GS Paper: GS1-14.Important Geophysical phenomena such as earthquakes, Tsunami, Volcanic activity, cyclone etc.,

A recent study from IIT Kharagpur called “Anthropogenic forcing exacerbating the urban heat islands in India” noted that the relatively warmer temperature in urban areas, compared to suburbs, may contain potential health hazards due to heat waves apart from pollution.

About the study

• The research did study the difference between urban and surrounding rural land surface temperatures, across all seasons in 44 major cities from 2001 to 2017.
• It found evidence of mean daytime temperature of surface urban heat island (UHI Intensity) going up to 2 degrees C for most cities, as analysed from satellite temperature measurements in monsoon and post monsoon periods.
• Other researchers from elsewhere have also noticed similar rise in daytime temperatures in Delhi, Mumbai, Bengaluru, Hyderabad and Chennai.

What is an Urban Heat Island?

• An urban heat island (abbreviated as UHI) is where the temperature in a densely populated city is as much as 2 degrees higher than suburban or rural areas.
• This happens because of the materials used for pavements, roads and roofs, such as concrete, asphalt (tar) and bricks, which are opaque, do not transmit light, but have higher heat capacity and thermal conductivity than rural areas, which have more open space, trees and grass.
• Trees and plants are characterised by their ‘evapotranspiration’— a combination of words wherein evaporation involves the movement of water to the surrounding air, and transpiration refers to the movement of water within a plant and a subsequent lot of water through the stomata (pores found on the leaf surface) in its leaves.
• Grass, plants and trees in the suburbs and rural areas do this. The lack of such evapotranspiration in the city leads to the city experiencing higher temperature than its surroundings.

Latent impacts

• UHI s also decrease air quality in the cities, thanks to pollution generated by industrial and automobile exhaust, higher extent of particulate matter and greater amounts of dust than in rural areas.
• Due to this higher temperature in urban areas, the UHI increases the colonization of species that like warm temperatures, such as lizards and geckos.
• Insects such as ants are more abundant here than in rural areas; these are referred to as ectotherms.
• In addition, cities tend to experience heat waves which affect human and animal health, leading to heat cramps, sleep deprivation and increased mortality rates.
• UHIs also impact nearby water bodies, as warmer water (thanks to the pavements, rooftops and so on) is transferred from the city to drains in sewers, and released into nearby lakes and creeks, thus impairing their water quality.

Control of UHIs and mitigation

• Industrialization and economic development are vital to the country, but the control of UHIs and their fallouts are equally vital. Towards this, several methods are being, and can be, tried.
• One of them is to use greener rooftops, using light-coloured concrete (using limestone aggregates along with asphalt (or tar) making the road surface greyish or even pinkish (as some places in the US have done); these are 50% better than black, since they absorb less heat and reflect more sunlight.
• Likewise, we should paint rooftops green, and install solar panels there amidst a green background.
• The other is to plant as many trees and plants as possible

Why plant more trees?

Relevant to the present context are:

• they combat climate change; clean the surrounding air by absorbing pollutant gases (NXOy, O3, NH3, SO2, and others) and trapping particulates on their leaves and bark;
• they cool the city and the streets; conserve energy (cutting air-conditioning costs by 50%); save water and help prevent water pollution; help prevent soil erosion; protect people and children from UV light;
• they offer economic opportunities; bring diverse group of people together; encourage civic pride by giving neighborhoods a new identity; mask concrete walls, thus muffling sounds from streets and highways, and eye-soothing canopy of green; and the more a business district has trees, more business follows.

In the Antarctic floats a massive glacier, roughly the size of Britain, whose melting has been a cause of alarm for scientists over the years. Now, a new study has pinned the cause of the melting to the presence of warm water at a vital point beneath the glacier.

Thwaites Glacier

• The Thwaites Glacier is 120 km wide at its broadest, fast-moving and melting fast over the years.
• Because of its size (1.9 lakh square km), it contains enough water to raise the world sea level by more than half a metre.
• Studies have found the amount of ice flowing out of it has nearly doubled over the past 30 years. Today, Thwaites’s melting already contributes 4% to global sea level rise each year.
• It is estimated that it would collapse into the sea in 200-900 years. Thwaites is important for Antarctica as it slows the ice behind it from freely flowing into the ocean.
• Because of the risk it faces — and poses — Thwaites is often called the Doomsday Glacier.

What has the new study found?

• A 2019 study had discovered a fast-growing cavity in the glacier.
• More recently researchers detected warm water at a vital point below the glacier.
• Scientists dug a 600-m-deep and 35-cm-wide access hole, and deployed an ocean-sensing device called Icefin to measure the waters moving below the glacier’s surface.
• The study reported water at just two degrees above freezing point at Thwaites’s “grounding zone” or “grounding line”.

What is the grounding line?

• The grounding line is the place below a glacier at which the ice transitions between resting fully on bedrock and floating on the ocean as an ice shelf.
• The location of the line is a pointer to the rate of retreat of a glacier.
• When glaciers melt and lose weight, they float off the land where they used to be situated. When this happens, the grounding line retreats.
• That exposes more of a glacier’s underside to seawater, increasing the likelihood it will melt faster.
• This resulted in the glacier speeding up, stretching out, and thinning, causing the grounding line to retreat ever further.

A recent study makes a disturbing connection between the loss of Arctic sea ice and thawing (melting) of permafrost in the region, with global implications.

What is Permafrost?

• ‘Permafrost’ or permanently frozen ground is land that has been frozen at or below 0 degrees Celsius for two or more consecutive years.
• A staggering 17 per cent of Earth’s entire exposed land surface is comprised of permafrost.
• Composed of rock, sediments, dead plant and animal matter, soil, and varying degrees of ice, permafrost is mainly found near the poles, covering parts of Greenland, Alaska, Northern Canada, Siberia and Scandinavia.
• The Arctic region is a vast ocean, covered by thick ice on the surface (called sea ice), surrounded by land masses that are also covered with snow and ice.

Permafrost thawing

• When permafrost thaws, water from the melted ice makes its way to the caves along with ground sediments, and deposits on the rocks.
• In other words, when permafrost thaws, the rocks grow and when permafrost is stable and frozen, they do not grow.

Why thawing?

• The link between the Siberian permafrost and Arctic sea ice can be explained by two factors:
• One is heat transport from the open Arctic Ocean into Siberia, making the Siberian climate warmer.
• The second is moisture transport from open seawater into Siberia, leading to thicker snow cover that insulates the ground from cold winter air, contributing to its warming.
• This is drastically different from the situation just a couple of decades ago when the sea ice acted as a protective layer, maintaining cold temperatures in the region and shielding the permafrost from the moisture from the ocean.
• If sea ice (in the summer) is gone, permafrost start thawing.

Impact on Climate Change

• Due to relentlessly rising temperatures in the region, since the late-twentieth century, the Arctic sea ice and surrounding land ice are melting at accelerating rates.
• When permafrost thaws due to rising temperatures, the microbes in the soil decompose the dead organic matter (plants and animals) to produce methane (CH4) and carbon dioxide (CO2), both potent greenhouse gases.
• CH4 is at least 80 times more powerful than CO2 on a decadal timescale and around 25 times more powerful on a century timescale.
• The greenhouse gases produced from thawing permafrost will further increase temperatures which will, in turn, lead to more permafrost thawing, forming an unstoppable and irreversible self-reinforcing feedback loop.
• Experts believe this process may have already begun. Giant craters and ponds of water (called ‘thermokarst lakes’) formed due to thawing have been recorded in the Arctic region. Some are so big that they can be seen from space.

Why a matter of concern?

• An estimated 1,700 billion tonnes — twice the amount currently present in the atmosphere — of carbon is locked in all of the world’s permafrost.
• Even if half of that were to be released to the atmosphere, it would be game over for the climate.
• Scientific estimates suggest that the Arctic Ocean could be largely sea ice-free in the summer months by as early as 2030, based on observational trends, or as late as 2050, based on climate model projections.