The extreme cold lasted for weeks, killing people, animals and trees. Wine in barrels and water in wells were frozen over.
In Venice the ice sheet was thick, and could bear the load of people, animals, barrels, carts or wagons transporting food supplies. For instance, for the year we found several local sources stating that the Lagoon and all canals were frozen over by an exceptionally cold wind from the North combined with a modest tidal range, and that it was possible to safely reach on foot the Giudecca, Murano and other islands transporting food and other supplies.
People walked in strict processional order to reach the hinterland and to stay on an already tested path, considered safe, without knowing that the repeated vibrations of each step were extremely dangerous for ice breaking. This means that the ice thickness exceeded 20 cm. The situation was described in a number of chronicles and other written sources, as well as in paintings that clearly show what happened Fig. People are crossing the ice sheet to reach the hinterland and transporting supplies.
The hinterland and the mountains in the background are covered with snow. A remarkable attenuation in the severity of winters was found in the 17 th century two GW followed by the 19 th no GW and 20 th centuries one GW. The most frequent occurrence of extreme winter was not coincident with the periods of minimum solar activity, when sunspots became rare and solar irradiation was lower. The intensity and duration of winds are the most critical factor in forming an ice sheet on the Lagoon waters.
The above results show that the severity of winter is related to meteorological blocking, but this weather situation was frequent during LIA. It is unclear why winter blocking is related to solar activity and the time lag between the two makes even weaker a justification of this relationship. However, when we have in addition the instrumental observations, VSW and GW are easily recognized on the daily series, but are often masked when monthly averages are considered. The reason is that the intense cold is a relatively short-term event that in some cases may be partitioned between two consecutive months.
In addition, the end of the cold period is generally followed by a warm wind, i. Sirocco, blowing from Africa, which tends to raise the monthly average. The situation is accentuated with regards to seasonal averages, because the contribution of a few weeks is diluted over three months.
The definition of winter severity, the averaging period or the way in which data are handled, are often crucial in defining the exceptionality of some events. These two event types, i. The comparison with other water bodies or other proxies might be misleading because it is based on a different definition or responding to other additional variables that are included in the process. In Venice, regular tide-gauge records began in and they provide evidence for relative sea-level rise i. Locally, sea level has been affected by some other factors, e.
To reconstruct sea level over recent centuries means to identify the thermal expansion of waters in response to climate change from the LIA to present-day global warming. However, the above estimates are based on the measurement of tides, the average high tide being 30 cm above MSL.
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The contribution of waves due to wind and traffic was not included. In the camera obscura the light beam penetrating from the objective was projected on an inclined mirror and reflected onto a glass located on the upper surface of the box, where a sheet of paper was placed making it possible to draw precise contour lines.
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The visibility of the pale reflected image was improved with a mobile screen on the top that shielded against external light. It operates like a modern reflex camera. The light beam white arrow from the objective O is projected on an inclined mirror M, visible for having removed the left side of the box and reflected onto a transparent glass surface on the upper surface of the box. On the top of the box, a mobile screen S shields the image from external light.
In historic palaces, the basement was made of big stones, decorations and several architectural features that make it easy to identify the exact level of the front of the algae. The above methodology was applied to all the available paintings in which buildings had a clearly visible algae belt and were unaffected by renovation works. The palace was reproduced with extreme precision and documents have been found suggesting that Veronese probably also used a camera obscura to improve the accuracy of his rederings. The Venetian palaces, with their stairs, offer a novel proxy and the possibility to verify the findings from the above paintings.
These palaces have secondary doors onto the narrow streets, but monumental doors and external water stairs face the canals Fig. Venice palaces were built on closely spaced wooden piles deeply implanted in sand and mud until they reached the underlying layer of hard clay MIOZZI, Under anoxic conditions, the wood remains almost unaffected by deterioration and biological attack. The building foundations and the water stairs remain on the implanted piles. Under normal conditions, water stairs had the necessary number of steps, with the lowest step being positioned on a vertical basement Fig.
The total run and total rise of water stairs was kept to the necessary minimum because the submerged part was useless, expensive and constituted a risk for boats. The water stairs were necessary for everyday life, and their use was possible with the assistance of two or more mooring piles that helped to avoid collision with the underwater steps and to allow boats to moor alongside while people unloaded supplies or guests jumped from the gondola to the emerging steps of the stairs. The mooring piles were implanted on the canal bottom just in front of the stair, and the emerging part was coloured like a flag for each family.
Today, sea-level rise has changed the distance from the usable steps and has forced most palaces to add a wooden wharf to facilitate boat docking Fig. A Grassi Palace, on the Canal Grande, with most of the water stair presently under water. There is no conclusive evidence of such behavior in response to the rapid warming of the last two decades, but simulations with climate models indicate that more pronounced warming like that predicted to occur by the end of the twenty-first century could serve to increase the frequency of drought episodes and the risk of irreversible desertification Rind et al.
Instrumental records are becoming long enough to show trends in climate, although the distinction between trends and longer cycles is never simple. The Little Ice Age set the stage for the global warming of the last century, which probably had both natural and anthropogenic causes Intergovernmental Panel on Climate Change, b.
A brief review of some of the main trends is provided here, showing that these trends often exhibit regional abruptness and are linked to modes of climate variability, again documenting the importance of instrumental records to the study of abrupt climate change. Most long instrumental records were initiated in the nineteenth and twentieth centuries. The central England temperature time series is one of the longest continuous instrumental climate records Figure 2.
Top figure shows summer and bottom figure shows winter. Temperature scale is in degrees Celcius. Data courtesy of P. Jones, University of East Anglia. Long cool periods, such as the summers throughout the nineteenth century, were punctuated by extreme events. The cold phases were known to have had important effects on human activity, as in the abrupt European cooling from the unusually warm s to the cold s.
Famine occurred across western Europe, especially in Ireland and France, where farmers who depended on wheat and potatoes were slow to adapt. Snow fell in July in northern New England, farming was disrupted, and crops failed.
The event might have spurred the westward migration of farmers from the thin soils of the hill farms of New Hampshire. There was severe drought in Brazil in Single volcanic eruptions often have a widespread cooling effect e.
Volcanic forcing also represents an experiment in which the response of global climate modes can be observed in great detail, helping understand how modes might respond to other forcings. The winter atmospheric circulation in the Northern Hemisphere has undergone some remarkable changes during the last several decades. Sea-level pressures over the Arctic have fallen by about 6 hPa Walsh et al.
Related circulation changes have favored mild winters over most of Russia, China and Japan, and drought over southern Europe and parts of the Middle East Hurrell, ; Thompson et al. Warming during the period has been concentrated in central and northern Asia and northwestern North America.
Retreating glaciers, warming permafrost, and decreasing sea-ice cover have been observed in Alaska, where temperatures increased abruptly in the late s, distinct from the post acceleration of globally averaged temperature rise. The patterns in these. There are indications of analogous trends in the Southern Hemisphere, in association with its annular mode Thompson et al. Several ideas have been put forth concerning the cause of those trends. Shindell et al. Indeed, similar trends have been simulated in an atmospheric model driven by increasing concentrations of greenhouse gases. It has also been suggested that stratospheric ozone depletion Volodin and Galin, and trends in sea-surface temperatures Rodwell et al.
Because favored patterns of variability tend to be highly sensitive to external forcing, it is indeed quite plausible that they can be changed in a number of ways.
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Fyfe et al. The trend has altered the distribution of deep convection over the North Atlantic Lilly et al. For example, the recovery of the stratospheric ozone layer from human-induced depletion during the twentieth century could be delayed by several decades Shindell et al. Global-average surface temperature records show two principal periods of warming during the twentieth century. The warming following has occurred widely, yet with regions of concentration in northern Asia and northwestern North America. Anthropogenic forcing is widely suspected to be a contributing cause Intergovernmental Panel on Climate Change, b.
The warming earlier in the century is less likely to be of anthropogenic origin, although this is an unsettled issue; solar and volcanic forcing may have played a role Delworth and Knutson, ; Stott et al. Global temperature has evolved very differently, in space, during the two warmings Figure 2. The earlier twentieth-century episode was concentrated in the far north. The warming seems to have appeared first in the Barents Sea; for example, in the records from Turuhansk, a city on the Yenisey River in northern Siberia. Sparse temperature records are supplemented by observations of a strong increase in ocean salinity and decrease in sea ice cover in the Nordic Seas Kelley et al.
Land stations only Delworth and Knutson, Reading figure from left to right, one sees the rapid, concentrated arrival of warm temperatures in the s, contrasting the late twentieth century warming that is spread across many latitudes. Temperature scale is in degrees Celsius. Effects of those sudden changes on oceanic ecosystems were widespread Intergovernmental Panel on Climate Change, a, Ch.
Northward dislocations of plankton, fish, mammals, and birds were extreme, including the range of economically important species, such as herring Figure 2. In the case of cod, the warm ocean greatly extended their range, as larvae were transported north by the Irminger Current from the waters around Iceland. The northern catch rose from nothing to , tons per year in the s and s, then declined abruptly when the surface cold water reappeared in the late s.
Earlier successful cod fisheries were seen near Greenland in the s and s, but none had occurred in the wide interval between then and Such effects were also widespread in the Nordic and Barents Seas. Causes of the abrupt yet long-lasting northern warming are not clear. The Arctic region as a whole seems to amplify climate variability, as we are witnessing now.
Climate-model simulations Delworth and Mann, suggested that the warming could have occurred with strong natural variability, through an increase in oceanic meridional overturning circulation, which brought warm, saline surface waters into the sub-Arctic and Arctic.
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Durre, personal communication, SSB bold line ; temperature thin line. The close proximity of the northern Atlantic focus of this warming to the dominant sinking regions of the global deep-ocean circulation makes this episode particularly relevant to global climate. Long-term measurements appropriate to climate variability studies are scarce in the ocean.