[geo] Re: [prag] Important paper out concluding that SRM would need to be deployed in excess of 100 years to stabilize temp increases at 1.5 C.

[Ron Baiman]

Thanks for sharing, Herb!  I haven't read the paper, but from a skim, it
looks like maybe some sanity is emerging among climate modelers on this
issue. Enough with "shaving the peak", it seems to me that we're going to
need cooling (including probably OTEC type generating energy from and
cooling ocean heat) for a very long time, even with robust GHG emissions
and drawdown, and nature regeneration programs!
Ron

On Wed, Mar 29, 2023 at 2:37 PM H simmens  wrote:

> “We generate a large dataset of 355 emission scenarios in which SRM is
> deployed to keep warming levels at 1.5 ∘C global mean temperature.
> Probabilistic climate projections from this ensemble result in a large
> range of plausible future warming and cooling rates that lead to various
> SRM deployment timescales. In all pathways consistent with extrapolated
> current ambition, SRM deployment would exceed 100 years even under the most
> optimistic assumptions regarding climate response.“
>
> [image: esd-14-367-2023-avatar-web.png]
>
> The deployment length of solar radiation modification: an interplay of
> mitigation, net-negative emissions and climate uncertainty
> 
> esd.copernicus.org 
> 
>
>
> Herb Simmens
> Author A Climate Vocabulary of the Future
> @herbsimmens
>
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> 
> .
>

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[geo] Important paper out concluding that SRM would need to be deployed in excess of 100 years to stabilize temp increases at 1.5 C.

[H simmens]

“We generate a large dataset of 355 emission scenarios in which SRM is deployed to keep warming levels at 1.5 ∘C global mean temperature. Probabilistic climate projections from this ensemble result in a large range of plausible future warming and cooling rates that lead to various SRM deployment timescales. In all pathways consistent with extrapolated current ambition, SRM deployment would exceed 100 years even under the most optimistic assumptions regarding climate response.“The deployment length of solar radiation modification: an interplay of mitigation, net-negative emissions and climate uncertaintyesd.copernicus.orgHerb SimmensAuthor A Climate Vocabulary of the Future@herbsimmens



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[geo] New reflection physics

[Ronal Larson]

Ye and list

Probably well known to you already, but is a paper being given this 
week - and quite surprising new “paint” capability.

https://onlinelibrary.wiley.com/doi/full/10.1002/advs.202104758

Ron

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[geo] Re: low cloud over sub-tropical oceans produces a heating effect ?

[Michael Diamond]

Hi Colin,

Great question! We are extremely certain that low-altitude subtropical 
clouds cool the climate by reflecting sunlight but not having a strong 
impact on the amount of heat escaping to space. Unfortunately for us, this 
type of cloud is projected to become less common as sea surface 
temperatures warm — the loss of these clouds leads to additional warming 
(positive feedback). Marine cloud brightening, on the other hand, is a 
proposal to use sea salt aerosol to make these clouds more reflective when 
they do occur, and potentially make them occur more frequently/over larger 
areas. This would cool the climate by increasing the amount and/or 
brightness of these clouds (negative forcing).

In short: increasing low-altitude clouds leads to cooling (MCB) and 
decreasing them leads to warming (positive feedback to global warming).

Cheers,
Michael

On Tuesday, March 28, 2023 at 11:44:25 AM UTC-4 Colin Forrest wrote:

> From AR6 WG 1 full report ch 7 page 926..
>
> An assessment of the low-altitude cloud feedback over the subtropical
> oceans, which was previously the major source of uncertainty in the
> net cloud feedback, is improved owing to a combined use of climate
> model simulations, satellite observations, and explicit simulations
> of clouds, altogether leading to strong evidence that this type of
> cloud amplifies global warming. 
>
> How does this square will the modelling of MCB which predicts a cooling 
> effect from increasing this type of cloud cover ?
>
> Best Wishes,  Colin Forrest
>
> PS the reference for my previous post on SSPs and climate forcing was 
> wrong. It's om page 926, not 928
>

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[geo] The deployment length of solar radiation modification: an interplay of mitigation, net-negative emissions and climate uncertainty

[Geoengineering News]

https://esd.copernicus.org/articles/14/367/2023/

*Authors*
Susanne Baur , Alexander Nauels, Zebedee
Nicholls, Benjamin
M. Sanderson, and Carl-Friedrich Schleussner

*28 March 2023*

https://doi.org/10.5194/esd-14-367-2023

*Abstract*

A growing body of literature investigates the effects of solar radiation
modification (SRM) on global and regional climates. Previous studies have
focused on the potentials and the side effects of SRM, with little
attention being given to possible deployment timescales and the levels of
carbon dioxide removal required for a phase out. Here, *we investigate the
deployment timescales of SRM and how they are affected by different levels
of mitigation, net-negative emissions (NNEs) and climate uncertainty*. We
generate a large dataset of 355 emission scenarios in which SRM is deployed
to keep warming levels at 1.5 ∘C global mean temperature. Probabilistic
climate projections from this ensemble result in a large range of plausible
future warming and cooling rates that lead to various SRM deployment
timescales. In all pathways consistent with extrapolated current ambition,
SRM deployment would exceed 100 years even under the most optimistic
assumptions regarding climate response. As soon as the temperature
threshold is exceeded, neither mitigation nor NNEs or climate sensitivity
alone can guarantee short deployment timescales. Since the evolution of
mitigation under SRM, the availability of carbon removal technologies and
the effects of climate reversibility will be mostly unknown at its
initialisation time, it is impossible to predict how temporary SRM
deployment would be. Any deployment of SRM therefore comes with the risk of
multi-century legacies of deployment, implying multi-generational
commitments of costs, risks and negative side effects of SRM and NNEs
combined.


[image: https://esd.copernicus.org/articles/14/367/2023/esd-14-367-2023-f02]


Figure 2Calculating required SRM. (a) Calculating warming to 2035 using an
NDC-like pathway (in this case, SSP2-4.5). (b) Determining a 1.5 ∘C
temperature trajectory for ensemble members that have not already overshot
1.5 ∘C by 2035. (c) Determining a 1.5 ∘C temperature trajectory for
ensemble members that have already overshot 1.5 ∘C by 2035. (d, e) Calculating
required solar radiation modification (SRM) for each scenario–ensemble
member combination, whether it overshoots 1.5 ∘C (e) or remains below 1.5 ∘C
at all times (d).

[image: https://esd.copernicus.org/articles/14/367/2023/esd-14-367-2023-f03]


Figure 3SRM deployment length for all scenarios and all ensemble members.
One bar spans a range of 50 years. Marked in black are pathways consistent
with current 2100 warming projections for NDCs (2.4 ∘C; CAT, 2022).

[image: https://esd.copernicus.org/articles/14/367/2023/esd-14-367-2023-f04]


Figure 4Interdependencies of mitigation, negative emissions and climate
uncertainty with SRM deployment length. (a) Relationship between cumulative
CO2 emissions from 2030 until net-zero CO2 and SRM deployment length.
Colour coding is according to annual average NNEs in Gt CO2 yr−1. (b)
Relationship
between cumulative CO2 emissions from net-zero CO2 until the reattainment
of 1.5 ∘C and SRM deployment length. Colour coding is according to annual
average NNEs in Gt CO2 yr−1. (c) Relationship between eTCRE ratio and SRM
deployment length. Colour coding is according to cumulative CO2 emissions
from the time of peak warming until the reattainment of 1.5 ∘C. Plot shows
data points that fall in the 1st–99th percentile range.

[image: https://esd.copernicus.org/articles/14/367/2023/esd-14-367-2023-f05]


Figure 5Relationship between cumulative CO2 emissions from net-zero CO2 until
the reattainment of 1.5 ∘C and SRM deployment length. (a) Colour coding is
according to the maximum deployed annual NNEs. (b) Colour coding is
according to the entire ratio. See the clean figure without descriptions in
the Supplement (Fig. S03)

*Source: Europeans Geosciences Union*

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Re: [geo] positive forcing in all SSPs but GMST falls ?

[Govindasamy Bala]

It is all "relative". The 1.9 Wm-2 is relative to the pre-industrial times
and hence there is a warming in 2100 relative to the preindustrial time.

However, in the SSP1-1.9 scenario, the forcing and warming peak somewhere
around 2050, and then the forcing (and hence warming) decline slightly
because of net negative emissions after 2050. Yes, there is slight cooling
in 2100 relative to 2050..

Cheers,
Bala

On Tue, Mar 28, 2023 at 9:14 PM Colin Forrest 
wrote:

> Hi,  could someone perhaps explain why the SSP 1.9 for example has a
> climate forcing of 1.9 W.m-2 at 2100, yet is modelled to produce a
> reduction in GMST ?
>
> Considering that current net anthropogenic forcing is 2.72 W.m-2 (AR6, WG
> 1, full report, ch 7 page 926 )
>
> Thanks,  Colin Forrest
>
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> 
> .
>


-- 
With Best Wishes,

---
G. Bala
Professor
Center for Atmospheric and Oceanic Sciences
Indian Institute of Science
Bangalore - 560 012
India

Tel: +91 80 2293 3428; +91 80 2293 2505
Fax: +91 80 2360 0865; +91 80 2293 3425
Email: gb...@iisc.ac.in; bala@gmail.com
Google Scholar 
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