Know : About Daylight Saving Time

Daylight saving time (DST) or summer time is the practice of advancing clocks during the summer months that have more sunlight so that people get up later in the morning and go to bed later at night. Typically clocks are adjusted forward one hour near the start of spring and are adjusted backward in the autumn.

The modern idea of daylight saving was first proposed in 1895 by George Vernon Hudson, and it was first implemented by Germany and Austria-Hungary starting on 30 April 1916. Many countries have used it at various times since then, most consistently since the energy crisis of the 1970s.

DaylightSaving-World-Subdivisions

The practice has been both advocated and criticized. Putting clocks back benefits retailing, sports, and other activities that exploit sunlight after working hours, but can cause problems for evening entertainment and other activities tied to the sun (such as farming) or to darkness (such as firework shows). Although an early goal of DST was to reduce evening use of incandescent lighting (formerly a primary use of electricity), modern heating and cooling usage patterns differ greatly, and research about how DST currently affects energy use is limited or contradictory.

Other problems sometimes caused by DST clock shifts are: they complicate timekeeping, and can disrupt meetings, travel, billing, record keeping, medical devices, heavy equipment, and sleep patterns. Software can often adjust computer clocks automatically, but this can be limited and error-prone, particularly when DST dates are changed.

Country/Territory Continent Summer/Hemisphere DST start
(adjust clocks forward)
DST end
(adjust clocks backward)
Notes and other mentions
Afghanistan Asia Does not use DST
Akrotiri and Dhekelia(UK) Europe Boreal/North Last Sunday March Last Sunday October
Albania Europe Boreal/North Last Sunday March Last Sunday October Observed DST in 1940-1943, and since 1974.
Algeria Africa Observed DST in 1916-1921, in the autumn of 1939, in 1944-1945, 1971, 1977-1978 and 1980-1981 .
American Samoa (US) Oceania Does not use DST
Andorra Europe Boreal/North Last Sunday March Last Sunday October Observed DST since 1985.
Angola Africa Does not use DST
Anguilla (UK) Central America Does not use DST
Antigua and Barbuda Central America Does not use DST
Argentina South America Observed DST in 1930-1969, 1974, 1988-2000, 2007-2009.
Armenia Europe Observed DST in 1981-1995, 1997-2011.
Aruba (NL) Central America Does not use DST
Australia Oceania Austral/South First Sunday October First Sunday April

DST used only in Australian Capital Territory,VictoriaNew South WalesTasmaniaSouth Australia and Lord Howe Island.

Austria Europe Boreal/North 01:00 UTC on last Sunday March 01:00 UTC on last Sunday October Observed DST in 1916-1918, 1920, 1940-1948 and since 1980.
Azerbaijan Europe Boreal/North Last Sunday March Last Sunday October Observed DST in 1981-1992 and since 1996.Nagorno-Karabakh abolished DST in 2012.
Bahamas North America Boreal/North Second Sunday March First Sunday November Observed DST since 1964.
Bahrain Asia Does not use DST
Bangladesh Asia Observed DST in 2009.
Barbados Central America Observed DST from 1977-1980.
Belarus Europe Observed DST in 1941-1944, 1981-2010.
Belgium Europe Boreal/North 01:00 UTC on last Sunday March 01:00 UTC on last Sunday October Observed DST in 1916-1940, 1942-1946 and since 1977.
Belize Central America Observed DST in 1973-1974 and 1982-1983.
Benin Africa Does not use DST
Bermuda (UK) North America Boreal/North Second Sunday March First Sunday November Observed DST since 1974.
Bhutan Asia Does not use DST
Bolivia South America Observed DST in 1931-1932.
Bonaire (NL) Central America Does not use DST
Bosnia and Herzegovina Europe Boreal/North Last Sunday March Last Sunday October Observed DST in 1941-1945 and since 1983.
Botswana Africa Observed DST in 1943-1944.
Brazil South America Austral/South Third Sunday October Third Sunday February

DST end delays one week during Carnival week. Only these south and central states use DST: São PauloRio de JaneiroFederal District Brasilia,Santa CatarinaParanáGoiásRio Grande do Sul,Mato Grosso do SulEspírito SantoMinas Geraisand Mato Grosso (some exceptions).

British Virgin Islands(UK) Central America Does not use DST
Brunei Asia Does not use DST
Bulgaria Europe Boreal/North 01:00 UTC on last Sunday March 01:00 UTC on last Sunday October Observed DST in 1943-1944 and since 1979.
Burkina Faso Africa Does not use DST
Burma Asia Does not use DST
Burundi Africa Does not use DST
Cambodia Asia Does not use DST
Cameroon Africa Does not use DST
Canada North America Boreal/North Second Sunday March First Sunday November

Some regions in Quebec, east of 63° westlongitude, most of SaskatchewanSouthampton Island and some areas in British Columbia do not observe DST. Saskatchewan however, observes Central Time even though it is located in the Mountain Time Zone, meaning it effectively observes DST year round.

Cape Verde Africa Observed DST in 1942-1945.
Cayman Islands (UK) Central America Does not use DST
Central African Republic Africa Does not use DST
Chad Africa Observed DST in winter 1979-1980.
Chile South America Austral/South Second Sunday September Last Sunday April Observed DST in 1927-1946 (excluding Easter Island which observed it in 1932-1946 ) and since 1968. Easter Island starts on Saturday to sync withChile
China Asia Observed DST in 1986-1991.
Christmas Island (AU) Asia Does not use DST
Cocos Island (AU) Asia Does not use DST
Colombia South America Observed DST in 1992-1993.
Comoros Africa Does not use DST
Congo Africa Does not use DST
Cook Islands (NZ) Oceania Observed DST in 1978-1991.
Costa Rica Central America Observed DST in 1954, 1979-1980 and 1991-1992.
Croatia Europe Boreal/North 01:00 UTC on last Sunday March 01:00 UTC on last Sunday October Observed DST in 1941-1945 and since 1983.
Cuba Central America Boreal/North Second Sunday March First Sunday November Observed DST in 1928, 1940-1942, 1945-1946 and since 1965.
Curacao (NL) Central America Does not use DST
Cyprus Europe Boreal/North 01:00 UTC on last Sunday March 01:00 UTC on last Sunday October Observed DST since 1975.
Czech Republic Europe Boreal/North 01:00 UTC on last Sunday March 01:00 UTC on last Sunday October Observed DST in 1916-1918, 1940-1949 and since 1979.
Democratic Republic of Congo Africa Does not use DST
Denmark Europe Boreal/North 01:00 UTC on last Sunday March 01:00 UTC on last Sunday October Observed DST in 1916, 1940-1948 and since 1980.
Djibouti Africa Does not use DST
Dominica Central America Does not use DST
Dominican Republic Central America Observed DST in 1966-1967, 1969-1974.
East Timor Asia Does not use DST
Ecuador South America Does not use DST
Egypt Africa/Asia Boreal/North Last Friday April Last Friday September Observed DST in 1940-1945 and 1957-2010. Re-introduces DST in 2014. DST is stopped during Ramadan
El Salvador Central America Observed DST in 1987-1988.
Equatorial Guinea Africa Does not use DST
Eritrea Africa Does not use DST
Estonia Europe Boreal/North 01:00 UTC on last Sunday March 01:00 UTC on last Sunday October Observed DST in 1918, 1940-1944 and since 1981.
Ethiopia Africa Does not use DST
Falkland Islands (UK) South America Keeps on continuous DST since 2011
Faroe Islands (DK) Europe Boreal/North Last Sunday March Last Sunday October Observed DST since 1981.
Fiji Oceania Austral/South Last Sunday October Third Sunday January Observed DST in 1998-2000 and since 2009.
Finland Europe Boreal/North Last Sunday March Last Sunday October Observed DST in 1942 and since 1981.
France Europe Boreal/North 01:00 UTC on last Sunday March 01:00 UTC on last Sunday October Observed DST in 1916-1945 and since 1976.
French Guyana (FR) South America Does not use DST
French Polynesia (FR) Oceania Does not use DST
French Southern and Antarctic Lands (FR) Antarctica Does not use DST
Gabon Africa Does not use DST
Gambia Africa Does not use DST
Georgia Europe Observed DST in 1981-2005.
Germany Europe Boreal/North 01:00 UTC on last Sunday March 01:00 UTC on last Sunday October Observed DST in 1916-1918, 1940-1949, and since 1980.
Ghana Africa Observed DST from 1936-1942.
Greece Europe Boreal/North 01:00 UTC on last Sunday March 01:00 UTC on last Sunday October Observed DST in 1916-1968 and since 1971.
Greenland North America Boreal/North 22:00 local time on Saturday before last Sunday March 23:00 local time on Saturday before last Sunday October Observed DST since 1980.Follows European Union practice, although not a member: hence start & end times correspond to 01:00 UTC on the respective Sunday. See Daylight saving time in the Americas—Greenland Qaanaaquses US and Canada rules. Danmarkshavn does not use DST.
Grenada Central America Does not use DST
Guadeloupe (FR) Central America Does not use DST
Guam (US) Oceania Does not use DST
Guatemala Central America Observed DST in 1973-1974, 1983, 1991 and 2006.
Guernsey (UK) Europe Boreal/North 01:00 GMT on last Sunday March 01:00 GMT on last Sunday October Observed DST in 1916-1968 and since 1972.
Guinea Africa Does not use DST
Guinea-Bissau Africa Does not use DST
Guyana South America Does not use DST
Haiti Central America Boreal/North Second Sunday March First Sunday November Observed DST in 1983-1997, 2005-2006 and from 2012 onwards.
Heard and McDonald Islands (AU) Antarctica Does not use DST
Holy See Europe Boreal/North Last Sunday March Last Sunday October Observed DST in 1916-1920, 1940-1948 and since 1966.
Honduras Central America Observed DST in 1987-1988 and 2006 .
Hong Kong Asia Observed DST in 1941, 1945-1976 and 1979.
Hungary Europe Boreal/North 01:00 UTC on last Sunday March 01:00 UTC on last Sunday October Observed DST in 1916-1920, 1941-1950, 1954-1957 and since 1980.
Iceland Europe Observed DST in 1917-1918 and 1939-1968.
India Asia Observed DST in 1942-1945.
Indonesia Asia Does not use DST
Iran Asia Boreal/North March 21–22 September 21–22 Observed DST in 1977-1980, 1991-2005 and since 2008.
Iraq Asia Observed DST in 1982-2007.
Ireland Europe Boreal/North 01:00 UTC on last Sunday March 01:00 UTC on last Sunday October Observed DST in 1916-1968 and since 1972.
Isle of Man (UK) Europe Boreal/North 01:00 GMT on last Sunday March 01:00 GMT on last Sunday October Observed DST in 1916-1968 and since 1972.
Israel Asia Boreal/North Friday before last Sunday March Last Sunday October Observed DST in 1940-1946, 1948-1957, 1974-1975 and since 1985.
Italy Europe Boreal/North 01:00 UTC on last Sunday March 01:00 UTC on last Sunday October Observed DST in 1916-1920, 1940-1948 and since 1966.
Ivory Coast Africa Does not use DST
Jamaica Central America Observed DST in 1974-1983.
Japan Asia Observed DST in 1948-1951.
Jersey (UK) Europe Boreal/North 01:00 GMT on last Sunday March 01:00 GMT on last Sunday October Observed DST in 1916-1968 and since 1971.
Jordan Asia Boreal/North Last Friday March Last Friday October Returned again to UTC+2 on Dec, 20 2013, Previsible with DST
Kazakhstan Asia Observed DST in 1981-1990 and 1992-2004.
Kenya Africa Does not use DST
Kiribati Oceania Does not use DST
Kosovo Europe Boreal/North Last Sunday March Last Sunday October Observed DST since 1983.
Kuwait Asia Does not use DST
Kyrgyzistan Asia Observed DST in 1981-2005.
Laos Asia Does not use DST
Latvia Europe Boreal/North 01:00 UTC on last Sunday March 01:00 UTC on last Sunday October Observed DST in 1918-1919, 1941-1944 and since 1981.
Lebanon Asia Boreal/North Last Sunday March Last Sunday October Observed DST in 1920-1923, 1957-1961, 1972-1978 and since 1984.
Lesotho Africa Observed DST in 1943-1944.
Liberia Africa Does not use DST
Libya Africa Observed DST in 1951, 1955, 1957, 1982-1989,1997.and 2013.
Liechtenstein Europe Boreal/North Last Sunday March Last Sunday October Observed DST since 1981.
Lithuania Europe Boreal/North 01:00 UTC on last Sunday March 01:00 UTC on last Sunday October Observed DST in 1941-1944, 1981-1999 and since 2003.
Luxembourg Europe Boreal/North 01:00 UTC on last Sunday March 01:00 UTC on last Sunday October Observed DST in 1916-1946 and since 1977.
Macao (CH) Asia Observed DST in 1961-1980.
Macedonia Europe Boreal/North Last Sunday March Last Sunday October Observed DST in 1941-1945 and since 1983.
Madagascar Africa Observed DST in 1954.
Malawi Africa Does not use DST
Malaysia Asia Observed DST in 1933-1935.
Maldives Asia Does not use DST
Mali Africa Does not use DST
Malta Europe Boreal/North 01:00 UTC on last Sunday March 01:00 UTC on last Sunday October Observed DST in 1916-1920, 1940-1948 and since 1966.
Marshall Islands Oceania Does not use DST
Martinica (FR) Central America Observed DST in 1980.
Mauritania Africa Does not use DST
Mauritius Africa Observed DST in 1982-1983 and 2008-2009.
Mexico North America Boreal/North First Sunday April Last Sunday October Observe DST since 1996, but Baja Californiaobserve DST since 1942. Sonora observed DST 1996–1997. Locations less than 20 km from the US border use US DST.
Micronesia Oceania Does not use DST
Midway (US) Oceania Observed DST in 1956.
Moldova Europe Boreal/North Last Sunday March Last Sunday October Observed DST in 1932-1944, 1981-1989 and since 1991.
Monaco Europe Boreal/North Last Sunday March Last Sunday October Observed DST in 1916-1945 and since 1976.
Mongolia Asia Observed DST in 1983-1998 and 2001-2006.
Montenegro Europe Boreal/North Last Sunday March Last Sunday October Observed DST 1941-1945 and since 1983.
Montserrat (UK) Central America Does not use DST
Morocco Africa Boreal/North Last Sunday March Last Sunday October Observed DST in 1939-1945, 1950, 1967, 1974, 1974-1976 and since 2008. DST stops during Ramadan.
Mozambique Africa Does not use DST
Namibia Africa Austral/South First Sunday September First Sunday April Observed DST in 1942-1943 and since 1994.
Nauru Oceania Does not use DST
Nepal Asia Does not use DST
Netherlands Europe Boreal/North 01:00 UTC on last Sunday March 01:00 UTC on last Sunday October Observed DST in 1916-1945 and since 1977.
New Caledonia (FR) Oceania Observed DST in 1977-1979 and 1996-1997.
New Zealand Oceania Austral/South Last Sunday September First Sunday April Observed DST in 1927-1946 and since 1974.
Nicaragua Central America Observed DST in 1973-1975, 1979-1980, 1992-1994 and 2005-2006.
Niger Africa Does not use DST
Nigeria Africa Does not use DST
Niue (NZ) Oceania Does not use DST
North Korea Asia Does not use DST
Northern Mariana Islands (US) Oceania Does not use DST
Norway Europe Boreal/North 01:00 UTC on last Sunday March 01:00 UTC on last Sunday October Observed DST in 1916, 1940-1945, 1959-1965 and since 1980.Follows European Union practice, although not a member.
Oman Asia Does not use DST
Pakistan Asia Observed DST in 1942-1945 (as belonging to India) and 2002.
Palau Oceania Does not use DST
Palestine Asia Boreal/North Last Friday March Last Friday September Observed DST in 1940-1946, 1957-1967, 1974-1975 and since 1985.
Panama Central America Does not use DST
Papua New Guinea Oceania Does not use DST
Paraguay South America Austral/South First Sunday October Fourth Sunday March Observed DST since 1975. Current start and end dates last updated in 2013.
Peru South America Observed DST in 1938-1940, 1986-1987, 1990 and 1994.
Philippines Asia Observed DST in 1936-1937, 1954, 1978 and 1990.
Pitcairn Islands (UK) Oceania Does not use DST
Poland Europe Boreal/North 01:00 UTC on last Sunday March 01:00 UTC on last Sunday October Observed DST in 1916-1919, 1940-1949, 1957-1964 and since 1977.
Portugal Europe Boreal/North 01:00 UTC on last Sunday March 01:00 UTC on last Sunday October Observed DST in 1916-1921, 1924, 1926-1929, 1931-1932, 1934-1949, 1951-1965 and since 1977.
Puerto Rico (US) Central America Observed DST in 1942-1945.
Qatar Asia Does not use DST
Romania Europe Boreal/North 01:00 UTC on last Sunday March 01:00 UTC on last Sunday October Observed DST in 1932-1939 and since 1979.
Russia Asia/Europe Observed DST in 1917-1919 and 1921 (some areas), 1981-2010 . Since 2011 abolishes DST.
Rwanda Africa Does not use DST
Saba (NL) Central America Does not use DST
Saint Barthélemy (FR) Central America Does not use DST
Saint Helena, Ascension and Tristan da Cunha (UK) Africa/South America Does not use DST
Saint Kitts and Nevis Central America Does not use DST
Saint Lucia Central America Does not use DST
Saint Martin (FR) Central America Does not use DST
Saint Pierre and Miquelon (FR) North America Boreal/North Second Sunday March First Sunday November Observed DST since 1987.
Saint Vincent and the Grenadines Central America Does not use DST
Samoa Oceania Austral/South Last Sunday September First Sunday April Observed DST since 2011
San Marino Europe Boreal/North Last Sunday March Last Sunday October Observed DST in 1916-1920, 1940-1948 and since 1966.
Sao Tome and Príncipe Africa Does not use DST
Saudi Arabia Asia Does not use DST
Senegal Africa Does not use DST
Serbia Europe Boreal/North Last Sunday March Last Sunday October Observed DST in 1941-1945 and since 1983.
Seychelles Africa Does not use DST
Sierra Leone Africa Observed DST in 1935-1942 and 1957-1962.
Singapore Asia Observed DST in 1933-1935 by adding 20 minutes to standard time. On January 1, 1936, country changed their time zone to UTC+7:20.
Sint Eustatius (NL) Central America Does not use DST
Sint Maarten (NL) Central America Does not use DST
Slovakia Europe Boreal/North 01:00 UTC on last Sunday March 01:00 UTC on last Sunday October Observed DST in 1916-1918, 1940-1949 and since 1979.
Slovenia Europe Boreal/North 01:00 UTC on last Sunday March 01:00 UTC on last Sunday October Observed DST in 1941-1945 and since 1983.
Solomon Islands Oceania Does not use DST
Somalia Africa Does not use DST
South Africa Africa Observed DST in 1942-1944.
South Georgia Islands(UK) Antarctica Does not use DST
South Korea Asia Observed DST in 1948-1951, 1955-1960 and 1987-1988.
South Sandwich Islands (UK) Antarctica Does not use DST
South Sudan Africa Observed DST in 1970-1985.
Spain Europe Boreal/North 01:00 UTC on last Sunday March 01:00 UTC on last Sunday October Observed DST in 1917-1919, 1924, 1926-1929, 1937-1946, 1949 and since 1974. On Canary Islands DST observed since 1980.
Sri Lanka Asia Observed DST in 1942-1945.
Sudan Africa Observed DST in 1970-1985.
Suriname South America Does not use DST
Swaziland Africa Does not use DST
Sweden Europe Boreal/North 01:00 UTC on last Sunday March 01:00 UTC on last Sunday October Observed DST 15 May–30 September 1916, and since the first Sunday of April in 1980. Before 1996 it ended on the last Sunday of September.
Switzerland Europe Boreal/North 01:00 UTC on last Sunday March 01:00 UTC on last Sunday October Observed DST in 1941-1942 and since 1980.Follows European Union practice, although not a member.
Syria Asia Boreal/North Last Friday March Last Friday October Observed DST in 1920-1923, 1962-1968 and since 1983.
Taiwan Asia Observed DST in 1945-1962, 1974, 1975 and 1979.
Tajikistan Asia Observed DST in 1981-1991.
Tanzania Africa Does not use DST
Thailand Asia Does not use DST
Togo Africa Does not use DST
Tokelau (NZ) Oceania Does not use DST
Tonga Oceania Observed DST from 1999-2002.
Trinidad and Tobago Central America Does not use DST
Tunisia Africa Observed DST in 1939-1945, 1977-1978, 1988-1990 and 2005-2008.
Turkey Asia/Europe Boreal/North 01:00 UTC on last Sunday March 01:00 UTC on last Sunday October Observed DST in 1916, 1920-1922, 1924-1925, 1940-1942, 1945-1951, 1962, 1964, 1970-1983 and since 1985.Follows European Union practice, although not a member.
Turkmenistan Asia Observed DST in 1981-1991.
Turks and Caicos (UK) Central America Boreal/North Second Sunday March First Sunday November Observed DST since 1979.
Tuvalu Oceania Does not use DST
Uganda Africa Does not use DST
Ukraine Europe Boreal/North Last Sunday March Last Sunday October Observed DST in 1941-1943, 1981-1989 and since 1992.The Crimean Supreme Council announced thatCrimea will switch to Moscow time (which does not observe DST) in March 2014 .
United Arab Emirates Asia Does not use DST
United Kingdom Europe Boreal/North 01:00 GMT on last Sunday March 01:00 GMT on last Sunday October
Main article: British Summer Time

Observed DST (British Summer Time (BST)) since 1916.Year-round Summer Time (BST) + Double Summer Time (BDST) 1940-1945. Two-stage Double Summer Time (BDST) 1947. Year-round Summer Time (BST) 1968-1971.

United States North America Boreal/North Second Sunday March First Sunday November

Arizona (except the Navajo Nation Community) and Hawaii do not use DST.[10]

United States Virgin Islands (US) Central America Does not use DST
Uruguay South America Austral/South First Sunday October Second Sunday March Observed DST in 1923-1926, 1933-1943, 1959-1960, 1965-1970, 1972, 1974-1980, 1987-1993 and since 2004.
Uzbekistan Asia Observed DST in 1981-1991.
Vanuatu Oceania Observed DST in 1983-1993.
Venezuela South America Does not use DST
Vietnam Asia Does not use DST
Wallis and Futuna(FR) Oceania Does not use DST
Western Sahara Africa Boreal/North Last Sunday March Last Sunday October Observed DST since 2008. DST is stopped during Ramadan. Only areas controlled by Morocco uses DST.
Yemen Asia Does not use DST
Zambia Africa Does not use DST
Zimbabwe Africa Does not use DST

Courtesy : CGP Grey via Youtube and Wikipedia

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Know : Atmospheric Circulation

Atmospheric circulation is the large-scale movement of air, and the means (together with the smaller ocean circulation) by which thermal energy is distributed on the surface of the Earth.

Earth_Global_CirculationThe large-scale structure of the atmospheric circulation varies from year to year, but the basic climatological structure remains fairly constant. Individual weather systems – mid-latitude depressions, or tropical convective cells – occur “randomly”, and it is accepted that weather cannot be predicted beyond a fairly short limit: perhaps a month in theory, or (currently) about ten days in practice (see Chaos theory and Butterfly effect). Nonetheless, as the climate is the average of these systems and patterns – where and when they tend to occur again and again – it is stable over longer periods of time.

As a rule, the “cells” of Earth’s atmosphere shift polewards in warmer climates (e.g. interglacials compared toglacials), but remain largely constant even due to continental drift; they are, fundamentally, a property of the Earth’s size, rotation rate, heating and atmospheric depth, all of which change little. Tectonic uplift can significantly alter major elements of it, however – for example the jet stream -, and plate tectonics shift ocean currents. In the extremely hot climates of the Mesozoic, indications of a third desert belt at the Equator has been found; it was perhaps caused by convection. But even then, the overall latitudinal pattern of Earth’s climate was not much different from the one today.

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See More Know : Weakening Trade Winds and Global Warming

Courtesy : Mr. Smajda’s Class Videos, YouTube and Wikipedia

Know : Weakening Trade Winds and Global Warming

What are the trade winds?

globalcircThe trade winds are just air movements toward the equator. They are warm, steady breezes that blow almost continuously. The Coriolis Effect makes the trade winds appear to be curving to the west, whether they are traveling to the equator from the south or north.

The trade winds (also called trades) are the prevailing pattern of easterly surface winds found in the tropics, within the lower portion of the Earth’s atmosphere, in the lower section of the troposphere near the Earth’s equator. The trade winds blow predominantly from the northeast in the Northern Hemisphere and from the southeast in the Southern Hemisphere, strengthening during the winter and when the Arctic oscillation is in its warm phase. Historically, the trade winds have been used by captains of sailing ships to cross the world’s oceans for centuries, and enabled European empire expansion into the Americas and trade routes to become established across the Atlantic and Pacific oceans.

In meteorology, the trade winds act as the steering flow for tropical storms that form over the Atlantic, Pacific, and southern Indian Oceans and make landfall in North America, Southeast Asia, and Madagascar and eastern Africa, respectively. Trade winds also steer African dust westward across the Atlantic Ocean into the Caribbean Sea, as well as portions of southeastern North America. Shallow cumulus clouds are seen within trade wind regimes, and are capped from becoming taller by a trade wind inversion, which is caused by descending air aloft from within the subtropical ridge. The weaker the trade winds become, the more rainfall can be expected within neighboring landmasses.

Understand Atmospheric Circulation better from the basics here

windpatThe trade winds in the Pacific Ocean are weakened as a result of global warming, according to a new study that indicates changes to the region’s biology are possible.

Using a combination of real-world observations and computer modeling, researchers conclude that a vast loop of circulating wind over the Pacific Ocean, known as the Walker circulation, has weakened by about 3.5 percent since the mid-1800s. The trade winds are the portion of the Walker circulation that blow across the ocean surface.

The researchers predict another 10 percent decrease by the end of the 21st century. 

The effect, attributed at least in part to human-induced climate change, could disrupt food chains and reduce the biological productivity of the Pacific Ocean, scientists said.

Humans to blame

The researchers used records of sea-level atmospheric pressure readings from as far back as the mid-1800s to reconstruct the wind intensity of the Walker circulation over the past 150 years. A computer climate model replicated the effect seen in the historical record.

Some of the computer simulations included the effects of human greenhouse gas emissions; others included only natural factors known to affect climate such as volcanic eruptions and solar variations.

“We were able to ask ‘What if humans hadn’t done anything? Or what if volcanoes erupted? Or if the sun hadn’t varied?'” Vecchi said. “Our only way to account for the observed changes is through the impact of human activity, and principally from greenhouse gases from fossil fuel burning.”

The earth’s average temperature has risen by about 1 degree Fahrenheit over the past century and many scientists believe greenhouse gases and carbon dioxide emissions from human activities are to blame.

“This is evidence supporting global warming and also evidence of our ability to make reasonable predictions of at least the large scale changes that we should expect from global warming,” Vecchi told LiveScience.

By extrapolating their data and combining it with results from other models, the researchers predict the Walker circulation could slow by an additional 10 percent by 2100.

Driving force

The trade winds blow from the east at an angle towards the equator and have been used by sailors for centuries seeking to sail west. Christopher Columbus relied on the Atlantic’s trade winds to carry him to North America. The winds get their name from their reliability: To say that a “wind blows trade” is to say that it blows on track.

The overall Walker circulation is powered by warm, rising air in the west Pacific Ocean and sinking cool air in the eastern Pacific.

This looping conveyer belt of winds has far-reaching effects on climate around the globe. It steers ocean currents and nourishes marine life across the equatorial Pacific and off the coast of South America by driving the upwelling of nutrient-rich cold water from the ocean depths to the surface.

The Walker circulation is also primarily responsible for transporting water vapor that evaporates from the ocean surface west, towards Indonesia; there, the moisture rises up into the atmosphere, condenses, and falls back to Earth as rain.

The effects of global warming

Several theories on the effects of global warming predict a weakening of the Walker circulation. Scientists think it works like this:

To remain energetically balanced, the rate at which the atmosphere absorbs water vapor must be balanced by the rate of rainfall. But as temperatures rise and more water evaporates from the ocean, water vapor in the lower atmosphere increases rapidly. Because of various physical processes, however, the rate of rainfall does not increase as fast.

Since the atmosphere is absorbing moisture faster than it can dump it, and because wind is the major transporter of moisture into the atmosphere, air circulation must slow down if the energy balance is to be maintained.

A drop in winds could reduce the strength of both surface and subsurface ocean currents and dampen cold water upwelling at the equator.

“This could have important effects on ocean ecosystems,” Vecchi said. “The ocean currents driven by the trade winds supply vital nutrients to near-surface ocean ecosystems across the equatorial Pacific, which is a major fishing region.”

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Courtesy : Global Warming Weakens Trade Winds | LiveScience