<p><strong>Question</strong>: <br />
Is there scientific consensus on the existence of the <a href="https://en.wikipedia.org/wiki/Iris_hypothesis" rel="nofollow noreferrer">Iris Effect</a> and whether it is a positive or negative feedback mechanism? If so, can you refer to a recent publication?</p>
<p><strong>Background</strong>: <br />
In 2001 Lindzen et. al. published this: <a href="https://journals.ametsoc.org/view/journals/bams/82/3/1520-0477_2001_082_0417_dtehaa_2_3_co_2.xml?tab_body=fulltext-display" rel="nofollow noreferrer">Does the Earth Have an Adaptive Infrared Iris?</a>
They propose that current climate models (back in 2001) may underestimate the influence of a negative cloud feedback which today is called the iris effect (negative feedback: feedback that reduces an initial warming).</p>
<p>In brief, the iris effect is proposed to work as follows: A global warming will lead to an enhanced tropical circulation and thus lead to more subsiding air in the subtropics. The subsiding air will lead to fewer (cirrus) clouds and thus, allows outgoing long wave radiation to evade to space. Therefore, temperatures will decrease.</p>
<p><strong>Own findings</strong>: <br />
I did a little research myself which leads me to think that there is no consensus whether the feedback is positive or negative but there are many studies that at least hint the existence of the iris effect. For example I found this: &quot;The decrease of anvil coverage with warming can be associated with both an increase in the outgoing long-wave radiation and a decrease in planetary albedo.&quot; - <a href="https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2020GL089059" rel="nofollow noreferrer">Saint-Lu et. al., 2020</a>,<br />
and this: <a href="https://www.nature.com/articles/ngeo2414" rel="nofollow noreferrer">Mauritsen, Stevens, 2015</a>.<br />
My hope is, however, that there is someone with more detailed knowledge who can help me. Sorry in advance if this question is too broad and &quot;unspecific&quot;.</p>
<p>Please keep in mind that my question addresses the iris effect only. I'm aware that the effect of clouds on radiation is a highly active are of research. See e.g. <a href="https://www.ipcc.ch/site/assets/uploads/2018/02/WG1AR5_Chapter07_FINAL-1.pdf" rel="nofollow noreferrer">IPCC on clouds and aerosols</a>.</p>

CC BY-SA 4.0
2020-12-10T02:02:55.713Z
So far any such effect has been too small to be the self limiting brake on global warming proponents expect.
Ken Fabian
<climate-change><climate><clouds>
Is there scientific consensus on the existence of the iris effect
Joscha Fregin
# Is there scientific consensus on the existence of the iris effect

(Asked by: username_0 on 2020-12-07)

**Question**:   
Is there scientific consensus on the existence of the [Iris Effect](https://en.wikipedia.org/wiki/Iris_hypothesis) and whether it is a positive or negative feedback mechanism? If so, can you refer to a recent publication?

**Background**:   
In 2001 Lindzen et. al. published this: [Does the Earth Have an Adaptive Infrared Iris?](https://journals.ametsoc.org/view/journals/bams/82/3/1520-0477_2001_082_0417_dtehaa_2_3_co_2.xml?tab_body=fulltext-display)
They propose that current climate models (back in 2001) may underestimate the influence of a negative cloud feedback which today is called the iris effect (negative feedback: feedback that reduces an initial warming).

In brief, the iris effect is proposed to work as follows: A global warming will lead to an enhanced tropical circulation and thus lead to more subsiding air in the subtropics. The subsiding air will lead to fewer (cirrus) clouds and thus, allows outgoing long wave radiation to evade to space. Therefore, temperatures will decrease.

**Own findings**:   
I did a little research myself which leads me to think that there is no consensus whether the feedback is positive or negative but there are many studies that at least hint the existence of the iris effect. For example I found this: "The decrease of anvil coverage with warming can be associated with both an increase in the outgoing long-wave radiation and a decrease in planetary albedo." - [Saint-Lu et. al., 2020](https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2020GL089059),  
and this: [Mauritsen, Stevens, 2015](https://www.nature.com/articles/ngeo2414).  
My hope is, however, that there is someone with more detailed knowledge who can help me. Sorry in advance if this question is too broad and "unspecific".

Please keep in mind that my question addresses the iris effect only. I'm aware that the effect of clouds on radiation is a highly active are of research. See e.g. [IPCC on clouds and aerosols](https://www.ipcc.ch/site/assets/uploads/2018/02/WG1AR5_Chapter07_FINAL-1.pdf).

**Tags:** climate-change, climate, clouds

> **Comments:**
> **username_1**: So far any such effect has been too small to be the self limiting brake on global warming proponents expect.  

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## 0 answers

