaria vermiculophylla, which is known for its high tolerance to environmental stress. We investigated the direct and interactive effects of warming and co-occurrence of the two algal species on their performance, by applying four climate change-relevant temperature scenarios: 1) cooling ) 2 °C below ambient - representing past conditions), 2) ambient summer temperature (18 °C), 3) IPCC RCP2.6 warming scenario (1 °C above ambient), and 4) RCP8.5 warming (3 °C above ambient) for 30 days and two compositional levels (mono and co-cultured algae) in a fully-crossed design. The RCP8.5 warming scenario increased photosynthesis, respiration, and nutrients' uptake rates of mono- and co-cultured G. vermiculophylla while growth was reduced. An increase in photosynthesis and essential nutrients' uptake and, at the same time, a growth reduction might result from increasing stress and energy demand of G. vermiculophylla under warming. In contrast, the growth of mono-cultured F. vesiculosus significantly increased in the highest warming treatment (+3 °C). The cooling treatment (-2 °C) exerted a slight negative effect only on co-cultured F. vesiculosus photosynthesis, compared to the ambient treatment. Interestingly, at ambient and warming (RCP2.6 and RCP8.5 scenarios) treatments, both F. vesiculosus and G. vermiculophylla appear to benefit from the presence of each other. Our results suggest that short exposure of F. vesiculosus to moderate or severe global warming scenarios may not directly affect or even slightly enhance its performance, while G. vermiculophylla net performance (growth) could be directly hampered by warming.

AbstractEcosystem functioning is simultaneously affected by changes in community composition and environmental change such as increasing atmospheric carbon dioxide (CO2) and subsequent ocean acidification. However, it largely remains uncertain how the effects of these factors compare to each other. Addressing this question, we experimentally tested the hypothesis that initial community composition and elevatedCO2are equally important to the regulation of phytoplankton biomass. We full‐factorially exposed three compositionally different marine phytoplankton communities to two differentCO2levels and examined the effects and relative importance (ω2) of the two factors and their interaction on phytoplankton biomass at bloom peak. The results showed that initial community composition had a significantly greater impact than elevatedCO2on phytoplankton biomass, which varied largely among communities. We suggest that the different initial ratios between cyanobacteria, diatoms, and dinoflagellates might be the key for the varying competitive and thus functional outcome among communities. Furthermore, the results showed that depending on initial community composition elevatedCO2selected for larger sized diatoms, which led to increased total phytoplankton biomass. This study highlights the relevance of initial community composition, which strongly drives the functional outcome, when assessing impacts of climate change on ecosystem functioning. In particular, the increase in phytoplankton biomass driven by the gain of larger sized diatoms in response to elevatedCO2potentially has strong implications for nutrient cycling and carbon export in future oceans.

Climate change during the late Pleistocene is dominated by periodicities on millennial time scales as documented by ice cores and sedimentary marine and terrestrial records of global distribution. Interannual to decadal variations have also been demonstrated in dust concentrations in Greenland ice cores but there is lack of comparable detail in sedimentary records. An 8.5 m long multiproxy record from Lake Albano (central Italy) spanning the time interval between B15.0 and 28.0 cal kyr BP reveals a high temporal resolution window into climate change during the Last Glacial Maximum (LGM). Distinct warm/cold cycles of millennial to centennial duration indicate a major response of the lake to climate-induced environmental changes. Flickering interannual to interdecadal variations within these cycles are interpreted to reflect oscillations of the North Atlantic (NAO) implying shifts in temperature, wind strength, source of moisture and atmospheric circulation pattern. r 2004 Elsevier Ltd and INQUA. All rights reserved.

Energy is an essential ingredient of socio-economic development and economic growth. Renewable energy sources like wind energy is indigenous and can help in reducing the dependency on fossil fuels. Wind is the indirect form of solar energy and is always being replenished by the sun. Wind is caused by differential heating of the earth's surface by the sun. It has been estimated that roughly 10 million MW of energy are continuously available in the earth's wind. Wind energy provides a variable and environmental friendly option and national energy security at a time when decreasing global reserves of fossil fuels threatens the long-term sustainability of global economy. This paper reviews the wind resources assessment models, site selection models and aerodynamic models including wake effect. The different existing performance and reliability evaluation models, various problems related to wind turbine components (blade, gearbox, generator and transformer) and grid for wind energy system have been discussed. This paper also reviews different techniques and loads for design, control systems and economics of wind energy conversion system.

Abstract Agriculture in the Black Sea catchment is responsible for a considerable share of the area's total water withdrawal and the majority of its total water consumption. It therefore plays a key role in sustainable water resources management. However, in the future water resources will be exposed to climate change. This assessment aims at identifying the most vulnerable regions and to explain the reasons of this vulnerability. It is based on a combination of the well-known Driver–Pressure–State–Impact–Response framework (DPSIR) and the vulnerability concept as defined by the Intergovernmental Panel on Climate Change (IPCC). Three distinctive climate change scenarios are used to assess their impacts on water resources for agriculture: (1) an increase in temperature; (2) a decrease in precipitation; and (3) a combination of the first and second scenarios. The data for this assessment is derived from a SWAT model (Soil and Water Assessment Tool). The results show that the regions of the Black Sea catchment are impacted by climate change differently. Some countries benefit from climate change (e.g., Turkey, Ukraine, Romania, Moldova, Hungary, Bulgaria) while others will encounter considerably worse agro-climatic conditions in the future (e.g., Montenegro, Austria, Bosnia–Herzegovina). Additionally, natural plant growth conditions mostly improve due to more suitable temperature conditions. In contrast, the deteriorating agricultural conditions mainly result from a diminishing irrigation potential that is caused by reduced precipitation. The conclusion emphasises the important role of the legal framework as well as more sustainable agronomic practices and proposes improvements for future assessment methods in this research field.

The resilience of ecological communities is often defined by one or a few species that have disproportionately important roles influencing many other species in the community. This is true for some areas of the Mediterranean Sea that are characterized by large brown fucoid algae in the genus Cystoseira that form dense underwater forests structurally similar to the giant kelps of the Pacific. While shorter than the giant kelp, Cystoseira form dense underwater stands, contributing to the three‐dimensional complexity of the seascape (Fig. 1). These canopy‐forming seaweeds play a crucial role in primary production and nutrient cycling of temperate coastal ecosystems from the Mediterranean Sea to the Atlantic Ocean (Mineur et al., 2015) and act as ‘ecosystem engineers', providing food, nursery, and shelter for a rich associated biota. Our study highlighted potential disruptive effects of winter hot spells on reproductive timing, recruitment, and adult survival that could severely affect the persistence of Cystoseira populations. Because extreme climate episodes are increasing in intensity and frequency, implementing coordinated initiatives connecting centers for climate alerts and algologists may shed light on how these phenomena impact population dynamics of Cystoseira species, and help current attempts to restore algal forests.

Benthic suspension feeders in shallow waters develop in relation to the food availability and the variation of physical parameters giving rise to complex communities that act as a control factor on the plankton biomass. The aim of the work is to establish the role of the hydrozoan Eudendrium racemosum in the energy transfer from the plankton to the benthos in marine food chains of the North Adriatic Sea. This study highlighted that the hydroid biomass changed over time in relation to temperature and irradiance, and the highest abundance was observed during summer with about 400,000 polyps m-2 (about 19 g C m-2). The population suffered an evident summer decrease in relation to a peak of abundance of its predator, the nudibranch Cratena peregrina, whose adult specimens were able to eat up to 500 polyps day-1 and reached an abundance of 10 individuals m-2. The gut content analysis revealed that the hydroid diet was based on larvae of other benthic animals, especially bivalves and that the amount of ingested preys changed during the year with a peak in summer when it was estimated an average predation rate of 13.7 mg C m-2 day-1. In July, bivalves represented over 60 % of the captured items and about 18 mg C m-2 day-1. Values of biomass of E. racemosum are the highest ever recorded in the Mediterranean Sea, probably supported by the eutrophic conditions of the North Adriatic Sea. Moreover, our data suggest that settling bivalves provide the greater part of the energetic demand of E. racemosum.