Group E: polar climates, and highland (H) climates

Detail

1. Polar climates (E): the basic rule

• Polar climates (E): climates where every month has an average temperature below 10°C. No month is warm enough for trees to grow.
• Where: mostly poleward of about 70° latitude in both hemispheres.
• Two types, based on how warm the warmest month gets:

Feature	Tundra (ET)	Ice cap (EF)
Rule	Warmest month between 0°C and 10°C	Every month below 0°C
Summer	No true summer; short, cool thaw season	No thaw at all; summer stays below freezing
Ground	Permafrost with a thin thawed active layer	Thick ice sheets
Plant life	Mosses, lichens, low flowering plants	Almost none
Where	Northern Canada, Alaska, Siberia, coastal Greenland	Interior Greenland, Antarctica
Station example	—	Plateau Station, Antarctica (79°S)

2. Tundra climate (ET)

• Rule: the warmest month averages between 0°C and 10°C.
• Name: the climate takes its name from its vegetation. Tundra means the treeless cover of mosses, lichens (lichen: a small crusty plant made of a fungus and an alga living together) and low flowering plants.
• No true summer. The thaw season is short and cool.
• Very long summer daylight. Near the poles the sun stays above the horizon for weeks or months in summer, but it stays low in the sky, so its heat is weak.
• Why only low plants grow:
• The growing season is very short.
• Only the top layer of soil thaws in summer. The ground below stays frozen.

• Water cannot drain down through the frozen ground → the surface becomes waterlogged (soaked, boggy) → tree roots cannot grow, so only shallow-rooted low plants survive.

• Locations: northern Canada, Alaska (USA), northern Siberia (Russia) and the coastal strip of Greenland (Denmark), all along the Arctic Ocean.

3. Permafrost

• Permafrost: ground (soil, rock or sediment) that stays at or below 0°C for at least two years in a row.
• Active layer: the thin top layer above the permafrost. It thaws each summer and freezes again in autumn.

• In the coldest areas it is only about 10–15 cm thick. In warmer permafrost areas it can be several metres thick [5].

• Extent: permafrost zones cover nearly a quarter of the exposed land of the Northern Hemisphere [4].

• Permafrost thaw as a climate feedback (feedback: a result that makes its own cause stronger):
• The world warms → permafrost thaws.
• Microbes start to break down old plant matter frozen in the soil → they release carbon dioxide and methane, both greenhouse gases [6].
• More greenhouse gas in the air → more warming → more thaw (see climate-change).

• More than 50% of yearly methane release from Arctic soils happens in the cold season, not just in summer [4].

• Damage to infrastructure:

• Frozen ground acts like rock. When it thaws, it turns soft and sinks.
• Buildings tilt, roads crack and pipelines break.
• Example: the Norilsk fuel spill (2020), Siberia, Russia. A fuel tank failed and spilled diesel into rivers; sinking of thawing ground under the tank was blamed.

4. Ice cap climate (EF)

• Rule: every month averages below 0°C. Even summer stays below freezing.
• Where: the interior of Greenland and Antarctica.
• Example station (NCERT): Plateau Station, Antarctica (79°S).
• Polar desert: precipitation is very low because very cold air holds little water vapour.

• Antarctica's interior gets only about 2.5–5 cm of precipitation a year (as melted water). This makes it one of the world's major cold deserts [10].

• How ice sheets form and move:

• Snow falls and does not melt → it piles up year after year.
• The weight of the upper layers presses the snow below into solid ice → an ice sheet forms.
• The great weight makes the ice flow slowly outward towards the sea.

• At the edges the ice breaks off (calves) into icebergs, which float in Arctic and Antarctic waters.

• Size: the Antarctic Ice Sheet covers about 13.8 million sq km. It stays balanced because snowfall is offset mainly by ice moving out to sea through ice-shelf flow, ice-stream flow and sheet flow [10].

• Coldest temperatures on Earth:
• World lowest: −89.2°C at Vostok station, Antarctica, on 21 July 1983 [2].
• Vostok lies at 77°32′S, 106°40′E, at 3,420 m height [2].
• Why so cold: no sunlight in the polar winter, clear skies, calm air for a long time, little mixing of air and a very high station [2].
• Northern Hemisphere lowest: −69.6°C in Greenland, verified by the WMO [3].

5. Icebergs

• Iceberg: a large floating block of freshwater ice that has broken off a glacier or ice sheet.
• It is fresh water because it formed from snow, not from frozen sea water.

• About nine-tenths (90%) lies below the water. Only one-tenth shows above the surface, so ships can easily misjudge its size.

• Path in the North Atlantic:

• Icebergs break off Greenland's glaciers.
• The cold Labrador Current carries them south past Newfoundland to the Grand Banks, off south-eastern Canada [8].

• This area lies on busy North Atlantic shipping lanes between Europe and North America.

• Titanic disaster (1912):

• On 14 April 1912 the Titanic hit an iceberg south-east of Cape Race, Newfoundland, and sank. About 1,500 of its 2,200 passengers died [9].

• International Ice Patrol (1914):

• Set up in 1914 by agreement of 16 nations with shipping interests in the North Atlantic [7].
• It finds icebergs, follows and predicts their drift, and warns nearby ships [7].

6. Highland climates (H)

• H (highland climates): a group added by Glenn Trewartha (his revision of Koeppen's scheme). It is not in NCERT's Koeppen table.
• Why a separate group:
• Temperature falls as height increases. This is called the normal lapse rate (the fall of temperature with height, about 6.5°C for every 1,000 m).
• So, climate belts stack one above another on a mountain. Walking up a few kilometres can take you from a warm valley to a tundra-like zone and then to snow and ice.

• The climate changes over very short distances, so it cannot be drawn as one broad belt like other climates.

• World examples: the Andes (South America), the Tibetan Plateau, the Himalaya and the East African highlands (e.g. Kilimanjaro, Ethiopian Highlands).

• India's examples: Ladakh and the high Himalayan peaks (see india-structure-physiography).
• On Koeppen maps: these high areas are often marked as ET (tundra) or Dw (cold climate with a dry winter), because Koeppen used only temperature and rainfall, not height.

Prelims Hooks

• E group rule: all months below 10°C. ET: warmest month 0–10°C. EF: all months below 0°C.
• The tundra (ET) is named after its vegetation (mosses, lichens, low flowering plants), not after a place.
• Permafrost = ground frozen for at least two consecutive years. The active layer is the part that thaws in summer.
• Permafrost zones cover nearly a quarter of the Northern Hemisphere's exposed land [4].
• World lowest temperature: −89.2°C, Vostok, Antarctica, 21 July 1983 [2]. Northern Hemisphere lowest: −69.6°C, Greenland [3].
• Plateau Station (79°S) is NCERT's example station for EF.
• The Labrador Current (a cold current) carries Greenland icebergs to the Grand Banks/Newfoundland. The Titanic (1912) sinking led to the International Ice Patrol (1914) [7][8].
• Trap: the H (highland) group was added by Trewartha. It is not part of Koeppen's original scheme or NCERT's table.
• Trap: the interiors of Antarctica and Greenland are deserts (very low precipitation), even though they are covered in ice [10].
• An iceberg is freshwater ice with about nine-tenths below water.

Mains Points

• Permafrost thaw as a climate tipping risk (GS-I/GS-III):
• Warming thaws permafrost → microbes release CO₂ and methane → more warming [6].

• Large release even in the cold season [4] makes Arctic methane a hidden climate threat.

• Infrastructure and disaster risk:

• Thawing ground sinks → buildings, roads and pipelines in Russia, Canada and Alaska fail (Norilsk fuel spill, 2020).

• Similar risks exist for roads and buildings in India's high Himalaya and Ladakh.

• Distribution pattern explained by temperature alone:

• Polar climates follow latitude (poleward of about 70°). Highland climates follow height.

• Koeppen's temperature-and-rainfall rules mark high mountains as ET/Dw. That is why Trewartha added a separate H group, a useful point when discussing the limits of Koeppen's scheme.

• Polar ice and navigation safety:

• Ice sheets calve icebergs that drift into shipping lanes. After the Titanic, 16 nations set up the International Ice Patrol (1914) to track icebergs and warn ships [7].
• It is an early example of international cooperation against a natural hazard.