Reflective Roofs and Pavements Could Fight Climate Change

8/2/2019 Reflective Roofs and Pavements Could Fight Climate Change

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Reflective roofs and pavements could fight climate changeApr 13, 2012

A traditional approach to geoengineering

Replacing roofs and pavements with more reflective versions could lower global temperatures by up

to 0.07 C, equivalent to a reduction in carbon-dioxide emissions of about 150 billion tonnes. That is

according to researchers in Canada who used a global climate model to look at the effects of such

albedo changes in urban areas.

"Scientists have been proposing novel ideas mostly untested for the geoengineering of global

climate," says Hashem Akbari of Concordia University. "But humans have had experience with white

buildings and reflective pavements for thousands of years without any unknown negative side effects.

Hence, cool urban surfaces should be our geoengineering 101."

From Lyon to DunedinAkbari and colleagues from Concordia used the University of Victoria Earth System Climate Model to

investigate the effect of albedo increases of 0.1 until 2300 over all land between latitudes of 20 (i.e.

roughly from Mexico City and Hanoi in the north to Bulawayo, Zimbabwe, in the south), and between

45 (approximately from Lyon in France and Portland in the US to Dunedin in New Zealand). The

team used both a business-as-usual emissions scenario and an aggressive mitigation scenario.

The albedo increase on all land between 20 latitude would decrease temperature by roughly one

degree over 20 years, while the 45 latitude case would double this decrease. After 200 years, the

decreases would be 1.33 C. The scientists estimated that urban areas make up roughly 1% of the

total land area in these regions; increasing albedo by 0.1 only in urban areas would be equivalent to a

global change in land-surface albedo of 0.001.

"Increasing albedo of urban areas by about 0.1 increasing flat-roof albedo by 0.4, increasing sloped-

roof albedo by 0.25 and pavement albedo by 0.15 cools the globe equivalent to offsetting more than

100 billion tonnes of carbon-dioxide emissions," says Akbari. "This is equivalent to offsetting the

emissions for all the cars in the world for the next 20 to 30 years."

In order to firm up their calculations, the researchers employed two estimates of urban area: one from

the Global Rural and Urban Mapping Project (GRUMP), and another from an analysis based on

MODIS satellite data. The GRUMP results suggest that global urban areas are more than five times

larger than the MODIS data set indicates.

Urban-only cooling significantThe climate model revealed that increasing albedo by 0.1 only in GRUMP-designated urban areas

would produce long-term cooling of 0.07 C, equivalent to 130150 billion tonnes of carbon. Using the

MODIS data for urban areas, in contrast, would cool the Earth by 0.01 C, equivalent to 2530 billiontonnes of carbon.
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According to Akbari, albedo increases could lead to air-conditioning savings of about 20% for space

under roofs. "This is a saving of about $50bn per year and carbon-dioxide savings of about 0.4 billion

tonnes per year; over the next 100 years; that is an emission reduction of 40 billion tonnes, "he says.

"The direct cooling of the Earth by reflecting radiation back into space is an added bonus that actually

counters global warming while putting dollars in our pocket."

The researchers found that the effect of albedo change did not depend to a large extent on thecarbon-dioxide emissions scenario. That said, aggressive mitigation appeared to produce a roughly

10% larger temperature decrease, which the team ascribed to stronger snow-albedo feedback.

"We should develop policies for no-regret, no-cost global-cooling measures," says Akbari. "Cool cities

will save all the people in the world equally and the value of the dollar saved is significantly higher in

developing countries than the developed country (e.g. $1 saved in the US pays for 10 min of a

labourer in the US; in the developing countries that pays for a day of labourer)."

The scientists report their work inEnvironmental Research Letters.

About the authorLiz Kalaugher is editor ofenvironmentalresearchweb
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Ultrasound waves with a twistApr 11, 2012 26 comments

Twist and turn

An international team of physicists has simultaneously measured the angular momentum and torque

exerted by acoustic waves for the first time. It found that this ratio agrees exactly with the predicted

theory for acoustic and optical waves. According to the researchers, their techniques may also have

potential in medical imaging and treatment.

A fundamental principle of optics and acoustics is that waves carry momentum, and can therefore

exert a force. Equally important is the notion that they can also carry angular momentum and exert a

torque. The ratio between these two quantities the push and the twist is central to the physics of

waves and has long been taken for granted without direct experimental proof of its validity.

Difficulties with opticsThe concept of radiation pressure has traditionally been explored and exploited in optics for

example, it is the basis of the "optical tweezers" used to grab and manipulate microscopic objects in

microbiology and nanotechnology. The force of a light beam is equal to its power divided by the speed

of light. Its torque is proportional to the radiation pressure, which depends on the varying properties of

acoustic and optical beams. Because the speed of light is extremely large, the force and torque

exerted by a light beam are very small and therefore difficult to measure. To complicate matters

further, it is hard for scientists to work out precisely how well an object absorbs linear and angular

momentum from a light beam, and hence to calculate the forces and torques exerted.

Sound versus lightFor these reasons, nobody has ever managed to measure simultaneously the force and torque of a

light beam on an object. Fortunately, the same equations apply in acoustics, where the speed of lightis replaced by the much smaller speed of sound. A sound beam of the same power therefore exerts

both a stronger push and twist, making it easier to measure the ratio between the two.
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Experimental set-up

Now, ultrasound physicist Christine Demore, biophotonics researcher Mike MacDonald and

colleagues from the Institute for Medical Science and Technology at the University of Dundee in the

UK, together with Gabriel Spalding from Illinois Wesleyan University in the US, have levitated and

twisted a rubber puck in water by bombarding it with a "vortex beam" of ultrasound a twisted coil of

sound shaped a bit like a DNA double helix. This was done to verify experimentally the angular

momentum to torque ratio and directly prove this fundamental theory. The researchers found as

expected that the ratio of the torque to the linear force on the puck was equal to the ratio of the

number of intertwined helices per wavelength.

Applications beyond physics"The key part of thepaperis the fact that we've demonstrated that ratio," explains MacDonald, "but

the advance that we had to make to get that result was the level of control over the ultrasound beams,which hasn't been possible before." Demore adds that developing focused ultrasound has

applications well beyond pure research. "There's a whole field developing of using ultrasound to kill

tumours completely non-invasively," she says. There is also a project to develop "sonotweezers" that

are based on optical tweezers but which are able to move larger and heavier objects.

Optical physicist Miles Padgett from the Glasgow University in the UK describes the work as "a

beautiful experiment". He feels that "people active in the field won't be surprised by the ratio because

essentially the results show are as one would expect". "But if you never checked the things that we

know, you'd never find the things that we don't," he says.

The paper has been accepted for publication in Physical Review Letters.

About the authorTim Wogan is a science writer based in the UK
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The perfect stormApr 2, 2012 5 comments

A century on from the Titanictragedy, Richard Corfield says that the cascade of fateful

events that led to her demise was partly caused by the science of the ship's construction

That sinking feeling

One hundred years ago this month, the world reverberated to the news that the largest ship in the

world had met with destruction on her first ever outing.

At 11.40 p.m. on Sunday 14 April 1912, the Royal Mail SteamerTitanic, bound from Southampton to

New York, collided with an iceberg and sank within three hours, with the loss of more than two-thirds

of the 2224 passengers and crew.

The world was stunned, for the superlatives that had followed the launch of the Titanicfrom the

Harland and Wolff shipyard in Belfast had been stupendous some would say almost say hubris-inducing. Nature stepped up to the challenge and with almost contemptuous ease sent the Titanicto

an icy grave 4 km deep at 41 43' N, 49 56' W off the Grand Banks of Newfoundland. The Titanic's

last reported position was 41 46' N, 50 14' W, although this was later shown to be out by more than

20 km, an inaccuracy that greatly contributed to the difficulties encountered while trying to locate the

wreck.

When people ask the question "What sank the Titanic?", at first glance the answer is obvious: she hit

an iceberg. But that simplistic answer masks deeper and more substantive questions: why did

theTitanichit the berg in the first place and why did she sink so quickly?

It is a mistake to regard the Titanicas somehow primitive. She was the most modern ship of her day

in a world that relied on its steam trade to maintain communications between Europe and America in

the same way that today we rely on aviation. The Titanicincorporated the latest technologicalinnovations of the age to help ensure her safety. For example, she was one of the first ships to have

sealable watertight bulkheads transverse partitions that cross the ship at right angles to its long axis

with electrically operated doors that could be closed from the bridge at a moment's notice. The hull,

as was standard for the day, was made of mild steel (steel with a maximum content of 0.35% carbon,

0.7% manganese and 0.5% silicon) and was held together by three million steel and wrought-iron

rivets. Although steel rivets are stronger than wrought iron, for technical reasons (as we shall see)

they could only be used in the middle three-fifths of the ship's length. She also carried the latest

Marconi wireless equipment the most powerful in use at the time with a 5000 W transmitter that

gave a radio range of more than 500 km.
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Under the sea

On the face of it, the human factors were stacked in the Titanic's favour too. For her maiden voyage

she had the most experienced crew of the entire White Star Line (one of the premier British shipping

lines of the day) on board and it in turn was commanded by Capt. Edward J Smith, the commodore ofthe line.

It is also worth noting that the North Atlantic shipping run was very far from being an unknown quantity

in the Edwardian era. It was as busy as the air route between Europe and America is today, and the

chances of seeing a fellow ship en route were as high as an air traveller seeing a fellow aircraft today.

But the simple truth is that against all odds and expectations, including those of the ship's designers,

Lord Pirrie of the Harland and Wolff shipyard and Thomas Andrews of the White Star Line itself,

theTitanicsank as completely as a stone, less than three hours after she had hit the iceberg. If she

had stayed afloat longer, then rescue ships could have got to her and the tragic loss of life mitigated

or averted. This is the real question of the Titanicmystery: how could a 46,000 tonne ship sink so

quickly? The answer is to be found within the science of the Titanic's construction and the events that

occurred on that fateful voyage.Details emergeAfter the sinking of the iconic ship there was no shortage of theories as to why the pride of the White

Star Line had foundered. Two inquiries in 1912 led by Senator William Alden Smith in the US and

Lord Mersey in the UK both reached remarkably similar conclusions. The Titanichad been travelling

too fast, Smith had paid too little heed to iceberg warnings and, of course, there had not been enough

lifeboats on board to carry every passenger to safety. Although this last fact is inescapable, it is less

well known that the Titaniccarried more lifeboats than she was required by lawto do. It seems that in

1912, in a way not dissimilar to our own box-ticking, responsibility-avoiding culture today, lack of

effective oversight on the part of the authorities caused the consequences of the disaster to be much

worse than they might have been.

As the inquiries unfolded, other details began to emerge. There had been a reshuffle of officers justbefore the ship had sailed and the second officer, David Blair, had left the ship bumped from the

roster by the more senior Charles Lightoller. Blair had taken with him the key to the locker that held

the binoculars used by the lookouts in the crow's nest. Also, the more senior of the two radio

operators Jack Philips had not passed on the fifth and most specific ice warning of the day

received from the SS Mesaba. Mesaba gave the precise location (42 to 41, 25' N; 49 to 50, 30'

W) of an area of icebergs that, at the time, approximately 9.40 p.m., was only 50 miles dead ahead of

the Titanic. Because the message "Saw great number large icebergs also field ice. Weather clear."

was not prefixed with "MSG" "Masters' Service Gram"), which would have required a personal

acknowledgement from the captain, Philips interpreted it as non-urgent and returned to sending

passenger messages to the receiver on shore at Cape Race, Newfoundland, before it went out of

range.The physical facts
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There is one aspect of the Titanicdisaster that was known from the time the ship hit the iceberg: if

more than four of the 16 watertight compartments into which the interior space of the Titanicwas

divided were flooded, the ship could not stay afloat. The Titanic's designer Thomas Andrews was on

board and was asked by Capt. Smith to accompany him to assess the damage immediately after the

collision. The impact had been on the for'ard starboard side below the water line and once Andrews

had discovered the extent of the damage he warned Smith that since more than four compartmentshad been ruptured (six in fact had been breached) "it was a math- ematical certainty that the ship

would sink".

This, of course, the Titanicduly did.

Yet the detailed science behind the sinking of the Titanichad to wait 90 years to be explored. Her

wreck was discovered by the submersible Alvin during a joint FrenchAmerican expedition in 1985 of

which the archaeological oceanographer Robert Ballard was a prominent member. Ballard returned

the next year to start analytical work on the wreck and since then there have been many expeditions

to the site mostly, it has to be said, for the purposes of sightseeing, with a handful of scientific

expeditions thrown in.

Curiously enough, Ballard had not been driven to develop his new technology (the Argo-Jason

system) specifically to find the Titanic's ancient wreck. As he told the US Academy of Achievement inan interview in 1991, he simply wanted to test his system in the deepest water he could easily get to.

"If the Titanichad been in the Indian Ocean, I probably would have never found her," Ballard said.

"But the fact that she was in my backyard, I went, 'Let's go find the Titanic.' "

Fit for purpose?

An early attempt to explain the cause of the Titanic's rapid sinking was related to physical tests on the

steel comprising the ship's plates. Early tests made by metallurgists in Canada suggested that the

steel of her hull plates became brittle at about 32 C, suggesting that it would have been prone to

fracture at the temperatures the ship would have been operating at. This contrasts with modern steels

where the ductilebrittle transition temperature is 27 C. However, more sensitive tests that have

since been carried out, which conform more closely to the characteristics of the Titanic's impact with

the iceberg, suggest that the steel of the ship's plating was adequate to bend with the impact rather

than fracture.

In the mid-2000s two metallurgists, Tim Foecke at the US National Institute of Standards and

Technology and Jennifer Hooper McCarty, then at Johns Hopkins University in the US, focused their

attention on the composition of the Titanic's rivets. They combined their metallurgical analysis with a

methodical sweep through the records of the Harland and Wolff shipyard in Belfast where

the Titanicwas built. Combining physical and historical analysis in this way proved to be a powerful

trick.


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Foecke and McCarty found that the rivets that held the mild-steel plates of the Titanic's hull together

were not of uniform composition or quality and had not been inserted in a uniform fashion.

Specifically, Foecke and McCarty found that the rivets at the front and rear fifths of the Titanicwere

made only of "best" quality iron, not "best-best", and had been inserted by hand. The reason for this

was that, at the time of the Titanic's construction, the hydraulic presses used to insert the rivets used

in the middle three-fifths of the ship could not be operated where the curvature of the hull was tooacute (i.e. at bow and stern).

But why did Harland and Wolff use "best" quality rivets rather than "best-best?" Foecke and McCarty

speculate that it may simply have been a cost-saving exercise. "Best" rivets were cheaper than "best-

best" but also had a higher concentration of impurities known as "slag". This higher concentration of

slag meant that the rivets were particularly vulnerable to shearing stresses precisely the kind of

impact they were subjected to that long-ago night in April 1912. Lab tests have shown that the heads

of such rivets can pop off under extreme pressure, which on the Titanicwould have allowed the steel

plates on the hull to come apart, exposing her inner chambers to an onslaught of water.

Riveting stuffJames Cameron, director of the film Titanic(which is this month re-released in 3D), seems clear that it

was the rivets that were at fault. If you look at the relevant section of his film, at about 100 minutes in,you will see the bulkheads being split asunder along the line of rivets, which pop like champagne

corks into the interior of the vessel. This sequence is worth watching and rewatching because it is

spot-on in terms of accuracy. Cameron, incidentally, began a degree in physics at Fullerton College in

the US and is well known for his unstinting obsession with accuracy an accuracy that is apparent in

the detail of his Titanic.

For example, in the film, just prior to the iceberg impact you will notice that First Officer Murdoch

telegraphs to the engine room for the engines to be put into reverse. Of the Titanic's three engines,

the central engine (a Parson's turbine with a screw mounted directly behind the rudder) could not be

reversed and so only slowed to a standstill. The two reciprocating engines driving the port and

starboard screws on either side of it could, however, be reversed, and Cameron faithfully records the

central propeller as being stationary as the ship starts the dramatic evasive manoeuvre, even as heshows the outboard propellers beginning to reverse.

The configuration of the propellers and rudder that Cameron so faithfully renders also bears on the

reasons for the ship's sinking. On the one hand, it took time for the propellers to be stopped and then

put into full reverse, plus, as we have seen, the steering propeller was stationary. On the other hand,

because the rudder, which steers the ship, was most effective when controlling the laminar flow of

water created by the steering propeller, the fact that the steering propellor was not rotatingseverely

diminished the turning ability of the ship. It is one of the many bitter ironies of the Titanictragedy that

the ship might well have avoided the iceberg if Murdoch had not told the engine room to reduce and

then reverse thrust.

Effects from afarFinally, there is a new twist to the science of why the Titanicfoundered. North Atlantic icebergs are

calved on the western coast of Greenland, then circulate anticlockwise through the Labrador Sea

before drifting into the North Atlantic off the Newfoundland coast. There they meet the Gulf Stream

heading north-east on its long journey to bathe the shores of north-western Europe. There are

significant temperature and density differences between these two currents and when they are most

pronounced for example when the Gulf Stream is warmer than usual the icebergs tend to be

corralled into an approximately straight line along the axis of the boundary interface. In other words,

they make a barrier of ice.


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Doomed

Richard Norris of the Scripps Institution of Oceanography in San Diego, California, is leading an

expedition of the Integrated Ocean Drilling Program to the area this summer. "The Titanichit the

iceberg right at the intersection of the Labrador Current and the Gulf Stream," he says. "1912 had an

unusually hot summer in the Caribbean and so the Gulf Stream was particularly intense that year.

Oceanographically, the upshot of that was that icebergs, sea ice and growlers were concentrated in

the very position where the collision happened."

New research raises the possibility that celestial influences conspired to doom the Titanicfrom even

further afield. Astronomers Donald Olson and Russell Doescher from Texas State UniversitySan

Marcos this month published their findings about an extraordinary event on 4 January 1912, three

months before the disaster. On that day the Sun was aligned with the Moon in a way that enhancedits gravitational pull, causing a higher-than-usual "spring tide". This is nothing exceptional in itself.

More remarkable was that on the same day in 1912 the Moon made its closest approach to the Earth

in more than 1400 years in other words, its tide-raising forces were at a maximum. On top of that,

the Earth had reached its closest position to the Sun the "perihelion" the day before.

At first glance it is hard to see how an unusually high tide might have affected the Titanicmore than

three months later. The North Atlantic shipping lanes were peppered with icebergs in April, but if the

high tide had caused new icebergs to calve in Greenland in January, they would have had to travel

unusually fast to get there by then. But the bergs may have come from a source nearer by. When

icebergs pass through the Labrador Sea, they often become stuck in shallow waters and it can take

several years for them to be dislodged and continue their journey southward. Writing in the April issue

ofSky & Telescope magazine, Olson and Doescher suggest that the high tide in January 1912 couldhave given many trapped icebergs the buoyancy they needed to lift up away from the ground and

continue their journey to the Titanic's future graveyard.

It seems therefore that the climate thousands of miles from where theTitanicsank, as well as the

positions of the Sun and Moon astronomical distances away, may have been yet further links in the

chain that led to the loss of the greatest ship in the world.

Event cascadeSo what conclusions can we draw from the events of 14 April 1912, a century after the Titanicsank?

First, there can be no doubt that at the very start of the ship's construction there was a problem with

the materials. The steel plates of the time may have been inadequate for the task in waters of those

temperatures, and the rivets were of inferior quality. Second, mistakes were made by the crew oncethe vessel was under way: the absence of binoculars in the crow's nest; Smith's decision to maintain a


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high speed despite the abundance of iceberg warnings; the radio operators' tardiness in getting

crucial information to the officers and their emphasis on passenger messages rather than operational

ones; and, of course, the almost cynical lack of lifeboats.

Then there are the maths and physics of the collision: six compartments flooded when, if it had only

been four, the ship would not have sunk. And finally, there was the complex interplay of two surface-

water currents, as well as the extraordinarily high spring tide three months earlier, that concentratedicebergs as if they were tank traps.

No one thing sent the Titanicto the bottom of the North Atlantic. Rather, the ship was ensnared by a

perfect storm of circumstances that conspired her to doom. Such a chain is familiar to those who

study disasters it is called an "event cascade". The best planning in the world cannot eliminate

every factor that might negatively impact on the design and operation of a complicated machine such

as a massive passenger ship. Eventually, and occasionally, enough of these individual factors

combine and the "event cascade" becomes long enough and complicated enough that tragedy cannot

be averted.

PoorTitanic.

Costa Concordia

Hazards of the sea

It may have been 100 years since the Titanicwent down, but recent events have shown that the sea

remains as hazardous as ever if not treated with respect. On 13 January the Italian cruise linerCosta

Concordia struck a rock just off the shore of Giglio Island on the west coast of Italy, tearing a 49 m

gash in her hull. The ship, flooding and listing, grounded on the island, where it still lies on its side in

shallow water, pending salvage. All but 32 of the total 4252 passengers and crew were saved.

It is too early to speculate on the causes of the crash but there have been reports that the alarm on

the navigation computer which is linked to GPS and has an accuracy of a few metres may not

have been functioning as it should.

If that is the case then the safety features of the Costa Concordiawere reduced towards Titaniclevels

at a stroke. Yet the Costa Concordia still had radar and modern-day echo-sounding equipment, both

technologies that were not available to the Titanic.

How these latter were overlooked is, of course, a matter for the board of inquiry, but there may be a

cause for concern that modern-day computerized navigation systems have blunted the caution that

should run in the veins of all those who "go down to the sea in ships".

About the author

Richard Corfield is a science writer based in West Oxfordshire, UK
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Reflective Roofs and Pavements Could Fight Climate Change

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