Advanced science, Astrophysics, International, Technical

Stephen Hawking: The supernova of cosmology

In 1974, by predicting the apparently paradoxical concept of radiation emanating from black holes, Hawking reminded us that mass and energy are two sides of the same coin.


We humans are a recent phenomenon in the Universe that is very old, mostly imperceptible and beyond our comprehension. Had it not been for great scientists like Isaac Newton, Albert Einstein, Edwin Hubble, Karl Schwarzschild, Subrahmanyan Chandrasekhar, Stephen Hawking and many more who unlocked the enduring mysteries of the boundless Universe, it would have been a struggle for lesser mortals like us getting our bearings straightened about our place in the cosmos. Their ground-breaking work, forever, changed our view of the “heavens.”

Postulated in 1687, Newton’s law of gravity was a beautiful synthesis between terrestrial and celestial phenomenon, reaching across the vast expanse of the Universe. It allows us to study the waltzing motion of the planets, moons, stars and other objects in the sky with clockwork precision.

Einstein’s special relativity, published in 1905, tells us that time is not only elastic, it is also the fourth component of the spacetime fabric of the Universe. Ten years later, his general relativity redefined gravity as matter’s response to the curving of spacetime caused by surrounding massive objects.

In 1916, Schwarzschild found that the solution of Einstein’s general relativity equations characterized something that confounds common sense ‒ an unfathomable hole drilled in the superstructure of the Universe. Today, we call this voracious gravitational sinkhole a black hole, a single point of zero volume and infinite density.

Much to Einstein’s consternation, in 1929, Hubble discovered that the Universe is expanding in size. His “constant” enabled us to estimate the age of the Universe. In 1930, Chandrasekhar’s calculations indicated that when a massive star runs out of fuel, it would blow itself apart in a spectacular but violent explosion and then collapse into a black hole.

Black holes were discovered in 1971, when astronomers detected a hint of radio wave emissions coming from an object in the constellation Cygnus. The emissions were later interpreted as the fingerprint of the black hole Cygnus X-1. Since then, numerous black holes, including supermassive ones, have been detected in our own Galaxy ‒ The Milky Way, and elsewhere in the Universe. According to NASA, supermassive black holes are growing faster than the rate at which stars are being formed in their galaxies.

Cloaked behind the event horizon, which is not a physical barrier but just an information barrier, it must seem that there is no way of getting mass from the black hole back out into outer space. No way, that is, not until the British physicist Stephen Hawking, arguably one of the greatest minds in scientific history, joined the Big League of Cosmology in the mid-twentieth century. With his seminal contributions to the fields of astrophysics, general relativity, quantum gravity and black holes, he raised the field of cosmology from a niche topic to a well-developed subject in the forefront of science.

In 1974, by predicting the apparently paradoxical concept of radiation emanating from black holes, Hawking reminded us that mass and energy are two sides of the same coin. He was able to show that a black hole, like any other body whose temperature is not absolute zero, emits energy in the form of radiation, energy now known as Hawking Radiation.

The continual emission of radiation causes the black hole to shrink in mass. In other words, black holes “evaporate,” although the time it takes for a solar-mass black hole to evaporate completely is immensely long ‒ vastly larger than the age of the Universe, which is 13.7 billion years. The implications are nonetheless important ‒ even black holes evolve and die.

One of the Gordian knots of cosmology is the missing mass of the Universe. There is irrefutable evidence that visible matter accounts for only four percent of the Universe’s mass. The remaining 96 percent is invisible of which 73 percent is attributed to a pervasive “dark energy,” believed to be manifestation of an extremely powerful repulsive force that is causing the expansion of the Universe to accelerate. The additional 23 percent is thought to be dark matter whose origin obviously is the many black holes spread throughout the cosmos. However, their total mass does not add up to account for all the dark matter.

To address this issue, in 1971, Hawking advanced the idea that in the intergalactic space, there may be “mini” black holes with very small masses ‒ much smaller than the mass of the Earth ‒ yet numerous enough to account for most of the unaccounted dark matter. He hypothesized that they may have been formed during the first instants of chaos following the Big Bang when matter existed in a hot, soupy plasma. Since mini black holes have not been detected so far, Hawking lamented: “This is a pity, because if they had, I would have got a Nobel Prize.”

During the 1980s, Hawking devoted much of his time contributing to the theory of cosmic inflation ‒ the expansion of the Universe at an exponential pace before settling down to expand at a slower pace. In particular, he demonstrated how minuscule variations in the distribution of matter during this period of expansion, known as the Planck era, helped shape the spread of galaxies in the Universe.

As noted above, the core remnant of a high-mass star would eventually collapse all the way to a point ‒ a so-called singularity. Having said that, singularities are places where laws of physics break down. Consequently, some very strange things may occur near them. As suggested by Hawking, these strange things could be, for instance, gateway to other universes, or time travel, but none has been proved, and certainly none has been observed. These suggestions cause serious problems for many of our cherished laws of physics, including causality ‒ the idea that cause should precede the effect, which runs into immediate problem if time travel is possible ‒ and energy conservation, which is violated if matter can hop from one universe to another through a black hole.

While scientists know Hawking for his work on cosmology, millions of others know him because of his book “A Brief History of Time.” His lucid explanation of the mechanism leading to the creation of the Universe, our place in it, how we got there, where did space and time come from, and where we might be going made the notoriously difficult subject of cosmology more understandable to the layperson.
In a follow-up book titled “The Grand Design,” Hawking outlines his consuming quest for the long-dreamed-of “Theory of Everything,” the quantum theory of gravity. Such a theory would unify the two pillars of twentieth century physics, general relativity and quantum theory.

Known as the M-Theory (M stands for Mother-of-All), it would enable us to understand all phenomena in space-time, especially the first split second of cosmic creation, when everything was unimaginably small and densely packed.

Hawking was about as pure an atheist as one can be. He dismissed the existence of an omnipotent by noting that “regularities in the motion of astronomical bodies such as the sun, the moon, and the planets suggested that they were governed by fixed laws rather than being subjected to the arbitrary whims of gods and demons.” Nevertheless, in December 2016, he had a surprising but cordial encounter with Pope Francis at a convention on Big Bang in Rome.

Besides being a genius, Hawking’s celebrity status derives from his spunk in the face of physical adversity. Born on 8 January 1942 in Oxford, England, Hawking was diagnosed with a debilitating, incurable neuromuscular disorder, commonly known as motor neurone disease (MND), when he was just 21 years old. Although doctors predicted that he has only two more years to live, he lived another 55 years and died on 14 March, 2018. There are some interesting anecdotal coincidences. Hawking was born on the 300th anniversary of Galileo’s death and died on the 139th anniversary of Einstein’s birth. Following his cremation, his ashes will be interred on 15th June 2018 in Westminster Abbey’s nave, next to the grave of Isaac Newton and close to Charles Darwin.

Instead of ruing about his mortality, Hawking considered his illness as a blessing, allowing him, in his own words, “to focus more resolutely on what he could do with his life.” Indeed, with a crumpled, voiceless body ensconced in a wheelchair, he soared and established an exalted scientific reputation as the most recognizable scientist of the modern era. The name of this supernova of cosmology will be engraved in the sands of time as long as humanity lives.

The writer, Quamrul Haider, is a Professor of Physics at Fordham University, New York


Advanced science, International, Technical

Cutting edge in Physics

Nobel Laureates

It is beyond dispute that the subject matter of physics demands high level of intellectual ingenuity, mathematical prowess and, above all, perseverance to muster the subject. It is not the subject matter that one can just browse through relevant books, learn by highlighting some key points and fill in the details later with creative flavour, as could be done in history or politics or sociology etc. Either you learn physics by hard graft or you are just monkeying around with it.

Physics had advanced a lot since late 19th century. There is a very interesting anecdote involving Max Planck, the pioneer of quantum mechanics. When Max Planck, an aspiring physics student in late 19th century, approached a professor of physics seeking advice on the prospect of a research career in physics, he was told by the respected professor that there was nothing more in physics to discover and any research work would only involve in better accuracy of known physical quantities to higher decimal figures. However, Max Planck doggedly pursued his physics career and in less than fifteen years of that advice laid the foundation of a new branch of physics, called the quantum mechanics, which is still being pursued most vigorously nearly 120 years later today.

From minutest particles called quarks in particle physics to the mind-boggling expanse of cosmology, universe and even multiverse and the theory of relativity, gravitational waves, dark matter and dark energy; physics is the field that excites the brightest minds of the world today. Theoretical studies and experimental works requiring billions of dollars are pushing forward this field at utmost vigour.

To get a glimpse of the cutting edges in physics, one may look at the advanced topics that the Nobel Committee had recently recognised and rewarded. The Nobel Prize in physics has been awarded 111 times, from 1901 to 2017, to 207 Laureates, with gaps in 6 years due to world wars and great depression. The list of Nobel Laureates from 2000 to 2017 are given below in reverse chronological order.

   Year                 Nobel Laureate(s)                                  Research topic

2017      Rainer Weiss, Barry C Barish      For the decisive contribution to the LIGO and                      Kip S Thorne                                   detector and the observation of gravitational                                                                                 waves

2016      David J Thouless, F Duncan M    For theoretical discoveries of topological phase                   Haldane and J Michael Kosterlitz  transitions and topological phases of matter

2015      Takaaki Kajita and Arthur B       For the discovery of neutrino oscillations                              McDonald                                        showing neutrinos have mass

2014      Isamu Akasaki, Hiroshi Amano  For the invention of efficient blue light- emitting                and Shuji Nakamura                     diodes which enabled bright energy saving                                                                                     white light sources

2013     Francois Englert and Peter          For theoretical discovery and  understanding  of                 W Higgs                                           origin of mass in subatomic particles, which was                                                                           confirmed in CERN’s Large Hadron Collider

2012     Serge Haroche and David J        For experimental methods enabling measurement               Wineland                                       and manipulation of individual quantum systems

2011     Saul Perlmutter, Brian P             For discovery of accelerating expansion of the                     Schmidt and Adam G Riess        Universe through observations of distant                                                                                         supernovae

2010     Andre Geim and Konstantin      For experiment on two-dimensional material                       Novoselov                                      graphene

2009     Charles Kuen Kao                         For work concerning transmission of light in                                                                                   fibres for optical communication                                             Willard S Boyle and George        For invention of imaging semiconductor                               E Smith                                            circuit – CCD sensor

2008     Yoichiro Nambu                           For the discovery of mechanism of spontaneous                                                                            broken symmetry in subatomic physics                                   Makoto Kobayashi and               For the origin of broken symmetry predicting                       Toshihide Maskawa                    existence of at least three families of quarks in                                                                             nature

2007    Albert Fert and Peter                    For the discovery of Giant Magneto resistance                      Grunberg

2006      John C Mather and George      For anisotropy of the cosmic microwave                                    F Smoot                                        background radiation

2005      Roy J Glauber                             For quantum theory of optical coherence                                  John L Hall and Theodor         For the development of laser-based precision                          W Hansch                                    precision spectroscopy

2004     David J Gross, H David              For the discovery of asymptotic freedom in the                       Politzer and Frank Wilczek     in the theory of strong interaction

2003      Alexei A Abrikosov, Vitaly L   For contributions to the theory of superconductors                Ginzburg and Anthony J Leggett  and super-fluids

2002      Raymond Davis Jr. and           For contributions to the detection of cosmic                                Masatoshi                                  neutrinos                                                                                            Riccardo Giacconi                    For contributions to the discovery of cosmic                                                                                   cosmic X-ray sources

2001      Eric A Cornell, Wolfgang       For Bose-Einstein condensation of dilute gases of                      Ketterle                                     alkali atoms and studies of the properties of the                                                                            condensates

2000     Zhores I Alferov and              For the development of semiconductor hetero-                           Herbert Kroemer                   structures used in high-speed opto-electronics                             Jack S Kilby                              Invention of integrated circuit

From a cursory glance at the table above, one can pick out some important points:

First, the mind-boggling expanse of the universe entailing cosmology and the minutest world of particle physics requiring quantum mechanics are the two most dominant fields of advanced physics. They may be at the two extreme ends of dimensional scale, but they are interconnected, as planets, stars, galaxies, black holes, quasars etc. are all made up of tiniest quantum particles and these giant astronomical bodies came into being due to quantum fluctuations at the very beginning of creation.

Secondly, there seems to be disproportionately large number of Japanese physicists, from a small country, who were successful in receiving Nobel prizes. This may be due to their value system, since WWII, where they concentrated on furtherance of knowledge than on military hardware or political dominance.

Thirdly, on religious grounds, Jews seems to be extremely successful in achieving highest accolades in physics. This is not only since the year 2000 listed above, but also from the very beginning of Nobel prizes. All the top quantum physicists, from Max Planck to Wolfgang Pauli, to Neils Bohr, Albert Einstein, Erwin Josef Schrodinger, Paul Ehrenfest and so forth were all Jews. No wonder, Hitler once dubbed quantum physics as the Jewish science! A tiny population of 16 million people worldwide, comprising less than 0.25% of world population, Jews received over 80 of 207 of Nobel prizes (nearly 40%) in physics!

As an aside, 1600 million Muslims comprising over 22% of world population received no Nobel prize in physics! Although one and only one Muslim, Prof. Abdus Salam, from Pakistan was awarded a physics Nobel prize in 1979, but Pakistan declared him non-Muslim as he belonged to an Islamic sect, Ahmadi, which Pakistan declared non-Muslim in 1974. Religion in Islamic countries overrides almost everything. In Islam, it is stated that all knowledge comes from Allah and it had been handed down in the religious book of Islam, called Quran, and individuals must derive knowledge from it. No wonder, there is a severe dearth of pioneering physics practitioners in the Muslim world leading to Noble prizes in physics!

A. Rahman is an author and a columnist.






Bangladesh, Cultural, International, Life as it is, Literary

Origin of Bengali Calendar and the celebration of ‘Noboborsho’

cc614c7fe3b876a539e58a314e7a94c5[1]Only three more days to go before another Bengali New Year (also known as Noboborsho), year 1425 on the 14th of April 2018, ushers in sweeping away the misery and pain of the past year. Welcoming the Noboborsho (also known as Pohela Baishakh i.e. the first of the Bengali month called Baishakh) is a very joyous occasion in Bengali culture and it is very much steeped in tradition. That tradition overrides any religious divide, narrow sectarianism and tribalism.

The day normally starts with boys and girls, men and women, all waking up early in the morning before the sun-rise. They are all dressed in bright colourful outfits and women are donned in bright yellow saris and garlands in their hair. The women carry garlands in their hands as they walk the streets, as if to offer garlands to the exalted souls of the New Year and they chant Noboborsho-welcoming songs. As the sun rises, they would welcome the new day ushering in the new year and pray in songs and kirtons that the new year will bring peace, prosperity and happiness. The procession of men and women in convivial mood continues throughout the day and in the evening, there are theatre stages where songs (mainly Tagore songs), plays, dramas etc. are presented.

The Noboborsho (New Year) is not just the beginning of a year in Bengali tradition, it is the beginning of a new chapter, a new undertaking in life. In olden days (before the creation of Pakistan), the Noboborsho would also see the beginning of a new book – a business ledger – for the traders, small businesses or even professionals such as teachers, doctors, engineers etc. For them the new book was like a diary where past experiences, present accomplishments and future aspirations are all depicted. And, as usual, no big occasion in Bengal would go without distribution of sweets!

There used to be a Ponjika – a short printed book giving major events of the next one year and guiding people through thick and thin of their lives. Altogether, Noboborsho is the culmination of the past year and the beginning of a new year, both of them are of equal significance.

This tradition stretching back centuries was temporarily interrupted by the new state, Pakistan, which was created in 1947 on the basis of religious doctrines. Since the Bengali language and culture evolved over the centuries in the land where Hindus and Muslims (as well as Buddhists, Jains and so forth) lived side by side, Islamic fundamentalists of Pakistan felt threatened by this long-held tradition. They insisted that Bengali language, Bengali tradition are all Hindu tradition and Muslims of Bangladesh should avoid, indeed boycott, these things and become ‘true Muslims’ by adopting Pakistan’s Urdu language. For the Bengali Muslims, it was like tearing up the age-old tradition and identity for the sake of imported religion. This conflict eventually led to the breakup of Pakistan and thence Bengali Muslims reclaimed their tradition and identity now.

Even now, nearly fifty years after the creation of Bangladesh on the basis of language and culture, there are strident calls by the over-jealous Islamists within the country to stop celebrating Bangla Noboborsho on the plea that it is anti-Islamic and blatantly Hinduism. Even the Bengali Calendar is viewed as anti-Islamic practice. These religious bigots preach things without any shred of knowledge and understanding.

The view that Bangla Noboborsho and Bangla calendar are imports from Hindu culture to Muslim Bangladesh is not only blatantly communal and racist, but also grossly misconceived. This assertion on the basis of religious bigotry could not be farthest from the truth.

Let me give a brief background of the history of Bengali Calendar and how the 14th of April came to be used to usher in the Noboborsho, 1425 BS (Bangla Sôn).

The third Mughal Emperor, Muhammad Akbar (also reverentially addressed as Akbar the Great), was a great reformer and instrumental in promulgating a new Bengali Calendar after modifying the then existing calendar. He did so in order to facilitate the administrative procedures and to fix a firm tax collection date in Bengal.

At that time, the calendar that used to be utilised was known as Tarikh-e-Elahi, which followed the Islamic lunar calendar. The lunar year consists of twelve months, but has 354 or 355 days (following 12 lunar rotations round the earth). Thus, there is a drift of about 10 or 11 days every year between the lunar and solar (Gregorian) calendars. That created a major practical problem. A fixed date for the collection of taxes from the farmers and peasants, normally set at the end of a harvest period, gradually came forward by about 11 days every year and fell out of season.

That meant that whereas a tax collection date might have been originally fixed after the harvest period gradually drifted forward and became a date prior to the harvest after just a few years. That created immense misery to the farmers to pay taxes before the harvest! Realising this serious practical problem, Mughal Emperor, Akbar along with the royal astronomer, Fathullah Shirazi developed the Bengali calendar. It was a synthesis of Islamic lunar calendar and the modern solar calendar.

The year Akbar took over the reign of the Mughal Empire was 1556 AD (Gregorian Calendar). That year in Islamic calendar was 963 AH (Anno Hegirae). He promulgated that a new calendar would be started on the 1st of Muharram (which is the first month of the Islamic Calendar) in that year of 963 AH. Following that system, the year would follow the solar year (365 days) and so no mismatch between the new calendar and the seasons would arise from that time. That calendar came eventually to be known as the Bangla Calendar with Bangla months such as Boishakh, Jyoishto etc. assigned to it.

However, that calendar was slightly revised during the Pakistan days by a committee headed by Dr Mohammad Shahidullah under the auspices of the Bangla Academy in 1966. That revised version (when 14th April was fixed as the beginning of the year) was adopted officially in Bangladesh in 1987. That is the calendar that ushers in the Bengali Noboborsho.

Now the question is how do we get to the year 1425 BS on the 14th of April 2018 AD? The following consideration would show how it is done.

As the start of this calendar was 1556 AD (Akbar’s accession to the throne), which was also the beginning of the Islamic year 963 AH, 462 years (2018 AD – 1556 AD) had passed since then until now. Now adding 462 years to the Islamic year of 963 AH (when the system started), we get 1425. This is how we have the incoming New Year of 1425 BS this year.

Also, one can analyse the difference between the Bengali Calendar and the Islamic Calendar. The Islamic year now is 1439 AH, whereas the Bengali year is 1425 BS. The time when divergence took place was in 1556 AD and during these intervening 462 years (2018-1556) the Islamic calendar fell short by 462 x 11 = 5082 days with regard to solar calendar. This then produced over 14 years (5082/355) in Islamic calendar. In other words, an extra 14 years were produced in the Islamic calendar since the commencement of the Bengali calendar, and that explains why it is 1439 AH, but in Bangla calendar it is 1425 BS.

The adoption and modification of calendars are done by many countries – Islamic or non-Islamic – to suit their needs.

Islamic Republic of Iran uses the Solar Hijri Calendar, called the Sham Hijri (SH), which begins with the vernal equinox (the start of spring in the northern hemisphere). The length of time between vernal equinox and autumnal equinox is about 186 days and 10 hours and the other cycle is 178 days. Afghanistan uses a slight variation of the Iranian calendar. West Bengal uses a Bengali calendar where the Noboborsho is on 15th of April.

Thus, any claim that the Bengali Calendar belongs to a Hindu religion or culture and that adoption of this calendar is un-Islamic can be categorically rejected. Such assertions are utter rubbish and pure bigotry.
A. Rahman is an author and columnist.

Cultural, Life as it is, Religious

What is your life philosophy?

Are you a rationalist, a religious individual (deeply or not-so-deeply), an atheist or an agnostic or simply an individual with no particular view? Please check it out from the following simple test of only nine questions. Copy the URL given below, paste it in your address bar at the top and follow instructions. After you finish answering the questions, there would be a 30 second advertisement (during which time your answers are evaluated) and then you will get your life philosophy.




The Editor

Environmental, International, Political, Technical

Geo-engineering: A futuristic approach to tackling global warming

Many scientists believe that global warming caused by carbon dioxide buildup in the atmosphere is for all practical purposes irreversible. That is because the current concentration of carbon dioxide in the atmosphere will keep the engine of global warming running for thousands of years. Consequently, the common goal of keeping our planet from heating up more than two degrees Celsius before the end of this century, as agreed upon by the stakeholders in the 2016 Paris Agreement, will be extremely difficult to achieve, unless we go “carbon negative” by mid- to late twenty first century. (Carbon negative, or negative emissions, means removing more carbon dioxide from the atmosphere than adding it.) Scientists have, therefore, come to the conclusion that the only way we can tackle global warming is via geo-engineering, also called climate engineering.

Geo-engineering is defined as “human’s planned measures” to reverse or forestall some of the adverse effects of climate change. It encompasses two different classes of approach using a variety of cutting-edge technologies to undo the effects of two centuries of anthropogenic greenhouse gas emissions. These are:
1. Removal and sequestration of carbon dioxide to lower its concentration in the atmosphere;
2. Offsetting global warming by blocking some of the Sun’s rays from ever reaching the Earth’s surface via a program called solar radiation management.

Carbon Removal: The idea of removing carbon dioxide from the air was first proposed in 2008 at a workshop sponsored by the US National Science Foundation. The idea is simple. Emulate what trees and plants do already. They take in water and carbon dioxide from the atmosphere and through photosynthesis convert them into oxygen and organic compounds. Accordingly, there are two carbon dioxide removal (CDR) approaches ‒ Direct Air Capture (DAC) and Bioenergy with Carbon Capture and Sequestration (BECCS).

A pilot project for DAC was started in 2009 by a Vancouver-based company called Carbon Engineering. A giant network of fans is used to suck ambient air into a “gas-liquid contactor,” where a strong hydroxide solution reacts with carbon dioxide in the air to form carbonate pellets. The pellets are processed and converted back into carbon dioxide and water vapour, which could be used as synthetic fuel, or stored in porous rocks or depleted oil wells for later use.

A Swiss company called Climeworks compresses the captured carbon dioxide and uses it as fertilizer, or manufacture fuel and carbonated soft drinks. The long-term goal of the company is to capture at least one percent of the global annual carbon dioxide emissions by 2025. Industry experts estimate that in order to meet this goal, approximately 250,000 DAC plants would have to be built.

The other CDR approach, Bioenergy with Carbon Capture and Sequestration, was proposed in 2001 by a doctoral student from Sweden. At its most basic, BECCS involves growing crops, burning them to generate electricity, capturing the carbon dioxide emitted during combustion and storing it deep down into the Earth’s crust.

In little more than a decade, BECCS had gone from being a highly theoretical proposal to being one of the most viable and cost-effective negative emissions technologies. According to the International Energy Agency, there are currently about two dozen BECCS pilot projects operated by big companies like Shell, Chevron and Archer Daniels Midland that capture and store around 0.1 percent of the total global emissions of carbon dioxide. The amount, albeit miniscule, is nonetheless an indication that the technology is a promising one.

Solar Radiation Management: A range of options for solar radiation management (SRM) has been proposed. They include reflecting sunlight away from the Earth by an occulting disk or space-based mirrors to seeding clouds so that they become more reflective to simulating the effects of volcanic eruptions or asteroid impact to building homes with white roofs.

Occultation: Perhaps the most practical but challenging SRM concept to reduce solar insolation was advanced in the early 2000s by space scientists at the Lawrence Livermore National Laboratory in California. They proposed deploying a large occulting disk that would act as a sunshade at a gravitationally stable point, called the Lagrange point, between the Earth and the Sun. Calculations indicate that a disk roughly the size of Greenland would be able to block one to two percent of the sunlight ‒ enough to reduce substantially the amount of solar radiation reaching the Earth.

Another suggestion involves deploying an array of reflecting mirrors covering the equivalent shading area of the occulting disk. By incorporating the effect of mirrors to different climate models, researchers at the Max Planck Institute for Meteorology in Hamburg obtained an overly optimistic result ‒ the average global temperature could be lowered to preindustrial levels, although “unevenly.” Sea levels would still rise because they respond slowly to changes in Earth’s temperature.

As an aside, NASA is currently working on solar sail propulsion system that would use large mirrors to harness solar radiation and redirect it towards Mars in order to initiate greenhouse effect on the planet. These mirrors could also be used to reflect sunlight away from the Earth.

Cloud Seeding: The fraction of incident solar radiation that is reflected back into space by a non-luminous body is determined by a quantity called albedo. The albedo of Earth is thirty percent, of which clouds account for twenty percent, air for six percent and surface (land and water) for four percent. Since the albedo of clouds is high, they have greater cooling effects locally as well as globally.

Albedo can readily be changed by human action. Hence, it should be possible to increase the albedo of low-level clouds by spraying seawater into the air where they would evaporate to form sea salt which would seed the clouds above the oceans. The best part of this plan is that it involves spraying seawater instead of harmful chemicals into the air.

At the University of Washington, an international research collaboration of atmospheric scientists called The Marine Cloud Brightening Project (formerly Silver Lining) developed a machine that can suck up ten tons of seawater per second, turn them into tiny particles and shoot them up over a kilometre into the air. They are currently conducting limited area field experiments with the spray technology to “provide new understanding of the interactions between aerosols and clouds.”

The technology has a long way to go before it can significantly lower the Earth’s temperature. A recent study showed that about 2,000 ships equipped with the spray machines would have to ply the seas and oceans just to stop the temperature from rising.
Another proposed cloud-based approach involves thinning the high-altitude Cirrus clouds by seeding them with heterogeneous ice nuclei. While this method is not technically an example of SRM, thinner clouds would allow more temperature-raising trapped infrared radiation to escape to space, and thus, potentially cool the Earth’s climate.

Simulating the Effects of Volcanic Eruption: Gaseous and minute solid particles, such as sulphate aerosols, injected into the atmosphere after a massive volcanic eruption or a series of lesser intensity eruptions could linger as long as three to four years in the stratosphere ‒ a layer of the atmosphere extending to about 50 km above the Earth’s surface. As a result, the Earth-shrouding gases and aerosols could impact global climate by increasing the Earth’s albedo. As an example, the abnormally cold summer of 1783, both in Europe and in the US, is attributed to the enormous eruptions of a chain of volcanoes in Iceland that lasted for eight months.

Indeed, inspired by the 1783 eruptions and the eruption of Mount Pinatubo in the Philippines in 1991 and the subsequent cooling effect of their sunlight-blocking plume of sulphate particles, scientists are considering injecting sulphate aerosols into the stratosphere. In the year following the Pinatubo eruption, global temperatures did cool by approximately 0.5 degree Celsius.

Asteroid Impact: Approximately 65 million years ago, an asteroid impact cooled the Earth by probably four or five degrees. Since the possibility of an asteroid slamming into Earth during our lifetime, or in the next 100 years or so, is very remote, space scientists at the University of Strathclyde in Scotland suggest an out-of-this-world solution ‒ blasting off a few near-Earth asteroids, so that the resulting dust cloud in space would protect the Earth from excessive solar radiation.

Under the auspices of Asteroid Redirect Mission, NASA is developing a robotic mission to collect a large boulder from an asteroid’s surface and redirect it into a stable orbit around the moon. If the mission succeeds, the technique could be used to generate a dust cloud by steering asteroids into a collision course with each other.

Surface-Based Option: A technology with a proven record of success in mitigating global warming is white roofed houses. Since light-coloured surfaces such as white have a high albedo, these roofs keep the Earth cool by reflecting more sunlight back to space. In fact, according to the article “Economic comparison of white, green, and black flat roofs in the United States” published in the March 2014 volume of Energy and Buildings, researchers at the Lawrence Berkeley National Laboratory in California noted that a simple white roof reflects three times the sunlight as a green rooftop garden. They also presented evidence that by absorbing less sunlight, a 100 square meter area of rooftop painted white has about the same one-time impact on global warming as cutting ten tons of carbon dioxide emissions.

Time Frame of the Programs’ Effectiveness: Once geoengineering program starts, the completion time of the CDR and SRM approaches in tackling global warming would be different. Most of the SRM approaches would act fast, producing a detectable climate response within months, scientists conclude. By contrast, the CDR approaches would be slow to reduce climate risks, requiring decades to make an appreciable impact on atmospheric concentrations of carbon dioxide.

Nevertheless, scientists almost unanimously agree that if SRM and CDR programs are implemented in tandem, then even a reduction of two percent of solar radiation could offset the effects of two degrees Celsius increase in temperature. Otherwise, we may not be able to achieve the desired result.

Challenges and Environmental Implications: Out of the many approaches, DAC and BECCS are perhaps the most benign form of geoengineering. However, as BECCS uses a relatively clean source of fuel (energy-generating biomass) to produce negative emissions, it is a clear-cut winner over DAC and other technologies designed to combat global warming.
A challenge for DAC is that the atmosphere blanketing the Earth is very big, and carbon dioxide is a relatively small part of it ‒ about 0.04 percent. That’s why the technology will work effectively only in the vicinity of power plants where the gas is emitted in large concentrations.
Another area of concern with DAC is energy efficiency. Carbon dioxide itself is not a very reactive molecule, so extracting it is both energy and resource intensive. Based on a 2011 report prepared by the American Physical Society, it is estimated that to extract a billion ton of carbon dioxide, a figure viewed by many experts as climatically significant, maximally efficient DAC systems would require about 10 GW of power. This is equal to about three times the capacity of the Palo Verde Generating Station ‒ largest nuclear power plant in the US.
If BECCS is to succeed on a wide scale, its demand for land could be massive, especially if only exclusive crops, such as corn or soybean, are used as raw materials. In that case, BECCS plants will start eating into our food supplies. This problem can be alleviated to some extent if the plants use waste products in agriculture, animal farms and forestry, too.
In order for both CDR technologies to be feasible, it is crucial that the amount of carbon dioxide removed is appreciably greater than the amount of carbon dioxide emitted in the removal process. In addition, the CDR schemes could find themselves in a continuous game of catch-up with the voluminous output of greenhouse gases, unless we rein in on their emissions.
Despite the many benefits, some of the SRM approaches have limitations and they are also a route that could adversely affect the environment. While the magnitude of the consequences is generally proportional to the scale of deployment of the technologies, several issues ‒ scientific, environmental, ethical, economic and political ‒ are yet to be resolved.

In the case of occultation, the potential for unintended consequences, such as drought, are high. In particular, studies show that a reduction of 1.7 percent insolation could bring about important changes to regional climates, with warming at high latitudes while cooling below necessary level in sub-tropical regions. These residual changes to regional climates may cause important damage to the local ecosystems and economies, too. The prohibitively large cost of space transportation and the high number of launches required to deploy the occulting disk(s) and mirrors are also seen as shortcomings of this program.

Seeding low-level clouds with seawater could produce changes in regional rainfall amounts and patterns, as well as changes in ocean currents. A decrease in rainfall, which is a conclusion of several studies, would significantly reduce agricultural yield. On the other hand, targeting Cirrus clouds could result in changes to the precipitation even in regions far away from geo-engineered regions, underscoring the risks of remote side effects.

Spraying the stratosphere with sulphate aerosols could also have “catastrophic effects in parts of the world already battered by natural disasters,” as noted in a research article published in Nature Communications in 2016. The authors caution that it may increase the frequency of cyclones and droughts in some parts of the world. The aerosols could also deplete the ozone layer that protects us from the harmful ultraviolet radiation. After the Mt. Pinatubo eruption, there was a three percent reduction in the amount of ozone in the atmosphere and a measurable decrease in rainfall in some parts of the world.
As for the dust cloud produced by breaking up asteroids, the particles in the cloud run the risk of getting dispersed over time by solar radiation and the gravitational pull of the Sun, moon, satellites and nearby planets. They could also interfere with the operation of communication satellites orbiting the Earth.

A fundamental problem with SRM approaches is that they would require continual refreshing. Additionally, once they are put into operation, they have to be continued indefinitely in order to counterbalance the forcing associated with greenhouse gas emissions. Since SRM only offsets warming, once the programs are stopped following their deployment, temperature changes caused by greenhouse gases would manifest themselves suddenly and could rise beyond the level they otherwise would have by 2100.

Risks and Concerns: Although the prospect of cooling the Earth seems real, unease surrounds the questions pertaining to ethics, costs, limitations, feasibility, benefits and risks of geoengineering. To the critics of geoengineering, the wisdom of the program remains highly controversial because of underlying scientific and technological uncertainties. They are particularly concerned about the SRM approaches which are still at the level of relatively simple analyses, small-scale laboratory experiments and preliminary computer simulations. They are also apprehensive that the governance and financial challenges have not yet been fully studied. One of their strongest fears though is that geoengineering technologies may divert resources and momentum away from already waning efforts to reduce emissions of carbon dioxide.
Moreover, critics are troubled at the thought that our attempt to control the Earth’s climate system by deliberate, large-scale manipulation is possibly a matter of hubris rather than a desirable evolution. Besides, before shifting the gear to overdrive, they would like to know whether the advantages of geoengineering outweigh the risks of climate change and how it would alter humanity’s delicate relationship to Nature.
More importantly, critics believe that within social and political context, deployment of space-based technologies has the risk of “reckless pursuit of self-interest by powerful actors” on the world stage. In other words, the spectre of incompetent, negligent, or even malicious uses of the yet-to-be fully developed SRM technologies by rogue leaders alarms the critics.

Proponents of geoengineering hold that because the Earth’s atmospheric system is large and complex, it is impossible to anticipate fully all the consequences, detrimental and beneficial, of intentional intervention in advance. They, however, believe that through dedicated research and critical discussions with the global community, it would be possible to develop an understanding of the technical, political, social, cultural, environmental and ethical issues pertaining to geoengineering. At the same time, they are worried that research on geoengineering could be hijacked by climate change deniers, such as the US administration led by a self-proclaimed “very stable genius.”
Furthermore, if the past is any indication of human apathy towards Nature, it is exceedingly likely that once we design a system that would reverse global warming, we may no longer feel any incentive to change our carbon-emitting lifestyles. Eventually the problem will just build up and we will once again be back at square one.

In conclusion, we are at a crossroad. We have to decide whether to allow the Paris Accord run its course while our planet heats up threatening our very existence. Or should we resort to geoengineering to manage the climate the way we have managed so many other things successfully.

The writer, Quamrul Haider, is a Professor of Physics at Fordham University, New York