The expansion of the high pressure system over the Atlantic, popularly known as Azores anticycloneis causing the driest conditions in the Iberian Peninsula in the last thousand years, according to a model published today Nature Geoscience and that points to human action as responsible. A team led by American scientists from the Woods Hole Oceanographic Institution modeled how the Azores anticyclone has changed in size and spatial extent over the past 1,200 years. The research indicates that this high pressure system began to cover, on average, a larger area about 200 years ago, when human emissions of greenhouse gases began to increase substantially, and this spatial expansion was accentuated in the 20th century.
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The authors conclude that it will continue to expand in the 21st century as greenhouse gas levels continue to rise, leading to a high risk of drought in the Iberian Peninsula. Weather and long-term climate patterns in Western Europe are strongly affected by the atmospheric circulation associated with this persistent, clockwise rotating high pressure zone.
The dry air that descends towards the surface within the system is one of the main causes of hot and arid summers in much of Portugal and Spain, as well as in the western Mediterranean in general. During the characteristically wetter winter months, changes in the position of the Azores anticyclone are responsible for westerly winds, displacing moisture towards the Iberian Peninsula, but these winter rains have decreased in recent decades.
The team developed several models and compared them with geochemical indicators of past precipitation levels preserved in Portuguese stalagmites dating back to AD 850, suggesting that the expansion of the anticyclone is linked to the onset of drier winters in the Mediterranean. western.
Observations and climate model simulations noted that winters with an “extremely large” Azores anticyclone are significantly more common in the industrial era (about 1850) than in the pre-industrial era, resulting in “anomalous dry conditions” throughout the western Mediterranean, including the Iberian Peninsula.
The simulations of the last millennium indicate that the expansion of the anticyclone in the industrial era is “unprecedented in the last millennium”, which is consistent with the approximation tests of precipitation in Portugal.
The expansion emerges after 1850 and is reinforced in the 20th century, which is consistent with warming of anthropogenic origin, the authors state. The tendencies of the Iberian hydroclimate suggest, therefore, a change in the behavior of the anticyclone. The study notes that it has changed “dramatically in the last century and these changes in the North Atlantic climate are unprecedented in the last millennium.”