1488 D. Swingedouw et al.: Mechanisms for European summertemperature response to solar forcing
is a complex flux that couples both the energy and water bud- get of the soil.
The uncertainty for the summer evapotranspiration re- sponse of models participating in IPCC-AR4 necessitates evaluating their sensitivity to change in radiative forcing for past periods over sufficiently long time scale. Using recon- struction of the last few decades is a possibility, but analysing longer time scale will certainly help to filter out the signa- ture of internal climate variability. The last millennium, with well-documented variations in solar forcing (although uncer- tainties remain concerning its amplitude) appears to be an in- teresting candidate. Hunt (2006) actually shows that climate variability over this period could not be explained only by the internal variability of a climate model, but needs exter- nal forcing. Hegerl et al. (2011) confirm the importance of external forcing for the temperature variability over Europe for the last 500 yr. They also show that these forcings are mainly detectable in winter and less in summer, notably be- cause dynamics are involved in winter and not only pure local radiative forcing. Moreover, they question the detectability of solar forcing in summer over this 500-yr time frame.
are scarce such that this area is under-represented in global temperature reconstructions. To fill this lack of knowledge and identify the most important processes influencing cli- mate variability, this study presents the first summer tem- perature reconstruction for eastern Canada based on a mil- lennial oxygen isotopic series (δ 18 O) from tree rings. For this purpose, we selected 230 well-preserved subfossil stems from the bottom of a boreal lake and five living trees on the lakeshore. The sampling method permitted an annually re- solved δ 18 O series with a replication of five trees per year. The June to August maximal temperature of the last mil- lennium has been reconstructed using the statistical rela- tion between Climatic Research Unit (CRU TS3.1) and δ 18 O data. The resulting millennial series is marked by the well- defined Medieval Climate Anomaly (MCA; AD 1000–1250), the Little Ice Age (AD 1450–1880) and the modern period (AD 1950–2010), and an overall average cooling trend of − 0.6 ◦ C millennium − 1 . These climatic periods and climatic low-frequency trends are in agreement with the only recon- struction available for northeastern Canada and others from nearby regions (Arctic, Baffin Bay) as well as some remote regions like the Canadian Rockies or Fennoscandia. Our tem- perature reconstruction indicates that the Medieval Climate Anomaly was characterized by a temperature range similar to the one of the modern period in the study region. How- ever, the temperature increase during the last 3 decades is one of the fastest warming observed over the last millennium
der (AD 1600–1650) and Spörer (AD 1410–1480) minima (Fig. 6). A simple re-sampling method involving 1000 iter- ations of re-sampling (bootstrapped) has demonstrated that the low temperature periods were always associated to low solar radiation periods (p < 0.05). Proposing that solar radia- tion represents an important control on temperature in north- eastern Canada is in agreement with the hypothesis that the solar forcing was important during the last millennium (AD 1000 to ∼ 1900), except during the modern period (Breit- enmoser et al., 2012; Keller, 2004), implying that recent an- thropogenic impact is the main control at that time. However, even i-STREC is not significantly influenced by volcanism, as determined by superimposed epoch analysis (results not shown), the possibility that successive strong volcanic erup- tions combined with solar minima could have contributed to the important LIA cooling in Northeastern Canada cannot be discarded. Strong eruptions and solar minima coincide dur- ing the Maunder minimum with the Kuwae eruption, and the Dalton minimum with the unknown (1809), Tambora (1815) and Cosiguïna (1835) eruptions. The role of coinciding natu- ral forcings is also invoked in other paleoclimatic studies that have compared Northern Hemisphere reconstructions with solar radiation series (e.g., Bard et al., 2006; Breitenmoser et al., 2012; Crowley, 2000; Lean et al., 1995; Shindell et al., 2003). These studies have shown that temperature changes were largely due to solar forcing alone during the first part of the last millennium, and to volcanic and solar forcings (i.e, Breitenmoser et al., 2012), or to volcanic eruptions (i.e., Crowley et al., 2000; Keller et al., 2004) during the end of the LIA (after 1600). In addition, Tingley et al. (2014) have demonstrated, by analyzing the ring density in trees grow- ing at high latitude, that the trees recorded not only volcanic eruptions but also variations in light intensity. This finding indicates that both isotopes and density of trees can record changes in solar radiations.
both timing (ca. 110 years, limited by our sampling tech- nique) and amplitude of change (3 ˚C).
The HTM lasted between 11 and 5k cal a BP in the Northern Hemisphere, but with many regional variations (Renssen et al., 2009). Based on pollen data from sites in north-western Quebec, Viau and Gajewski (2009) highlighted high temperatures between 6 and 2k cal a BP. Our results show summer temperatures higher than or similar to today between ca. 8.3 and 4.9k cal a BP, but with a sharp decline around ca. 6.5k cal a BP. Our reconstruction matches paleoclimate records obtained from the Arctic (GISP2 ice core; Kobashi et al., 2010), from pollen across north-eastern America (Viau et al., 2006) and from a chironomid record on Baffin Island (Axford et al., 2009) (Fig. 4A). The increase in temperature (þ2–3 ˚C in three samples at the beginning of the record) was similarly recorded in the ice core (þ3 ˚C) and from Baffin Island (þ4 ˚C) (Fig. 4a). However, the combined pollen records registered an increase in temperature of about only 1 ˚C (Viau et al., 2006). This could be due to the merging of various fossil records across north-eastern Canada. Stacking of records of different amplitudes at many locations, as per Viau et al. (2006), decreases the average variation. Another reason for differences in amplitude is the use of different models to infer climate. The modern analogue technique generally provides changes of much lower amplitude than the weighted average method used here (Birks, 2003). The amplitude of change has been shown to reach 5 ˚C at the highest latitudes, between 2.5 and 5 ˚C in our study region, and smaller amplitudes at lower latitudes (Renssen et al., 2012). Thus, the amplitude of change reconstructed by chironomids at Lac Aurelie seems to be plausible. Further- more, the decrease in temperature from the late Holocene (4.5–1.5k cal a BP) could be the result of the cold and wet Neoglacial period (Viau and Gajewski, 2009).
Abstract. Climatic reconstructions for northeastern Canada are scarce such that this area is under-represented in global temperature reconstructions. To fill this lack of knowledge and identify the most important processes influencing cli- mate variability, this study presents the first summer tem- perature reconstruction for eastern Canada based on a mil- lennial oxygen isotopic series (δ 18 O) from tree rings. For this purpose, we selected 230 well-preserved subfossil stems from the bottom of a boreal lake and five living trees on the lakeshore. The sampling method permitted an annually re- solved δ 18 O series with a replication of five trees per year. The June to August maximal temperature of the last mil- lennium has been reconstructed using the statistical rela- tion between Climatic Research Unit (CRU TS3.1) and δ 18 O data. The resulting millennial series is marked by the well- defined Medieval Climate Anomaly (MCA; AD 1000–1250), the Little Ice Age (AD 1450–1880) and the modern period (AD 1950–2010), and an overall average cooling trend of
The use of a different data set also raises important methodo- logical questions. Compared to precipitation recorded from 1993 to 2011, the hypothesis of stationarity used by Bernard et al. (2013)
is on shaky ground for temperature maxima over the period 1950 – 2005. The trend effect is removed from the observed and simu- lated temperatures before computing our distance between time series of maxima, thus explicitly focusing on spatially analyzing temperature maxima patterns that result from internal variability of the climate system. This approach provides complements to the large number of studies that have focused on changes in absolute temperature extremes over this time period in climate model ensembles (e.g., Kharin et al., 2007 ; IPCC, 2012 ; Sillmann et al., 2013 ).
2 Laboratoire de M´et´eorologie Dynamique/IPSL, 4 Place Jussieu, 75005 Paris, France
3 EDF, D´epartement M´ecanique des Fluides, Energies et Environnement, 78401 Chatou, France
Received: 17 September 2007 – Revised: 4 April 2008 – Accepted: 4 April 2008 – Published: 6 May 2008
Abstract. Extreme Value Theory (EVT) is a useful tool to describe the statistical properties of extreme events. Its un- derlying assumptions include some form of temporal station- arity in the data. Previous studies have been able to treat long-term trends in datasets, to obtain the time dependence of EVT parameters in a parametric form. Since there is also a dependence of surface temperature and precipitation to weather patterns obtained from pressure data, we deter- mine the EVT parameters of those meteorological variables over France conditional to the occurrence of North Atlantic weather patterns in the summer. We use a clustering algo- rithm on geopotential height data over the North Atlantic to obtain those patterns. This approach refines the straightfor- ward application of EVT on climate data by allowing us to assess the role of atmospheric variability on temperature and precipitation extreme parameters. This study also investi- gates the statistical robustness of this relation. Our results show how weather regimes can modulate the different be- havior of mean climate variables and their extremes. Such a modulation can be very different for the mean and extreme precipitation.
growing season, and warm temperatures during this period can promote earlier snowmelt and more rapid warming of soils, thereby increasing the growing sea- son length and resulting in faster leaf, shoot, and stem growth (Körner 1998, Peterson & Peterson 2001, Des - lauriers et al. 2003). In contrast, cold nighttime temper- atures in summer not only increase the frequency of frost rings and missing rings, but can also limit the growth of roots and their function in water uptake (Körner & Paulsen 2004). These negative climatic ef - fects may limit cambial activity by affecting the photo- synthetic rate and, hence, the possibility of radial expansion (DeLucia & Smith 1987). The climatic vari- able most strongly correlated to radial growth is also summertemperature for the east and northeast Tibetan Plateau (Bräuning 2006), the source region of the Yangtze River (Liang et al. 2008), the central Hengduan Mountains (Fan et al. 2009a, Li et al. 2011a), and the Western Sichuan Plateau (Shao & Fan 1999, Li et al. 2010, 2011b).
The spatial context is critical when assessing present-day climate anomalies, attributing them to potential forcings and making statements regarding their frequency and severity in a long-term perspective. Recent international initiatives have expanded the number of high-quality proxy-records and developed new statistical reconstruction methods. These advances allow more rigorous regional past temperature reconstructions and, in turn, the possibility of evaluating climate models on policy-relevant, spatio- temporal scales. Here we provide a new proxy-based, annually-resolved, spatial reconstruction of the European summer (June–August) temperature ﬁelds back to 755 CE based on Bayesian hierarchical modelling (BHM), together with estimates of the European mean temperature variation since 138 BCE based on BHM and composite-plus-scaling (CPS). Our reconstructions compare well with independent instrumental and proxy-based temperature estimates, but suggest a larger amplitude in summertemperature variability than previously reported. Both CPS and BHM reconstructions indicate that the mean 20th century European summertemperature was not signiﬁcantly different from some earlier centuries, including the 1st, 2nd, 8th and 10th centuries CE. The 1st century (in BHM also the 10th century) may even have been slightly warmer than the 20th century, but the difference is not statistically signiﬁcant. Comparing each 50 yr period with the 1951–2000 period reveals a similar pattern. Recent summers, however, have been unusually warm in the context of the last two millennia and there are no 30 yr periods in either reconstruction that exceed the mean average European summertemperature of the last 3 decades (1986–2015 CE). A comparison with an ensemble of climate model simulations suggests that the reconstructed European summertemperature variability over the period 850–2000 CE reﬂects changes in both internal variability and external forcing on multi-decadal time-scales. For pan-European temperatures we ﬁnd slightly better agreement between the reconstruction and the model simulations with high-end estimates for total solar irradiance. Temperature differences between the medieval period, the recent period and the Little Ice Age are larger in the reconstructions than the simulations. This may indicate inﬂated variability of the reconstructions, a lack of sensitivity and processes to changes in external forcing on the simulated European climate and/or an underestimation of internal variability on
The 21st century projections of summer Arctic sea ice are now available from the most recent effort of coupled model intermodel comparison, CMIP5. Here we consider 29 models available to date, starting from from the principle that none of the available CMIP5 models should be dismissed prior to the analysis (e.g. Arzel et al., 2006). Noticing a consider- able spread in the summer sea ice simulations over the 21st century, we raise the question of model selection as an op- portunity to reduce these uncertainties. In a first step, we find that the CMIP5 projected changes in September sea ice ex- tent (SSIE) with respect to their own 1979–2010 climatology are linked in a complicated manner to the 1979–2010 char- acteristics of their sea ice cover, owing to an acceleration of the trends (and thus larger changes) in SSIE, which occurs at different times during the 21st century, but at a mean SSIE of ∼ 2–4 million km 2 . Nonetheless, the year at which SSIE drops below a certain value correlates well with the 1979– 2010 sea ice properties. This supports the idea that a reduc- tion of spread through model selection is still possible.
11th Canadian neutron scattering summer school Yamani, Zahra-Sadat (Zahra)
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I also contacted Rogers Cable 9 who asked for my e-mail address and they sent me the form to fill out the PSA. It can only be up to 6 lines in length or 150 characters, so a lot shorter than the PSA that I used for radio.
I also placed a PSA in the Evening Telegram’s GoGuide, which is in Thursday’s issue of the paper, this is free and all you have to do is e-mail the telegram. This PSA brought in a lot of people especially locals. I only put it in three issues of it in the paper in August, so maybe next summer start off earlier and you will definitely get a lot more calls.
Cyanobacterial blooms in Wallonia during the summer of 2019
W.H.R. Van Hassel 1,2 , B. Huybrechts 1 , M. Andjelkovic 2 , N. Burlion 3 , A. Wilmotte 4
1 Organic contaminants and additives, Sciensano, Belgium; 2 Risk and health impact assessment,
Decrease in soil moisture is a drought indicator more particularly associated with agricultural droughts [ 13 ]. Thus, direct investigations of the linkage between soil moisture and climate factors aid in finding key factors that control drought. Several factors, such as temperature, precipitation, solar radiation, and atmospheric CO 2 concentration, regulate soil moisture [ 14 ]. Among these factors, change in precipitation has been hypothesized to impose a first-order control on variation in soil moisture at seasonal and annual scales [ 15 ]. However, the relationship between precipitation change and soil moisture has not been adequately quantified, because most previous studies focused mainly on responses of soil moisture to precipitation amount. Change in precipitation frequency is also one of the most important characteristics in current climate change [ 10 , 12 , 16 ], and has been expected to significantly affect hydrological and carbon cycles [ 17–19 ], but very few studies have investigated the influence of precipitation frequency on soil moisture [ 20 ] due to the lack of long-term observation data. In this study, we use summer soil moisture measurement data to explore the change in summer soil moisture in China from 1981 to 2002 and its relationships with precipitation through considering both precipitation amount and frequency.