<p>You probably want to have a look at the more recent ZECMIP (zero emissions commitment) paper MacDougall et al (2020) <a href="https://doi.org/10.5194/bg-17-2987-2020" rel="nofollow noreferrer">https://doi.org/10.5194/bg-17-2987-2020</a>, along with the schematic on the right from the IPCC AR6 Technical Summary:</p>
<p><a href="https://i.sstatic.net/UIOMz.png" rel="nofollow noreferrer"><img src="https://i.sstatic.net/UIOMz.png" alt="enter image description here" /></a></p>
<p>That schematic suggests that the bulk of the warming since the pre-industrial period will come while we have net-positive emissions and that the post-net zero emissions committed warming will be some small addition on top of this.</p>
<p>To understand this we need to think about the net radiative imbalance (currently +0.6 W/m2) rather than the radiative forcing (currently +2.2 W/m2).  That imbalance is the net result of the radiative forcing and the various feedbacks, some of which are negative feedbacks (e.g., the Planck response, land and ocean carbon uptake).  The Planck response to surface temperature is about -3 W/m2/K, so, once net-zero emissions are achieved, the surface would only need to warm by a further 0.2 K to erode the 0.6 W/m2 radiative imbalance through this mechanism alone.</p>
<p>But there are other feedbacks in play.  Once net-zero emissions are reached the existing land and ocean carbon sinks will continue to take up CO2, so atmospheric CO2 will decrease and its contribution to radiative forcing and radiative imbalance will decrease.  This reduces the amount of work the Planck response has to do to achieve radiative balance.  The faster the carbon sinks work, the less additional warming will be needed to before radiative balance is achieved.</p>
<p>On the other hand, ocean heat uptake will likely weaken once net-zero emissions are reached, because the current ocean heat sink is partly driven by the ocean-atmosphere temperature gradient.  This effectively becomes a positive feedback on surface temperature change.  Going back to MacDougall et al (2020), it turns out that these feedbacks are strong and the zero emissions committed surface warming is a subtle balance between these components, giving a best estimate range of -0.3 to +0.3 K (see plots below).</p>
<p>A key thing here it that this is a measure of the atmospheric response, which doesn't have a great deal of thermal inertia.  The ocean is still out of balance and accumulating heat, and the carbon cycle is still out of balance removing CO2 from the atmosphere.  Equilibration of other components of the Earth system would take much longer, as you say, but that's not the goal of net-zero.</p>
<p><a href="https://i.sstatic.net/zvdhE.png" rel="nofollow noreferrer"><img src="https://i.sstatic.net/zvdhE.png" alt="enter image description here" /></a></p>

CC BY-SA 4.0
2022-07-18T13:25:45.280Z
2022-07-18T13:25:45.280Z
Deditos
<p>As argued in this Nature letter [1] by Matthews and Weaver, when we achieve net-zero emissions further warming will cease. The authors cite numerous models, and say that future emissions are a leading order factor in warming, due to the propensity for Earth's carbon sinks to start sucking up carbon. However as a Physicist it seems like an incorrect claim. The Earth's thermal system will remain out of equilibrium until a new equilibrium is reached, as the carbon cycle's time-scale is 10s of thousands of years, net-zero will change little in terms of a heated climate.</p>
<p>Furthermore, even looking at a single one of their own references [2], one can see that the research into the long-livedness of atmospheric carbon, and the resulting temperature anomaly is of the order of tens of thousands of years, reflecting the large inertia of the Earth's climate system, in direct contradiction to the claims of [1]!</p>
<p>So my question is, who is correct according to current research? Why was this published in a Nature journal, when its claims are misleading?</p>
<p>And finally, I would appreciate anyone could direct me to any bleeding edge research on.</p>
<p>[1] <a href="https://www.nature.com/articles/ngeo813" rel="nofollow noreferrer">https://www.nature.com/articles/ngeo813</a>
[2] <a href="https://journals.ametsoc.org/view/journals/clim/22/10/2008jcli2554.1.xml" rel="nofollow noreferrer">https://journals.ametsoc.org/view/journals/clim/22/10/2008jcli2554.1.xml</a></p>

<climate><carbon-cycle>
If radiative forcing will remain the same when 'net-zero' is achieved, why do some experts think the climate will not warm after this?
user27203
# If radiative forcing will remain the same when 'net-zero' is achieved, why do some experts think the climate will not warm after this?

(Asked by: username_0 on 2022-07-17)

As argued in this Nature letter [1] by Matthews and Weaver, when we achieve net-zero emissions further warming will cease. The authors cite numerous models, and say that future emissions are a leading order factor in warming, due to the propensity for Earth's carbon sinks to start sucking up carbon. However as a Physicist it seems like an incorrect claim. The Earth's thermal system will remain out of equilibrium until a new equilibrium is reached, as the carbon cycle's time-scale is 10s of thousands of years, net-zero will change little in terms of a heated climate.

Furthermore, even looking at a single one of their own references [2], one can see that the research into the long-livedness of atmospheric carbon, and the resulting temperature anomaly is of the order of tens of thousands of years, reflecting the large inertia of the Earth's climate system, in direct contradiction to the claims of [1]!

So my question is, who is correct according to current research? Why was this published in a Nature journal, when its claims are misleading?

And finally, I would appreciate anyone could direct me to any bleeding edge research on.

[1] <https://www.nature.com/articles/ngeo813>
[2] <https://journals.ametsoc.org/view/journals/clim/22/10/2008jcli2554.1.xml>

**Tags:** climate, carbon-cycle


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## 1 answers

### Answer by username_1 on 2022-07-18. Score: 1

You probably want to have a look at the more recent ZECMIP (zero emissions commitment) paper MacDougall et al (2020) <https://doi.org/10.5194/bg-17-2987-2020>, along with the schematic on the right from the IPCC AR6 Technical Summary:

[![enter image description here](https://i.sstatic.net/UIOMz.png)](https://i.sstatic.net/UIOMz.png)

That schematic suggests that the bulk of the warming since the pre-industrial period will come while we have net-positive emissions and that the post-net zero emissions committed warming will be some small addition on top of this.

To understand this we need to think about the net radiative imbalance (currently +0.6 W/m2) rather than the radiative forcing (currently +2.2 W/m2). That imbalance is the net result of the radiative forcing and the various feedbacks, some of which are negative feedbacks (e.g., the Planck response, land and ocean carbon uptake). The Planck response to surface temperature is about -3 W/m2/K, so, once net-zero emissions are achieved, the surface would only need to warm by a further 0.2 K to erode the 0.6 W/m2 radiative imbalance through this mechanism alone.

But there are other feedbacks in play. Once net-zero emissions are reached the existing land and ocean carbon sinks will continue to take up CO2, so atmospheric CO2 will decrease and its contribution to radiative forcing and radiative imbalance will decrease. This reduces the amount of work the Planck response has to do to achieve radiative balance. The faster the carbon sinks work, the less additional warming will be needed to before radiative balance is achieved.

On the other hand, ocean heat uptake will likely weaken once net-zero emissions are reached, because the current ocean heat sink is partly driven by the ocean-atmosphere temperature gradient. This effectively becomes a positive feedback on surface temperature change. Going back to MacDougall et al (2020), it turns out that these feedbacks are strong and the zero emissions committed surface warming is a subtle balance between these components, giving a best estimate range of -0.3 to +0.3 K (see plots below).

A key thing here it that this is a measure of the atmospheric response, which doesn't have a great deal of thermal inertia. The ocean is still out of balance and accumulating heat, and the carbon cycle is still out of balance removing CO2 from the atmosphere. Equilibration of other components of the Earth system would take much longer, as you say, but that's not the goal of net-zero.

[![enter image description here](https://i.sstatic.net/zvdhE.png)](https://i.sstatic.net/zvdhE.png)


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