scholarly journals Regional Influences of Natural External Forcings on the Transition from the Medieval Climate Anomaly to the Little Ice Age

2016 ◽  
Vol 29 (16) ◽  
pp. 5779-5800 ◽  
Author(s):  
Heather J. Andres ◽  
W. R. Peltier
Keyword(s):  
Sea Ice ◽  
Spectral Resolution ◽  
Little Ice Age ◽  
Ice Age ◽  
Last Millennium ◽  
Medieval Climate Anomaly ◽  
Volcanic Emissions ◽  
Climate Anomaly ◽  
Model Simulations ◽  
Climate Forcings

Abstract Reconstructions of historical climate changes indicate that surface air temperatures decreased over the preindustrial last millennium. Conflicting explanations have been proposed for the cause of the transition from the Medieval Climate Anomaly (MCA) in the early part of the last millennium to the Little Ice Age (LIA) near its end. The possible causes include volcanic emissions, total solar irradiance (TSI) variations, greenhouse gas concentration fluctuations, and orbital forcing variations. In the present paper, it is demonstrated that all of these climate forcings contribute significantly to simulated surface air temperature (SAT) and sea ice concentration changes over this period. On the other hand, simulated ocean heat content appears to respond significantly only to volcanic and TSI variations. In model simulations at T85 spectral resolution, TSI reductions and volcanic emissions together generate significant increases in sea ice extent in the Barents Sea, which is found to be responsible for most of the temperature reductions over northwestern Europe. TSI appears less important to Arctic sea ice and SAT changes in simulations at T42 spectral resolution, which are weaker than at T85 resolution. Such resolution dependence is attributed to differences in background conditions in the responses to these external climate forcings. Nonlinearities in the forcing responses and sensitivities to background conditions challenge the assumption that sensitivity tests for given forcings can be run independently. Additionally, it is demonstrated that an ensemble of model simulations is required to isolate forcing responses even over a period as long as the last millennium.

scholarly journals The Medieval Climate Anomaly and the Little Ice Age in the eastern Ecuadorian Andes

2013 ◽  
Vol 9 (1) ◽  
pp. 307-321 ◽  
Author(s):  
M.-P. Ledru ◽  
V. Jomelli ◽  
P. Samaniego ◽  
M. Vuille ◽  
S. Hidalgo ◽  
...  
Keyword(s):  
Little Ice Age ◽  
Water Storage ◽  
Ice Age ◽  
Last Millennium ◽  
Medieval Climate Anomaly ◽  
Climate Anomaly ◽  
Abrupt Decrease ◽  
Enso Variability ◽  
P Index ◽  
Poaceae Pollen

Abstract. To better characterize the climate variability of the last millennium in the high Andes, we analyzed the pollen content of a 1150-yr-old sediment core collected in a bog located at 3800 m a.s.l. in the páramo in the eastern Cordillera in Ecuador. An upslope convective index based on the ratio between cloud transported pollen from the Andean forest to the bog (T) and Poaceae pollen frequencies, related to the edaphic moisture of the páramo (P), was defined. This index was used to distinguish changes in the atmospheric moisture from the soil moisture content of the páramo and their associated patterns of interdecadal El Niño–Southern Oscillation (ENSO) variability and South American summer monsoon (SASM) activity. Results show that between 850 and 1250 AD, the Medieval Climate Anomaly interval was warm and moist with a high transported pollen/Poaceae pollen (T/P) index linked to high ENSO variability and weak SASM activity. Between 1250 and 1550 AD, a dry climate prevailed, characterized by an abrupt decrease in the T/P index and therefore no upslope cloud convection, related to lower ENSO variability and with significant impact on the floristic composition of the páramo. During the Little Ice Age, two phases were observed: first, a wet phase between 1550 and 1750 AD linked to low ENSO variability in the Pacific and warm south equatorial Atlantic sea surface temperatures (SSTs) favored the return of a wet páramo, and then a cold and dry phase between 1750 and 1800 AD associated with low ENSO variability and weak SASM activity resulted in drying of the páramo. The current warm period marks the beginning of a climate characterized by high convective activity – the highest in the last millennium – and weaker SASM activity modifying the water storage of the páramo. Our results show that the páramo is progressively losing its capacity for water storage and that the interdecadal variability of both tropical Pacific and Atlantic SSTs matter for Andean climate patterns, although many teleconnection mechanisms are still poorly understood.

scholarly journals The Medieval Climate Anomaly and the Little Ice Age in the Eastern Ecuadorian Andes

2012 ◽  
Vol 8 (5) ◽  
pp. 4295-4332 ◽  
Author(s):  
M.-P. Ledru ◽  
V. Jomelli ◽  
P. Samaniego ◽  
M. Vuille ◽  
S. Hidalgo ◽  
...  
Keyword(s):  
Little Ice Age ◽  
Floristic Composition ◽  
Ice Age ◽  
Last Millennium ◽  
Medieval Climate Anomaly ◽  
Equatorial Atlantic ◽  
Climate Anomaly ◽  
Abrupt Decrease ◽  
Enso Variability ◽  
P Index

Abstract. To better characterize the climate variability of the last millennium in the high Andes, we analysed the pollen content of a 1100-yr-old sediment core collected in a bog located at 3800 m a.s.l. in the páramo in the Eastern Cordillera in Ecuador. An upslope convective index based on the ratio between cloud transported pollen from the andean forest to the bog (T) and Poaceae pollen frequencies, related to the edaphic moisture of the páramo (P), was defined to distinguish the atmospheric moisture from the soil moisture content of the páramo. Results showed that between 900 AD and 1230 AD, the Medieval Climate Anomaly interval was warm and moist with high T/P index linked to a high ENSO variability and a weak South American Summer Monsoon (SASM) activity. Between 1230 and 1650 AD, a dry climate prevailed characterized by an abrupt decrease in the T/P index related to lower ENSO variability with significant impact on the floristic composition of the páramo. During the Little Ice Age, two phases were observed, first a wet phase between 1650 and 1750 AD linked to low ENSO variability in the Pacific and warm south equatorial Atlantic SSTs favored the return of a wet páramo, and a cold and dry phase between 1750 and 1810 AD associated with low ENSO variability and weak SASM activity resulting in drying of the páramo. The Current Warm Period marks the beginning of a climate characterized by high convective activity, the highest in the last millennium, and weaker SASM activity modifying the water stock of the páramo. Our results show that the páramo is progressively loosing its capacity for water storage and that the variability of both tropical Pacific and Atlantic SSTs matters for Andean climate patterns although many teleconnection mechanisms are still poorly understood.

Characterization of the Medieval Climate Anomaly, Little Ice Age and recent warming in northern Lapland

2017 ◽  
Vol 37 ◽  
pp. 1257-1266 ◽  
Author(s):  
Tomi P. Luoto ◽  
E. Henriikka Kivilä ◽  
Marttiina V. Rantala ◽  
Liisa Nevalainen
Keyword(s):  
Little Ice Age ◽  
Ice Age ◽  
Medieval Climate Anomaly ◽  
Climate Anomaly ◽  
Recent Warming

Lacustrine stable isotope record of precipitation changes in Nicaragua during the Little Ice Age and Medieval Climate Anomaly

Geology ◽  
2013 ◽  
Vol 41 (2) ◽  
pp. 151-154 ◽  
Author(s):  
Nathan D. Stansell ◽  
Byron A. Steinman ◽  
Mark B. Abbott ◽  
Michael Rubinov ◽  
Manuel Roman-Lacayo
Keyword(s):  
Stable Isotope ◽  
Little Ice Age ◽  
Ice Age ◽  
Medieval Climate Anomaly ◽  
Climate Anomaly ◽  
Isotope Record ◽  
Precipitation Changes ◽  
Stable Isotope Record

scholarly journals South Atlantic Surface Boundary Current System during the Last Millennium in the CESM-LME: The Medieval Climate Anomaly and Little Ice Age

Geosciences ◽  
2019 ◽  
Vol 9 (7) ◽  
pp. 299
Author(s):  
Fernanda Marcello ◽  
Ilana Wainer ◽  
Peter R. Gent ◽  
Bette L. Otto-Bliesner ◽  
Esther C. Brady
Keyword(s):  
Little Ice Age ◽  
South Atlantic ◽  
Subtropical Gyre ◽  
Ice Age ◽  
Surface Boundary ◽  
South American ◽  
Last Millennium ◽  
Medieval Climate Anomaly ◽  
The South ◽  
Gyre Circulation

Interocean waters that are carried northward through South Atlantic surface boundary currents get meridionally split between two large-scale systems when meeting the South American coast at the western subtropical portion of the basin. This distribution of the zonal flow along the coast is investigated during the Last Millennium, when natural forcing was key to establish climate variability. Of particular interest are the changes between the contrasting periods of the Medieval Climate Anomaly (MCA) and the Little Ice Age (LIA). The investigation is conducted with the simulation results from the Community Earth System Model Last Millennium Ensemble (CESM-LME). It is found that the subtropical South Atlantic circulation pattern differs substantially between these natural climatic extremes, especially at the northern boundary of the subtropical gyre, where the westward-flowing southern branch of the South Equatorial Current (sSEC) bifurcates off the South American coast, originating the equatorward-flowing North Brazil Undercurrent (NBUC) and the poleward Brazil Current (BC). It is shown that during the MCA, a weaker anti-cyclonic subtropical gyre circulation took place (inferred from decreased southern sSEC and BC transports), while the equatorward transport of the Meridional Overturning Circulation return flow was increased (intensified northern sSEC and NBUC). The opposite scenario occurs during the LIA: a more vigorous subtropical gyre circulation with decreased northward transport.

Vegetation shifts, human impact and peat bog development in Bassa Nera pond (Central Pyrenees) during the last millennium

The Holocene ◽  
2016 ◽  
Vol 27 (4) ◽  
pp. 553-565 ◽  
Author(s):  
Sandra Garcés-Pastor ◽  
Núria Cañellas-Boltà ◽  
Albert Clavaguera ◽  
Miguel Angel Calero ◽  
Teresa Vegas-Vilarrúbia
Keyword(s):  
Environmental Changes ◽  
Ice Age ◽  
Peat Bog ◽  
High Mountain ◽  
Last Millennium ◽  
Medieval Climate Anomaly ◽  
Human Pressure ◽  
Climate Anomaly ◽  
Vegetation Shifts ◽  
Central Pyrenees

High-mountain lakes are suitable ecosystems for studying local environmental shifts driven by large-scale climate changes, with potential applications to predict future scenarios. The precise features in the response of species assemblages are not fully understood, and human pressure may often hide climatic signals. To investigate the origin and impact of past environmental changes in high-mountain ecosystems and apply this palaeoecological knowledge to anticipate future changes, we performed a multi-proxy study of a sediment core from Bassa Nera, a pond located close to montane–subalpine ecotone in the southern central Pyrenees. Combining pollen and diatom analysis at multidecadal resolution, we inferred vegetation shifts and peat bog development during the past millennium. We introduced a montane pollen ratio as a new palaeoecological indicator of altitudinal shifts in vegetation. Our results emphasize the sensitivity of the montane ratio to detect upward migrations of deciduous forest and the presence of the montane belt close to Bassa Nera pond during the Medieval Climate Anomaly. Changes in aquatic taxa allowed to date the onset of the surrounding peat bog which appeared and infilled the coring site around AD 1565. Overall, our results suggest a low-intensity human pressure and changes in management of natural resources during the last millennium, where farming was the main activity from the Medieval Climate Anomaly until AD 1500. Afterwards, people turned to highland livestock raising coinciding with the ‘Little Ice Age’.

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