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Topic 230 · Environment, Climate & Biodiversity

AMOC slowdown and India's monsoon

10 MCQs · tap an option to check it · All answers

Revise the 12 points first Book 1 RATNA

Core Trigger: A Bordeaux/CNRS study in Science Advances, published 15 April 2026, projected AMOC weakening of 51 ± 8% by 2100.
Study Title: 'Observational constraints project a ~50% AMOC weakening by the end of this century'; four authors.
Lead Author: Valentin Portmann of the EPOC laboratory, University of Bordeaux/CNRS, France.
Unit: AMOC strength is measured in sverdrups; one equals a million cubic metres of water per second.
Data / Report: The 51% estimate spans about 43–59%, 60% above the model average; CMIP6 models give 32 ± 37% under SSP2-4.5.
Stakeholders: IPCC AR6 projects AMOC decline this century; Nimmakanti Mahendra led a separate AGU Advances monsoon study.
India Link: The study does not model India; the monsoon link rests on assessments that AMOC collapse would cut summer monsoon rainfall.
Monitoring Site: The RAPID array at 26.5°N, between the Bahamas and Canary Islands, measures the AMOC.
Measured Since: RAPID has recorded the AMOC since 2004; it averaged 15–17 Sv in 2011–2020, down from 18–19 Sv in 2004–08.
Mechanism: Meltwater and heavier rain freshen the North Atlantic, so water sinks less easily and the AMOC slows.
Scenario: SSP2-4.5 is the intermediate IPCC emissions scenario used for CMIP6 projections.
Definition: Thermohaline circulation is driven by temperature and salt density; a tipping point is a threshold beyond which change may not reverse.

Question 1 of 10

A Bordeaux/CNRS study published on 15 April 2026 projected AMOC weakening of how much by 2100?

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Answer: (A) 51 ± 8%

Core Trigger: A Bordeaux/CNRS study in Science Advances, published 15 April 2026, projected AMOC weakening of 51 ± 8% by 2100.From Book 1 RATNA, topic 230, point 1

Question 2 of 10

How many authors does the study 'Observational constraints project a ~50% AMOC weakening by the end of this century' have?

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Answer: (B) Four

Study Title: 'Observational constraints project a ~50% AMOC weakening by the end of this century'; four authors.From Book 1 RATNA, topic 230, point 2

Question 3 of 10

Who is the lead author of the study?

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Answer: (A) Valentin Portmann

Lead Author: Valentin Portmann of the EPOC laboratory, University of Bordeaux/CNRS, France.From Book 1 RATNA, topic 230, point 3

Question 4 of 10

One sverdrup, the unit of AMOC strength, equals how much water per second?

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Answer: (C) A million cubic metres

Unit: AMOC strength is measured in sverdrups; one equals a million cubic metres of water per second.From Book 1 RATNA, topic 230, point 4

Question 5 of 10

Under SSP2-4.5, CMIP6 models give what AMOC weakening?

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Answer: (D) 32 ± 37%

Data / Report: The 51% estimate spans about 43–59%, 60% above the model average; CMIP6 models give 32 ± 37% under SSP2-4.5.From Book 1 RATNA, topic 230, point 5

Question 6 of 10

Consider: 1) IPCC AR6 projects that AMOC will strengthen this century. 2) Nimmakanti Mahendra led a separate AGU Advances monsoon study. Which is/are correct?

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Answer: (B) Only 2

Stakeholders: IPCC AR6 projects AMOC decline this century; Nimmakanti Mahendra led a separate AGU Advances monsoon study.From Book 1 RATNA, topic 230, point 6

Question 7 of 10

At which latitude does the RAPID array measure the AMOC?

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Answer: (A) 26.5°N

Monitoring Site: The RAPID array at 26.5°N, between the Bahamas and Canary Islands, measures the AMOC.From Book 1 RATNA, topic 230, point 8

Question 8 of 10

Since which year has the RAPID array recorded the AMOC?

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Answer: (D) 2004

Measured Since: RAPID has recorded the AMOC since 2004; it averaged 15–17 Sv in 2011–2020, down from 18–19 Sv in 2004–08.From Book 1 RATNA, topic 230, point 9

Question 9 of 10

Meltwater and heavier rain freshen the North Atlantic, so surface water does what?

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Answer: (B) Sinks less easily

Mechanism: Meltwater and heavier rain freshen the North Atlantic, so water sinks less easily and the AMOC slows.From Book 1 RATNA, topic 230, point 10

Question 10 of 10

Consider: 1) SSP2-4.5 is the intermediate IPCC emissions scenario used for CMIP6 projections. 2) A tipping point is a threshold beyond which change may not reverse. Which is/are correct?

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Answer: (C) Both 1 and 2

Scenario: SSP2-4.5 is the intermediate IPCC emissions scenario used for CMIP6 projections.From Book 1 RATNA, topic 230, point 11

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