Earth

Modeling study reveals that ‘greening’ of Africa’s Sahara Desert could change the climate of the Northern Hemisphere

Winter temperature (a, b), summer temperature (c, d), and annual precipitation (e, f) between preindustrial values, paleoclimate model (MH-PMIP), and Sahara Greening Model (MH). Comparison of the reconstructed model and environmental surrogate-GS). Credit: Past Climate (2024). DOI: 10.5194/cp-20-1735-2024

Africa’s Sahara Desert may be considered an extreme environment for flora and fauna to thrive, with vast expanses of barren sand and limited vegetation, but life always finds a way out. . In fact, vegetation growth in deserts has waxed and waned over thousands of years, and there have been periods of accelerated growth known as “greening”.

One such period of flora expansion occurred during the first half of the Holocene epoch, between 5,000 and 11,000 years ago. Because the summer solstice coincided with Earth’s perihelion orbit (when the Earth is closest to the sun), solar radiation increases in the northern summer (June to August), producing seasonal changes across the tropics, mid-latitudes, and high latitudes. I did.

As a result, stronger monsoons in the Northern Hemisphere are thought to have played an important role in increasing humidity across Africa, creating conditions suitable for the growth of evergreen shrubs in the Sahara Desert.

A new study published in Climate of the Past used climate model simulations to reconstruct the effects of this Saharan greening in mid-latitudes during the mid-Holocene. Numerical simulations by Associate Professor Marco Gaetani and colleagues at the IUSS School of Advanced Studies in Pavia, Italy, show that the greening of the Sahara Desert affects atmospheric circulation in the Northern Hemisphere throughout the year, particularly in the Northern Hemisphere summer when the African monsoon develops. It turned out that there was.

As a result, regions of the Northern Hemisphere will experience extreme weather conditions, with warmer and drier Scandinavia and North America, colder winters and warmer summers in Western Europe, overall warming in Central Europe, and colder and wetter Mediterranean conditions. Furthermore, the winters were warm and the summers were cold. Precipitation increases throughout the year in Central Asia.

To explain these changes, the research team found that during the mid-Holocene, the Walker Circulation (air rising westward as air moves westward at high latitudes and air rising westward as air moves eastward through the tropics) discovered that the atmospheric loop that sank to the east) moved westward. . This had important effects on the jet stream, with the North Atlantic component strengthening and changing course in the summer, followed by the North Pacific in the winter.

They also show that changes in the North Atlantic Oscillation (changes in surface sea level pressure across this ocean basin lead to changes in temperature and precipitation patterns on neighboring continents) are causing changes in both winter (December to February) and summer in the Northern Hemisphere. We identified a change from positive to negative over the period. A few months.

As a result, summers were warmer and drier in the eastern Mediterranean, northern Africa, and polar North America, while summers were cooler and wetter in northern, central, and eastern Europe, and eastern North America.

All of these climate changes are due to an 80% drop in dust emissions and an increase in albedo (a unitless measure of how much of the Earth’s surface reflects the sun’s energy, where 0 is black and 1 is white). As it decreased, it persisted for thousands of years. 0.30 in deserts drops to 0.15 in shrubs, promoting tropical warming. Due to the presence of more vegetation, water recycling also increased and drought conditions were avoided.

The interconnected nature of the atmosphere and ocean means there is further scope to explore the impacts of Saharan greening across both terrestrial and oceanic domains in the future.

Recent reports have highlighted the role of climate change in changing long-established weather patterns, with the northward movement of weather systems across Africa bringing heavy rains and the formation of vegetation corridors across the Sahara Desert. This is impacting the distribution and survival of life in this previously relatively barren region. landscape.

Further information: Marco Gaetani et al., Mid-Holocene climate in the mid-latitudes: assessing the impact of Saharan greening, past climate (2024). DOI: 10.5194/cp-20-1735-2024

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Citation: ‘Greening’ of Africa’s Sahara desert could change northern hemisphere climate, modeling study results (November 2, 2024) https://phys.org/news/2024-11-african-sahara- Retrieved November 2, 2024 from greening-northern-hemisphere.html

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