GS-1 

1. Aksai Chin

·      News: The United Nations has released a new world map that shows Arunachal Pradesh and Aksai Chin — which India affirms is part of Ladakh — as separate regions lying between the "claim lines" of India and China.

·      More on the news: at a UN General Assembly session, 164 countries (including India) voted to adopt the 2018 Equal Earth design, which draws attention to distortions in the widely used Mercator projection.

·      Location

o Located in eastern Ladakh (Union Territory of Ladakh).

o Bordered to the west by the Karakoram Range, and to the north and northeast by the Kunlun Mountains.

o Forms the western sector of the India–China boundary dispute.

o Claimed by India as part of Ladakh, but currently under Chinese control

o Lies at the junction of China's Xinjiang Uyghur Autonomous Region and the Tibet Autonomous Region.

o Provides the shortest land link between Xinjiang and Tibet.

·      In simple words: Xinjiang is a mostly desert region that produces about a fifth of the world's cotton, and is rich in oil and natural gas. Because it sits close to Central Asia and Europe, Beijing sees it as an important trade link. The Uyghurs are a Turkic-speaking Muslim people of inner Asia. The Tibetan Plateau, further east, is often called the "roof of the world."

·      Major Passes Around Aksai Chin

Pass

Key Fact

Karakoram Pass

Connects Ladakh with Xinjiang; one of the oldest routes on the Silk Route network

Lanak La Pass

On the eastern side of Ladakh near Aksai Chin, northeast of Pangong Tso

Kongka La Pass

In the Aksai Chin region, lying between Ladakh and Tibet

·      The Johnson Line — India's Claim

o Proposed in 1865 by British surveyor William H. Johnson.

o Places the entire Aksai Chin region within Jammu & Kashmir (present-day Ladakh).

o Forms the basis of India's territorial claim over Aksai Chin.

·      G219 Highway (Xinjiang–Tibet Highway)

o Connects Yecheng (Xinjiang) with Lhatse (Tibet), passing through Aksai Chin.

o Its construction in the 1950s was one of the major factors leading to the 1962 India–China War.

·      Xinjiang–Tibet Railway

o China is constructing this railway to improve connectivity between Xinjiang and Tibet.

o The proposed route connects Hotan (Xinjiang) with Shigatse (Tibet).

o It is expected to pass through or near Aksai Chin, close to the Line of Actual Control (LAC).

·      DO NOT CONFUSE — Johnson Line vs. Line of Actual Control (LAC)

The Johnson Line is India's claim line (1865) — it places all of Aksai Chin inside Ladakh/J&K.

The LAC is the de facto control line today — China actually holds Aksai Chin on the ground.

The gap between what India claims (Johnson Line) and what China controls (LAC) is exactly why Aksai Chin stays disputed.

·      Major Territorial and Boundary Disputes Around India

Disputed Area

Countries

Location

Type

Key Fact

Aksai Chin

India–China

Ladakh (UT)

Land Boundary

Claimed by India, controlled by China

Arunachal Pradesh (Zangnan)

India–China

Arunachal Pradesh

Territorial Claim

Entire state claimed by China

Depsang Plains

India–China

Ladakh (UT)

LAC Friction Point

Near Daulat Beg Oldie (DBO)

Demchok

India–China

Ladakh (UT)

LAC Friction Point

Eastern Ladakh border village

Pangong Tso

India–China

Ladakh (UT)

LAC Dispute

Lake shared by India and China

Galwan Valley

India–China

Ladakh (UT)

LAC Dispute

Clash occurred in June 2020

Doklam Plateau

China–Bhutan (India involved)

Sikkim–Bhutan–Tibet tri-junction

Tri-junction Dispute

Important for Siliguri Corridor security

Shaksgam Valley

India–China–Pakistan

North of Ladakh

Territorial Claim

Ceded by Pakistan to China in 1963

Siachen Glacier

India–Pakistan

Ladakh (UT)

Boundary/Military

World's highest battlefield

Sir Creek

India–Pakistan

Gujarat (Kutch)

Maritime Boundary

Tidal estuary opening into Arabian Sea

Kalapani

India–Nepal

Uttarakhand (Pithoragarh)

Land Boundary

Near India-Nepal-China tri-junction

Lipulekh Pass

India–Nepal

Uttarakhand

Boundary Dispute

Route to Kailash Mansarovar

Limpiyadhura

India–Nepal

Uttarakhand

Boundary Dispute

Claimed by Nepal since its 2020 map

Katchatheevu Island

India–Sri Lanka

Palk Strait (Tamil Nadu coast)

Maritime/Fishing

Transferred to Sri Lanka in 1974

2. Yemen

·      News: Fighting between Yemen's Saudi-backed government forces and the country's Houthi rebels recently killed more than 60 people.

·      Quick Facts

o Located at the south-western corner of the Arabian Peninsula, in West Asia.

o Shares land borders with Saudi Arabia (north) and Oman (east).

o Bordered by the Red Sea (west), the Gulf of Aden, the Arabian Sea, and the Guardafui Channel (south).

o Strategic importance: it sits at the entrance of the Bab-el-Mandeb Strait, which connects the Red Sea with the Gulf of Aden and the Indian Ocean.

o Capital: Sanaa.

o Climate: shaped by both Mediterranean northerly winds and the southwest monsoon.

o Highest peak: Jabal an Nabi Shu'ayb (3,760 m).

o Major desert: the Rub' al Khali (Empty Quarter).

GS-2 

1.      National Register of Citizens (NRC)

·      News: Manipur's Home Minister recently informed the 60-member Assembly that the NRC in the State would be updated using 1951 as the base year.

·      About the NRC

o The NRC is an official record containing the names of genuine Indian citizens residing in the country.

o It is meant to identify illegal immigrants and distinguish them from lawful citizens.

o Legal basis: the Citizenship Act, 1955, and the Citizenship (Registration of Citizens and Issue of National Identity Cards) Rules, 2003.

o The first and only nationwide NRC was prepared in 1951, following the 1951 Census.

·      NRC in Assam

o Assam is currently the only State where the NRC has been updated.

o The exercise was monitored by the Supreme Court of India, starting in 2014.

o To be included, a person (or their descendants) must prove their name appeared in the 1951 NRC, or in any electoral roll up to 24 March 1971.

o Nodal agency: the Registrar General and Census Commissioner of India (RGI).

o Related constitutional provision: Article 355 places a duty on the Union to protect States against external aggression and internal disturbance.

·      Major Tribes of Manipur

Tribe

Key Facts

Meitei

Included in the Eighth Schedule of the Constitution; classified as OBC in Manipur; demand inclusion in the ST list

Naga Tribes

Speak several Tibeto-Burman languages; recognised as Scheduled Tribes

Kuki-Zo Tribe

Recognised as Scheduled Tribes

·      Financial Action Task Force (FATF)_GS2 IR

·      News: An FATF report has identified the fusion of virtual assets with the traditional "hawala" system as a significant development.

·      About FATF

o FATF is an intergovernmental body that develops international standards to combat money laundering (AML), terrorist financing (CFT), and proliferation financing related to weapons of mass destruction.

o Established in 1989 by the G7 countries: Canada, France, Germany, Italy, Japan, the UK, and the US.

o Headquarters: the FATF Secretariat, hosted by the OECD in Paris, France.

o Decision-making body: the FATF Plenary, which meets three times a year.

o Membership: 40 members — 38 countries/jurisdictions, plus 2 regional organisations, the European Commission and the Gulf Cooperation Council (GCC).

o It also has 9 Associate Member organisations and other global partners, including the IMF and World Bank.

·      FATF Monitoring Mechanism

o Under Mutual Evaluation, FATF periodically assesses member countries' technical compliance with FATF standards, and how effectively they implement them.  

Grey List

Black List

Full name

Jurisdictions Under Increased Monitoring

High-Risk Jurisdictions Subject to a Call for Action

Who's on it

Countries with strategic deficiencies in their AML/CFT regimes

Jurisdictions with serious, persistent AML/CFT deficiencies

Implications

Increased international scrutiny; reduced investor confidence; higher compliance costs

Severe restrictions on international financial transactions; reduced access to global financial markets

Current examples

DR Congo, Haiti, Iraq, Lebanon, Nepal, Syria, Yemen

North Korea (DPRK), Iran, Myanmar

·      India and FATF

o India became a full member of FATF in 2010.

o India takes part in FATF plenary meetings, mutual evaluation processes, and global AML/CFT policy formulation.

·      Defence Acquisition Council (DAC)_Polity _GS2

·      News: The DAC, chaired by Defence Minister Rajnath Singh, has cleared ₹1.10 lakh-crore worth of defence procurement proposals — 98% of which will be sourced from Indian industry.

·      About the DAC

o The highest decision-making body for defence procurement in the Ministry of Defence.

o It is an executive body — created by a government/cabinet order, not by a specific law (which would make it a statutory body).

o Responsible for approving major proposals for acquiring defence equipment and platforms for the Armed Forces.

o Constituted in 2001, following the recommendations of the Group of Ministers (GoM) formed after the Kargil War (1999).

o Chairperson: the Union Defence Minister.

·      Key Systems Approved Under the ₹1.10 Lakh Crore Procurement

System

What It Does

CBRN Reconnaissance Vehicles

Detect, identify, monitor, and mark areas contaminated by Chemical, Biological, Radiological and Nuclear (CBRN) agents. DRDO has transferred technology for the tracked Mk-II version to Bharat Electronics Limited, built on the re-engineered BMP-II platform

CBRN Mini UGV

An unmanned ground vehicle for detecting, sampling, and marking contaminated zones without exposing personnel

High Mobility Vehicles (HMVs)

Strengthen logistics support, troop movement, and operational mobility in difficult terrain

Self-Propelled Mechanical Mine Layers

Enable rapid minelaying for both defensive and offensive missions

Advanced Light Helicopters (ALHs)

Let the Army and Air Force undertake complex missions across varied terrain

Arudhra Radars

Navy radars replacing older Air Route Surveillance Radars; a medium-power 4D active phased array radar by DRDO and BEL

Marine Gas Turbines

Reduce Navy dependence on foreign vendors for warship propulsion

Ground-Based Multi-Purpose Jammer (GBMPJ)

Electronic-warfare capability that jams adversarial radar systems

Defence Forces Secure Access Card (DEFSAC)

Replaces paper ID with interoperable RFID smart cards for secure access

Trawl Tanks & Sarvatra Bridge System

Support river/obstacle crossings; Sarvatra is a mobile bridging system by DRDO, built by BEML

·      In simple words: Two other radars are useful context here, though not part of this procurement: Ashwini is a fully indigenous DRDO Low-Level Transportable Radar for the Air Force, and Rohini is a DRDO ground-based radar covering medium-range airspace surveillance, with a tracking range of about 150 km. 

GS-3 

1. Regional Rural Banks (RRBs)

·      News: Former RBI Governor C. Rangarajan has warned that RRB consolidation is a step in the wrong direction, and could weaken their local character. He urged the RBI to incentivise more Small Finance Banks to address India's unmet rural credit needs.

·      About RRBs

o M. Narasimham is widely regarded as the conceptualiser — often called the "father" — of RRBs in India.

o RRBs are specialised financial institutions set up to provide financial inclusion, banking, and credit facilities in rural areas.

o They were created to meet the needs of small and marginal farmers, agricultural labourers, rural artisans, and small entrepreneurs and other weaker sections.

o Established on the recommendations of the Narasimham Working Group (1975).

o Created under the Regional Rural Banks Act, 1976.

o The first RRB, Prathama Grameen Bank, was established on 2 October 1975.

Shareholder

Share

Central Government

50%

State Government

15%

Sponsor Bank

35%

o Each RRB is sponsored by a Public Sector Commercial Bank, which gives it managerial and financial support.

·      Priority Sector Lending (PSL)

o RRBs must lend a larger share of credit to priority sectors: agriculture, MSMEs, export credit, education, housing, social infrastructure, renewable energy, and weaker sections.

·      In simple words: "Adjusted Net Bank Credit" is just the base amount used to calculate a bank's PSL obligation — the target is a percentage of this figure.

Bank Type

PSL Target

Regional Rural Banks (RRBs)

75% of Adjusted Net Bank Credit

Scheduled Commercial Banks

40%

·      Sources of Funds

o RRBs mobilise funds through share capital (owned funds), public deposits, and borrowings from NABARD and sponsor banks.

o They also receive assistance from institutions such as SIDBI and the National Housing Bank (NHB).

·      Regulation and Supervision

o Regulator: Reserve Bank of India (RBI).

o Supervisory institution: National Bank for Agriculture and Rural Development (NABARD).

·      One State, One RRB Policy

o A consolidation initiative of the Department of Financial Services, Ministry of Finance.

o Under this policy, multiple RRBs operating within a State are merged into a single RRB.

o RRB amalgamation is carried out under the Regional Rural Banks Act, 1976.

·      Small Finance Banks (SFBs)

o SFBs are specialised banking institutions set up to promote financial inclusion for underserved and unbanked sections of society.

o They primarily serve small business units, micro and small enterprises, marginal and small farmers, micro-entrepreneurs, and unorganised-sector workers.

o SFBs are registered as public limited companies under the Companies Act, 2013.

o They are regulated by the RBI, and governed by the Banking Regulation Act, 1949 and the Reserve Bank of India Act, 1934.

·      DO NOT CONFUSE — Regional Rural Banks (RRBs) vs. Small Finance Banks (SFBs)

RRBs are jointly owned by the Centre, a State Government, and a sponsor bank (50:15:35) — SFBs are standalone public limited companies with no government shareholding structure of this kind.

RRBs were created by a specific 1976 Act aimed at rural credit — SFBs are a more recent RBI licensing category (post-2014) aimed at financial inclusion more broadly, in both urban and rural areas.

Today's news is about RRBs being consolidated (fewer, larger RRBs) while Rangarajan wants MORE SFBs — the two trends are pulling in opposite directions. 

2. UNEP's "Limiting Overshoot" Report on 1.5°C

·      News: The UN Environment Programme (UNEP) has released a report titled "Limiting Overshoot: Navigating Exceedance of 1.5°C and Pathways Towards Return." It acknowledges that a temporary breach of the 1.5°C global warming threshold — set under the Paris Agreement — is now increasingly likely in the near future.

·      In simple words: "Overshoot" means temporarily going past a limit before coming back under it — like overshooting a monthly budget for a few months, then cutting spending until you're back within it. The report says the world will likely overshoot 1.5°C of warming for a while before (hopefully) coming back down.

·      Key Findings

o The world is likely to exceed the 1.5°C global warming limit within the next few years.

o Since crossing 1.5°C now looks increasingly unavoidable, the priority should shift to limiting the peak level of warming reached, and minimising how long temperatures stay above 1.5°C.

o Under the most ambitious mitigation scenario, warming could still peak at around 1.8°C in the mid-century period.

o Under existing national policies, global warming could reach approximately 2.6°C by 2100.

o The report proposes an "Overshoot–Peak–Decline" pathway: temperatures temporarily exceed 1.5°C, reach a peak, and then gradually decline — with the long-term goal of returning below 1.5°C.

o Getting back below 1.5°C needs a significant cut in greenhouse gas emissions and a rapid phase-down of fossil fuels.

o The US is the largest historical emitter of carbon dioxide.

o India ratified and joined the Paris Agreement on 2 October 2016.

o Carbon dioxide removal (CDR) technologies will play an important role in cutting atmospheric CO₂ levels.

o Methane currently contributes about 0.5°C of warming — a significant share.

o The Global Methane Pledge aims to cut human-caused methane by at least 30% below 2020 levels by 2030.

o India, China, Russia, and Iran remain outside the Global Methane Pledge.

·      Climate Tipping Points

o In simple words: A climate tipping point is a critical threshold in the Earth's systems — once crossed, it triggers large, rapid, and often irreversible change.

o Higher temperatures raise the risk of crossing such tipping points.

o Examples: melting of the Greenland Ice Sheet, destabilisation of the West Antarctic Ice Sheet, degradation of the Amazon Rainforest, and disruption of the Atlantic Meridional Overturning Circulation (AMOC).

·      International Recognition of the Overshoot Challenge

o This recognition gained momentum at COP30, held in Belém, Brazil, in 2025.

o The "Global Mutirão" decision, adopted at COP30, was the first COP outcome document to acknowledge that a temporary overshoot of 1.5°C is increasingly likely.

·      The Paris Agreement

o A legally binding international treaty on climate change.

o Adopted by 195 Parties at COP21 in Paris, France, on 12 December 2015.

o Under it, countries submit Nationally Determined Contributions (NDCs) — their own climate-action commitments.

·      DO NOT CONFUSE — What's Legally Binding in the Paris Agreement vs. What Isn't

Legally binding: every participating country MUST create, communicate, and maintain successive NDCs, once every five years.

Not legally binding: actually HITTING the emission-reduction targets stated in a country's own NDC is not enforceable under international law.

·      India's Updated NDC (2022) — Target Year 2030

Target

Detail

Emissions intensity of GDP

Reduce by 45% from 2005 levels by 2030

Non-fossil power capacity

Achieve 50% cumulative installed electric power capacity from non-fossil sources by 2030

Additional carbon sink

Create 2.5–3 billion tonnes of CO₂-equivalent through forest and tree cover by 2030  

3. U.K. Recognises India's Carbon Credit Trading Scheme

·      News: In a major breakthrough, the U.K. has recognised India's Carbon Credit Trading Scheme (CCTS) as a qualifying criterion for pricing relief under its own carbon border adjustment mechanism (CBAM) — a move that would reduce the tax burden on domestic exporters.

·      In simple words: U.K. importers of eligible Indian goods can now claim carbon-price relief matching what those goods already paid under India's CCTS. That lowers their CBAM bill, which directly benefits Indian exporters — the whole point being to avoid taxing the same carbon twice.

·      Carbon Border Adjustment Mechanism (CBAM)

o A carbon tariff imposed by the European Union on selected carbon-intensive imports.

o Part of the "Fit for 55" package — the EU's plan to cut greenhouse gas emissions by at least 55% by 2030, compared to 1990 levels.

o Its definitive phase came into force on 1 January 2026, making CBAM fully operational and legally enforceable.

o It aims to prevent "carbon leakage" — production shifting to countries with weaker or no carbon-pricing rules.

o Under CBAM, EU importers must buy CBAM certificates linked to the carbon emissions embedded in their imported goods — one certificate per tonne of CO₂ (or equivalent) released in production.

o Certificate prices are aligned with the carbon price under the EU Emissions Trading System (EU ETS).

o If a producer outside the EU has already paid a domestic carbon price, that amount can be deducted from their CBAM liability.

o CBAM is designed to be compatible with WTO rules.

o Initial coverage: iron and steel, cement, fertilisers, aluminium, electricity, and hydrogen — sectors seen as highly vulnerable to carbon leakage.

o It may affect India's exports of steel, aluminium, cement, and other carbon-intensive products to the EU.

·      Carbon Credit Trading Scheme (CCTS)

o India operationalised the CCTS in June 2023, under the Energy Conservation (Amendment) Act, 2022.

o It establishes a domestic carbon market, building on the earlier Perform, Achieve and Trade (PAT) framework.

o It forms the foundation of the Indian Carbon Market (ICM).

o The World Bank's State and Trends of Carbon Pricing 2025 report recognised India's growing role in shaping global carbon-pricing and climate-finance frameworks.

·      DO NOT CONFUSE — CBAM vs. CCTS

CBAM is the EU's own carbon tariff on imports — a foreign tax India's exporters must pay.

CCTS is India's domestic carbon market, where Indian entities earn or trade credits at home.

Today's news links the two: because CCTS proves Indian goods already carry a carbon cost, the U.K. now lets that reduce the CBAM bill on those same goods — avoiding double taxation.

·      How CCTS Works: the ETS Model

o India follows a Rate-Based Emissions Trading System (ETS).

o Total emissions are not capped; instead, each entity gets a Greenhouse Gas Emission Intensity (GEI) benchmark.

o The focus is on cutting emissions intensity, not imposing an absolute emissions limit — giving flexibility for economic growth alongside emission cuts.

o Gases initially covered: Carbon Monoxide (CO) and Perfluorocarbons (PFCs).

o Carbon Credit Certificates (CCCs) are issued to facilities that outperform their emission-intensity benchmarks, and can be traded within the ICM.

Mechanism

How It Works

Compliance Mechanism

Applies to emission-intensive "Obligated Entities," which must hit prescribed GEI targets; those that outperform earn CCCs

Offset Mechanism

Voluntary — open to Non-Obligated Entities; projects that reduce, remove, or avoid emissions can earn CCCs

o  Sectors covered initially: aluminium, cement, chlor-alkali, iron and steel, pulp and paper, refineries, petrochemicals, and textiles.

o Important exception: Thermal Power Plants have not yet moved from the PAT scheme to the CCTS Compliance Mechanism.

o Recently approved Offset Mechanism methodologies (by the Ministry of Power) cover renewable energy, green hydrogen production, industrial energy efficiency, landfill methane recovery, and mangrove afforestation/reforestation.

·      Institutional Framework

Body

Role

Ministry of Environment, Forest and Climate Change (MoEFCC)

Designates facilities covered under CCTS; notifies GHG emission targets under the Environment (Protection) Act, 1986

Ministry of Power (MoP)

Responsible for national energy policy and the national carbon market; recommends GHG emission targets for notification

Bureau of Energy Efficiency (BEE)

Nodal agency for administering and implementing CCTS

o India's national energy policy focuses on raising domestic energy production, expanding renewable capacity, and reaching net-zero emissions by 2070.

o India balances development with lower emissions through the Common but Differentiated Responsibilities and Respective Capabilities (CBDR-RC) principle, highlighted at COP27.

o Related initiatives: Mission LiFE (Lifestyle for Environment), the Green Credit Programme (GCP), and the National Steering Committee for the Indian Carbon Market (NSCICM). 

4. Steel

·      News: India's steelmaking emissions are among the highest in the world — roughly 32% higher than the global average — and account for nearly 12% of the country's total greenhouse gas emissions. Global steel production overall accounts for around 8% of global emissions.

·      How Steel Is Made — and Where the Emissions Come From

Route

How It Works

Emissions

Blast Furnace–Basic Oxygen Furnace (BF–BOF)

Iron ore is smelted in a blast furnace using coking coal, then refined in a basic oxygen furnace with pure oxygen

The most carbon-intensive route — coking coal is both a fuel AND a reducing agent, so CO₂ comes from combustion and the chemical reaction itself

Electric Arc Furnace (EAF)

Melts recycled steel scrap using electricity, bypassing ore reduction entirely

Less than half the emissions intensity of BF–BOF

Direct Reduced Iron (DRI)

Oxygen is removed from iron ore using a gas rather than coal; the resulting solid iron is then melted in an electric furnace

About 1.2 tonnes CO₂/tonne of steel on natural gas; near zero on green hydrogen

·       India's Steel Emissions Challenge

o India's steel sector has an emissions intensity about 32% higher than the global average.

o The steel industry accounts for nearly 12% of India's total greenhouse gas emissions.

o India produced around 160 million tonnes of crude steel in FY 2025–26.

o India is the second-largest steel producer in the world, after China.

o Demand growth is driven by infrastructure development, construction, and automobile manufacturing.

o India has a relatively limited stock of recyclable scrap steel compared to developed economies — this restricts large-scale expansion of the lower-emission EAF route.

·      Government Initiatives: National Mission on Green Steel

o Target: cut steelmaking emissions intensity from about 2.55–2.65 tCO₂e/tonne to 2.2 tCO₂e/tonne by 2029–30.

o Key components: a Production Linked Incentive (PLI) scheme for low-emission/green steel; renewable-energy incentives; a government procurement mandate for green steel; green-hydrogen integration; and steel scrap recycling.

o Financial support: a ₹5,000 crore decarbonisation scheme has been announced to speed up the transition.

·      Green Steel Certification

o India launched the world's first Green Steel Taxonomy on 12 December 2024.

o This framework classifies steel as "green" if emissions are below 2.2 tCO₂e/tonne.

Category

Emission Intensity

Five-Star Green Steel

Below 1.6 tCO₂e/tfs

Four-Star Green Steel

1.6 – 2.0 tCO₂e/tfs

Three-Star Green Steel

2.0 – 2.2 tCO₂e/tfs

Not Eligible for Green Rating

Above 2.2 tCO₂e/tfs

·      India's Steel Production Mix

o Current furnace mix: 43% BF–BOF, 22% Electric Arc Furnaces (EAFs), 35% Electric Induction Furnaces (EIFs).

o EIFs use electromagnetic induction to melt scrap steel or direct reduced iron, and are widely used by small and medium producers.

o The share of BF–BOF capacity is projected to rise to about 56% by 2030 due to planned expansion.

o Globally, around 70.4% of steel production still relies on the coal-based BF–BOF route; the rest is mostly EAF. 

5. Air Cooling for Data Centrezs

·      News: After sustained local protests and pressure from civil society groups, Google has said its planned 1-GW data centre in Visakhapatnam district will use air-cooling technology to cool its servers. Air-cooling needs less water — but it comes with its own trade-offs.

·      Why Data Centres Generate Heat

o A data centre contains millions of processors, each built from billions of transistors.

o As transistors process data, electrical resistance and constant charging/discharging generate heat.

o Since trillions of transistors operate at once, the total heat generated is enormous.

o A 1 GW data centre can produce nearly 1 GW of heat, which must be continuously removed to keep it running.

·      Hierarchy of a Data Centre

o Think of it this way: Transistors build up into a processor. One or more processors form a server. Multiple servers sit in a rack. Multiple racks form a cluster. Multiple clusters together make up the data centre.

·      Major Cooling Technologies

Technology

How It Works

Advantage

Limitation

Air Cooling

Fans push cool air through server racks; hot air is collected and cooled before recirculating

Low initial cost; mature, widely used; large trained-technician base; efficient in naturally cool/dry climates

Impractical alone for modern 1 GW centres — removes only ~40 kW/rack, while AI servers may generate 120–150 kW/rack; needs many fans/chillers; noisy

Direct Liquid Cooling (DLC)

Liquid is brought close to heat-generating parts; in cold-plate cooling, a metal plate carrying coolant sits directly on processors

More efficient than air; water-based liquids absorb more heat; suits high-performance/AI workloads

Higher installation cost — needs specialised piping and coolant systems

Immersion Cooling

Electronic components are immersed directly in a non-conductive liquid (single-phase or two-phase)

Highly efficient heat transfer; suits very high power-density computing

Needs specialised hardware and coolant management

Evaporative Cooling

Heat is transferred to water, which is evaporated through cooling towers or condensers

Highly energy-efficient in dry climates

Needs large quantities of water

Dry Cooling

Heat exchangers release heat directly into ambient air through large finned surfaces

Minimal water requirement

Less efficient in warm climates; needs larger infrastructure

·       Common Air-Cooling Methods

Method

What It Does

CRAC (Computer Room Air Conditioner)

Uses refrigerants to cool air

CRAH (Computer Room Air Handler)

Uses chilled water to cool air

Hot-Aisle/Cold-Aisle Containment

Separates hot and cold air streams

Free Cooling

Expels heat directly into naturally cooler outside air

Rear-Door Heat Exchanger

Chilled water absorbs heat from air exiting server racks  

·      Other Cooling Methods

o Chilled Water Systems — use a central chilled-water plant.

o Geothermal Heat Rejection — transfers heat underground through heat exchangers.

o Natural Water Cooling — uses nearby lakes or water bodies as heat sinks.

o Heat Reuse — redirects waste heat for industrial applications or desalination.