Shulou(Shulou.com)11/24 Report--

This article comes from the official account of Wechat: Earth knowledge Bureau (ID:diqiuzhishiju), author: Xiao Kai, revised manuscript: Chao Qian / Editor: fruit Chestnut Ride

On January 9 this year, the World Meteorological Organization (WMO) and the United Nations Environment Programme issued a news release saying that if current initiatives are maintained, the Antarctic ozone hole will return to 1980 levels in 2066. At that time, for the first time, mankind will solve a major environmental problem that has a bearing on the survival of civilization through close international cooperation.

The report says the ozone layer is expected to recover within 40 years.

(2022 Scientific Assessment of Ozone depletion report figure: unric.org) ▼

The dawn of victory is hard-won, and behind it is a tortuous history full of accidents.

90% of the ozone in the Antarctic ozone hole atmosphere is concentrated in the stratosphere 10-50 km high, much higher than the well-known westerly belt, where the air is thin and the total amount of ozone is only equivalent to a layer of gas 5 mm thick under normal temperature and pressure.

The relative abundance of ozone molecules in the atmosphere is relatively low.

In the stratosphere, there are usually only a few thousand ozone molecules per billion air molecules.

(figure: WMO) ▼

Regular observation of ozone content in the atmosphere began in the 1920s, when Gordon Dobson, a researcher at the University of Oxford in England, organized scientists from around the world to make regular observations in the United States, Egypt, India, the Soviet Union, and even the Spitsbergen Islands in the Arctic Circle. But no measurements were made at that time in Antarctica, an extremely cold place covered by a few kilometers of ice sheet.

The original ozone spectrometer used by Gordon Dobson

(figure: Science Museum Group) ▼

After World War II, the Royal Society's expedition set up a Harley station on the Brent Ice Shelf in Antarctica to carry out long-term atmospheric observations. At that time, no one could have imagined that every ozone record here would shock the world more than 30 years later, completely subverting people's perception of the relationship between man and nature.

Horizontal screen-the largest annual range of the ozone hole since 1979

(figure: CAMS) ▼

In 1974, Americans Mario Molina and Sherwood Roland published an article in the journal Nature, arguing that chlorofluorocarbons (CFC), known as freons, pose a threat to the ozone layer. They recognize that after the chemically stable chlorofluorocarbons are diffused into the ozone layer, they will decompose chlorine atoms under ultraviolet radiation, and chlorine atoms are an efficient catalyst for ozone decomposition.

Chlorine atoms are thought to be the catalyst for ozone destruction because

Cl and ClO are re-formed when each reaction cycle is completed.

Thereby further destroying ozone.

(figure: NASA) ▼

According to their estimates, if HCFCs continue to be produced at an annual growth rate of 10% at that time, ozone in the atmosphere will be reduced by 5-7% in 20 years' time and 30-50% in 75 years' time (that is, 27 years from now).

If HCFCs are not banned,

Prediction of stratospheric ozone concentration by NASA

(figure: NASA) ▼

At that time, a large amount of ultraviolet radiation can reach the ground directly, causing many people to develop skin cancer or cataracts, and the temperature in the stratosphere will drop significantly, which can cause destructive climate change.

A schematic diagram of the multi-step process of photocarcinogenesis

(figure: Eva Rawlings Parker) ▼

At that time, there were great differences among scientists, industry and policy makers. The $8 billion chlorofluorocarbon industry in the United States employs more than 1.4 million workers directly or indirectly. Most industry leaders refuse to give up the use of HCFCs, lobbying government departments not only to delay or abandon plans to ban HCFCs, but also to use the media to win public support, which allows HCFCs to remain in large quantities for a decade.

In the last two decades of the 20th century

The concentration of chlorofluorocarbons in the atmosphere rises instead of decreasing.

(figure: WMO&NOAA) ▼

It wasn't until 1985 that atmospheric scientists from the British Antarctic investigation Bureau published findings that shocked the world in the journal Nature. They analyzed atmospheric ozone observations collected at Harley Station since its establishment in 1956 and found that total ozone in spring (September, October and November) over Harley Bay, Antarctica, decreased by more than 40 per cent between 1977 and 1984. before that, the total amount of ozone remained almost unchanged.

Data from Harley Research Station show that since the 1980s

The content of atmospheric ozone decreases sharply.

(total atmospheric ozone measured in Antarctica in 1956-2022: NASA) ▼

These figures far exceed Molina and Roland's estimates and are equivalent to hammering the lethality of HCFCs to the ozone layer. One stone stirs up thousands of waves, and the scientific community has set off an upsurge in the chemistry and dynamics of atmospheric ozone. Both theory and observation have proved that human beings have unimaginable destructive power to nature.

The crime of chlorofluorocarbons is hard to escape. With the efforts of the whole society, in 1987, the international community signed the Montreal Protocol on substances that deplete the Ozone layer, strengthening the control of substances that deplete the Ozone layer (ODS) to deal with the problem of ozone hole.

(map of parties to the Montreal Protocol: wiki) ▼

It should be noted here that the so-called ozone-depleting substances contain not only chlorofluorocarbons, a chemical that directly destroys the ozone layer, but also halogenated hydrocarbons, halons and methyl bromide. After they are exposed to ultraviolet radiation in the stratosphere, they can decompose chlorine free radicals or bromine free radicals, and further have a complex chain reaction with ozone, thus destroying the ozone layer.

Halogen-containing gases in the stratosphere can be divided into

Halogen source gas and active halogen gas ▼

Ozone depletion changes the Earth's Climate? After years of research in the scientific community, the impact of the ozone layer on the earth's ecosystem has been proved, and its importance has long been deeply rooted in the hearts of the people. After stratospheric ozone depletion, animal skin and plant epidermis will be exposed to high intensity ultraviolet radiation, genetic material will be damaged, canceration rate will increase, plant growth rhythm will be disordered, and even abnormal development will occur.

The damage of the ozone layer will do more harm than good.

(figure: twitter@MBRSpaceCentre) ▼

In recent years, with the deepening of people's understanding of climate change, the climate effect of ozone depletion has been widely studied. It has been found that the chemical changes taking place in the stratosphere are changing the earth's climate in unexpected ways.

Last year, China experienced the hottest summer since 1961, and people's worries about global warming once again reached a climax. But global warming is only a simple expression of climate change.

Hotter days are one of the effects of global warming on climate change.

(photo: national Climate Center) ▼

Global warming actually means that "in the long run, the average global surface temperature has been getting higher and higher since the industrial revolution," while the increase in temperature is not sustained in time and is not uniform in space. In terms of time, we have experienced the so-called "stagnation of global warming" from 1998 to 2012. Spatially, surface temperatures in many parts of the world have not changed significantly or even decreased a lot over the past 40 years.

The concept of global warming is based on ▼ on a longer time scale.

Move the picture and feel (photo: NASA) ▼

If we look at the temperature change from the vertical direction, we will find that the temperature of each layer of the atmosphere is not always increasing. Research shows that the middle and upper stratosphere is cooling at a rate of about 0.6 ℃ per decade, and ozone and ozone-depleting substances are one of the main driving forces behind it.

From the middle troposphere to the upper stratosphere (from bottom to top)

Time series ▼ of global wide layer mean temperature anomaly

Ozone can convert the absorbed ultraviolet radiation into molecular kinetic energy, thus heating the stratosphere, and the hotter the higher the troposphere, which is different from the life experience that the higher the tropospheric altitude is, the colder it is.

When ozone is depleted, more ultraviolet radiation directly penetrates the stratosphere, resulting in a drop in stratospheric temperature.

Trend of 40-year land surface temperature from 1981 to 2020

(figure: IPCC) ▼

The temperature, pressure, wind, humidity and other characteristics of the atmosphere are coupled together, and the change of temperature will often cause changes in other characteristics, resulting in abnormal atmospheric circulation in the stratosphere.

Generally speaking, the stratosphere heats up greatly because ozone absorbs a large amount of ultraviolet radiation. But this law is not true in one case, that is, the polar night between the north and south poles.

Polar night and aurora borealis in Antarctica

(figure: NOAA) ▼

During the polar night, due to the lack of sunlight, the stratosphere no longer heats up by absorbing radiation, but cools by emitting radiation, resulting in a sharp drop in temperature, thus widening the temperature difference with the mid-latitude stratosphere.

The change of temperature brings about changes in the wind field, which forms a strong westerly wind around the poles, which firmly confines the cold air in the poles. This forms what we often hear as the "polar vortex". It should be noted that the westerly wind mentioned here is in the stratosphere, not the tropospheric westerly belt we generally hear.

The polar vortex at the end of last year

The cold wave swept across the United States from west to east.

(December 22, 2022, 500hPa: central Meteorological Observatory) ▼

Tropospheric westerlies and stratospheric westerlies

(zonal mean zonal wind-stratospheric view: ECMWF) ▼

After the formation of the Antarctic ozone hole, Antarctica has just emerged from the polar night in the spring of the southern hemisphere (September, October and November), when the radiation effect of ozone appears, and the polar temperature is much lower than when there is no ozone hole. this leads to a stronger polar vortex caused by cold and a more rapid westerly wind around Antarctica.

The impact of the ozone hole is not limited to the stratosphere, but also affects the weather changes in the troposphere to a great extent.

This is because the changes in temperature, pressure and wind field in the stratosphere transmit signals to the troposphere in the form of waves, thus changing the horizontal transport of heat and momentum in the troposphere. In short, after a more complex process, abnormal signals in the stratosphere can reach the troposphere after about half a month, and continue to affect the surface weather in the next month or two.

▼

The stratospheric westerly wind caused by the ozone hole can reduce the surface pressure and accelerate the westerly wind around the Antarctic continent. Historical statistics show that the strengthening of the westerly wind is often accompanied by a contraction to the polar regions, which leads to the movement of the three tropospheric circulation (Hadley circulation, Ferrer circulation and polar circulation) to the south pole.

This effect is significantly reflected in the variation of precipitation in the southern hemisphere. In summer in the southern hemisphere, the area originally located in the sinking branch of the three-circle circulation will usher in more rainfall, while the previously humid area will be easily occupied by dry downdraft. The southward movement of the circulation in the southern hemisphere caused by ozone depletion in Antarctica is its most important climate effect.

Ozone-induced Circulation changes in the Southern Hemisphere ▼

The above picture shows the precipitation changes observed by meteorology.

The following figure shows the computer simulation of the effect of ozone on ▼

The earth's climate system is very complex, which often affects the whole body. The change of ozone can also affect the sea surface temperature and polar sea ice, indirectly causing climate change. New evidence suggests that ozone depletion, along with greenhouse gases, may have contributed to an increase in the surface temperature of the Southern Ocean since 1950. But greenhouse gases play a dominant role.

The effect of ozone on SST is realized by affecting the wind field. On the one hand, the westerly belt on the Southern Ocean drives the sea water from west to east, and on the other hand, it blows the surface water from the poles to the equator. The east-west wind can cause the movement of sea water in the north-south direction, a phenomenon known as "Ekmen transport".

Ekmen Transportation schematic (Picture: wiki) ▼

As ozone depletion strengthens westerly winds, more surface water in the Southern Ocean leaves the same place, warmer water in the lower layer surges to the surface, and sea surface temperatures rise. The warming of the sea may accelerate the melting of sea ice floating around Antarctica, and the Antarctic sea ice may be further reduced.

Polar sea ice can strongly reflect solar radiation and play a significant role in regulating the energy balance of the earth. But Antarctic sea ice has shown complex changes over the past four decades. Antarctic summer sea ice expanded before 2015, but shrank rapidly after 2016. Current climate models are difficult to simulate such changes, so it is difficult to prove the impact of ozone on Antarctic sea ice.

The summer minimum in February has changed greatly in the past decade.

Hit both the historic high and the historic low ▼

Average concentration of Antarctic sea ice in February 2022

The sea ice in that month reached the minimum range in summer.

(figure: NOAA) ▼

The situation in the Arctic is different. The northern hemisphere has a wide continental area and a large population, and the Arctic sea ice is closely related to the cold wave weather in the northern hemisphere. In the long run, ozone depletion in the Arctic has not had a long-term and lasting impact on Arctic sea ice. However, some studies have shown that in the years of serious ozone depletion in the Arctic, the sea ice in the Arctic Kara Sea, the Laptev Sea and the East Siberian Sea decreased significantly.

Whether it's the South Pole or the North Pole

Less sea ice is not a good thing.

(figure: NASA) ▼

The ozone layer that is being restored has phased out 99% of the ozone-depleting substances worldwide since the implementation of the Montreal Protocol, and the ozone layer is expected to return to the state of 1980 within this century.

A study by American meteorologist Antara Banerjee and others pointed out that it is precisely due to the influence of the Protocol that the changes in atmospheric circulation caused by the ozone hole in Antarctica have stopped.

The evolution path of the ozone layer ▼

With the recovery of the ozone layer, the change of atmospheric circulation caused by ozone depletion may be compensated in the future. But as another driver of polar eddies in the southern hemisphere, greenhouse gases are likely to continue to increase in this century. As a result, scientists predict that the recovery of polar vortex changes in the southern hemisphere may not be realized until the end of this century.

Ozone-depleting substances are also important greenhouse gases, such as chlorofluoromethane, which cause 5160 times more atmospheric warming than carbon dioxide of the same mass. If mankind continues to faithfully implement the Montreal Agreement, global warming will be reduced by 0.5 ℃ by the middle of this century due to the reduction of ozone-depleting substances, which is as significant as mitigating climate change through afforestation.

ODS and Ozone schedule ▼

Today, the climate effect of the Montreal Protocol is just emerging, and whether the future recovery of the ozone layer can completely reverse the climate change caused by ozone depletion may only be known in the future.

We can't stop our efforts to protect the earth's environment.

(figure: PBS.org) ▼

Although the future of the ozone problem is not very clear, there is no doubt that mankind has avoided a major disaster of human civilization through unity and cooperation. Human beings have made important achievements in ozone control, will the successful control of greenhouse gas emissions be far away?

Reference:

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[16] J. Zhang et al., "Responses of Arctic sea ice to stratospheric ozone depletion," Science Bulletin, vol. 67, no. 11, pp. 1182-1190, Jun. 2022, doi: 10.1016/j.scib.2022.03.015.

"Viruses, microscopy and fast radio bursts: 10 remarkable discoveries from 2020." Https://www.nature.com/articles/d41586-020-03514-8

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