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144-506: The scale was developed by Canadian scientists in 1992, and then adopted and standardized by the UN's World Health Organization and World Meteorological Organization in 1994. Public health organizations recommend that people protect themselves (for example, by applying sunscreen to the skin and wearing a hat and sunglasses ) if they spend substantial time outdoors when the UV index is 3 or higher; see

288-464: A UNEP 1994 Assessment overestimated ozone loss for the 1994–1997 period. Chlorofluorocarbons (CFCs) and other halogenated ozone-depleting substances (ODS) are mainly responsible for man-made chemical ozone depletion. The total amount of effective halogens (chlorine and bromine) in the stratosphere can be calculated and are known as the equivalent effective stratospheric chlorine (EESC). CFCs as refrigerants were invented by Thomas Midgley Jr. in

432-674: A "systemic failure". In 2010, the organization suffered the worst loss of life in its history, when 101 personnel died in the Haiti earthquake . Acting under the United Nations Security Council Resolution 1973 in 2011, NATO countries intervened in the First Libyan Civil War . The Millennium Summit was held in 2000 to discuss the UN's role in the 21st century. The three-day meeting was

576-722: A 10 percent increase in UV-B radiation was associated with a 19 percent increase in melanomas for men and 16 percent for women. A study of people in Punta Arenas , at the southern tip of Chile , showed a 56 percent increase in melanoma and a 46 percent increase in non-melanoma skin cancer over a period of seven years, along with decreased ozone and increased UVB levels. Epidemiological studies suggest an association between ocular cortical cataracts and UV-B exposure, using crude approximations of exposure and various cataract assessment techniques. A detailed assessment of ocular exposure to UV-B

720-607: A 1976 report by the United States National Academy of Sciences concluded that credible scientific evidence supported the ozone depletion hypothesis a few countries, including the United States, Canada, Sweden, Denmark, and Norway, moved to eliminate the use of CFCs in aerosol spray cans. At the time this was widely regarded as a first step towards a more comprehensive regulation policy, but progress in this direction slowed in subsequent years, due to

864-621: A UN official, negotiated an armistice to the resulting conflict , with the Security Council deciding that “an armistice shall be established in all sectors of Palestine”. On 7 November 1956, the first UN peacekeeping force was established to end the Suez Crisis ; however, the UN was unable to intervene against the Soviet Union's simultaneous invasion of Hungary , following the country's revolution . On 14 July 1960,

1008-624: A cascade of ecological impacts, harming soil microbes, insects, wildlife, and entire ecosystems. Ozone depletion would magnify all of the effects of UV on human health , both positive (including production of vitamin D) and negative (including sunburn, skin cancer, and cataracts). In addition, increased surface UV leads to increased tropospheric ozone, which is a health risk to humans. The most common forms of skin cancer in humans, basal and squamous cell carcinomas, have been strongly linked to UV-B exposure. The mechanism by which UVB induces these cancers

1152-482: A combination of political factors (continued resistance from the halocarbon industry and a general change in attitude towards environmental regulation during the first two years of the Reagan administration) and scientific developments (subsequent National Academy assessments that indicated that the first estimates of the magnitude of ozone depletion had been overly large). A critical DuPont manufacturing patent for Freon

1296-412: A cycle, a chlorine atom reacts with an ozone molecule ( O 3 ), taking an oxygen atom to form chlorine monoxide (ClO) and leaving an oxygen molecule ( O 2 ). The ClO can react with a second molecule of ozone, releasing the chlorine atom and yielding two molecules of oxygen. The chemical shorthand for these gas-phase reactions is: The overall effect is a decrease in the amount of ozone, though

1440-672: A limited ability to adapt to increased levels of UVB, therefore plant growth can be directly affected by UVB radiation." Over the years, the Arctic ozone layer has depleted severely. As a consequence species that live above the snow cover or in areas where snow has melted abundantly, due to hot temperatures, are negatively impacted due to UV radiation that reaches the ground. Depletion of the ozone layer and allowing excess UVB radiation would initially be assumed to increase damage to plant DNA. Reports have found that when plants are exposed to UVB radiation similar to stratospheric ozone depletion, there

1584-1013: A myriad of autonomous, separately administered funds, programmes, research and training institutes, and other subsidiary bodies . Each of these entities have their own area of work, governance structure, and budgets such as the World Trade Organization (or the WTO) and the International Atomic Energy Agency (or the IAEA), operate independently of the UN but maintain formal partnership agreements. The UN performs much of its humanitarian work through these institutions, such as preventing famine and malnutrition (the World Food Programme ), protecting vulnerable and displaced people (the UNHCR ), and combating

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1728-547: A permanent member to block adoption of a resolution, though not debate. The ten temporary seats are held for two-year terms, with five members elected each year by the General Assembly on a regional basis . The presidency of the Security Council rotates alphabetically each month. The UN Secretariat carries out the day-to-day duties required to operate and maintain the UN system. It is composed of tens of thousands of international civil servants worldwide and headed by

1872-606: A plane crash . Months later he was posthumously awarded the Nobel Peace Prize . In 1964, Hammarskjöld's successor, U Thant , deployed the UN Peacekeeping Force in Cyprus , which would become one of the UN's longest-running peacekeeping missions. With the spread of decolonization in the 1960s, the UN's membership shot up due to an influx of newly independent nations. In 1960 alone, 17 new states joined

2016-403: A scientific consensus was established or important uncertainties in the science field were being resolved. The ozone case was understood comparably well by lay persons as e.g. Ozone shield or ozone hole were useful "easy-to-understand bridging metaphors". Americans voluntarily switched away from aerosol sprays, resulting in a 50 percent sales loss even before legislation was enforced. After

2160-445: A two-thirds majority of those present and voting is required. All other questions are decided by a majority vote. Each member has one vote. Apart from the approval of budgetary matters, resolutions are not binding on the members. The Assembly may make recommendations on any matters within the scope of the UN, except matters of peace and security that are under consideration by the Security Council. Draft resolutions can be forwarded to

2304-889: A wide variety of complex tasks. The UN comprises six principal operational organizations: the General Assembly , the Security Council , the Economic and Social Council , the International Court of Justice , the UN Secretariat , and the Trusteeship Council , although the Trusteeship Council has been suspended since 1994. The UN System includes a multitude of specialized agencies , funds, and programmes, including

2448-1033: A wide variety of topics. These include the United Nations Permanent Forum on Indigenous Issues , which advises UN agencies on issues relating to indigenous peoples , the United Nations Forum on Forests , which coordinates and promotes sustainable forest management, the United Nations Statistical Commission , which co-ordinates information-gathering efforts between agencies, and the Commission on Sustainable Development , which co-ordinates efforts between UN agencies and NGOs working towards sustainable development . ECOSOC may also grant consultative status to non-governmental organizations. as of April 2021 almost 5,600 organizations have this status. The UN Charter stipulates that each primary organ of

2592-672: A wide-brimmed hat, and UV-blocking sunglasses. Generously apply broad spectrum SPF 50+ sunscreen every 1.5 hours, even on cloudy days, and after swimming or sweating. Bright surfaces, such as sand, water, and snow, will increase UV exposure. Try to avoid sun exposure between 10 a.m. and 4 p.m. If outdoors, seek shade and wear sun-protective clothing, a wide-brimmed hat, and UV-blocking sunglasses. Generously apply broad spectrum SPF 50+ sunscreen every 1.5 hours, even on cloudy days, and after swimming or sweating. Bright surfaces, such as sand, water, and snow, will increase UV exposure. Some sunshine prediction and advice apps have been released. These use

2736-574: Is headquartered in New York City , in international territory with certain privileges extraterritorial to the United States, and the UN has other offices in Geneva , Nairobi , Vienna , and The Hague , where the International Court of Justice is headquartered at the Peace Palace . The UN was established after World War II with the aim of preventing future world wars , and succeeded

2880-454: Is 1 UV index hour. United Nations The United Nations ( UN ) is a diplomatic and political international organization with the intended purpose of maintaining international peace and security , developing friendly relations among nations, achieving international cooperation, and serving as a center for coordinating the actions of member nations. It is widely recognised as the world's largest international organization. The UN

3024-404: Is a continuing process that terminates when an oxygen atom recombines with an ozone molecule to make two O 2 molecules. It is worth noting that ozone is the only atmospheric gas that absorbs UVB light. The total amount of ozone in the stratosphere is determined by a balance between photochemical production and recombination. Ozone can be destroyed by a number of free radical catalysts;

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3168-458: Is an area of the Antarctic stratosphere in which the recent ozone levels have dropped to as low as 33 percent of their pre-1975 values. The ozone hole occurs during the Antarctic spring, from September to early December, as strong westerly winds start to circulate around the continent and create an atmospheric container. Within this polar vortex , over 50 percent of the lower stratospheric ozone

3312-467: Is defined in the UN Charter as the organization's chief administrative officer. Article 99 of the charter states that the secretary-general can bring to the Security Council's attention "any matter which in their opinion may threaten the maintenance of international peace and security", a phrase that secretaries-general since Trygve Lie have interpreted as giving the position broad scope for action on

3456-426: Is destroyed during the Antarctic spring. As explained above, the primary cause of ozone depletion is the presence of chlorine-containing source gases (primarily CFCs and related halocarbons). In the presence of UV light, these gases dissociate, releasing chlorine atoms, which then go on to catalyze ozone destruction. The Cl-catalyzed ozone depletion can take place in the gas phase, but it is substantially enhanced in

3600-455: Is even more efficient than chlorine at destroying ozone on a per-atom basis, but there is much less bromine in the atmosphere at present. Both chlorine and bromine contribute significantly to overall ozone depletion. Laboratory studies have also shown that fluorine and iodine atoms participate in analogous catalytic cycles. However, fluorine atoms react rapidly with water vapour, methane and hydrogen to form strongly bound hydrogen fluoride (HF) in

3744-487: Is formed in the stratosphere when oxygen gas molecules photodissociate after absorbing UVC photons. This converts a single O 2 into two atomic oxygen radicals . The atomic oxygen radicals then combine with separate O 2 molecules to create two O 3 molecules. These ozone molecules absorb UVB light, following which ozone splits into a molecule of O 2 and an oxygen atom. The oxygen atom then joins up with an oxygen molecule to regenerate ozone. This

3888-524: Is generally recognized to be a health risk, as ozone is toxic due to its strong oxidant properties. The risks are particularly high for young children, the elderly, and those with asthma or other respiratory difficulties. At this time, ozone at ground level is produced mainly by the action of UV radiation on combustion gases from vehicle exhausts. Vitamin D is produced in the skin by ultraviolet light. Thus, higher UVB exposure raises human vitamin D in those deficient in it. Recent research (primarily since

4032-567: Is integrated over the whole spectrum. This gives a weighted figure called the Diffey-weighted UV irradiance (DUV) or the erythemal dose rate. Since the normalization weight is 1 for wavelengths between 250nm and 298nm, a source of a given DUV irradiance causes roughly as much sunburn as a radiation source emitting those wavelengths at the same intensity, although inaccuracies in the spectrum definition and varying reactions by skin type may mean this relationship does not actually hold. When

4176-605: Is more likely to be significant on species interactions than on plants themselves. Another significant impact of ozone depletion on plant life is the stress experienced by plants when exposed to UV radiation. This can cause a decrease in plant growth and an increase in oxidative stress, due to the production of nitric oxide and hydrogen peroxide. In areas where substantial ozone depletion has occurred, increased UV-B radiation reduces terrestrial plant productivity (and likewise carbon sequestration) by about 6%. Moreover, if plants are exposed to high levels of UV radiation, it can elicit

4320-478: Is partly because UVA , which has also been implicated in some forms of skin cancer, is not absorbed by ozone, and because it is nearly impossible to control statistics for lifestyle changes over time. Ozone depletion may also influence wind patterns. Ozone, while a minority constituent in Earth's atmosphere, is responsible for most of the absorption of UVB radiation. The amount of UVB radiation that penetrates through

4464-467: Is still growing. Its source remains a mystery, but illegal manufacturing is suspected by some. CFC-113a seems to have been accumulating unabated since 1960. Between 2012 and 2017, concentrations of the gas jumped by 40 percent. A study by an international team of researchers published in Nature found that since 2013 emissions that are predominately from north-eastern China have released large quantities of

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4608-429: Is the reason why the Antarctic ozone depletion is greatest during spring. During winter, even though PSCs are at their most abundant, there is no light over the pole to drive chemical reactions. During the spring, however, sunlight returns and provides energy to drive photochemical reactions and melt the polar stratospheric clouds, releasing considerable ClO, which drives the hole mechanism. Further warming temperatures near

4752-548: Is well understood—absorption of UV-B radiation causes the pyrimidine bases in the DNA molecule to form dimers , resulting in transcription errors when the DNA replicates. These cancers are relatively mild and rarely fatal, although the treatment of squamous cell carcinoma sometimes requires extensive reconstructive surgery. By combining epidemiological data with results of animal studies, scientists have estimated that every one percent decrease in long-term stratospheric ozone would increase

4896-655: The Battle of Mogadishu . The UN mission to Bosnia faced worldwide ridicule for its indecisive and confused mission in the face of ethnic cleansing. In 1994, the UN Assistance Mission for Rwanda failed to intervene in the Rwandan genocide amidst indecision in the Security Council. From the late 1990s to the early 2000s, international interventions authorized by the UN took a wider variety of forms. The United Nations Security Council Resolution 1244 authorised

5040-833: The Earth's atmosphere . These wavelengths cause skin cancer , sunburn , permanent blindness, and cataracts , which were projected to increase dramatically as a result of thinning ozone, as well as harming plants and animals. These concerns led to the adoption of the Montreal Protocol in 1987, which bans the production of CFCs, halons, and other ozone-depleting chemicals. Over time, scientists have developed new refrigerants with lower global warming potential (GWP) to replace older ones. For example, in new automobiles, R-1234yf systems are now common, being chosen over refrigerants with much higher GWP such as R-134a and R-12 . The ban came into effect in 1989. Ozone levels stabilized by

5184-528: The Four Power Declaration on General Security which aimed for the creation "at the earliest possible date of a general international organization". This was the first public announcement that a new international organization was being contemplated to replace the League of Nations. The Tehran Conference followed shortly afterwards at which Roosevelt, Churchill and Joseph Stalin , the leader of

5328-540: The Group of 77 under the leadership of Algeria, which briefly became a dominant power at the UN. On 10 November 1975, a bloc comprising the Soviet Union and Third World nations passed a resolution , over strenuous American and Israeli opposition, declaring Zionism to be a form of racism . The resolution was repealed on 16 December 1991, shortly after the end of the Cold War. With an increasing Third World presence and

5472-472: The ICJ Statute , which forms an integral part of the UN Charter, and non-members may also become parties. The ICJ's rulings are binding upon parties and, along with its advisory opinions, serve as sources of international law . The court is composed of 15 judges appointed to nine-year terms by the General Assembly. Every sitting judge must be from a different nation. The Economic and Social Council (or

5616-547: The International Labour Organization (ILO). The recommendations below are for average adults with lightly tanned skin ( Fitzpatrick scale of skin colour : Type II). Those with darker skin (Type IV+) are more likely to withstand greater sun exposure, while extra precautions are needed for children, seniors, particularly fair-skinned adults, and those who have greater sun sensitivity for medical reasons or from UV exposure in previous days. When

5760-743: The League of Nations , which was characterized as being ineffective. On 25 April 1945, 50 nations assembled in San Francisco , California, for a conference and initialised the drafting of the UN Charter , which was adopted on 25 June 1945. The charter took effect on 24 October 1945, when the UN began operations. The UN's objectives, as outlined by its charter, include maintaining international peace and security, protecting human rights , delivering humanitarian aid , promoting sustainable development , and upholding international law . At its founding,

5904-528: The NATO -led Kosovo Force beginning in 1999. The UN mission in the Sierra Leone Civil War was supplemented by a British military intervention . The invasion of Afghanistan in 2001 was overseen by NATO. In 2003, the United States invaded Iraq despite failing to pass a UN Security Council resolution for authorization, prompting a new round of questioning of the UN's effectiveness. Under

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6048-820: The Paris Peace Conference . The League of Nations was approved and started operations, but the United States never joined. On 10 January 1920, the League of Nations formally came into being when the Covenant of the League of Nations , ratified by 42 nations in 1919, took effect. The League Council acted as an executive body directing the Assembly's business. It began with four permanent members—the United Kingdom , France , Italy , and Japan . After some limited successes and failures during

6192-591: The Richter scale , which are logarithmic (the severity multiplies for each step on the scale, growing exponentially). An index of 0 corresponds to zero UV radiation, as is essentially the case at night. An index of 10 corresponds roughly to midday summer sunlight in the tropics with a clear sky when the UV index was originally designed; now summertime index values in the tens are common for tropical latitudes, mountainous altitudes, areas with ice/water reflectivity and areas with above-average ozone layer depletion . While

6336-546: The Total Ozone Mapping Spectrometer (TOMS). Reductions of up to 70 percent in the ozone column observed in the austral (southern hemispheric) spring over Antarctica and first reported in 1985 (Farman et al.) are continuing. Antarctic total column ozone in September and October have continued to be 40–50 percent lower than pre-ozone-hole values since the 1990s. A gradual trend toward "healing"

6480-686: The United States launched the UV Alert. While the two countries have different baseline UV intensity requirements before issuing an alert, their common goal is to raise awareness of the dangers of over-exposure to the Sun on days with intense UV radiation. In 2007, the United Nations honored UV index inventors Kerr, McElroy, and Wardle with the Innovators Award for their far-reaching work on reducing public health risks from UV radiation. In

6624-753: The White House in December 1941 for the Arcadia Conference . Roosevelt is considered a founder of the UN, and coined the term United Nations to describe the Allied countries . Churchill accepted it, noting its use by Lord Byron . The text of the Declaration by United Nations was drafted on 29 December 1941, by Roosevelt, Churchill, and Harry Hopkins . It incorporated Soviet suggestions but included no role for France. One major change from

6768-646: The World Bank Group , the World Health Organization , the World Food Programme , UNESCO , and UNICEF . Additionally, non-governmental organizations may be granted consultative status with the Economic and Social Council and other agencies. The UN's chief administrative officer is the secretary-general , currently António Guterres , who is a Portuguese politician and diplomat. He began his first five-year term on 1 January 2017 and

6912-525: The World Health Organization and World Meteorological Organization in 1994, gradually replaced the inconsistent regional versions, specifying not only a uniform calculation method (the Canadian definition) but also standard colors and graphics for visual media. On December 29, 2003, a world-record ground-level UV index of 43.3 was detected at Bolivia 's Licancabur volcano, though other scientists dispute readings higher than 26. In 2005, Australia and

7056-406: The secretary-general , who is assisted by the deputy secretary-general . The Secretariat's duties include providing information and facilities needed by UN bodies for their meetings and carrying out tasks as directed by the Security Council, the General Assembly, the Economic and Social Council, and other UN bodies. The secretary-general acts as the spokesperson and leader of the UN. The position

7200-702: The 1920s, the League proved ineffective in the 1930s, as it failed to act against the Japanese invasion of Manchuria in 1933. Forty nations voted for Japan to withdraw from Manchuria but Japan voted against it and walked out of the League instead of withdrawing from Manchuria. It also failed to act against the Second Italo-Ethiopian War , after the appeal for international intervention by Ethiopian Emperor Haile Selassie I at Geneva in 1936 went with no avail, including when calls for economic sanctions against Italy failed. Italy and other nations left

7344-458: The 1930s. They were used in air conditioning and cooling units, as aerosol spray propellants prior to the 1970s, and in the cleaning processes of delicate electronic equipment. They also occur as by-products of some chemical processes. No significant natural sources have ever been identified for these compounds—their presence in the atmosphere is due almost entirely to human manufacture. As mentioned above, when such ozone-depleting chemicals reach

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7488-496: The 1991 eruption of Mt. Pinatubo in the Philippines. Ozone depletion also explains much of the observed reduction in stratospheric and upper tropospheric temperatures. The source of the warmth of the stratosphere is the absorption of UV radiation by ozone, hence reduced ozone leads to cooling. Some stratospheric cooling is also predicted from increases in greenhouse gases such as CO 2 and CFCs themselves; however,

7632-531: The Antarctic winter and spring, reactions on the surface of the polar stratospheric cloud particles convert these "reservoir" compounds into reactive free radicals (Cl and ClO). Denitrification is the process by which the clouds remove NO 2 from the stratosphere by converting it to nitric acid in PSC particles, which then are lost by sedimentation. This prevents newly formed ClO from being converted back into ClONO 2 . The role of sunlight in ozone depletion

7776-636: The Atlantic Charter was the addition of a provision for religious freedom , which Stalin approved after Roosevelt insisted. Roosevelt's idea of the " Four Powers ", refers to the four major Allied countries, the United States, the United Kingdom, the Soviet Union, and China , emerged in the Declaration by the United Nations. On New Year's Day 1942, Roosevelt, Churchill, the Soviet Union's former Foreign Minister Maxim Litvinov , and

7920-602: The CONIDA, the Peruvian Space Agency, published its own study, which yielded almost the same findings as the Ecuadorian study. The main public concern regarding the ozone hole has been the effects of increased surface UV radiation on human health. So far, ozone depletion in most locations has been typically a few percent and, as noted above, no direct evidence of health damage is available in most latitudes. If

8064-562: The Charter by the five permanent members of the Security Council : the United States, the United Kingdom, France, the Soviet Union and China — and by a majority of the other 46 nations. The first meetings of the General Assembly , with 51 nations represented, and the Security Council took place in London beginning in January 1946. Debates began at once, covering topical issues such as

8208-666: The Chinese Premier T. V. Soong signed the " Declaration by United Nations ", and the next day the representatives of twenty-two other nations added their signatures. During the war, the United Nations became the official term for the Allies. In order to join, countries had to sign the Declaration and declare war on the Axis powers . The October 1943 Moscow Conference resulted in the Moscow Declarations , including

8352-428: The ECOSOC) assists the General Assembly in promoting international economic and social co-operation and development. It was established to serve as the UN's primary forum for global issues and is the largest and most complex UN body. The ECOSOC's functions include gathering data, conducting studies and advising and making recommendations to member states. Its work is carried out primarily by subsidiary bodies focused on

8496-463: The Earth's stratosphere, while organic molecules containing iodine react so rapidly in the lower atmosphere that they do not reach the stratosphere in significant quantities. A single chlorine atom is able to react with an average of 100,000 ozone molecules before it is removed from the catalytic cycle. This fact plus the amount of chlorine released into the atmosphere yearly by chlorofluorocarbons (CFCs) and hydrochlorofluorocarbons (HCFCs) demonstrates

8640-420: The General Assembly by its six main committees: As well as by the following two committees: The Security Council is charged with maintaining peace and security among nations. While other organs of the UN can only make recommendations to member states, the Security Council has the power to make binding decisions that member states have agreed to carry out, under the terms of Charter Article 25. The decisions of

8784-496: The Gulf of California and found "widespread evidence of epidermal damage commonly associated with acute and severe sunburn", having cells that form when the DNA is damaged by UV radiation. The findings suggest "rising UV levels as a result of ozone depletion are to blame for the observed skin damage, in the same way that human skin cancer rates have been on the increase in recent decades." Apart from whales many other animals such as dogs, cats, sheep and terrestrial ecosystems also suffer

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8928-568: The HIV/AIDS pandemic (the UNAIDS ). Ozone depletion Ozone depletion consists of two related events observed since the late 1970s: a steady lowering of about four percent in the total amount of ozone in Earth's atmosphere, and a much larger springtime decrease in stratospheric ozone (the ozone layer ) around Earth's polar regions. The latter phenomenon is referred to as the ozone hole . There are also springtime polar tropospheric ozone depletion events in addition to these stratospheric events. The main causes of ozone depletion and

9072-422: The League. When war broke out in 1939 , the League effectively closed down. The first step towards the establishment of the United Nations was the Inter-Allied Conference in London that led to the Declaration of St James's Palace on 12 June 1941. By August 1941, American President Franklin Roosevelt and British Prime Minister Winston Churchill had drafted the Atlantic Charter ; which defined goals for

9216-496: The Montreal Protocol) shows that many humans have less than optimal vitamin D levels. In particular, in the U.S. population, the lowest quarter of vitamin D (<17.8 ng/ml) were found using information from the National Health and Nutrition Examination Survey to be associated with an increase in all-cause mortality in the general population. While blood level of vitamin D in excess of 100 ng/ml appear to raise blood calcium excessively and to be associated with higher mortality,

9360-427: The Soviet Union, and the signing of the Korean Armistice Agreement on 27 July 1953. On 29 November 1947, the General Assembly approved resolution 181 , a proposal to partition Palestine into two state, with Jerusalem placed under a special international regime. The plan failed and a civil war broke out in Palestine, that led to the creation of the state of Israel afterward. Two years later, Ralph Bunche ,

9504-400: The Soviet Union, before all the issues were resolved. By 1 March 1945, 21 additional states had signed the Declaration by the United Nations. After months of planning, the UN Conference on International Organization opened in San Francisco on 25 April 1945. It was attended by 50 nations' governments and a number of non-governmental organizations. The delegations of the Big Four chaired

9648-451: The Soviet Union, met and discussed the idea of a post-war international organization. The new international organisation was formulated and negotiated amongst the delegations from the Allied Big Four at the Dumbarton Oaks Conference from 21 September to 7 October 1944. They agreed on proposals for the aims, structure and functioning of the new organization. It took the conference at Yalta in February 1945, and further negotiations with

9792-499: The UN authorized a US-led coalition that repulsed Iraq's invasion of Kuwait . Brian Urquhart , the under-secretary-general of the UN from 1971 to 1985, later described the hopes raised by these successes as a "false renaissance" for the organization, given the more troubled missions that followed. Beginning in the last decades of the Cold War , critics of the UN condemned the organization for perceived mismanagement and corruption. In 1984, American President Ronald Reagan withdrew

9936-412: The UN established the United Nations Operation in the Congo (or UNOC), the largest military force of its early decades, to bring order to Katanga , restoring it to the control of the Democratic Republic of the Congo by 11 May 1964. While travelling to meet rebel leader Moise Tshombe during the conflict, Dag Hammarskjöld , often named as one of the UN's most effective secretaries-general, died in

10080-562: The UN had 51 member states ; as of 2024 , it has 193 sovereign states , nearly all of the world's recognized sovereign states. The UN's mission to preserve world peace was complicated in its initial decades due in part to Cold War tensions that existed between the United States and Soviet Union and their respective allies. Its mission has included the provision of primarily unarmed military observers and lightly armed troops charged with primarily monitoring, reporting and confidence-building roles. UN membership grew significantly following

10224-430: The UN itself and operate with almost complete independence from it". These include specialized agencies, research and training institutions, programmes and funds and other UN entities. All organizations in the UN system obey the Noblemaire principle , which calls for salaries that will attract and retain citizens of countries where compensation is highest, and which ensures equal pay for work of equal value regardless of

10368-529: The UN's focus on promoting development, peacekeeping, human rights and global security. The Sustainable Development Goals (or SDGs) were launched in 2015 to succeed the Millennium Development Goals. In addition to addressing global challenges, the UN has sought to improve its accountability and democratic legitimacy by engaging more with civil society and fostering a global constituency. In an effort to enhance transparency, in 2016

10512-520: The UN's primary mandate was peacekeeping , the division between the United States and the Soviet Union often paralysed the organization; generally allowing it to intervene only in conflicts distant from the Cold War . Two notable exceptions were a Security Council resolution on 7 July 1950 authorizing a US-led coalition to repel the North Korean invasion of South Korea , passed in the absence of

10656-582: The UN, 16 of them from Africa. On 25 October 1971, with opposition from the United States, but with the support of many Third World nations, the People's Republic of China was given the Chinese seat on the Security Council in place of the Republic of China (also known as Taiwan). The vote was widely seen as a sign of waning American influence in the organization. Third World nations organized themselves into

10800-577: The UV index and Fitzpatrick scale skin type to calculate the maximum exposure time before receiving a sunburn. The Fitzpatrick scale is not sufficient to precisely estimate the minimum radiation dose needed for sunburn. Research has found broad variation within and between populations, e.g. for skin type V subjects the MED in the US is 60–100 mJ/cm vs. 120–240 mJ/cm in Taiwan. Neglecting weighting, 9 mJ/cm

10944-426: The UV index can be calculated from a direct measurement of the UV spectral power at a given location, as some inexpensive portable devices are able to approximate, the value given in weather reports is usually a prediction based on a computer model. Although this may be in error (especially when cloud conditions are unexpectedly heavy or light), it is usually within ±1 UV index unit as that which would be measured. When

11088-559: The UV index is presented on a daily basis, it represents UV intensity around the sun's highest point in the day, called solar noon , halfway between sunrise and sunset . This typically occurs between 11:30 and 12:30, or between 12:30 and 13:30 in areas where daylight saving time is being observed. Predictions are made by a computer model that accounts for the effects of sun-earth distance , solar zenith angle , total ozone amount, tropospheric aerosol optical depth, elevation, snow/ice reflectivity and cloud transmission, all of which influence

11232-580: The United Nations can establish various specialized agencies to fulfill its duties. Specialized agencies are autonomous organizations working with the United Nations and each other through the coordinating machinery of the Economic and Social Council. Each was integrated into the UN system through an agreement with the UN under UN Charter article 57. There are fifteen specialized agencies, which perform functions as diverse as facilitating international travel, preventing and addressing pandemics, and promoting economic development. The United Nations system includes

11376-560: The United States' funding from the United Nations Educational, Scientific and Cultural Organisation (or UNESCO) over allegations of mismanagement, followed by the United Kingdom and Singapore. Boutros Boutros-Ghali , the secretary-general from 1992 to 1996, initiated a reform of the Secretariat, somewhat reducing the size of the organisation. His successor, Kofi Annan , initiated further management reforms in

11520-429: The amount of UV radiation at the surface. The UV index is a number linearly related to the intensity of sunburn-producing UV radiation at a given point on the Earth's surface. It cannot be simply related to the irradiance (measured in W / m ) because the UV of greatest concern occupies a spectrum of wavelengths from 295 to 325 nm, and shorter wavelengths have already been absorbed a great deal when they arrive at

11664-709: The assembly gathers at annual sessions at the General Assembly Hall , but emergency sessions can be summoned. The assembly is led by a president , elected by the member states on a rotating regional basis, and 21 vice-presidents. The first session convened on 10 January 1946 in the Methodist Central Hall in London and comprised representatives of 51 nations. When the General Assembly decides on seminal questions such as those on peace and security, admission of new members and budgetary matters,

11808-631: The banned chemical Chlorofluorocarbon-11 (CFC-11) into the atmosphere. Scientists estimate that without action, these CFC-11 emissions will delay the recovery of the planet's ozone hole by a decade. Satellites burning up upon re-entry into Earth's atmosphere produce aluminum oxide (Al 2 O 3 ) nanoparticles that endure in the atmosphere for decades. Estimates for 2022 alone were ~17 metric tons (~30   kg of nanoparticles per ~250   kg satellite). Increasing populations of satellite constellations can eventually lead to significant ozone depletion. Scientists have attributed ozone depletion to

11952-529: The basis of the Convention on the Privileges and Immunities of the United Nations , the UN and its agencies are immune from the laws of the countries where they operate, safeguarding the UN's impartiality with regard to host and member countries. Below the six organs are, in the words of the author Linda Fasulo, "an amazing collection of entities and organizations, some of which are actually older than

12096-481: The body has mechanisms that prevent sunlight from producing vitamin D in excess of the body's requirements. A November 2011 report by scientists at the Institute of Zoology in London, England found that whales off the coast of California have shown a sharp rise in sun damage, and these scientists "fear that the thinning ozone layer is to blame". The study photographed and took skin biopsies from over 150 whales in

12240-589: The body's former headquarters in the Peace Palace in The Hague, Netherlands , making it the only principal organ not based in New York City. The ICJ's main function is adjudicating disputes among nations. Examples of issues they have heard include war crimes, violations of state sovereignty and ethnic cleansing. The court can also be called upon by other UN organs to provide advisory opinions on matters of international law. All UN member states are parties to

12384-622: The century prior to the UN's creation, several international organizations such as the International Committee of the Red Cross were formed to ensure protection and assistance for victims of armed conflict and strife. During World War I , several major leaders, especially U.S. President Woodrow Wilson , advocated for a world body to guarantee peace. The winners of the war, the Allies , met to decide on formal peace terms at

12528-537: The council are known as United Nations Security Council resolutions . The Security Council is made up of fifteen member states: five permanent members (China, France, Russia, the United Kingdom and the United States) and ten non-permanent members (currently Algeria , Ecuador , Guyana , Japan , Malta , Mozambique , the Republic of Korea , Sierra Leone , Slovenia and Switzerland ). The five permanent members hold veto power over UN resolutions, allowing

12672-406: The current regulations the ozone layer will completely regenerate by 2045. The Montreal Protocol is considered the most successful international environmental agreement to date. Three forms (or allotropes ) of oxygen are involved in the ozone-oxygen cycle : oxygen atoms (O or atomic oxygen), oxygen gas ( O 2 or diatomic oxygen), and ozone gas ( O 3 or triatomic oxygen). Ozone

12816-576: The danger of CFCs and HCFCs to the environment. The ozone hole is usually measured by reduction in the total column ozone above a point on the Earth's surface. This is normally expressed in Dobson units ; abbreviated as "DU". The most prominent decrease in ozone has been in the lower stratosphere. Marked decreases in column ozone in the Antarctic spring and early summer compared to the early 1970s and before have been observed using instruments such as

12960-648: The day's predicted UV index is within various numerical ranges, the recommendations for protection are as follows: Wear sunglasses on bright days. If you burn easily, cover up and use broad spectrum SPF 15+ sunscreen. Bright surfaces, sand, water, and snow, will increase UV exposure. Stay in shade near midday when the sun is strongest. If outdoors, wear sun-protective clothing, a wide-brimmed hat, and UV-blocking sunglasses. Generously apply broad spectrum SPF 50+ sunscreen every 1.5 hours, even on cloudy days, and after swimming or sweating. Bright surfaces, such as sand, water, and snow, will increase UV exposure. Reduce time in

13104-433: The day. It is known that they are able to shift the levels and types of UV sunscreens (i.e. flavonoids), that they contain, throughout the day. This allows them to increase their protection against UV radiation. Plants that have been affected by radiation throughout development are more affected by the inability to intercept light with a larger leaf area than having photosynthetic systems compromised. Damage from UVB radiation

13248-481: The earth's surface. However, skin damage from sunburn is related to wavelength, the shorter wavelengths being much more damaging. The UV power spectrum (expressed as watts per square meter per nanometer of wavelength) is therefore multiplied by a weighting curve known as the CIE -standard McKinlay–Diffey erythemal action spectrum. There are some older formulas for the spectrum, resulting in differences of up to 2%. The result

13392-883: The eighth secretary-general, Ban Ki-moon , the UN intervened with peacekeepers in crises such as the War in Darfur in Sudan and the Kivu conflict in the Democratic Republic of the Congo and sent observers and chemical weapons inspectors to the Syrian Civil War . In 2013, an internal review of UN actions in the final battles of the Sri Lankan Civil War in 2009 concluded that the organization had suffered

13536-500: The employee's nationality. In practice, the International Civil Service Commission , which governs the conditions of UN personnel, takes reference to the highest-paying national civil service. Staff salaries are subject to an internal tax that is administered by the UN organizations. The General Assembly is the primary deliberative assembly of the UN. Composed of all UN member states ,

13680-466: The end of spring break up the vortex around mid-December. As warm, ozone and NO 2 -rich air flows in from lower latitudes, the PSCs are destroyed, the enhanced ozone depletion process shuts down, and the ozone hole closes. Most of the ozone that is destroyed is in the lower stratosphere, in contrast to the much smaller ozone depletion through homogeneous gas-phase reactions, which occurs primarily in

13824-488: The extreme cold of the Arctic and Antarctic stratosphere. This is why ozone holes first formed, and are deeper, over Antarctica. Early models failed to take PSCs into account and predicted a gradual global depletion, which is why the sudden Antarctic ozone hole was such a surprise to many scientists. It is more accurate to speak of ozone depletion in middle latitudes rather than holes. Total column ozone declined below pre-1980 values between 1980 and 1996 for mid-latitudes. In

13968-492: The face of threats from the US to withhold its UN dues. Though the UN Charter had been written primarily to prevent aggression by one nation against another, in the early 1990s the UN faced several simultaneous, serious crises within Somalia, Haiti, Mozambique, and the nations that previously made up Yugoslavia. The UN mission in Somalia was widely viewed as a failure after the United States' withdrawal following casualties in

14112-504: The failure of UN mediation in conflicts in the Middle East , Vietnam , and Kashmir , the UN increasingly shifted its attention to its secondary goals of economic development and cultural exchange. By the 1970s, the UN budget for social and economic development was far greater than its peacekeeping budget. After the Cold War, the UN saw a radical expansion in its peacekeeping duties, taking on more missions in five years than it had in

14256-612: The five principal organs are located at the main UN Headquarters in New York City, while the International Court of Justice is seated in The Hague . Most other major agencies are based in the UN offices at Geneva , Vienna , and Nairobi , and additional UN institutions are located throughout the world. The six official languages of the UN, used in intergovernmental meetings and documents, are Arabic , Chinese , English , French , Russian and Spanish . On

14400-467: The ground level up to the upper atmosphere, and it can stay there for about a century, destroying up to one hundred thousand ozone molecules during that time. 1,1,1-Trichloro-2,2,2-trifluoroethane , also known as CFC-113a, is one of four man-made chemicals newly discovered in the atmosphere by a team at the University of East Anglia. CFC-113a is the only known CFC whose abundance in the atmosphere

14544-455: The high levels of depletion seen in the ozone hole were to be common across the globe, the effects could be substantially more dramatic. As the ozone hole over Antarctica has in some instances grown so large as to affect parts of Australia , New Zealand , Chile , Argentina , and South Africa , environmentalists have been concerned that the increase in surface UV could be significant. Excessive ultraviolet radiation (UVR) has reducing effects on

14688-436: The huge absorption that has already taken place in the atmosphere at short wavelengths.) The erythemal weighting factors applied to these figures are 1.0, 0.22, and 0.003 respectively. (Also note the huge increase in sunburn damage caused by the shorter wavelengths; e.g., for the same irradiance, 305 nm is 22% as damaging as 295 nm, and 325 nm is 0.3% as damaging as 295 nm.) Integration of these values using all

14832-458: The incidence of these cancers by 2%. Another form of skin cancer, Melanoma , is much less common but far more dangerous, being lethal in about 15–20 percent of the cases diagnosed. The relationship between melanoma and ultraviolet exposure is not yet fully understood, but it appears that both UV-B and UV-A are involved. Because of this uncertainty, it is difficult to estimate the effect of ozone depletion on melanoma incidence. One study showed that

14976-557: The increase of man-made ( anthropogenic ) halogen compounds from CFCs by combining observational data with computer models. These complex chemistry transport models (e.g. SLIMCAT , CLaMS —Chemical Lagrangian Model of the Stratosphere) work by combining measurements of chemicals and meteorological fields with chemical reaction rate constants. They identify key chemical reactions and transport processes that bring CFC photolysis products into contact with ozone. The Antarctic ozone hole

15120-524: The index was designed, the typical midday summer sunlight was around 250 mW/m. Thus, for convenience, the DUV is divided by 25 mW/m to produce an index nominally from 0 to 11+, though ozone depletion is now resulting in higher values. To illustrate the spectrum weighting principle, the incident power density in midday summer sunlight is typically 0.6 mW/(nm m) at 295 nm, 74 mW/(nm m) at 305 nm, and 478 mW/(nm m) at 325 nm. (Note

15264-467: The intermediate weightings over the full spectral range of 290 nm to 400 nm produces a figure of 264 mW/m (the DUV), which is then divided by 25 mW/m to give a UV index of 10.6. After sporadic attempts by various meteorologists to define a "sunburn index" and growing concern about ozone depletion , Environment Canada scientists James B. Kerr, C. Thomas McElroy, and David I. Wardle invented

15408-481: The largest gathering of world leaders in history, and it culminated in the adoption by all member states of the Millennium Development Goals (or MDGs), a commitment to achieve international development in areas such as poverty reduction , gender equality and public health . Progress towards these goals, which were to be met by 2015, was ultimately uneven. The 2005 World Summit reaffirmed

15552-590: The last 28 years' data from 12 satellites of several countries, and found that the UV radiation reaching equatorial latitudes was far greater than expected, with the UV Index climbing as high as 24 in Quito ; the WHO considers 11 as an extreme index and a great risk to health. The report concluded that depleted ozone levels around the mid-latitudes of the planet are already endangering large populations in these areas. Later,

15696-444: The mid-1990s and began to recover in the 2000s, as the shifting of the jet stream in the southern hemisphere towards the south pole has stopped and might even be reversing. Recovery was projected to continue over the next century, with the ozone hole expected to reach pre-1980 levels by around 2075. In 2019, NASA reported that the ozone hole was the smallest ever since it was first discovered in 1982. The UN now projects that under

15840-495: The modern UV index in Toronto, Ontario. Environment Canada launched it as part of the weather forecast on May 27, 1992, making Canada the first country in the world to issue official predictions of UV levels for the next day. Many other countries followed suit with their own UV indices. Initially, the methods of calculating and reporting a UV index varied significantly from country to country. A global UV index, first standardized by

15984-473: The most important are the hydroxyl radical (OH·), nitric oxide radical (NO·), chlorine radical (Cl·) and bromine radical (Br·). The dot is a notation to indicate that each species has an unpaired electron and is thus extremely reactive. The effectiveness of different halogens and pseudohalogens as catalysts for ozone destruction varies, in part due to differing routes to regenerate the original radical after reacting with ozone or dioxygen. While all of

16128-455: The negative effects of increased UV-B radiations. An increase of UV radiation would be expected to affect crops. A number of economically important species of plants, such as rice , depend on cyanobacteria residing on their roots for the retention of nitrogen . Cyanobacteria are sensitive to UV radiation and would be affected by its increase. "Despite mechanisms to reduce or repair the effects of increased ultraviolet radiation, plants have

16272-668: The northern mid-latitudes, it then increased from the minimum value by about two percent from 1996 to 2009 as regulations took effect and the amount of chlorine in the stratosphere decreased. In the Southern Hemisphere's mid-latitudes, total ozone remained constant over that time period. There are no significant trends in the tropics, largely because halogen-containing compounds have not had time to break down and release chlorine and bromine atoms at tropical latitudes. Large volcanic eruptions have been shown to have substantial albeit uneven ozone-depleting effects, as observed with

16416-461: The organization are five principal organs established by the UN Charter: the General Assembly , the Security Council , the Economic and Social Council , the International Court of Justice and the UN Secretariat . A sixth principal organ, the Trusteeship Council , suspended its operations on 1 November 1994 upon the independence of Palau ; the last remaining UN trustee territory. Four of

16560-506: The organization held its first public debate between candidates for secretary-general. On 1 January 2017, Portuguese diplomat António Guterres , who had previously served as the UN High Commissioner for Refugees , became the ninth secretary-general. Guterres has highlighted several key goals for his administration, including an emphasis on diplomacy for preventing conflicts, more effective peacekeeping efforts, and streamlining

16704-482: The organization to be more responsive and versatile to international needs. On 13 June 2019, the UN signed a Strategic Partnership Framework with the World Economic Forum in order to "jointly accelerate" the implementation of the 2030 Agenda for Sustainable Development . The United Nations is part of the broader UN System, which includes an extensive network of institutions and entities. Central to

16848-424: The ozone hole are manufactured chemicals, especially manufactured halocarbon refrigerants , solvents , propellants , and foam- blowing agents ( chlorofluorocarbons (CFCs), HCFCs, halons ), referred to as ozone-depleting substances (ODS). These compounds are transported into the stratosphere by turbulent mixing after being emitted from the surface, mixing much faster than the molecules can settle. Once in

16992-578: The ozone layer decreases exponentially with the slant-path thickness and density of the layer. When stratospheric ozone levels decrease, higher levels of UVB reach the Earth's surface. UV-driven phenolic formation in tree rings has dated the start of ozone depletion in northern latitudes to the late 1700s. In October 2008, the Ecuadorian Space Agency published a report called HIPERION. The study used ground instruments in Ecuador and

17136-399: The ozone-induced cooling appears to be dominant. Predictions of ozone levels remain difficult, but the precision of models' predictions of observed values and the agreement among different modeling techniques have increased steadily. The World Meteorological Organization Global Ozone Research and Monitoring Project—Report No. 44 is strongly in favor of the Montreal Protocol , but notes that

17280-524: The plenary meetings. Previously, Churchill had urged Roosevelt to restore France to its status of a major power after the liberation of Paris in August 1944. The drafting of the Charter of the United Nations was completed over the following two months, and it was signed on 26 June 1945 by the representatives of the 50 countries. The UN officially came into existence on 24 October 1945, upon ratification of

17424-553: The post, but over the years it has become accepted that the position shall be held for one or two terms of five years. The current secretary-general is António Guterres of Portugal, who replaced Ban Ki-moon in 2017. The International Court of Justice (or ICJ), sometimes known as the World Court, is the primary judicial organ of the UN. It is the successor to the Permanent Court of International Justice and occupies

17568-600: The post-war world. At the subsequent meeting of the Inter-Allied Council in London on 24 September 1941, the eight governments in exile of countries under Axis occupation , together with the Soviet Union and representatives of the Free French Forces , unanimously adopted adherence to the common principles of policy set forth by Britain and the United States. Roosevelt and Churchill met at

17712-626: The presence of polar stratospheric clouds (PSCs). These polar stratospheric clouds form during winter, in the extreme cold. Polar winters are dark, consisting of three months without solar radiation (sunlight). The lack of sunlight contributes to a decrease in temperature and the polar vortex traps and chills the air. Temperatures are around or below −80 °C. These low temperatures form cloud particles. There are three types of PSC clouds—nitric acid trihydrate clouds, slowly cooling water-ice clouds, and rapid cooling water-ice (nacreous) clouds—provide surfaces for chemical reactions whose products will, in

17856-560: The presence of Russian troops in Iranian Azerbaijan and British forces in Greece . British diplomat Gladwyn Jebb served as interim secretary-general. The General Assembly selected New York City as the site for the headquarters of the UN. Construction began on 14 September 1948 and the facility was completed on 9 October 1952. The Norwegian Foreign Minister, Trygve Lie , was the first elected UN secretary-general . Though

18000-532: The previous four decades. Between 1988 and 2000, the number of adopted Security Council resolutions more than doubled, and the peacekeeping budget increased by more than tenfold. The UN negotiated an end to the Salvadoran Civil War , launched a successful peacekeeping mission in Namibia , and oversaw democratic elections in post- apartheid South Africa and post- Khmer Rouge Cambodia. In 1991,

18144-538: The production of harmful volatile organic compounds , like isoprenes. The emission of isoprenes into the air, by plants, can severely impact the environment by adding to air pollution and increasing the amount of carbon in the atmosphere, ultimately contributing to climate change. The full extent of the damage that CFCs have caused to the ozone layer is not known and will not be known for decades; however, marked decreases in column ozone have already been observed. The Montreal and Vienna conventions were installed long before

18288-511: The rate of these processes can be decreased by the effects of null cycles . More complicated mechanisms have also been discovered that lead to ozone destruction in the lower stratosphere. A single chlorine atom would continuously destroy ozone (thus a catalyst) for up to two years (the time scale for transport back down to the troposphere) except for reactions that remove it from this cycle by forming reservoir species such as hydrogen chloride (HCl) and chlorine nitrate ( ClONO 2 ). Bromine

18432-463: The rates of photosynthesis and growth of benthic diatom communities (microalgae species that increase water quality and are pollution resistant) that are present in shallow freshwater. Ozone depletion not only affects human health but also has a profound impact on biodiversity. It damages plants and trees at the cellular level, affecting their growth, vitality, photosynthesis, water balance, and defense mechanisms against pests and diseases. This sets off

18576-474: The relevant radicals have both natural and man-made sources, human activity has impacted some more than others. As of 2020, most of the OH· and NO· in the stratosphere is naturally occurring, but human activity has drastically increased the levels of chlorine and bromine. These elements are found in stable organic compounds, especially chlorofluorocarbons , which can travel to the stratosphere without being destroyed in

18720-673: The same year, a survey among meteorologists ranked the development of the UV index as #11 on The Weather Channel 's 100 Biggest Weather Moments . In 2022, a mobile phone application that provides localized information on ultraviolet (UV) radiation levels was launched by the World Health Organization (WHO), the World Meteorological Organization (WMO), the United Nations Environment Programme (UNEP) and

18864-546: The spring lead to ozone destruction. The photochemical processes involved are complex but well understood. The key observation is that, ordinarily, most of the chlorine in the stratosphere resides in "reservoir" compounds, primarily chlorine nitrate ( ClONO 2 ) as well as stable end products such as HCl. The formation of end products essentially removes Cl from the ozone depletion process. Reservoir compounds sequester Cl, which can later be made available via absorption of light at wavelengths shorter than 400 nm. During

19008-403: The stratosphere, they are dissociated by ultraviolet light to release chlorine atoms. The chlorine atoms act as a catalyst , and each can break down tens of thousands of ozone molecules before being removed from the stratosphere. Given the longevity of CFC molecules, recovery times are measured in decades. It is calculated that a CFC molecule takes an average of about five to seven years to go from

19152-480: The stratosphere, they release atoms from the halogen group through photodissociation , which catalyze the breakdown of ozone (O 3 ) into oxygen (O 2 ). Both types of ozone depletion were observed to increase as emissions of halocarbons increased. Ozone depletion and the ozone hole have generated worldwide concern over increased cancer risks and other negative effects. The ozone layer prevents harmful wavelengths of ultraviolet (UVB) light from passing through

19296-445: The sun between 10 a.m. and 4 p.m. If outdoors, seek shade and wear sun-protective clothing, a wide-brimmed hat, and UV-blocking sunglasses. Generously apply broad spectrum SPF 50+ sunscreen every 1.5 hours, even on cloudy days, and after swimming or sweating. Bright surfaces, such as sand, water, and snow, will increase UV exposure. Minimize sun exposure between 10 a.m. and 4 p.m. If outdoors, seek shade and wear sun-protective clothing,

19440-402: The table below for more detailed recommendations. The UV index is a linear scale that measures the intensity of UV radiation with respect to sunburn. For example, assuming similar spectral power distributions , radiation with a UV index of 12 is twice as intense as radiation at a UV index of 6. For a wide range of timescales, sunburn in response to controlled UV radiation occurs in proportion to

19584-446: The total number of photons delivered, not varying with the intensity or duration of exposure. Therefore, under similar conditions, a person who develops a sunburn after 30 minutes of exposure to UV index 6 radiation would most likely develop a sunburn after 15 minutes of exposure to UV index 12 radiation, since it is twice the intensity but half the duration. This linear scale is unlike other common environmental scales such as decibels or

19728-455: The troposphere due to their low reactivity. Once in the stratosphere, the Cl and Br atoms are released from the parent compounds by the action of ultraviolet light, e.g. Ozone is a highly reactive molecule that easily reduces to the more stable oxygen form with the assistance of a catalyst. Cl and Br atoms destroy ozone molecules through a variety of catalytic cycles. In the simplest example of such

19872-578: The upper stratosphere. Since the ozone layer absorbs UVB ultraviolet light from the sun, ozone layer depletion increases surface UVB levels (all else equal), which could lead to damage, including an increase in skin cancer . This was the reason for the Montreal Protocol. Although decreases in stratospheric ozone are well-tied to CFCs and increases in surface UVB, there is no direct observational evidence linking ozone depletion to higher incidence of skin cancer and eye damage in human beings. This

20016-416: The widespread decolonization in the 1960s. Since then, 80 former colonies have gained independence, including 11 trust territories that had been monitored by the Trusteeship Council . By the 1970s, the UN's budget for economic and social development programmes vastly exceeded its spending on peacekeeping . After the end of the Cold War in 1991, the UN shifted and expanded its field operations, undertaking

20160-404: The world stage. The office has evolved into a dual role of an administrator of the UN organization and a diplomat and mediator addressing disputes between member states and finding consensus to global issues . The secretary-general is appointed by the General Assembly, after being recommended by the Security Council, where the permanent members have veto power. There are no specific criteria for

20304-512: Was carried out in a study on Chesapeake Bay Watermen, where increases in average annual ocular exposure were associated with increasing risk of cortical opacity. In this highly exposed group of predominantly white males, the evidence linking cortical opacities to sunlight exposure was the strongest to date. Based on these results, ozone depletion is predicted to cause hundreds of thousands of additional cataracts by 2050. Increased surface UV leads to increased tropospheric ozone. Ground-level ozone

20448-434: Was no significant change in plant height or leaf mass, but showed a response in shoot biomass and leaf area with a small decrease. However, UVB radiation has been shown to decrease quantum yield of photosystem II. UVB damage only occurs under extreme exposure, and most plants also have UVB absorbing flavonoids which allow them to acclimatize to the radiation present. Plants experience different levels of UV radiation throughout

20592-447: Was re-elected on 8 June 2021. The organization is financed by assessed and voluntary contributions from its member states. The UN, its officers, and its agencies have won multiple Nobel Peace Prizes , although other evaluations of its effectiveness have been contentious. Some commentators believe the organization to be a leader in peace and human development, while others have criticized it for ineffectiveness, bias, and corruption . In

20736-579: Was reported in 2016. In 2017, NASA announced that the ozone hole was the weakest since 1988 because of warm stratospheric conditions. It is expected to recover around 2070. The amount lost is more variable year-to-year in the Arctic than in the Antarctic. The greatest Arctic declines are in the winter and spring, reaching up to 30 percent when the stratosphere is coldest. Reactions that take place on polar stratospheric clouds (PSCs) play an important role in enhancing ozone depletion. PSCs form more readily in

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