The scientific view is that the increase in global temperature should not exceed 20C above pre-industrial level. If the global temperature increases beyond 30C above the pre-industrial level, what can be its possible impact/impacts on the world? 1 Terrestrial biosphere tends toward a net carbon source. 2.Widespread coral mortality will occur. 3.All the global wetlands will permanently disappear. 4.Cultivation of cereals will not be possible anywhere in the world. Select the correct answer using the code given below:
Contents17
- A1 only
- B1 and 2 only
- C2, 3 and 4 only
- D1, 2, 3 and 4
Show answer
Answer: (B) 1 and 2 only
At 3°C+ warming above pre-industrial levels:
Statement 1 — CORRECT: The terrestrial biosphere (forests, soils) would shift from being a net carbon SINK (absorbing CO2) to a net carbon SOURCE (releasing CO2) — due to increased wildfires, droughts killing forests, and accelerated decomposition of soil organic matter.
This creates a dangerous positive feedback loop.
Statement 2 — CORRECT: Widespread coral mortality would occur.
Corals are extremely sensitive to temperature — even 1-2°C above normal causes coral bleaching.
At 3°C+ global warming, most tropical coral reefs would die.
Statement 3 — WRONG: 'ALL global wetlands will permanently disappear' is too extreme.
Some wetlands would be affected, but total permanent disappearance of ALL wetlands is not scientifically supported.
Statement 4 — WRONG: 'Cultivation of cereals will not be possible ANYWHERE' is also too extreme.
Some regions would lose agricultural productivity, but others (like parts of Canada, Russia) might gain it.
The 2°C and 3°C warming thresholds are critical benchmarks in international climate agreements like the Paris Accord, with 2°C as the danger line and 1.5°C as the preferred target.
UPSC is testing whether students can distinguish between scientifically supported severe impacts versus exaggerated absolute claims using words like 'all' and 'nowhere'.
Terrestrial Carbon Cycle Feedback
Environment Terrestrial biosphere net carbon source carbon sink
Terrestrial Carbon Cycle: From Sink to Source
Terrestrial biosphere normally acts as carbon sink — forests and soils absorb CO2
At 3°C+ warming, terrestrial biosphere becomes net carbon source
Caused by wildfires, drought-killed forests, accelerated soil decomposition
Creates dangerous positive feedback loop — more warming releases more carbon
Normal vs Warming Scenario
Under normal conditions, the terrestrial biosphere (forests, grasslands, soils) acts as a carbon sink — it absorbs more CO2 than it releases. This happens through photosynthesis and carbon storage in plant biomass and soil organic matter.
Carbon Sink to Source Transformation
%%{init: {"flowchart": {"wrappingWidth": 460}}}%%
flowchart TD
s1["`**Global warming exceeds 3°C**
Temperature stress on vegetation increases`"]
s2["`**Forest mortality increases**
Droughts, heat stress, pest outbreaks kill trees`"]
s3["`**Wildfire frequency rises**
Dry conditions lead to more frequent, intense fires`"]
s4["`**Soil decomposition accelerates**
Higher temperatures speed up microbial breakdown of soil carbon`"]
s5["`**Net carbon release**
Carbon released exceeds carbon absorbed — biosphere becomes source`"]
s1 --> s2
s2 --> s3
s3 --> s4
s4 --> s5Why This Creates Dangerous Feedback
Positive feedback loop: More warming → more carbon release → even more warming
Soil carbon: Contains 3x more carbon than atmosphere — its release accelerates climate change
Amazon tipping point: Could shift from rainforest to savanna, releasing massive stored carbon
Permafrost thawing: Arctic soils release methane and CO2 when they warm
Sink vs Source: Remember direction — sink absorbs carbon, source releases carbon
Statement 1 was correct — terrestrial biosphere becoming carbon source is scientifically established at 3°C+ warming
Don't confuse with ocean carbon cycle — oceans also absorb CO2 but through different mechanisms
Coral Bleaching & Temperature Thresholds
Environment coral mortality coral bleaching
Coral Temperature Sensitivity & Mass Mortality
Corals are extremely temperature-sensitive — even 1-2°C above normal causes bleaching
At 3°C+ global warming, widespread coral mortality occurs
Coral bleaching = corals expel symbiotic algae due to heat stress
Great Barrier Reef has already experienced multiple mass bleaching events
Coral-Algae Symbiosis
Corals have a symbiotic relationship with zooxanthellae algae that live inside coral tissues. These algae provide corals with nutrients through photosynthesis. When water temperature rises beyond coral tolerance, this relationship breaks down.
Temperature Impact Levels
Temperature Rise | Impact on Corals | Recovery Potential |
|---|---|---|
1°C above normal | Mild bleaching begins | Good recovery if temporary |
1-2°C sustained | Mass bleaching events | Partial recovery possible |
3°C+ global warming | Widespread coral mortality | Most tropical reefs die |
Repeated bleaching | Coral death, reef collapse | Ecosystem breakdown |
Why Corals Are Climate Indicators
Narrow temperature tolerance: Tropical corals adapted to stable 25-29°C water temperatures
Ocean heat absorption: Oceans absorb 90% of excess heat from global warming
Ecosystem services: Coral reefs support 25% of marine species, protect coastlines
Economic impact: Reefs support fishing, tourism worth billions globally
Global Coral Reef Locations
Source: ScienceDirect.com — Coral Reef - an overview | ScienceDirect Topics · www.sciencedirect.com
Statement 2 was correct — widespread coral mortality at 3°C+ is scientifically established
Don't confuse coral bleaching (stress response) with coral death (permanent damage)
Remember corals are sensitive to small temperature changes — not just extreme heat
Climate Change Extreme Claims
Environment All the global wetlands Cultivation of cereals will not be possible anywhere
Identifying Extreme Climate Claims in UPSC
UPSC often includes extreme absolute claims in environment questions
Words like 'all', 'everywhere', 'nowhere', 'permanently' are usually wrong
Climate impacts are regionally variable — some areas gain while others lose
Statements 3 & 4 were wrong due to extreme language
Extreme vs Realistic Climate Statements
Extreme Claim (Usually Wrong) | Realistic Version | Why Extreme is Wrong |
|---|---|---|
ALL wetlands disappear permanently | Many wetlands severely affected | Some wetlands adapt, migrate, or survive |
Cereals impossible ANYWHERE | Cereal production shifts geographically | Cold regions like Canada/Russia may gain productivity |
ALL species extinct | Mass species extinctions occur | Some species adapt or survive in refugia |
NO agriculture possible | Agricultural zones shift poleward | Technology and adaptation enable some farming |
Why Climate Impacts Aren't Uniform
Winners and losers: Climate change creates regional winners (northern latitudes) and losers (tropics/islands)
Adaptation capacity: Human societies adapt through technology, migration, crop varieties
Ecosystem resilience: Some ecosystems are more resilient than others
Thresholds vary: Different species and systems have different temperature tolerance limits
Question Context
This question tested understanding of 3°C+ warming impacts. Statement 3 (all wetlands permanently disappear) and Statement 4 (no cereal cultivation anywhere) were deliberately extreme to test if students could identify unrealistic absolute claims versus scientifically supported impacts.
Absolute words are red flags: all, none, everywhere, nowhere, always, never, permanently
Regional variation: Climate impacts vary by geography — avoid universal claims
Human adaptation: Don't underestimate technological and behavioral adaptation
Statements 3 & 4 were traps using extreme language while Statements 1 & 2 were scientifically accurate
Paris Agreement Temperature Targets
Environment 2°C above pre-industrial level 3°C above pre-industrial level
Global Temperature Targets & Climate Policy
Paris Agreement aims to keep warming well below 2°C above pre-industrial levels
Aspirational target is 1.5°C to avoid worst impacts
Pre-industrial baseline refers to 1850-1900 average temperatures
We've already warmed approximately 1.1°C above pre-industrial levels
Why These Targets Matter
The 2°C target represents the scientific consensus on the maximum 'safe' level of warming to avoid catastrophic climate impacts. Beyond 3°C warming, multiple climate systems could reach dangerous tipping points with irreversible consequences.
Temperature Targets & Impacts
Warming Level | Status | Key Impacts | Policy Goal |
|---|---|---|---|
1.5°C | Paris aspirational target | Severe but manageable impacts | Rapid emissions cuts needed |
2°C | Paris 'safe' limit | Dangerous but avoidable impacts | Strong mitigation required |
3°C+ | Current trajectory risk | Catastrophic impacts begin | Must be avoided at all costs |
4°C+ | Business as usual | Civilization-threatening impacts | Requires transformation now |
India's Climate Commitments
Net zero by 2070: India committed to achieve carbon neutrality
33-35% emissions intensity reduction by 2030 from 2005 levels
50% renewable energy capacity by 2030
CBDR principle: Common But Differentiated Responsibilities — developed countries lead
Pre-industrial baseline is 1850-1900, not some arbitrary historical period
2°C is the limit, 1.5°C is the aspiration — don't confuse these targets
Current warming is 1.1°C — we're already more than halfway to the 2°C limit
Question mentioned 2°C as context but tested impacts of 3°C+ warming