Internal waves, which move vertically through the ocean, can sometimes pass through “water staircases,” which are steplike variations of density of water, in such as manner as to churn up the underlying warm, salty water, thereby increasing the temperature of the top, cooler layers. This suggests a possible mechanism by which the upper layers of the Arctic Ocean warm up, causing the ice to melt.
Water staircases are steplike variations of density of water due to steplike changes in temperature and salinity. Though internal waves exist where the density gradually increases with depth, they cannot propagate where the density is uniform, for instance, within the steps of the staircase.
The Arctic Ocean has inflows coming from the Pacific Ocean and Atlantic Ocean. In this, the top layers consist of cooler and less saline water and below that is a layer of water coming from the Atlantic Ocean which is more saline and warmer, too. The effect of salinity wins over that of temperature and so, though the water below is warmer, it is heavier than the cooler, less saline layer on top..
“Warm, but salty water — ultimately originating from the Atlantic Ocean resides near the bottom of the Arctic Ocean. If turbulence could somehow mix this water with that above, then, eventually, the surface could warm more rapidly, and this would increase the rate of sea-ice melt.
The internal movement of water within seas from cold, dense regions to warmer, lighter ones constitutes the largest observable waves. These can stretch to wavelengths of over a hundred metres and travel from top to bottom.
Like normal water waves, these propagate due to a variation of density of the water and not when there is constant density. In a staircase-like formation, though the density is constant within the step, there is a jump in density from one step to another. Hence, the wave’s energy can be transmitted from one interface to another.
Though not predominant, thermohaline staircases do occur in many places. “As well as the Arctic, they are persistent in the Caribbean Sea. This is due to surface heating and evaporation resulting in warm salty water overlying colder fresher water. They do not exist where there are strong currents, as in the Antarctic, which have enough energy to stir up any staircases that might form.
So the scenario is that when an internal wave strikes a density staircase, a part of its energy may be transmitted through the staircase. In other words, density staircases in the ocean can act to reflect short wavelength internal waves and transmit longer wavelength waves. This is analogous to the selective transparency of glass windows on modern buildings that have multilayered coatings designed to reflect red light (long wavelength light) and allow green-blue (shorter wavelength) light through
On reaching the ocean floor, the long-wavelength waves which have been transmitted cause turbulence and mix up the water. The warm waters then rise to the top and warm the top layers.
“Strong storms passing over the Arctic typically generate waves on the order of 10-100 km horizontal scale. As sea-ice retreats and storms passing over the increasingly non-ice-covered ocean generate more and more waves, it seems that still a substantial fraction of this energy can transmit to depth, and this may consequently cause mixing at depth that could bring those deep warm (but salty) waters closer to the surface. The filtering that my theory predicts suggests that the energy transmitted to depth might be moderately smaller than one would expect in the absence of density staircases. But, for the most energetic waves — those transmitted by storms — the decrease is not substantial.
40 million Indians at risk from rising sea levels: UN report
Nearly 40 million Indians will be at risk from rising sea levels by 2050, with people in Mumbai and Kolkata having the maximum exposure to coastal flooding in future due to rapid urbanisation and economic growth, according to a UN environment report.
The ‘Global Environmental Outlook (GEO-6): Regional Assessments’ said the worst impacts of climate change are projected to occur in the Pacific and South and South-East Asia.
It said focussing on the population at risk from sea-level rise by 2050, seven of the 10 most vulnerable countries worldwide are in the Asia Pacific region.
India tops chart
India tops the chart with nearly 40 million people in the country projected to be at risk from rising sea levels, followed by more than 25 million in Bangladesh, over 20 million in China and nearly 15 million in the Philippines.
It said changes in settlement patterns, urbanisation and socio-economic status in Asia have influenced observed trends in vulnerability and exposure to climate extremes.
The report said in many coastal areas, growing urban settlements have also affected the ability of natural coastal systems to respond effectively to extreme climate events, rendering them more vulnerable.
“Some countries, such as China, India and Thailand, are projected to face increased future exposure to extremes, especially in highly urbanised areas, as a result of rapid urbanisation and economic growth,” it said.
It listed Mumbai and Kolkata in India, Guangzhou and Shanghai in China, Dhaka in Bangladesh, Yangon in Myanmar, Bangkok in Thailand, and Ho Chi Minh City and Hai Phong in Vietnam as projected to have the largest population exposure to coastal flooding in 2070.
The report, published ahead of the UN Environment Assembly taking place in Nairobi next week, said the worst impacts of climate change are projected to occur in the Pacific and South and Southeast Asia.
In 2011, six of the ten countries most vulnerable to climate change worldwide were in Asia and the Pacific.
On coastal areas highly exposed to cyclones and typhoons, the poor tend to be more exposed to natural disasters because they live on land open to hazards.
Evidence suggests that climate change and climate variability and sea-level rise will exacerbate multi-dimensional poverty in most developing countries.
By 2050, areas of storm surge zones are expected for Bangladesh, China, India, Indonesia, and the Philippines, with a combined total of over 58 million people at risk.
The UN report further said global urban populations are projected to increase by 2.5 billion by 2050, with nearly 90 per cent of the increase in Asia and Africa.
India fifth largest producer of e-waste: study
India, which has emerged as the world’s second largest mobile market, is also the fifth largest producer of e-waste, discarding roughly 18.5 lakh tonnes of electronic waste each year, a study says.
Telecom equipment alone accounts for 12 per cent of the e-waste, a joint study by Assocham-KPMG said.
Matter of concern
The rising levels of e-waste generation in India have been a matter of concern in recent years. With more than 100 crore mobile phones in circulation, nearly 25 per cent end up in e-waste annually, it said.
The Ministry of Environment, Forest and Climate Change has notified e-waste management rules, 2016, in which producers are for the first time covered under extended producers’ responsibility (EPR).
Waste collection target
The rules prescribe a waste collection target of 30 per cent waste generated under EPR for the first two years, progressively going up to 70 per cent in the seventh year of the rule.
The rules prescribe stringent financial penalties for non-compliance. However, the study said the unorganised sector in India is estimated to handle around 95 per cent of the e-waste produced in the country.
Given the huge user base and vast reach of telecom in India, it is practically difficult and expensive for the handset manufacturers to achieve the targets prescribed in the rules from first year, the study added.
ISRO plans to test air-breathing propulsion system
After successfully testing a technology demonstrator of a reusable launch vehicle, Indian Space Research Organisation (ISRO) is planning to test an air-breathing propulsion system, which aims to capitalise on the oxygen in the atmosphere instead of liquefied oxygen while in flight.
Generally, vehicles that are used to launch satellites use combustion of propellants with oxidiser and fuel. The air-breathing propulsion system aims at using oxygen present in the atmosphere up to 50 km from the earth’s surface to burn the fuel stored in the rocket.
Lower lift-off mass
The system, when implemented, would help in reducing the lift-off mass of the vehicle since liquefied oxygen need not be carried on board the vehicle. This would also help increasing the efficiency of the rocket and also make it cost-effective.
The new propulsion system, once mastered, would complement ISRO’s aim to develop a reusable launch vehicle that would have longer flight duration. The system, involving the scramjet engine, would become crucial while sending up the spacecraft.
ISRO is now evolving and testing various technologies to bring down the cost of launch vehicles. The national space agency has earlier developed rockets that can send multiple satellites in a single mission.
Ancient Mars hosted habitable environments: study
Scientists have found evidence for widespread buried deposits of iron- and calcium-rich carbonates on Mars, which suggests that the red planet once hosted habitable environments with liquid water.
Identification of these ancient carbonates and clays on Mars represents a window into history when the climate on Mars was very different from the cold and dry desert of today.
Carbonates beneath the surface of Mars point to a warmer and wetter environment in that planet’s past. The presence of liquid water could have fostered the emergence of life.
Subject of an energetic debate
The fate of water on Mars has been energetically debated by scientists because the planet is currently dry and cold, in contrast to the widespread fluvial features that etch much of its surface.
Scientists believe that if water did once flow on the surface of Mars, the planet’s bedrock should be full of carbonates and clays, which would be evidence that Mars once hosted habitable environments with liquid water.
And the carbon dioxide
Researchers have struggled to find physical evidence for carbonate-rich bedrock, which may have formed when carbon dioxide in the planet’s early atmosphere was trapped in ancient surface waters. They have focused their search on Mars’ Huygens basin.
This feature is an ideal site to study carbonates because multiple impact craters and troughs have exposed ancient, subsurface materials where carbonates can be detected across a broad region, researchers have said.
Outcrops in the 450-km wide Huygens basin contain both clay minerals and iron- or calcium-rich carbonate-bearing rocks.
The study has highlighted evidence of carbonate-bearing rocks in multiple sites across Mars, including Lucaya crater, where carbonates and clays 3.8 billion years old were buried by as much as 5 km of lava and caprock.
The researchers identified carbonates on the planet using data from the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM), which is on the Mars Reconnaissance Orbiter. This instrument collects the spectral fingerprints of carbonates and other minerals through vibrational transitions of the molecules in their crystal structure that produce infrared emission.
The team paired CRISM data with images from the High Resolution Imaging Science Experiment (HiRISE) and Context Camera (CTX) on the orbiter, as well as the Mars Orbiter Laser Altimeter (MOLA) on the Mars Global Surveyor, to gain insights into the geologic features associated with carbonate-bearing rocks.
The extent of the global distribution of martian carbonates is not yet fully resolved and the early climate on the red planet is still subject of debate.
However, this study is a forward step in understanding the potential habitability of ancient Mars.