Natural Hazards and Disasters

Class 3: Global Threats and Extraterrestrial Hazards

Class 3 Slides

CONTENTS

1. Extreme Natural Hazards
2. Global Risk Assessments
3. Risks Associated with Modern Global Change
4. Major Global Risks
5. Global Risk Governance
6. Extraterrestrial Hazards

Extreme Natural Hazards

Extreme natural hazards are often low-probability, high-impact events. Rare extreme events pose particular challenges for risk assessment and risk governance: they often are outside of past experience, and their likelihood is not well known or not known at all. Often these events come as so-called Black Swans (Taleb, 2012). Likewise, threats resulting from slow trends and slowly developing new circumstances are difficult to assess, and they can present extreme hazards. Moreover, while human individuals and communities posses the ability to react to severe individual events, slow trends with potential future threats are often ignored. Risk perception for slowly developing threats is often overly optimistic.

Global Risk Assessments

A number of groups and institutions are engaged in the assessment of global threats with the goal to inform leaders so that they can make better decisions. Examples are the assessment of Cotton-Barratt et al., 2016 and the annual assessment reports produced by the World Economic Forum (e.g., World Economic Forum, 2017, 2018). The reports produced by the World Economic Forum illustrate that risk and threat assessments keep changing over time a lot indicating both the uncertainty in the assessment as well as the development of new threats.

A particular case are the Doomsday Clock Statements published in the Bulletin of the Atomic Scientists since 1947 (e.g., Mecklin, 2017, 2018). In summary, these statements measure the global threat level by minutes humanity is away from midnight of doomsday. In recent years, the assessment has slowly moved the clock closer to midnight.

Risks Associated with Modern Global Change

Modern global change (MGC) refers to the changes in the Earth system humanity has caused or triggered. They include changes in the physiology of the Earth's life-support system by accelerating existing flows, interrupting flows, and creating new flows. Examples of accelerated flows are nutrients such as nitrogen and phosphorous, carbon, energy, and water. Examples of interrupted flows are movements of animals due to fragmentation of habitats, and flows in aquatic systems due to river dams, levies, and canals. Examples of new flows are new constituents that enter the air, soil and water systems as pollutants and plastics that are increasingly polluting the ocean and land.

MGC also includes rapid changes in land use. Deforestation is rapidly progressing and fragmentation has a severe impact on ecosystem stability. For example, 70% of the remain forests are less than 1 km away from a forest boundary.

These changes in flows are pushing the ELSS out of the global boundaries for the Holocene, which was an exceptionally stable geological epoch, which provide a "safe operating space for humanity" (SOSH). They have accelerated extinction rates and are causing rapid changes in climate. They also have the potential to trigger other natural hazards.

The energy usage of humanity is comparable to the energy associated with major volcanic eruptions or major impactors colliding with the Earths. The use of this large amount of energy to reengineer the planetary system is creating many novel threats and risk assessment for these threats is extremely challenging.

Major Global Risks

Despite a very low probability, extreme extraterrestrial hazards pose a large risk to humanity. Therefore, several space agencies collaborate in a near-earth object service to ensure that any large objects potentially colliding with Earth is discovered early enough to take action and divert the object from its trajectory.

Among extreme geohazards, large volcanic eruptions are associated with a very high risk. In the Holocene, at least seven large eruptions took place with severe impacts on humanity. It can be expected that a similar eruption today would cause a global disaster or catastrophe because of the interconnected and interdependent global civilization and an already stressed food security. Despite the high risk, no comprehensive monitoring of all volcanoes capable of large eruptions is in place.

Pandemics poses severe threat, and on many country and intergovernmental levels, monitoring and response programs are in place to counteract any emerging epidemic with a potential to develop into a pandemic.

The interactions of MGC with natural hazards will likely change the PDF of natural hazards, including those of droughts, heatwaves, wildfires, and storms. But even for volcanic eruptions, there are potential mechanisms that could lead to increased activity. In particular, mass movements on the earth surface (water, ice) can impact the stress field in the earth crust and asthenosphere and this can increase volcanic activity.

Global Risk Governance

A number of international and intergovernmental frameworks and conventions are aiming at risk management and risk reduction. However, an efficient governance for global risks has not been established. Plag et al. (2015) made recommendations for steps towards a global governance. Although their recommendations focus on governance for extreme geohazards, they apply entirely also for other extreme natural hazards.

There are several core elements that are needed to address the global risk from extreme geohazards:

• It is recommended that a joint international and synergistic e ort be made to establish a global scientific framework for strategic extreme geohazard science. This framework should be capable of delivering a tactical scientific response to hazards and extreme hazards. It should also seamlessly integrate and up-date science into warning, preparedness, mitigation and responses that are implemented by governments, communities, and the private sector on a global scale in order to min- imise the detrimental global impacts of extreme geohazards. Such a framework could take into account lessons learned from NEO tracking in terms of monitoring and from the IPCC model in terms of knowledge assessment. As of today, no such scientific framework is available to assess the knowledge on global threats resulting from modern society being exposed to low-probability high-impact events.
• It is recommended that a better understanding be gained of the interrelation between topography, geohazards and the environment. The temporal evolution of topography needs to be assessed, not only during the recent past but also during the last 10 or so million years. There are however some complex problems inherent to paleo-topography analysis. Apart from dealing with topography that no longer exists, the dimensions and timing of events and the underlying dynamic processes that controlled topographic development, as well as the topographic life cycle, pose major chal- lenges, the complexity of which cannot be solved by a single sub-discipline but requires support by other disciplines.
• It is recommended that scenario contingency planning be used to better understand the threats and reduce risk. For this, a few specific or generic extreme geohazards should be selected. A methodological and rational scientific analysis of event scenarios, including likely worst case scenarios, should be developed in cooperation with stakeholders and decision makers. A goal should be to work through the cascading hazards and outcomes identified by science and those recognised by stakeholders. The existing political opportuni- ties and constraints, including the difficulties of implementation and the cost of not implementing, should be assessed. Options should be developed for how to manage the situation with the resources that will be available, rather than those that the scenario dictates should be available.
• It is recommended that risk awareness be increased in the population through dissemination of con- cise and clear information on the risk associated with hazards and through training for coping with emergency scenarios.
• It is recommended that a global monitoring sys- tem be put in place with the goal of providing early warning for emerging extreme volcanic eruptions. Two core elements of this monitoring system would be the operational monitoring of solid Earth surface displacements and of infrasound waves. Both monitoring components would have major societal benefits besides the early detection of emerging extreme eruptions.
• It is considered important to develop an informed global governance structure that could respond to emerging global threats and coordinate global measures to increase preparedness and resilience and reduce the risk of global disasters. In this context, the recommended framework for strategic extreme geohazards science (and science for other extreme hazards) would inform the global governance system of any impending risk, and scenario contingency planning would provide guidance for disaster risk management.

Extraterrestrial Hazards

Earth is exposed to several hazards that originate in space. These include asteroids, meteorides, and comets that might lead to severe bollides or impacts, as well as radiation in form of space weather and solar storms, that can affect modern infrastructure. Gamma rays and proton storms also can pose hazards to life on Earth. There are many remanents of past impacts in form of meteor craters, and several mass extinction events are linked to extraterrestrial hazards. Today, several space agencies are engaged in monitoring Near-Earth Objects and space weather to provide timely warnings of emrging hazards.

Extraterrestrial hazards can be grouped into:

• Near-Earth Objects (NEOs): Meteoroids, asteroids and comets with orbits that intersect Earth’s orbit. Specifically:
  • Meteoroids and asteroids: Fragments of rock and/or metal in space. The smaller fragments generate light as meteors as they pass through Earth’s atmosphere. Larger fragments land as meteorites.
  • Comets: Balls of ice, dust, and rock that normally reside beyond the orbit of Neptune.
  • Bollides: Meteoroids and cometary fragments that explode on entering Earth’s atmosphere.
• Solar storms and space weather: Solar flares and coronal mass ejections occur frequently and can disrupt telecommunications or have more severe consequences for electrical and electronically infrastructure.
• Gamma Ray bursts: Extremely energetic explosions that have been observed in distant galaxies.
• Extraterrestrial intelligence.
• Human space debris: debris of satellites and rockets.

We will not discuss the threats associated with extraterrestrial intelligence and human debris in space.

NEO Search Program

Near Earth Objects (NEOs) are meteoroids, asteroids or comets that pass close to the Earth. Potentially hazardous NEOs are estimated to be greater than 20 m in diameter. NEOs greater than 1 km in diameter have the potential to severely disrupt and destroy life.

The United States of America leads discovery and tracking survey programs using optical telescopes; see https://cneos.jpl.nasa.gov/about/search_program.html for details. NASA and the European Space Agency determine the likelihood of an impact with the Earth. There are a number of NASA supported Near-Earth Object (NEO) discovery teams currently in operation. The early efforts to discover NEOs relied upon the comparison of photographic films of the same region of the sky taken several minutes apart. The vast majority of the objects recorded upon these films were stars and galaxies and their images were located in the same relative position on these films. Early discovery techniques included blink comparators and stereomicroscopes to examine the photographic images. Because a moving NEO would be in a slightly different position on each photograph and the background starts and galaxies were not, the NEOs appeared to jump back and forth when each image, in turn, was quickly viewed through a so-called blink comparator. Alternately, the NEO’s image appeared to “rise” above the background stars when two different and slightly offset images were viewed with a special stereo viewing microscope.

All of the NEO discovery teams currently use so-called charged couple devices (CCDs) rather than photographic images. These CCD cameras are similar in design to those used in cell phones and they record images digitally in many electronic picture elements (pixels). The length and width of a CCD detector is usually given in terms of pixel elements. A fairly common astronomical CCD detector might have dimensions of about 2000 x 2000 pixels. While the CCD technology allows today’s detectors to be more sensitive and accurate that the older photographic images, the modern discovery technique itself is rather similar. Separated by several minutes, three or more CCD images are taken of the same region of the sky. These images are then compared to see if any NEOs have systematically moved to different positions from one image to the next. For a newly discovered NEO, the separation of the object’s location from one image to the next, the direction it appears to be traveling and its brightness are helpful in identifying how close the object was to the Earth, its size and general orbital characteristics. For example, an object that appears to be moving very rapidly from one image to the next is almost certainly very close to the Earth. Sophisticated computer-aided analyses of the CCD images have replaced the older, manual detection techniques but often times, a new NEO discovery is still verified using the human eye.

Not surprisingly, discovery teams who search the largest amount of sky each month will have the most success in finding new NEOs. How much sky each telescope covers per month will depend upon a number of factors including the number of clear nights available for observing, the sensitivity and efficiency of the CCD detector and the field of view of the telescope. It is also important for search teams to extend their searches to greater and greater distances from the Earth or, in other words, go to fainter limiting magnitudes. A 6th magnitude star is roughly the limit of a naked eye object seen under ideal conditions by someone with very good eyesight. A 7th magnitude star would be 2.5 times fainter than a 6th magnitude star and an 8th magnitude star would be 6 times fainter than a 6th magnitude object (2.5 x 2.5 = 6.25). A difference of 5 magnitudes is a brightness difference of nearly 100 (2.5 x 2.5 x 2.5 x 2.5 x 2.5 is equal to about 100).

In 1998, NASA established a goal to discover 90% of the NEOs larger than one kilometer in diameter and in 2005, Congress extended that goal to include 90% of the NEOs larger than 140 meters. There are thought to be about 1000 NEAs larger than one kilometer and roughly 15,000 larger than 140 meters. The progress toward meeting these goals can be monitored on the NEO Discovery page.

Since NASA’s initiation of the NEO Observations program in 1998, Near-Earth Object (NEO) surveys have been extremely successful finding more than 90% of the Near-Earth Asteroids (NEAs) larger than one kilometer and a good fraction of the NEOs larger than 140 meters. The vast majority of NEO discoveries have been due to NASA-supported ground-based telescopic surveys including the Catalina Sky Survey (CSS) and Spacewatch near Tucson Arizona, the LINEAR project near Socorro New Mexico, Pans-STARRS1 on Haleakala, Maui, Hawaii, LONEOS near Flagstaff Arizona and the NEAT project run by NASA/JPL. Using a near-infrared space telescope in an Earth polar orbit, the NEOWISE project was actively discovering and characterizing NEOs for ten months in 2010 before its cryogens were exhausted. It continued another four months into early 2011 as a post-cryogenic mission. The LONEOS and NEAT surveys have been discontinued and Spacewatch is now primarily a follow-up facility. See https://cneos.jpl.nasa.gov/about/search_program.html for more information.

Meteoroids and Asteroids

A meteoroid is a small rocky or metallic body traveling through outer space. Meteoroids are significantly smaller than asteroids, and range in size from small grains to 1 meter-wide objects. Objects smaller than this are classified as micrometeoroids or space dust. Most are fragments from comets or asteroids, whereas others are collision impact debris ejected from bodies such as the Moon or Mars.

Asteroids are small, airless rocky worlds revolving around the sun that are too small to be called planets. They are also known as planetoids or minor planets. In total, the mass of all the asteroids is less than that of Earth's moon. But despite their size, asteroids can be dangerous. Many have hit Earth in the past, and more will crash into our planet in the future. That's one reason scientists study asteroids and are eager to learn more about their numbers, orbits and physical characteristics. If an asteroid is headed our way, we want to know that.

Asteroids reside in the asteroid belt within the inner solar system whereas comets originate from the Kuiper belt in the outer solar system. Their relatively stable orbits can be perturbed gravitationally so that their paths can intersect the trajectory of the Earth, possibly resulting in a collision.

A comet is a very small solar system body made mostly of ices mixed with smaller amounts of dust and rock. The main body of the comet is the nucleus, which can contain water, methane, nitrogen and other ices. Most comets are smaller than a few kilometres in diameter. When passing close to the Sun, a comet warms and its ices begin to release gas (outgasing). The mixture of ice crystals and dust blows away from the comet nucleus in the solar wind, creating a pair of tails. The dust tail is what normally can be seen from Earth.

Meteorites are rock and/or metal fragments that land on Earth after falling from space at an average speed of about 64,000 km/h. While still in space, they are called meteoroids – or asteroids if they are very large. When a stray meteoroid is captured by Earth’s gravitational field the heat generated as it passes through Earth’s atmosphere causes its outer skin to vaporize, glow, and become visible as a meteor streak.

Roughly 44,000 kg of meteoritic material falls onto Earth each day, almost all as fragments a millimeter or smaller in diameter. Larger pieces do fall, including a few in North America in recent times. Very large meteoroids and asteroids are extremely rare, but have caused catastrophic damage in the geological past.

Stony meteorites are rock-like pieces of left-over debris from our solar system’s formation. Stony meteorites, which are similar to rocks on Earth, comprise nearly 85% of meteorites found. They range widely in composition and also in size, from microscopic to several meters across. There are two main groups of stony meteorites:

• Chondrites, which have never melted and contain rounded, bead-like “chondrules” of silicate minerals and metal that were formed very early in the solar system’s formation, at about 4.6 billion years ago. They comprise 80% of all found meteorites.
• Achondrites, which once melted and then solidified again, comprise about 4% of all found meteorites. They have a composition similar to that of Earth’s mantle and are thought to have originated when extremely small planets that had already differentiated into crust/mantle and core were fragmented in collisions.

Iron meteorites are formed in the core of planetary bodies from a mixture of iron and nickel metal. Although most metallic meteorites are known as ‘iron meteorites’, they are really made of a mixture, known as an alloy, of solid iron and nickel. Such alloys do not occur naturally in Earth’s crust, but form inside its core, or the core of other large planetary bodies. Iron meteorites are magnetic due to their high iron content (90–95%) and they are very dense, which makes them easy to recognize. They may have an internal crystalline structure known as Widmanstätten pattern formed by slow exsolution of the solid alloy.

Many iron meteorites have a smooth, shiny surface with shallow depressions called regmaglypts that form as the meteorite passes through Earth’s atmosphere. This surface feature distinguishes iron meteorites from the left-over material from old iron foundries known as ‘slag,’ which does not have regmaglypts.

More than 8,000 asteroids and meteoroids orbit in the asteroid belt, between Jupiter and Mars. The asteroid belt, located in the orbital plane between Jupiter and Mars, contains at least 8,000 asteroids that are 10 to 20 km in diameter and millions of smaller ones. The orbits of asteroid belt objects are generally stable, although they are often much more elliptical than those of Earth or Mars.

However, not all of the asteroids are in the same orbital plane, which can lead to asteroid-asteroid collisions that in turn may knock an asteroid into a less stable orbit.

A few dozen of the objects in the asteroid belt are over 100 km across. Ceres is the largest at 960 km diameter, a little less than 1/4 the size of the Moon, and shows evidence of recent landslides and domes that have formed from sodium carbonate-rich ice oozing to its surface. Many of the asteroids are irregularly-shaped and pockmarked by craters that formed by collisions with smaller meteoroids and asteroids over their long history.

Meteor showers occur frequently, but large meteorite falls are very rare. Between 4.1 and 3.8 billion years ago, the solar system’s planets and their moons underwent a barrage of asteroid impacts known as the Late Heavy Bombardment. The frequency and size of asteroid impacts gradually reduced to only a few really large events since about 2.0 billion years ago. Today, at least one meteorite of several cm to a meter in size, with velocities of 15 km/s or more, lands on Earth each year, but larger meteorite falls are rare. When Earth’s orbit passes through locally high concentrations of space dust, sometimes left behind by a passing comet, we see meteor showers such as the mid-August Perseid Shower, named for the position in the sky from which the meteors appear to originate. Meteor showers are usually harmless events, although in 2003 a meteoroid impact that occurred during a meteor shower destroyed two houses and injured several people in India.

Energy release from a meteorite impact creates a circular crater with a characteristic morphology. When an asteroid or meteoroid impacts the surface of a planet, moon, or another asteroid, it releases energy as a shock wave. The kinetic energy E_k of the impact shock depends upon the mass m and velocity v of the impactor. The shock wave radiates outward and, instantaneously, fractures the surrounding rock into pieces, called breccia. The shock also melts rock at the impact site and blasts tiny globules of molten rock, along with pulverized rock fragments and meteoritic material, high into the atmosphere. The blasted-away material is called ejecta and it leaves behind a circular crater. Rock in the crater’s center rebounds almost instantaneously, creating a central uplift in the crater. The molten ejecta globules can be carried far in the atmosphere before they are strewn as glassy objects, called tektites, over a very wide region around impact sites.

Earth’s erosional and tectonic forces have removed much of the evidence for asteroid impact craters. There are presently 190 confirmed impact craters on Earth, ranging from about 50 m to 300 km in diameter, but this is a tiny number compared to the thousands of craters, large and small, that are visible on the Moon. Reasons for the lack of impact craters on Earth include: (i) tectonic processes have reworked the margins of the earliest stable continental crust, called cratons, leaving relatively small remnants of craton surface rocks preserved; (ii) there is no oceanic crust older than about 270 million years; (iii) erosion by wind, water and/or ice has modified crater morphology; (iv) younger sediments and volcanic rocks have covered many smaller craters; and (v) the friction of passing through Earth’s atmosphere slows down and melts or completely evaporates small meteoroids, whereas on the Moon these would still form craters in impact, albeit small ones.

There is evidence of large terrestrial impacts. The Vredefort structure in South Africa and the Sudbury Impact Crater in Canada, are the two largest known impact structures on Earth. The largest confirmed meteorite impact on Earth is the Vredefort Dome in South Africa, which was formed 2.02 billion years ago by a 10 km diameter impactor. The Vredefort crater is at least 120 km in diameter now, although some estimates put the crater’s original diameter at 300 km. Rocks from Earth’s lower crust are exposed in its center along with a large volume of impactgenerated melt rock called pseudotachylyte. The crater has a rim of upturned sedimentary rocks and contains numerous examples of shatter cones and shocked quartz grains. Earth’s second-largest impact crater formed near Sudbury, Canada. The originally circular, 1.85 billion year-old crater has been deformed into a roughly elliptical shape by younger tectonic events, but still contains shatter cones and other shock features, as well as high amounts of nickel, platinum, copper, and gold.

The Chicxulub impact has been linked to the end-Cretaceous mass extinction. Several mass extinctions of biota on Earth may have been caused by asteroid impacts. The most famous is the demise of dinosaurs at the end of the Cretaceous Period, 65.5 million years ago.

Impact of a large asteroid affected life on Earth 65.5 million years ago, at the end of the Cretaceous Period. The asteroid, estimated as 12–14 km in diameter, made a crater 170–180 km across on the edge of the Yucatán Peninsula. Known as the Chicxulub crater, the structure is best seen using remote sensing data. Surface rocks were pushed downward by as much as 30 km by the impact, and then rebounded to heights of 10 km above surface. The estimated energy released was equivalent to 5∙1023 J (about 100 times the energy released during the last eruption of the Yellowstone super volcano). Enormous tsunami waves would have been generated. Impact breccias, quartz grains with shock features, and tiny spherules made of melted rock, are common within the crater and around its rim. Vaporized ejecta reaching the stratosphere would have caused years of darkness. The timing of the Chicxulub impact coincides with the extinction of 85% of Earth’s animal and plant species, including almost all species of dinosaurs. All the major continents and oceans were affected. However, the concept of an impact origin for this mass extinction event was controversial for decades, until the Chicxulub crater was discovered and high IR concentrations were found in very thin layers of sediment of exactly the same age from locations around the world.

Comets

Comets are balls of ice, dust, and rock that normally reside beyond the orbit of Neptune. When the solar nebula of gas and dust condensed to form the Sun and its planets, some of the leftover material formed balls of frozen water (H2O) and rock fragments that we call comets. Some comets reside in the Kuiper Belt, beyond the orbit of Neptune, but most are in the Oort Cloud, well beyond Pluto, and some are occasionally perturbed into eccentric orbits. Some comets have a rocky center and many also contain small amounts of CO2, CO, ammonia, and methane. They only become visible when, as they approach the Sun, their frozen surfaces emit gas that streams behind them as they travel.

Comets that take less than 200 Earth-years to orbit the Sun have well-documented orbits, such as Halley’s Comet. Others take much longer to complete one orbit and are less well mapped, therefore their direction of approach and distance from Earth as they pass can be unpredictable.

Bolides

Bolides are meteoroids and cometary fragments that explode on entering Earth’s atmosphere. Asteroids, meteoroids, and fragments of comets that explode in Earth’s atmosphere before reaching the surface are called bolides. The explosions are seen as very bright meteors, sometimes called ‘fireballs.’ In a 20-year period, more than 500 bolides with diameters > 1 m are typical. A bolide thought to be at least 60 m in diameter and weighing 108 kg exploded in Earth’s atmosphere on June 30, 1908, high above a remote forested region of the Tunguska River in Siberia. Roughly 80 million trees were flatted by the blast. Energy estimates are between 1.3 and 2.1•10¹⁶ J. A man more than 65 km away from the blast epicenter reported being thrown out of his chair by the shock wave. A bolide of that size over a large city would be truly catastrophic.

A recent example of a bolide is the one that occurred over Chelyabinsk, Russia, in 2013. An unexpected bolide blast over southern Russia shattered windows and caused multiple injuries. On February 15, 2013, a bolide at least 17 m in diameter exploded at a height of about 20 km in the atmosphere above Chelyabinsk, Russia. The bolide had an estimated energy release equivalent to over 2•10¹⁵ J. The blast was recorded by seismic stations around the world. Although initial reports indicated a number of deaths, there were no direct fatalities from the bolide, but 1,500 people were injured, some seriously, by flying glass and debris. By coincidence, NASA had predicted that a different asteroid, they had named 2012DA14, would make a close approach to Earth on about the same day, however they were unaware of the Chelyabinsk asteroid; the two were on completely different and unconnected orbits.

Space Weather

Solar flares and coronal mass ejections occur frequently and can disrupt telecommunications. Streams of electrically charged particles are constantly emitted by the Sun as a ‘solar wind.’ We see the effects on our upper atmosphere most often as an Aurora Borealis at high latitudes. Variations in the Sun’s magnetic field, especially in its photosphere and chromosphere produce intense, localized solar X-ray and proton flares, whose frequency and strength are often correlated with sunspot activity. A solar X-ray burst does not produce an Aurora Borealis, but it does disturb the ionosphere and can jam both high- and low-frequency radio signals. Many solar flares trigger coronal mass ejections (CMEs), which blast billions of tons of charged gas into space at speeds of hundreds to thousands of km/s. CME’s are classified according to their speed, with the fastest also being the most rare. A CME can take from one to four days to reach Earth, where it can cause serous disruption to telecommunications and power grids. Because of their potential to disrupt human society on Earth, solar flares and CME’s are monitored as part of NASA’s Space Weather program.

The Carrington Superstorm illustrates the threats posed by solar storms. Records of major solar flares and their associated coronal mass ejections first began in 1859. Solar flares are classified today according to their strength in watts per square meter reaching Earth, using a lettered scale in which each level is 10 times greater than the next lower rating. For example, an M0 flare is ten times greater than a C9, and an M3 is ten times greater than an M2. The strongest, most damaging flares are given X values, with no upper limit. On September 1, 1859, an intense white-light solar flare was observed by British astronomer Richard Carrington. This was the first recorded observation of a solar flare, which lasted for about 5 minutes and is now classified as an X15 Super Geomagnetic Storm. When the intense burst of energy reached Earth it caused aurora-induced electrical currents in telegraph wires that were sufficient to give electric shocks to telegraph operators. In the hours before dawn next morning, bright auroras were visible as far south as Cuba.

A large solar flare on August 4, 1972, disrupted telephone communication across the state of Illinois and caused AT&T to redesign its power system for transatlantic cable.

On April 2, 2001, an X20 flare became the largest so far on record; it generated a 2,000 km/s CME blast that, fortunately, was not directed toward Earth.

The Earth’s safety shield is the magnetic field. Earth’s magnetic field deflects the solar wind, shielding the planet from harmful ions. Earth is protected from much of the ionized solar wind and from most solar emissions by its magnetosheath, which is the result of the magnetic field generated by electrical currents in Earth’s core. The magnetosheath is not symmetrical, but is compressed on the daylight side of Earth (the side facing the solar wind) and extended on the dark, night-time side into a long tail, called the magnetotail. Large solar flares and very fast-moving CMEs further distort Earth’s magnetosheath and cause geomagnetic storms that can seriously disrupt satellites and telecommunications.

A powerful geomagnetic storm occurred in May 1921, burning out telephone and telegraph wires across Europe and North America. On March 10, 1989, an X15 solar flare and CME caused a geomagnetic storm three days later that disrupted weather satellites and shut down the power grid of Quebec province, Canada, for over 9 hours.

Class Reading List

Global Threats

World Economic Forum, 2018.

World Economic Forum, 2017.

Cotton-Barratt et al., 2016.

Mecklin, 2018.

Mecklin, 2017.

Extraterrestrial Hazards

Lincoln, D., 2017. Earth dodges a cosmic bullet — for now. CNN, see here.

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