Historical air photo missions in the Maritimes during the early 1920s: coverage, thematic scope, and utility 100 years later

The historical and technological developments of powered flight and aerial photography have early connections in the Maritimes. Following the Great War (1914-18), a series of pioneering survey missions were initiated by the Canada Air Board in the civilian domain. From a science perspective, the air photos offer a unique opportunity for the detection of environmental change at an unusual centennial time scale. The missions of the early 1920s initially relied on military surplus seaplanes and innovative camera equipment that yielded several thousand high-resolution vertical air photos. This paper is focussed on the scope and outcome of the first experiments carried out over Nova Scotia and New Brunswick between 1921 and 1925, prior to more systematic use for topographic mapping during the remainder of that decade. The research is based on archival records and partial reconstruction of the digitized air photos into image mosaics. Photo interpretation and comparison with recent high-resolution satellite imagery offer insights concerning land use and land cover changes, coastal dynamics, and transformation of urban, rural and industrial landscapes. Experience todate with these early air photos and mosaics of the Maritimes holds promise for examining similar aerial survey missions in other parts of Canada.

Holocene hydroclimatic variability in the Zanskar Valley, Northwestern Himalaya, India

A 1.3-m-long sediment core from the Penzi-la pass, Zanskar Valley, provides a record of hydroclimatic conditions and abrupt climate changes over short time scales since the mid-Holocene. These climatic changes of centennial time scale are crucial to understanding the hydroclimatic variability in northwestern (NW) Himalaya. Relatively higher δ13C values complemented by total organic carbon, loss on ignition, grain size parameters, and lower Rubidium/Strontium ratios during the Late Northgrippian imply that the area had a dry climate during the period from ~6200–4500 cal yr BP. Subsequently, a relatively stable hydroclimatic environment was experienced between ~4500 and 3400 cal yr BP. After ~3400 cal yr BP the multiproxy data show gradual strengthening of hydroclimatic conditions, however, this trend is interrupted by high-amplitude abrupt reversals (dry events) with a stepwise decreasing intensity at ~3300, 2600, 1700, and 400 cal yr BP. The two most important climatic events of the last millennia (i.e., Medieval Climate Anomaly and the Little Ice Age) were also recorded from the sedimentary archive. Overall, our data show a progressive increase in the moisture availability in the Zanskar Valley and are in agreement with the late Holocene climatic trends of central and western Himalaya.

Extreme sea levels in the context of climate change

<p>The objective of this study is to investigate how extreme sea levels are changing, at a centennial time scale, in the context of climate change. We focus on Brest tide gauge (France), one of the longest time series in the world. First observations were recorded in 1701, and hourly data have been registered continuously since 1846 with little gaps. These data have been  carefully processed, in order to ensure good quality, especially regarding the datum continuity (Pouvreau, 2008) and stability (Poitevin, 2019).</p><p>Here, we investigate the evolution of the storm surges over the last 170 years. We focus on the skew surge, defined as the difference between the maximum observed water level and the maximum predicted tidal level (taking into account the mean sea level rise). This parameter is directly linked to the atmosphere variations, and may be correlated with regional climate parameters, such as the North Atlantic Oscillation (Menéndez and Woodworth, 2010). But it is also correlated with the evolution of the storminess in the North Atlantic. One of the challenges is to separate the natural interannual variability of the sea level from the long term trends at a centennial time scale.</p><p>We will discuss the variability of the storm surges, in terms of changes in the 99th percentile and the 5-year return period level. Statistical analysis will be based on extreme values theory (e.g. Generalized Extreme Value distribution, General Pareto Distribution). Correlation with other parameters such as the significant wave height (from buoys) and the wind and storm tracks (from global reanalysis, e.g. ERA5 from ECMWF) will also be investigated.</p><p>References<br>Menéndez M., Woodworth P. L. (2010). Changes in extreme high water levels based on a quasi-global tide-gauge dataset. J Geophys Res 115:C10011.<br>Poitevin (2019). Variabilité du niveau marin relatif le long du littoral de Brest (France) par combinaison de méthodes géodésiques spatiales (altimétrie radar, InSAR et GPS). PhD thesis, University of La Rochelle.<br>Pouvreau N. (2008). Trois cents ans de mesures marégraphiques en France : outils, méthodes et tendances des composantes du niveau de la mer au port de Brest. PhD thesis, University of La Rochelle.<br><br><br></p><p> </p>

Δ14C and δ13C in Annual Tree-Ring Samples from Sequoiadendron Giganteum, AD 998–1510: Solar Cycles and Climate

ABSTRACTTime series of annual Δ14C and δ13C in tree rings ofSequoiadendron giganteum, AD 998–1510, are similar in form. The Δ14C series completes, with data of Stuiver and Braziunas (1993), a 957-yr time-series. Discrete Fourier transformation of detrended Δ14C reveals periods of 126, 91, 56, 17.6, 13.6, 10.4, and 7.1 yr. Non-random differences exist between decadal averages of theSequoiadendronΔ14C data and data of Stuiver and Becker (1993). Periods of 7–17 yr may correspond to Schwabe or related climatic cycles; these have 10–17-yr periods and amplitudes < 6‰ (AD 1100–1250), and periods near 7 yr with amplitudes up to 10‰ (AD 1380–1420). Abrupt increases in Δ14C are mainly less than 5‰, and do not constitute convincing evidence of increased14C production from supernovae or solar proton events. The δ13C time-series is likely to reflect climate change, and for centennial periodicity lags behind Δ14C by 20–40 yr (centennial time-scale) and 25–50 yr (millennial). Phase-shifts between solar luminosity and surface Δ14C are 125–175 yr and 20 yr for millennial and centennial cycles, respectively. The study suggests that strongest climate effects may therefore follow peak luminosity by 125–175 yr for millennial cycles and 20–40 yr for centennial cycles.

Physical processes of cooling and megadrought in 4.2 ka BP event: results from TraCE-21ka simulations

It is widely believed that multidecadal to centennial cooling and drought occurred from 4500 BP to 3900 BP, known as the 4.2 ka BP event that triggered the collapse of many cultures. However, whether this event was a global event or a regional event and what caused this event remain unclear. In this study, we investigated the spatiotemporal characteristics, the possible causes and the related physical processes of the event using a set of long-term climate simulations, including one all-forcing experiment and four single-forcing experiments. The results derived from the all-forcing experiment show that this event occurred over most parts of the Northern Hemisphere (NH), indicating that this event could have been a hemispheric event. The cooler NH and warmer Southern Hemisphere (SH) illustrate that this event could be related to the slowdown of the Atlantic Meridional Overturning Circulation (AMOC). The comparison between the all-forcing experiment and the single-forcing experiments indicates that this event was likely caused by internal variability. A positive North Atlantic Oscillation (NAO)-like pattern in the atmosphere (low troposphere) triggered a negative Atlantic Multidecadal Oscillation (AMO)-like pattern in the ocean, which then triggered a Circumglobal Teleconnection (CGT)-like wave train pattern in the atmosphere (high troposphere). The positive NAO-like pattern and the CGT-like pattern are the direct physical processes that led to the NH cooling and megadrought. The AMO-like pattern plays a bridge role in maintaining this barotropic structure in the atmosphere at a multidecadal-centennial time scale. Our work provides a global image and dynamic background to help better understand the 4.2 ka BP event.

Climate Change and Carbon Cycle Feedbacks

Climate and carbon cycle are tightly coupled on many time scales, from the interannual to the multimillennial. Observation always shows a positive feedback between climate and the carbon cycle: elevated atmospheric CO2 leads to warming, but warming is expected to further release of carbon to the atmosphere, enhancing the atmospheric CO2 increase. Earth system models do represent these climate–carbon cycle feedbacks, always simulating a positive feedback over the 21st century; that is, climate change will lead to loss of carbon from the land and ocean reservoirs. These processes partially offset the increases in land and ocean carbon sinks caused by rising atmospheric CO2. As a result, more of the emitted anthropogenic CO2 will remain in the atmosphere. There is, however, a large uncertainty on the magnitude of this feedback. Recent studies now help to reduce this uncertainty. On short, interannual, time scales, El Niño years record larger-than-average atmospheric CO2 growth rate, with tropical land ecosystems being the main drivers. These climate–carbon cycle anomalies can be used as emerging constraint on the tropical land carbon response to future climate change. On a longer, centennial, time scale, the variability of atmospheric CO2 found in records of the last millennium can be used to constrain the overall global carbon cycle response to climate. These independent methods confirm that the climate–carbon cycle feedback is positive, but probably more consistent with the lower end of the comprehensive models range, excluding very large climate–carbon cycle feedbacks.

Salt-marsh evolution at Northwick and Aust warths, Severn Estuary, UK: a case of constrained autocyclicity.

Historic maps, remote imagery and field surveys reveal that a terraced sequence of four salt marshes has arisen on a decadal-centennial time-scale over a frontage of about 4 km at Northwick and Aust warths exposed to westerly to northerly winds on the east bank of the Severn Estuary, UK. Except for the youngest marsh, at present very immature, each marsh built up through differential sedimentation from a mudflat until the outer zone reached a critical steepness; at that point wave-attack caused erosion that led to the rapid landward retreat of a bold, laterally extensive, marsh-edge cliff. This observed behaviour is consistent with previous models of autocyclic marshes, but evidence suggests that the extrinsic factor of medium-scale changes in wind-wave climate constrained the particular timing of marsh responses.