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Subject: Climate Change

1. Global Warming and Issues
2. All about Pollution

  • When did CO2 become our planet’s arch enemy?

    Carbon dioxide was always essential for our planet. This newscard discusses when did it become too much.

    Try this question from CSP 2017:

    Q. In the context of mitigating the impending global warming due to anthropogenic emissions of carbon dioxide, which of the following can be the potential sites for carbon sequestration?

    1. Abandoned and uneconomic coal seams
    2. Depleted oil and gas reservoirs
    3. Subterranean deep saline formations

    Select the correct answer using the code given below:

    (a) 1 and 2 only

    (b) 3 only

    (c) 1 and 3 only

    (d) 1, 2 and 3

    GHGs in atmosphere

    • The Earth’s atmosphere is made up of different gases. The temperature of the atmosphere depends on a balance between the incoming energy from the sun and the energy that bounces back into space.
    • Greenhouse gases (GHG) such as carbon dioxide (CO2), methane and nitrous oxide play an important role in the atmosphere.
    • They absorb some of the sun’s heat and release it back in all directions, including back to the atmosphere.
    • Through this process, CO2 and other GHGs keep the atmosphere warmer than it would be without them.
    • However, fossil fuel-run industries and other human activities add GHGs to the atmosphere. This, in turn, increases atmospheric temperature, causing global warming.

    Assessing the carbon level

    • In 1958, American scientist Charles David Keeling calculated the amount of CO2 in our atmosphere.
    • When he started his measurements in 1958, the CO2 levels were around 315 parts per million (PPM).
    • When he died in 2005, the project was taken over by his son Ralph Keeling. By 2014, CO2 levels had increased to about 400 PPM.
    • With his systematic study of atmospheric CO2, Keeling became the first person to alert the world about the increasing levels of CO2 in the atmosphere.

    Reasons for rising CO2 levels

    • Scientists first argued that the increasing release of methane and CO2 was due to agriculture and livestock.
    • But, with the start of the Industrial Revolution in the 18th century, the use of fossil fuels and CO2 levels rose simultaneously.
    • Nations that underwent the Industrial Revolution used huge amounts of fossil fuels and became centres of high CO2 emissions, while nations with an agrarian economy emitted less GHGs.
    • Over the years, as CO2 levels increased, it sparked off debates and arguments between the GHG-emitting rich industrial nations and the victims of global warming — the poorer nations.

  • Will leaders act on the climate crisis as they did Covid-19?

    In the context of climate change, the rising concentration of carbon dioxide and rising global temperature are inextricably linked with each other. This article elaborates on two interlinked and rising curves-CO2 and temperature. The article is concluded on the positive note that leaders would act on climate change with same urgency as Covid.

    The upward journey of two curves

    • Two interrelated curves began their upward trend two centuries ago with the advent of the industrial age.
    • The first curve was the atmospheric concentration of carbon dioxide or, more generally, all greenhouse gases, GHGs.
    • And the second was the average global temperature curve.

    CO2 concentration at 407 ppm: But did we get here?

    • Actually, the CO2 curve began its upward march about 18,000 years ago when it was a little under 200 parts per million (ppm).
    • And earth was much colder back then.
    • By the time it reached 270 ppm about 11,500 years ago, the warmer conditions accompanying this curve made it possible for the emergence of agriculture.
    • Over the past million years, CO2 levels never exceeded 280-300 ppm.
    • They always went back to 200 ppm before rising again in a cyclical fashion.
    • They remained steady at close to 280 ppm for 10,000 years until, beginning in the mid-19th century.
    • They began to rise again as humans burnt coal and oil to fuel the industrial revolution, and burnt forests to expand agriculture and settlements.
    • From a mere 0.2 billion tonnes of CO2 emissions in 1850, annual emissions increased to 36 billion tonnes by 2018.
    • If all this CO2 had accumulated in the atmosphere, we can say that human life would have been altered beyond recognition.
    • Nature has been rather kind to us so far — about one-half of all CO2 emissions have been sanitised from the atmosphere, equally by growing vegetation on land and by absorption in the oceans.
    • Thus, the levels of CO2 in the atmosphere reached 407 ppm in 2018, a level last experienced by earth some three million years ago.

    Global temperature up by 1 degree Celcius

    •  From 1850 onwards, for over a century, the global temperature showed a slight warming trend.
    • But there was nothing suggestive of anything serious.
    • From 1975 onwards, the temperature graph has shown a distinct, upward trend.
    • By 2015, the globe had heated by a full degree Celsius relative to a hundred years previously.
    • Climate modellers unequivocally project that under the current trends of emissions the globe will heat up by 4˚C by the end of the century.
    • he 2003 European heat wave killed over 70,000 people.
    • The years 2015-19 have globally been the warmest years on record.
    • Leave aside the Amazon fire of 2019, the bush fires of 2019-20 in Australia were unprecedented in their scale and devastation.
    • March 2020 has been the second warmest March on record.

    But climate change is not just about temperature rise

    • Climate change involves not just a change in temperature but every other component of weather, including rainfall, humidity and wind speed.
    • Indirect effects follow, such as a rise in sea levels from melting glaciers.
    • Globally there have been several extreme weather events such as hurricanes, heat waves or droughts.
    • While no single event can be directly attributed to climate change, the collective trends are consistent with climate change predictions.

    Warning for India

    • The Climate Impact Lab at the University of Chicago put out a warning for India last year.
    • It says that if global CO2 emissions continue to gallop at the present rate, average summer temperatures would rise by 4˚C in most States.
    • Extremely hot days (days above 35˚C), which were only five days in 2010, would increase to 15 days by 2050 and to 42 days by 2100 on average across all districts.
    • A more moderate emissions scenario, as a result of countries largely fulfilling their commitments under the Paris Agreement, would keep average global temperature rise below 2˚C compared to pre-industrial levels.

    Let’s look into the financial dimension of tackling climate change

    • The most common excuse is that the world cannot afford to curb GHG emissions for fear of wrecking the economy.
    • An article in Nature in 2019 highlighted the financial dimensions of tackling the looming climate crisis.
    • Apparently, the wealthy nations are spending over $500 billion each year internally on projects aimed at reducing emissions.
    • The Intergovernmental Panel on Climate Change, however, estimates that a sustained annual investment of $2.4 trillion in more efficient energy systems is needed until 2035 in order to keep warming below the more ambitious 1.5˚C relative to pre-industrial levels.
    • To put this in perspective, that is about 2.5% of the global GDP.

    What happened to the $100 billion per year aid to poor countries?

    • Some of the wrangling over money relates to the amounts that the wealthy nations, agreed to pay other countries to cope with climate change.
    • Underlying idea was that these countries have caused most of the GHGs resulting in global warming,
    • At the UN Climate Conference in 2009, the richest nations had pledged to provide $100 billion in aid each year by 2020 to the poorer countries for climate change mitigation and adaptation.
    • In 2017, for which data are available, only $71 billion had been provided.
    • And most of the money was spent on mitigation and less than 20% towards climate adaptation.
    • Such numbers had been challenged prior to the 2015 Paris Summit by many countries, including India.
    • It was challenged because much of the so-called aid provided did not come out of dedicated climate funds but, rather, development funds or simply loans which had to be repaid.
    • It thus seems unlikely that the rich countries will deliver $100 billion in tangible climate finance during 2020.

    Time to act

    • COVID-19 has unwittingly given humanity a brief respite from the climate change curve.
    • Commentators are already talking about a paradigm shift in the structure and functioning of societies once the pandemic subsides.
    • This is also a make-or-break moment for the climate trajectory which has to be flattened within a few years if we are to avoid dangerous climate change.
    • Nature’s kindness is not expected to last beyond a 2˚C rise in temperature as the carbon sequestered into vegetation will be thrown back into the atmosphere.
    • Also remember that earth has already warmed by 1˚C and we really have only another 1˚C as a safety margin or 0.5˚C if we are concerned about island nations.

    Consider the mains question asked by the UPSC in 2017-‘Climate change’ is a global problem. How India will be affected by climate change? How Himalayan and coastal states of India will be affected by climate change?

    Conclusion

    There is no substitute to reducing GHG emissions. Technologists, economists and social scientists must plan for a sustainable planet based on the principles of equity and climate justice within and across nations. It is the responsibility of leaders to alter their mindset and act on the looming climate crisis with the same alacrity they have shown on COVID-19.

  • Environment Performance Index 2020

    India has secured 168 ranks in the 12th edition of the biennial Environment Performance Index (EPI Index 2020).

    CSP 2019 has been a year with two questions based on rankings and indices viz. the EoDB index and Global Competitiveness Index.  Note all such indices and their publishing agencies here at  [Prelims Spotlight] Important reports and indexes

    About EPI

    • The EPI measures the environmental performance of 180 countries.
    • It is biennially released by the Yale University.
    • It considers 32 indicators of environmental performance, giving a snapshot of the 10-year trends in environmental performance at the national and global levels.

    The performance on climate change was assessed based on the following indicators —

    • Adjusted emission growth rates;
    • Composed of growth rates of four greenhouse gases and one pollutant;
    • Growth rate in carbon dioxide emissions from land cover;
    • Greenhouse gas intensity growth rate; and
    • Greenhouse gas emissions per capita.

    Performance of the South Asian Region

    • The 11 countries lagging behind India were — Burundi, Haiti, Chad, Solomon Islands, Madagascar, Guinea, Côte d’Ivoire, Sierra Leone, Afghanistan, Myanmar and Liberia.
    • All South Asian countries, except Afghanistan, were ahead of India in the ranking.

    India’s performance

    • A ten-year comparison progress report in the index showed that India slipped on climate-related parameters.
    • India scored below the regional average score on all five key parameters on environmental health, including air quality, sanitation and drinking water, heavy metals and waste management.
    • It has also scored below the regional average on parameters related to biodiversity and ecosystem services too.
    • Among South Asian countries, India was at the second position (rank 106) after Pakistan on ‘climate change’. Pakistan’s score (50.6) was the highest under the category.

    Remarks for India

    • The report indicated that black carbon, carbon dioxide emissions and greenhouse emissions per capita increased in 10 years.
    • India needs to re-double national sustainability efforts on all fronts, according to the index.
    • It needs to focus on a wide spectrum of sustainability issues, with a high-priority to critical issues such as air and water quality, biodiversity and climate change.

  • Aerosols Radiative Effects in the Himalayas

    Indian researchers have found that the effect of anthropogenic aerosols is much higher over the high altitudes of western trans-Himalayas.

    Try this question from CSP 2019:

    Q. In the context of which of the following do some scientists suggest the use of cirrus cloud thinning technique and the injection of sulphate aerosol into the stratosphere?

    (a) Creating the artificial rains in some regions

    (b) Reducing the frequency and intensity of tropical cyclones

    (c) Reducing the adverse effects of solar wind on the Earth

    (d) Reducing the global warming

    What are Aerosols?

    • An aerosol is a suspension of fine solid particles or liquid droplets in air or another gas.
    • They can be natural or anthropogenic.
    • Examples of natural aerosols are fog, mist, dust, forest exudates and geyser steam. Examples of anthropogenic aerosols are particulate air pollutants and smoke.
    • The liquid or solid particles have diameters typically less than 1 μm; larger particles with a significant settling speed make the mixture a suspension, but the distinction is not clear-cut.
    • Technological applications of aerosols include dispersal of pesticides, medical treatment of respiratory illnesses, and combustion technology.

    Heat pump over the Himalayas

    • The transport of light-absorbing carbonaceous aerosols and dust from the polluted Indo-Gangetic Plain and desert areas over the Himalayas constitutes a major climatic issue due to severe impacts on atmospheric warming and glacier retreat.
    • This heating over the Himalayas facilitates the “elevated-hat pump” that strengthens the temperature gradient between land and ocean and modifies the atmospheric circulation and the monsoon rainfall.

    Findings of the research

    • The monthly-mean atmospheric radiative forcing of aerosols leads to heating rates of 0.04 to 0.13 C per day.
    • Further, the temperature over the Ladakh region is increasing 0.3 to 0.4 degrees Celsius per decades from the last 3 decades.

    How are aerosols fuelling the heat?

    • The atmospheric aerosols play a key role in the regional/global climate system through scattering and absorption of incoming solar radiation and by modifying the cloud microphysics.

    Assessing the Aerosol potential

    • Despite the large progress in quantifying the impact of different aerosols on radiative forcing, it still remains one of the major uncertainties in the climate change assessment.
    • Precise measurements of aerosol properties are required to reduce the uncertainties, especially over the oceans and high altitude remote location in the Himalayas where they are scarce.
    • Researchers have analysed the variability of aerosol optical, physical and radiative properties and the role of fine and coarse particles in aerosol radiative forcing (ARF) assessment.
    • ARF is the effect of anthropogenic aerosols on the radiative fluxes at the top of the atmosphere and at the surface and on the absorption of radiation within the atmosphere.

    Significance of ARF study

    • A scientific study of aerosol generation, transport, and its properties has important implications in our understanding and mitigation of climate change via atmospheric warming.
    • Aerosols impact the snow and glacier dynamics over the trans-Himalayan region.
    • The results from the study can help better understanding of aerosol effects in view of aerosol-climate implications.

  • ‘Race to Zero’ campaign

    The UN has launched the “Race to Zero” campaign ahead of delayed COP 26 Climate Talks.

    Possible question for prelims:

    The ‘Race to Zero’ campaign often seen in news is related to zeroing: Global Hunger/Carbon Emission/HR violations/None of these.

     ‘Race to Zero’ campaign

    • The campaign aims to codify commitments made via the Climate Ambition Alliance (CAA), which launched ahead of last year’s COP25 in Madrid.
    • It encourages countries, companies, and other entities to deliver structured net-zero greenhouse-gas emission pledges by the time the talks begin.
    • This messaging for the campaign — carried out under the aegis of the UNFCCC— seeks to emphasise the potential for non-state actors to raise climate ambition.
    • The campaign refers to these as ‘real economy actors’, noting they “cover just over half the gross domestic product, a quarter of global CO2 emissions and over 2.6 billion people”.

    About the Climate Ambition Alliance

    • The CAA currently includes 120 nations and several other private players that have committed to achieving zero net greenhouse gas emissions by 2050.
    • Signatories are responsible for 23 per cent of current greenhouse-gas emissions worldwide and 53 per cent of global GDP.

    What Are the Criteria?

    • The minimum criteria for establishing a recognized pledge were developed through dialogues coordinated by Oxford University.
    • The pledges must include a clear net-zero target date no later than 2050, they must also begin immediately and include interim targets.
    • Much like the Paris Agreement itself, the criteria are designed to strengthen over time, but they begin at a level that reflects current best practices.

    Issue over offsetting

    • Offsets are emission-reductions generated outside a company’s own operations, and they are used in both compliance programs to meet mandated emission caps (“cap and trade”) and involuntary programs to reduce a company’s overall impact (voluntary carbon markets).
    • The Race to Zero criteria emphasizes that if offsets are ultimately recognized, they must only be used to neutralize residual emissions that can’t be eliminated internally – at least not immediately.

  • Expansion of the Amery Ice Shelf

     

    There would be a 24% increase in the expansion of the Amery Ice Shelf (AIS) boundaries in Antarctica by 2021 and another 24 per cent by 2026 from its 2016 positions, the National Centre for Polar and Ocean Research (NCPOR) in Goa has predicted.

    Practice question for mains:

    Q. Discuss the interrelation between Cryosphere and Climate change in context to the melting ice shelves in the Antarctic region.

    Amery Ice Shelf (AIS)

    • The Amery Ice Shelf is a broad ice shelf in Antarctica at the head of Prydz Bay between the Lars Christensen Coast and Ingrid Christensen Coast.
    • It is part of Mac. Robertson Land.
    • The name “Cape Amery” was applied to a coastal angle mapped on February 11, 1931.
    • The AIS is one of the largest glacier drainage basins in the world, located on the east coast of Antarctica, at about 70ºS Latitude, 70ºE Longitude.
    • The AIS dynamics and mass balance help in understanding the changes in the global climate scenario.

    Significance of the study

    • NCPOR observations revealed a critical cooling of the sea surface temperature, resulting in an advancement of the ice shelf by 88 per cent in the past 15 years.
    • These changes would contribute in a major way to climate variability.
    • The study clearly demonstrated the future dynamism of ocean heat fluctuation and Antarctic Amery ice shelf mass shifting-extent.

    Back2Basics: Ice Shelves

    • The floating sheets of ice called ‘ice shelves’ play a multi-faceted role in maintaining the stability of a glacier. Ice shelves connect a glacier to the landmass.
    • The ice sheet mass balance, sea stratification, and bottom water formation are important parameters for the balancing of a glacier. Latent and sensible heat processes do play important roles here.
    • The insulation of ice shelves from atmospheric forcing is dependent on a temperature gradient that the ocean cavity beneath the ice shelves provides.
    • It is the pressure exerted by the ice shelves upon the ocean cavity that determines this temperature gradient.

  • [pib] Seasonal rapid advancement of Surging Glaciers in Karakoram Range

    Indian researchers have found a seasonal advancement in 220 surge-type glaciers in the Karakoram Range of Ladakh.

    Points to note:

    1) Open you map and revise the glaciers of Himalayan region.

    2) Glacial landforms as Geographic phenomenon.

    What are Glacial Surges?

    Click here to see the animated view

    • Glacial surges are short-lived events where a glacier can advance substantially, moving at velocities up to 100 times faster than normal.
    • Until recently, most glaciologists believed that a glacier’s physical characteristics, such as its thickness and shape, and the properties of the terrain it sits on determining whether it can surge.
    • Now, it is proved to believe an external factor also plays a major role: water from precipitation and melting.
    • Pooling on the surface, it can infiltrate the glacier through crevasses and reach its base, warming, lubricating, and, ultimately, releasing the ice.

    Why surging in the Karakoram is a concern?

    • The behaviour of these glaciers, which represent 40% of the total glaciated area of the Karakoram, goes against the normal trend.
    • Surging of glaciers is potentially catastrophic as it can lead to the destruction of villages, roads and bridges.
    • It can also advance across a river valley and form the ice-dammed lake.
    • These lakes can form catastrophic outburst floods.
    • Therefore, monitoring of glacier surges, ice-dammed lake formation, and drainage is of paramount importance.

    Which are these glaciers?

    • The scientists focused on the Shispare and Muchuhar glaciers, former tributaries of the once larger Hasanabad Glacier situated in Hunza Valley, Gilgit-Baltistan.

    Significance of the study

    • The Surge-type glaciers oscillate between brief (months to years) rapid flow and lengthy (tens to hundreds of years) slow flow or stagnation, which are called the ‘active’ (or ‘surge’) and ‘quiescent’ phases, respectively.
    • This unsteady glacier flow makes it difficult to accurately assess individual glacier mass balances using in-situ observations.
    • The study will help to understand the diversity of glacial behaviour and help make accurate assessments of individual glacier mass balances for disaster planning and management.

  • [pib] Petersberg Climate Dialogue

    India along with 30 countries deliberated on issues of Climate Change in first-ever virtual Petersberg Climate Dialogue.

    Climate change negotiations are somehow put to a halt due to ongoing pandemic. Such small dialogues are keeping alive the spirit of climate action.

    Petersberg Climate Dialogue

    • It has been hosted by Germany since 2010 to provide a forum for informal high-level political discussions, focusing both on international climate negotiations and the advancement of climate action.
    • This year’s virtual Dialogue was co-chaired by Germany and the UK.
    • The dialogue was crucial because of the efforts to contain coronavirus as well as countries preparing to move into the implementation phase of the Paris Agreement 2015 in the post-2020 period.

    India’s Contributions

    • Expressing solidarity with the world as it combats the COVID 19 pandemic the Union Minister highlighted how COVID – 19 has noticed that we can survive on less.
    • India pushed for having climate technology as an open source available to all countries at affordable prices.
    • India stressed on climate finance and urged to plan for 1 trillion USD in grants to the developing world immediately.
    • India focussed on the opportunity that the world has today to accelerate renewable energy deployment and creating new green jobs in the renewable energy and energy efficiency sector.

  • How the ozone layer hole over Arctic closed?

    Recently the EU’s Copernicus Atmosphere Monitoring Service (CAMS) announced that a hole in the Arctic ozone layer, believed to be the biggest reported, has closed.

    What healed the hole in the Ozone?

    • The ozone hole’s closing was because of a phenomenon called the polar vortex, and not because of reduced pollution levels due to Covid-19 lockdowns around the world.
    • The hole in the North Pole’s ozone layer, which was first detected in February, had since reached a maximum extension of around 1 million sq km.

    Ozone hole

    • The ‘ozone hole’ is not really a hole — it refers to a region in the stratosphere where the concentration of ozone becomes extremely low in certain months.
    • Ozone, made up of three oxygen atoms, occurs naturally in small amounts.
    • Roughly 10 km to 40 km up in the atmosphere (the layer called the stratosphere), the ozone layer is sunscreen, shielding Earth from harmful ultraviolet radiation.
    • Manufactured chemicals deplete the ozone layer. Each spring over Antarctica (it now springs there), atmospheric ozone is destroyed by chemical processes.
    • This creates the ozone hole, which occurs because of special meteorological and chemical conditions that exist in that region.

    The importance of the ozone layer

    • Ozone (chemically O3, a molecule of three oxygen atoms) is found mainly in the upper atmosphere, an area called the stratosphere, between 10 and 50 km from the earth’s surface.
    • Though it is talked of as a layer, ozone is present in the atmosphere in rather low concentrations.
    • Even at places where this layer is thickest, there are not more than a few molecules of ozone for every million air molecules.
    • They perform a very important function. By absorbing the harmful ultraviolet radiations from the sun, the ozone molecules eliminate a big threat to life forms on earth.
    • UV rays can cause skin cancer and other diseases and deformities in plants and animals.

    Why this year’s hole was massive?

    • This year, the ozone depletion over the Arctic was much larger.
    • Scientists believe that unusual atmospheric conditions, including freezing temperatures in the stratosphere, were responsible.
    • Cold temperatures (below -80°C), sunlight, wind fields and substances such as chlorofluorocarbons (CFCs) were responsible for the degradation of the Arctic ozone layer.
    • Although Arctic temperatures do not usually fall as low as in Antarctica, this year, powerful winds flowing around the North Pole trapped cold air within what is known as the polar vortex.
    • By the end of the polar winter, the first sunlight over the North Pole initiated this unusually strong ozone depletion—causing the hole to form.

    How long it will take for complete recovery?

    • As per the Scientific Assessment of Ozone Depletion data of 2018, the ozone layer in parts of the stratosphere has recovered at a rate of 1-3 per cent per decade since 2000.
    • At these projected rates, the Northern Hemisphere and mid-latitude ozone is predicted to recover by around 2030, followed by the Southern Hemisphere around 2050, and polar regions by 2060.

    Also read: Polar Vortex

    https://www.civilsdaily.com/news/whats-causing-extreme-cold-in-us-midwest/

  • Third mass bleaching of Great Barrier Reef

    A survey has found record sea temperatures had caused the third mass bleaching of the 2,300-kilometre Great Barrier Reef system in just five years.

    What is Coral Bleaching?

    • When corals face stress by changes in conditions such as temperature, light, or nutrients, they expel the symbiotic algae zooxanthellae living in their tissues, causing them to turn completely white.
    • This phenomenon is called coral bleaching.
    • The pale white colour is of the translucent tissues of calcium carbonate which are visible due to the loss of pigment-producing zooxanthellae.

    About Great Barrier Reef

    • The Great Barrier Reef is the world’s largest coral reef system composed of over 2,900 individual reefs and 900 islands.
    • It is stretched for over 2,300 kilometres over an area of approximately 344,400 square kilometres.
    • The reef is located in the Coral Sea, off the coast of Queensland, Australia.

    Importance of Corals

    Coral reefs are some of the most diverse and valuable ecosystems on Earth.

    • They support more species per unit area than any other marine environment, including about 4,000 species of fish, 800 species of hard corals and hundreds of other species.
    • This biodiversity is considered key to finding new medicines for the 21st century. Many drugs are now being developed from coral reef animals and plants as possible cures for cancer, arthritis, human bacterial infections, viruses, and other diseases.
    • Healthy coral reefs support commercial and subsistence fisheries as well as jobs and businesses through tourism and recreation.
    • Local economies receive billions of dollars from visitors to reefs through diving tours, recreational fishing trips, hotels, restaurants, and other businesses based near reef ecosystems.
    • Coral reef structures also buffer shorelines against 97 percent of the energy from waves, storms, and floods, helping to prevent loss of life, property damage, and erosion.
    • When reefs are damaged or destroyed, the absence of this natural barrier can increase the damage to coastal communities from normal wave action and violent storms.

    Back2Basics

    Coral Reefs

    • Coral reefs are built by and made up of thousands of tiny animals—coral “polyps”—that are related to anemones and jellyfish.
    • Polyps are shallow water organisms which have a soft body covered by a calcareous skeleton. The polyps extract calcium salts from sea water to form these hard skeletons.
    • The polyps live in colonies fastened to the rocky sea floor.
    • The tubular skeletons grow upwards and outwards as a cemented calcareous rocky mass, collectively called corals.
    • When the coral polyps die, they shed their skeleton on which new polyps grow.
    • The cycle is repeated for over millions of years leading to accumulation of layers of corals shallow rock created by these depositions is called reef.