Global terrestrial stilling is the decrease of

wind speed In meteorology, wind speed, or wind flow speed, is a fundamental atmospheric quantity caused by air moving from high to low pressure, usually due to changes in temperature. Wind speed is now commonly measured with an anemometer. Wind speed ...

observed near the

Earth Earth is the third planet from the Sun and the only astronomical object known to harbor life. While large volumes of water can be found throughout the Solar System, only Earth sustains liquid surface water. About 71% of Earth's surfa ...

's surface (~10-meter height) over the last three decades (mainly since the 1980s), originally termed "stilling". This slowdown of near-surface terrestrial winds has mainly affected mid-latitude regions of both hemispheres, with a global average reduction of −0.140 m s⁻¹ dec⁻¹ (meters per second per decade) or between 5 and 15% over the past 50 years.McVicar TR, Roderick ML, Donohue RJ, Li LT, Van Niel TG, Thomas A, Grieser J, Jhajharia D, Himri Y, Mahowald NM, Mescherskaya AV, Kruger AC, Rehman S, Dinpashoh Y (2012) Global review and synthesis of trends in observed terrestrial near-surface wind speeds: Implications for evaporation. J Hydrol 416–417: 182–205. With high-latitude (> 75° from the equator) showing increases in both hemispheres. In contrast to the observed weakening of winds over continental surfaces, winds have tended to strengthen over

ocean The ocean (also the sea or the world ocean) is the body of salt water that covers approximately 70.8% of the surface of Earth and contains 97% of Earth's water. An ocean can also refer to any of the large bodies of water into which the wo ...

regions.Wentz FJ, Ricciardulli L, Hilburn K, Mears C (2007) How much more rain will global warming bring? Science 317(5835): 233–235. Young IR, Zieger S, Babanin AV (2011) Global trends in wind speed and wave height. Science 332(6028): 451–455. . In the last few years, a break in this terrestrial decrease of wind speed has been detected suggesting a recovery at global scales since 2013.Dunn RJH, Azorin-Molina C, Mears CA, Berrisford P, McVicar TR (2016) Surface winds. In State of the Climate 2015, Bull Amer Meteor Soc 97 (8): S38-S40. The exact cause(s) of the global terrestrial stilling are uncertain and has been mainly attributed to two major drivers: (i) changes in large scale

atmospheric circulation Atmospheric circulation is the large-scale movement of air and together with ocean circulation is the means by which thermal energy is redistributed on the surface of the Earth. The Earth's atmospheric circulation varies from year to year, bu ...

, and (ii) an increase of surface roughness due to e.g.

forest A forest is an area of land dominated by trees. Hundreds of definitions of forest are used throughout the world, incorporating factors such as tree density, tree height, land use, legal standing, and ecological function. The United Nations' ...

growth,

land use Land use involves the management and modification of natural environment or wilderness into built environment such as settlements and semi-natural habitats such as arable fields, pastures, and managed woods. Land use by humans has a long ...

changes, and

urbanization Urbanization (or urbanisation) refers to the population shift from rural to urban areas, the corresponding decrease in the proportion of people living in rural areas, and the ways in which societies adapt to this change. It is predominantly t ...

. Given

climate change In common usage, climate change describes global warming—the ongoing increase in global average temperature—and its effects on Earth's climate system. Climate change in a broader sense also includes previous long-term changes to ...

, changes in wind speed are currently a potential concern for society, due to their impacts on a wide array of spheres, such as

wind power Wind power or wind energy is mostly the use of wind turbines to generate electricity. Wind power is a popular, sustainable, renewable energy source that has a much smaller impact on the environment than burning fossil fuels. Historically ...

generation, ecohydrological implications for

agriculture Agriculture or farming is the practice of cultivating plants and livestock. Agriculture was the key development in the rise of sedentary human civilization, whereby farming of domesticated species created food surpluses that enabled people t ...

and

hydrology Hydrology () is the scientific study of the movement, distribution, and management of water on Earth and other planets, including the water cycle, water resources, and environmental watershed sustainability. A practitioner of hydrology is call ...

, wind-related hazards and catastrophes, or

air quality Air pollution is the contamination of air due to the presence of substances in the atmosphere that are harmful to the health of humans and other living beings, or cause damage to the climate or to materials. There are many different types ...

and human health, among many others.

Causes

The attribution of this weakening of terrestrial near-surface wind speed is not conclusive, probably because of several factors which interact simultaneously, and may change in space in time. Scientists have pointed out various major causes influencing this slowdown in wind speed: (i) The increase in land-surface roughness (e.g. forest growth, land use changes and urbanization) near meteorological station where

anemometer In meteorology, an anemometer () is a device that measures wind speed and direction. It is a common instrument used in weather stations. The earliest known description of an anemometer was by Italian architect and author Leon Battista Alberti ...

instruments measure wind lead to a reinforcement of

friction Friction is the force resisting the relative motion of solid surfaces, fluid layers, and material elements sliding against each other. There are several types of friction: *Dry friction is a force that opposes the relative lateral motion of ...

force that weaken low-level winds. (ii) The variability of large-scale

, associated with the poleward expansion of the

Hadley cell The Hadley cell, named after George Hadley, is a global-scale tropical atmospheric circulation that features air rising near the equator, flowing poleward at a height of 10 to 15 kilometers above the earth's surface, descending in the subtropics ...

and the shifting of centers of action (i.e.

anticyclones An anticyclone is a weather phenomenon defined as a large-scale circulation of winds around a central region of high atmospheric pressure, clockwise in the Northern Hemisphere and counterclockwise in the Southern Hemisphere as viewed from abov ...

and cyclones) controlling changes in near-surface wind speed.Azorin-Molina C, Vicente-Serrano SM, McVicar TR, Jerez S, Sanchez-Lorenzo A, López-Moreno JI, Revuelto J, Trigo RM, Lopez-Bustins JA, Espirito-Santo F (2014) Homogenization and assessment of observed near-surface wind speed trends over Spain and Portugal, 1961–2011. J Climate 27 (10): 3692–3712. (iii) The changes in how wind speed is measured, including the deterioration or instrumental drift of anemometer devices; the technological improvement of anemometers; anemometer height changes; shifts in measurements sites; changes in the environment around the monitoring station;

calibration In measurement technology and metrology, calibration is the comparison of measurement values delivered by a device under test with those of a calibration standard of known accuracy. Such a standard could be another measurement device of kno ...

issues; and measuring time intervals. (iv) The "

global dimming Global dimming is the reduction in the amount of global direct irradiance at the Earth's surface that has been observed since systematic measurements began in the 1950s. The effect varies by location, but worldwide it has been estimated to be of ...

", i.e., the decrease in the amounts of

solar radiation Solar irradiance is the power per unit area (surface power density) received from the Sun in the form of electromagnetic radiation in the wavelength range of the measuring instrument. Solar irradiance is measured in watts per square metre ( ...

reaching the Earth's surface due to increased aerosol and greenhouse gas concentrations, forces a stabilization of the atmosphere resulting in weak winds. (v) Other causes, such as increasing trends in available soil moisture and astronomical changes have been put forward. However, the exact causes of global terrestrial stilling are still unresolved because of the many uncertainties behind this phenomenon across the world.

Uncertainties

The "global terrestrial stilling" is not affecting in the same way the whole Earth's surface across both land and ocean surfaces. Spatially, increasing wind speed trends have been reported for some regions, in particular for high-latitudes, coastal and for ocean surfaces where different authors have evidenced an increased global trend of wind speed using satellite measurements in the last 30–40 years. Recent studies have shown a break in the negative tendency of terrestrial wind speeds, with a recent widespread recovery / strengthening of wind speed since around 2013.Kim J, Paik K (2015) Recent recovery of surface wind speed after decadal decrease: a focus on South Korea. Clim Dyn 45(5): 1699–1712. This creates uncertainty in understanding the phenomenon. Most of the uncertainties behind the "global terrestrial stilling" debate resides in (i) the short wind speed data availability, with series starting in the 1960s, (ii) wind speed studies mainly carried on midlatitude regions where the majority of long-term measurements are available; and (iii) the low quality of anemometer records as pointed out by the Fifth Assessment Report (AR5) of the Intergovernmental Panel on Climate Change (IPCC). The low quality in wind speed series is mainly due to non-climatic factors (e.g. observing practice changes, station relocation, anemometer height changes) affecting those records, which result to be unrepresentative of the actual wind speed variations over time. Specific homogenization protocols for wind speed series have been developed in order to detect and adjust potential inhomogeneities.

Ongoing research

The current research on assessing and attributing this phenomenon has focused on reducing the limitation of short availability and low quality of wind speed data. The European funded research project STILLING is a current (2016–2018) initiative that aims to reduce this constraint by rescuing, homogenizing and recovering the longest and highest-quality wind speed series across the globe. The project is currently compiling wind speed records starting in the 1880s providing scientists with approximately 130-year records, roughly 80 years more than previous studies available in the scientific literature. The better knowledge of the past wind speed climate is crucial for understanding the present "global terrestrial stilling" phenomenon, detecting if

is behind this slowdown of wind or similar trends-cycles occurred in the past and could be expected for the future. That is with longer records decadal cycles may be detected.

Implications of wind speed changes

The "global terrestrial stilling" phenomenon is of great scientific, socioeconomic, and environmental interest because of the key impact of even small wind speed changes on atmospheric and ocean dynamics and related fields such as: (i) renewable wind energy; (ii) agriculture and hydrology due to evapotranspiration; (iii) migration of wind-dispersed plant species; (iv) wind-related natural disasters; (v) marine and coastal impacts due to wind-driven storm surges and waves; (vi) dispersion of air pollutants; among many other socioeconomic and environmental spheres. However, for wind energy near-surface wind speeds are mainly observed within 10m of the land surface, and with turbines being located some 60–80 m above the land surface more studies are needed here. More studies are also needed at higher elevation sites, which are often areas that yield much of our freshwater supplies, called water-towers, as wind speeds there have been shown to be decreasing more rapidly than those changes recorded at lower elevation sites, and there are several Chinese papers showing this for the Tibet Plateau.You, Q., Fraedrich, K., Min, J., Kang, S., Zhu, X., Pepin, N., Zhang, L. (2014) Observed surface wind speed in the Tibetan Plateau since 1980 and its physical causes. International Journal of Climatology 34(6), 1873–1882.

References

{{Global catastrophic risks Climate change