scholarly journals The climate of the Common Era off the Iberian Peninsula

2017 ◽  
Vol 13 (12) ◽  
pp. 1901-1918 ◽  
Author(s):  
Fátima Abrantes ◽  
Teresa Rodrigues ◽  
Marta Rufino ◽  
Emília Salgueiro ◽  
Dulce Oliveira ◽  
...  
Keyword(s):  
Iberian Peninsula ◽  
Atmospheric Circulation ◽  
20Th Century ◽  
Northern Hemisphere ◽  
Climate Warming ◽  
North Atlantic ◽  
Positive Phase ◽  
Future Climate Change ◽  
Fall Season ◽  
Nw Iberia

Abstract. The Mediterranean region is a climate hot spot, sensitive not only to global warming but also to water availability. In this work we document major temperature and precipitation changes in the Iberian Peninsula and margin during the last 2000 years and propose an interplay of the North Atlantic internal variability with the three atmospheric circulation modes (ACMs), (North Atlantic Oscillation (NAO), east atlantic (EA) and Scandinavia (SCAND)) to explain the detected climate variability. We present reconstructions of sea surface temperature (SST derived from alkenones) and on-land precipitation (estimated from higher plant n-alkanes and pollen data) in sedimentary sequences recovered along the Iberian Margin between the south of Portugal (Algarve) and the northwest of Spain (Galiza) (36 to 42° N). A clear long-term cooling trend, from 0 CE to the beginning of the 20th century, emerges in all SST records and is considered to be a reflection of the decrease in the Northern Hemisphere summer insolation that began after the Holocene optimum. Multi-decadal/centennial SST variability follows other records from Spain, Europe and the Northern Hemisphere. Warm SSTs throughout the first 1300 years encompass the Roman period (RP), the Dark Ages (DA) and the Medieval Climate Anomaly (MCA). A cooling initiated at 1300 CE leads to 4 centuries of colder SSTs contemporary with the Little Ice Age (LIA), while a climate warming at 1800 CE marks the beginning of the modern/Industrial Era. Novel results include two distinct phases in the MCA: an early period (900–1100 years) characterized by intense precipitation/flooding and warm winters but a cooler spring–fall season attributed to the interplay of internal oceanic variability with a positive phase in the three modes of atmospheric circulation (NAO, EA and SCAND). The late MCA is marked by cooler and relatively drier winters and a warmer spring–fall season consistent with a shift to a negative mode of the SCAND. The Industrial Era reveals a clear difference between the NW Iberia and the Algarve records. While off NW Iberia variability is low, the Algarve shows large-amplitude decadal variability with an inverse relationship between SST and river input. Such conditions suggest a shift in the EA mode, from negative between 1900 and 1970 CE to positive after 1970, while NAO and SCAND remain in a positive phase. The particularly noticeable rise in SST at the Algarve site by the mid-20th century (±1970), provides evidence for a regional response to the ongoing climate warming. The reported findings have implications for decadal-scale predictions of future climate change in the Iberian Peninsula.

scholarly journals Glacier response to North Atlantic climate variability during the Holocene

2015 ◽  
Vol 11 (3) ◽  
pp. 2009-2036 ◽  
Author(s):  
N. L. Balascio ◽  
W. J. D'Andrea ◽  
R. S. Bradley
Keyword(s):  
Climate Variability ◽  
20Th Century ◽  
Northern Hemisphere ◽  
North Atlantic ◽  
Late Holocene ◽  
North Atlantic Ocean ◽  
The Holocene ◽  
The Past ◽  
Summer Insolation ◽  
Geochemical Parameters

Abstract. Small glaciers and ice caps respond rapidly to climate variations and records of their past extent provide information on the natural envelope of past climate variability. Millennial-scale trends in Holocene glacier size are well documented and correspond with changes in Northern Hemisphere summer insolation. However, there is only sparse and fragmentary evidence for higher frequency variations in glacier size because in many Northern Hemisphere regions glacier advances of the past few hundred years were the most extensive and destroyed the geomorphic evidence of ice growth and retreat during the past several thousand years. Thus, most glacier records have been of limited use for investigating centennial scale climate forcing and feedback mechanisms. Here we report a continuous record of glacier activity for the last 9.5 ka from southeast Greenland, derived from high-resolution measurements on a proglacial lake sediment sequence. Physical and geochemical parameters show that the glaciers responded to previously documented Northern Hemisphere climatic excursions, including the "8.2 ka" cooling event, the Holocene Thermal Maximum, Neoglacial cooling, and 20th Century warming. In addition, the sediments indicate centennial-scale oscillations in glacier size during the late Holocene. Beginning at 4.1 ka, a series of abrupt glacier advances occurred, each lasting ~100 years and followed by a period of retreat, that were superimposed on a gradual trend toward larger glacier size. Thus, while declining summer insolation caused long-term cooling and glacier expansions during the late Holocene, climate system dynamics resulted in repeated episodes of glacier expansion and retreat on multi-decadal to centennial timescales. These episodes coincided with ice rafting events in the North Atlantic Ocean and periods of regional ice cap expansion, which confirms their regional significance and indicates that considerable glacier activity on these timescales is a normal feature of the cryosphere. The data provide a longer-term perspective on the rate of 20th century glacier retreat and indicate that recent anthropogenic-driven warming has already impacted the regional cryosphere in a manner outside the natural range of Holocene variability.

scholarly journals Anthropogenic aerosol forcing of the AMOC and the associated mechanisms in CMIP6 models

2020 ◽  
Author(s):  
Taufiq Hassan ◽  
Robert J. Allen ◽  
Wei Liu ◽  
Cynthia Randles
Keyword(s):  
Climate Variability ◽  
Atmospheric Circulation ◽  
20Th Century ◽  
North Atlantic ◽  
Meridional Overturning Circulation ◽  
Solar Variability ◽  
Anthropogenic Aerosols ◽  
Anthropogenic Aerosol ◽  
Aerosol Forcing ◽  
Volcanic Aerosols

Abstract. By regulating the global transport of heat, freshwater and carbon, the Atlantic Meridional Overturning Circulation (AMOC) serves as an important component of the climate system. During the late 20th and early 21st centuries, indirect observations and models suggest a weakening of the AMOC. Direct AMOC observations also suggest a weakening during the early 21st century, but with substantial interannual variability. Long-term weakening of the AMOC has been associated with increasing greenhouse gases (GHGs), but some modeling studies suggest the build up of anthropogenic aerosols (AAs) may have offset part of the GHG-induced weakening. Here, we quantify 1900–2020 AMOC variations and assess the driving mechanisms in state-of-the-art climate models from the Coupled Model Intercomparison Project phase 6 (CMIP6). The CMIP6 all forcing (GHGs, anthropogenic and volcanic aerosols, solar variability, and land use/land change) multi-model mean shows negligible AMOC changes up to ~1950, followed by robust AMOC strengthening during the second half of the 20th century (~1950–1990), and weakening afterwards (1990–2020). These multi-decadal AMOC variations are related to changes in North Atlantic atmospheric circulation, including an altered sea level pressure gradient, storm track activity, surface winds and heat fluxes, which drive changes in the subpolar North Atlantic surface density flux. Similar to previous studies, CMIP6 GHG simulations yield robust AMOC weakening, particularly during the second half of the 20th century. Changes in natural forcings, including solar variability and volcanic aerosols, yield negligible AMOC changes. In contrast, CMIP6 AA simulations yield robust AMOC strengthening (weakening) in response to increasing (decreasing) anthropogenic aerosols. Moreover, the CMIP6 all-forcing AMOC variations and atmospheric circulation responses also occur in the CMIP6 AA simulations, which suggests these are largely driven by changes in anthropogenic aerosol emissions. Although aspects of the CMIP6 all-forcing multi-model mean response resembles observations, notable differences exist. This includes CMIP6 AMOC strengthening from ~1950–1990, when the indirect estimates suggest AMOC weakening. The CMIP6 multi-model mean also underestimates the observed increase in North Atlantic ocean heat content. And although the CMIP6 North Atlantic atmospheric circulation responses–particularly the overall patterns–are similar to observations, the simulated responses are weaker than those observed, implying they are only partially externally forced. The possible causes of these differences include internal climate variability, observational uncertainties and model shortcomings–including excessive aerosol forcing. A handful of CMIP6 realizations yield AMOC evolution since 1900 similar to the indirect observations, implying the inferred AMOC weakening from 1950–1990 (and even from 1930–1990) may have a significant contribution from internal (i.e., unforced) climate variability. Nonetheless, CMIP6 models yield robust, externally forced AMOC changes, the bulk of which are due to anthropogenic aerosols.

The Significance of Anomalies of Atmospheric Circulation Over the North Atlantic in November with Regard to the Temperatures of the Following Winters in New England *

1951 ◽  
Vol 32 (9) ◽  
pp. 319-325 ◽  
Author(s):  
Franz Baur
Keyword(s):  
New England ◽  
Atmospheric Circulation ◽  
Northern Hemisphere ◽  
North Atlantic ◽  
Middle Latitudes ◽  
The North ◽  
The North Atlantic

Seven types are established for forms of the atmospheric circulation in certain portions of “circulation regions” of the middle latitudes of the northern hemisphere. Tendencies of persistence and recurrence are different for each type and are subject to an annual course. Certain rules may be derived from changes in these types.

North Atlantic atmospheric circulation and surface wind in the Northeast of the Iberian Peninsula: uncertainty and long term downscaled variability

2011 ◽  
Vol 38 (1-2) ◽  
pp. 141-160 ◽  
Author(s):  
E. García-Bustamante ◽  
J. F. González-Rouco ◽  
J. Navarro ◽  
E. Xoplaki ◽  
P. A. Jiménez ◽  
...  
Keyword(s):  
Iberian Peninsula ◽  
Atmospheric Circulation ◽  
North Atlantic ◽  
Surface Wind

scholarly journals Early 20th-century Arctic warming intensified by Pacific and Atlantic multidecadal variability

2017 ◽  
Vol 114 (24) ◽  
pp. 6227-6232 ◽  
Author(s):  
Hiroki Tokinaga ◽  
Shang-Ping Xie ◽  
Hitoshi Mukougawa
Keyword(s):  
Phase Shift ◽  
20Th Century ◽  
North Atlantic ◽  
Interdecadal Variability ◽  
The Arctic ◽  
Positive Phase ◽  
Northern Eurasia ◽  
Early 20Th Century ◽  
Arctic Warming ◽  
The Pacific

With amplified warming and record sea ice loss, the Arctic is the canary of global warming. The historical Arctic warming is poorly understood, limiting our confidence in model projections. Specifically, Arctic surface air temperature increased rapidly over the early 20th century, at rates comparable to those of recent decades despite much weaker greenhouse gas forcing. Here, we show that the concurrent phase shift of Pacific and Atlantic interdecadal variability modes is the major driver for the rapid early 20th-century Arctic warming. Atmospheric model simulations successfully reproduce the early Arctic warming when the interdecadal variability of sea surface temperature (SST) is properly prescribed. The early 20th-century Arctic warming is associated with positive SST anomalies over the tropical and North Atlantic and a Pacific SST pattern reminiscent of the positive phase of the Pacific decadal oscillation. Atmospheric circulation changes are important for the early 20th-century Arctic warming. The equatorial Pacific warming deepens the Aleutian low, advecting warm air into the North American Arctic. The extratropical North Atlantic and North Pacific SST warming strengthens surface westerly winds over northern Eurasia, intensifying the warming there. Coupled ocean–atmosphere simulations support the constructive intensification of Arctic warming by a concurrent, negative-to-positive phase shift of the Pacific and Atlantic interdecadal modes. Our results aid attributing the historical Arctic warming and thereby constrain the amplified warming projected for this important region.

scholarly journals Considerações acerca do arrefecimento Plistocénico em Portugal

Finisterra ◽  
2012 ◽  
Vol 35 (70) ◽  
Author(s):  
António Brum Ferreira
Keyword(s):  
Iberian Peninsula ◽  
Northern Hemisphere ◽  
North Atlantic ◽  
Western Europe ◽  
Climatic Conditions ◽  
The North ◽  
Last Glaciation ◽  
Summer Temperatures ◽  
The North Atlantic

NOTE ON THE PLEISTOCENE COOLING IN PORTUGAL – Prevailing conditionsin the North Atlantic and Western Europe during the Maximum Cooling of the Last Glaciation can be deduced from the Climap Project (1976) results and from the Atlas of Paleoclimates and Paleoenvironments of the Northern Hemisphere (FRENZEL et al., 1992). Taking into account this framework of extreme climatic conditions and the nature of the glacial and periglacial relict phenomena in the Iberian Peninsula, an attempt is made to evaluate the degree of cooling in Portugal during the Gerês and Estrela glaciations. A drop of about 10º C in summer temperatures is suggested.

scholarly journals Glacier response to North Atlantic climate variability during the Holocene

2015 ◽  
Vol 11 (12) ◽  
pp. 1587-1598 ◽  
Author(s):  
N. L. Balascio ◽  
W. J. D'Andrea ◽  
R. S. Bradley
Keyword(s):  
Climate Variability ◽  
20Th Century ◽  
Northern Hemisphere ◽  
North Atlantic ◽  
Late Holocene ◽  
North Atlantic Ocean ◽  
The Holocene ◽  
The Past ◽  
Summer Insolation ◽  
Geochemical Parameters

Abstract. Small glaciers and ice caps respond rapidly to climate variations, and records of their past extent provide information on the natural envelope of past climate variability. Millennial-scale trends in Holocene glacier size are well documented and correspond with changes in Northern Hemisphere summer insolation. However, there is only sparse and fragmentary evidence for higher-frequency variations in glacier size because in many Northern Hemisphere regions glacier advances of the past few hundred years were the most extensive and destroyed the geomorphic evidence of ice growth and retreat during the past several thousand years. Thus, most glacier records have been of limited use for investigating centennial-scale climate forcing and feedback mechanisms. Here we report a continuous record of glacier activity for the last 9.5 ka from southeast Greenland derived from high-resolution measurements on a proglacial lake sediment sequence. Physical and geochemical parameters show that the glaciers responded to previously documented Northern Hemisphere climatic excursions, including the "8.2 ka" cooling event, the Holocene Thermal Maximum, Neoglacial cooling, and 20th century warming. In addition, the sediments indicate centennial-scale oscillations in glacier size during the late Holocene. Beginning at 4.1 ka, a series of abrupt glacier advances occurred, each lasting ~100 years and followed by a period of retreat, that were superimposed on a gradual trend toward larger glacier size. Thus, while declining summer insolation caused long-term cooling and glacier expansion during the late Holocene, climate system dynamics resulted in repeated episodes of glacier expansion and retreat on multi-decadal to centennial timescales. These episodes coincided with ice rafting events in the North Atlantic Ocean and periods of regional ice cap expansion, which confirms their regional significance and indicates that considerable glacier activity on these timescales is a normal feature of the cryosphere. The data provide a longer-term perspective on the rate of 20th century glacier retreat and indicate that recent anthropogenic-driven warming has already impacted the regional cryosphere in a manner outside the natural range of Holocene variability.

scholarly journals Intensywność cyrkulacji termohalinowej na Atlantyku Północnym a susze w Polsce

2021 ◽  
Vol 66 (1) ◽  
pp. 63-80
Author(s):  
Andrzej Marsz ◽  
Anna Styszyńska
Keyword(s):  
20Th Century ◽  
North Atlantic ◽  
Thermohaline Circulation ◽  
Positive Phase ◽  
Positive Trend ◽  
The North ◽  
Nao Index ◽  
The North Atlantic ◽  
Drought Occurrence

The work considers the cause of the frequency of droughts occurrence variability in Poland. It was proven, that the frequency of droughts shows statistically significant relationship with intensity of thermohaline circulation (THC) in the North Atlantic. In periods of occurrence of positive phase the THC frequency of droughts’ occurrence in Poland grows up and it is about 3.6 times greater, than in periods of occurrence of negative phase the THC. The sign and the value of coefficient characterizing the THC determines the drought occurrence and its duration time. Changeability of the THC is not however the only factor influencing on droughts’ occurrence. The analyses show, that the probability of the Spring and Summer droughts’ occurrence in a year with a positive THC phase is considerably larger, if in period of Winter preceding the drought, the sign of NAO index will be positive. At present (the year 2019) we are presumably already after the culmination of the positive phase of the THC, lasting from the year 1989. As the long-term course of the THC changeability shows the quasi- periodicity, we can presume, that the strong positive trend of occurrence of droughts, lasting from the 80’ of 20th century, will undergo break down.

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