AMOC collapse adds only a few ppm of CO2
Forcing CESM2’s AMOC off with North Atlantic freshwater raises 2100 atmospheric CO2 by only 2.6–4.2 ppm under low and high emissions.
Source
Response of atmospheric pCO 2 to a strong AMOC weakening under low and high emission scenarios
Study at a glance
- Design
- Computational / modelling — CESM2 SSP runs with and without North Atlantic freshwater hosing to collapse AMOC
- N
- Paired control/hosing simulations under SSP1-2.6 and SSP5-8.5 (2015–2100)
- Population
- CESM2 global carbon cycle under AMOC collapse scenarios
- Outcome
- Small atmospheric CO2 increase (2.6–4.2 ppm by 2100) after strong AMOC weakening
Structured fields used in claim comparison tables when every cited study has a complete layer.
What they did
Authors ran CESM2 from 2015–2100 under SSP1-2.6 and SSP5-8.5, with control and hosing cases that added 0.5 Sv of freshwater at 50–70°N to collapse the AMOC, then diagnosed ocean and land carbon responses.
What they found
Hosing weakens the AMOC from 17 Sv to 6 Sv by 2045. Extra atmospheric CO2 in 2100 is 2.6 ppm (SSP1-2.6) and 4.2 ppm (SSP5-8.5). Feedbacks are 0.44 and 1.3 ppm Sv−1. Low-emission extra CO2 comes from land and ocean; high-emission extra CO2 is ocean-only. Compensating regional carbon changes keep the global signal small.
The limits
What it doesn't show
Hosing is an imposed freshwater flux, not a freely tipping AMOC. There is no dynamic vegetation, and the small multi-decadal CO2 response may differ on millennial timescales or in other ESMs.
Key terms
- AMOC
- Atlantic Meridional Overturning Circulation transporting heat and carbon northward.
- Hosing
- Adding freshwater to the North Atlantic to weaken or collapse the AMOC in a model.
- Bipolar seesaw
- Northern cooling and southern warming when AMOC heat transport shuts down.
- SSP1-2.6 / SSP5-8.5
- Low versus high 21st-century emission pathways.
- Sv
- Sverdrup: 10^6 m³ s−1, used for ocean volume transport.
Flashcards
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Quiz yourself
Hosing raises 2100 atmospheric CO2 by about:
Common questions
Does AMOC collapse dump a lot of extra CO2?
In CESM2 through 2100, only a few ppm—small versus the emission scenario itself.
Why is the signal small?
Land and ocean regional sources and sinks largely cancel.
Is the high-emission feedback relatively stronger?
Absolute ppm is larger, but relative to high background CO2 it is weaker.
What climate fingerprints appear?
Southward ITCZ shift and the bipolar temperature seesaw.
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