New evidence found of land and ocean responses to climate change over last millennium

New evidence found of land and ocean responses to climate change over last millennium


     21 July 2016 

Two recent marine records made in the Alboran Sea Basin and analysed at high-resolution have allowed scientists to reconstruct climate and oceanographic conditions in the westernmost Mediterranean region during the last millennium. They have also shed light on the human impact on the region.

The University of Granada, together with Germany’s Biodiversity and Climate Research Centre, the Spanish National Research Council (CSIC), the Autonomous University of Barcelona and the Royal Netherlands Institute for Sea Research (NIOZ), took part in this multidisciplinary research project.

A multidisciplinary research team, including the participation of the University of Granada (UGR) has made an important breakthrough in terrestrial and ocean responses to climate variability during the last millennium, including the industrial era.

The effects of global warming and climate change on health and security likely represent the most severe threats in the history of humankind. Recent reports by the Intergovernmental Panel on Climate Change (IPCC 2007, 2014) have provided scientific evidence of this, including the fact that the increase observed in the average temperature of the Earth’s surface since the beginning of the 20th century is most likely due to human influence.

The average global concentration of carbon dioxide in the atmosphere has also increased due to human activity since the industrial revolution and has surpassed the range recorded in ice cores from the last 800,000 years. Similarly, in January 2016, NASA and the National Oceanic and Atmospheric Administration (NOAA) revealed that the average global temperature in 2015 was the warmest since record-taking began in 1880.

Reconstructions of the global land surface temperature in the Northern Hemisphere over the last millennium indicate warm conditions during the so-called Medieval Climatic Anomaly (800-1300 AD) and colder temperatures during the Little Ice Age (1300-1850 AD).

Natural climate variability

Climate modelling provides a coherent explanation of progressive cooling during the last millennium due to natural climate variability (solar cycle modulations and volcanic eruptions). However, the global cooling trend was reversed over the course of the 20th century. Climate models are incapable of simulating the rapid warming observed during the previous century without including human influence along with natural climatic forcing mechanisms.

With this objective in mind, a multidisciplinary research team from the Biodiversity and Climate Research Centre in Germany (Vanesa Nieto Moreno), the University of Granada (Miguel Ortega Huertas), the CSIC (Francisca Martínez Ruiz, David Gallego Torres and Santiago Giralt), the Autonomous University of Barcelona (Jordi García Orellana and Pere Masqué) and the Royal Netherlands Institute for Sea Research (Jaap Sinninghe Damsté) carried out a study of the reconstruction of climatic and oceanographic conditions in the westernmost Mediterranean region using marine sediment recovered from the Alboran Sea Basin.

The area studied is of great interest as it is especially sensitive and vulnerable to climate and anthropogenic forcings due to its being a semi-closed marine basin. Its latitudinal position also causes it to be affected by different climate regimes. Different organic and inorganic geochemical proxies were integrated for the study, inferring climate variables such as sea-surface temperature, humidity, changes in land vegetation cover, fluctuations in ocean circulation, and human influence.

The indicators have revealed consistent climatic signals in both marine records of fundamentally warm and dry climate conditions during the Medieval Climate Anomaly (MCA), changing to mostly humid and cold conditions during the Little Ice Age (LIA). The industrial period was characterized by more humid conditions than during the previous Little Ice Age and by progressive aridity during the second half of the 20th century.

Climate variability in the Mediterranean region appears to be driven by variations in solar irradiance and the modulation of the North Atlantic oscillation (NAO) during the last millennium. The NAO alternates between two phases. One of them is positive and characterized by stronger western winds that carry storms towards northern Europe. This resulted in dry winters in the Mediterranean and northern Africa during the Medieval Climate Anomaly and the second half of the 20th century.

On the other hand, the negative phase of the NAO is associated with opposite conditions during the Little Ice Age and the industrial period. During prolonged positive phases of the NAO the records show a weakening in the thermohaline circulation current and a reduction of so-called “upwelling” events (a surge of deep, colder and more nutrient-rich waters) in 1450 AD and 1950 AD.

The anthropogenic influence is expressed through an unprecedented temperature increase, progressive aridification and soil erosion as well as through an increase in the concentration of contaminant elements since the industrial era. On a large scale, the atmospheric and ocean circulation patterns (the NAO and Atlantic meridional circulation) as well as variations in solar irradiance appear to have played a key role over the last millennium.

The results indicate that in the most recent records, the climate of the westernmost Mediterranean is determined by natural forcing as well as by human influence. The principle conclusions derived from the study have recently been published in a special edition of the Journal of the Geological Society of London about climate change during the Holocene.

Bibliographical References:

Nieto-Moreno, V.; Martínez-Ruiz, F.; Gallego-Torres, D.; Giralt, S.; García-Orellana, J.; Masqué, P.; Sinninghe Damsté, J.S.; Ortega-Huertas, M. ‘Paleoclimate and Paleoceanograhic Conditions in the Westernmost Mediterranean Over the Last Millennium: an Integrated Organic and Inorganic Approach’. Journal of the Geological Society of London. 2015, vol.172, p. 264271. doi: 10.1144/jgs2013105.

Contact Information:

Francisca Martínez Ruiz
Andalusian Institute of Earth Sciences (CSIC-UGR)

Miguel Ortega Huertas
Department of Mineralogy and Petrology at UGR
Phone: (0034) 958 243 342

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