New paper proposes that aerosol radiative forcing is less negative and more certain than is commonly believed.

[Hambone]

http://journals.ametsoc.org/doi/abs/10.1175/JCLI-D-14-00656.1

 

http://dailycaller.com/2015/03/31/scientists-say-new-study-is-a-death-blow-to-global-warming-hysteria/

 

 

"A new study out of Germany casts further doubt on the so-called global warming “consensus” by suggesting the atmosphere may be less sensitive to increases in carbon dioxide emissions than most scientists think.

A study by scientists at Germany’s Max Planck Institute for Meteorology found that man-made aerosols had a much smaller cooling effect on the atmosphere during the 20th Century than was previously thought. Why is this big news? It means increases in carbon dioxide emissions likely cause less warming than most climate models suggest.

What do aerosols have to do with anything? Well, aerosols are created from human activities like burning coal, driving cars or from fires. There are also natural aerosols like clouds and fog. Aerosols tend to reflect solar energy back into space, giving them a cooling effect that somewhat offsets warming from increased CO2 emissions.

The Max Planck study suggests “that aerosol radiative forcing is less negative and more certain than is commonly believed.” In layman’s terms, aerosols are offsetting less global warming than was previously thought. And if aerosols aren’t causing as much cooling, it must mean carbon dioxide must be causing less warming than climate models predict."

 

[A-L-E-K]

 

 

 And if aerosols aren’t causing as much cooling, it must mean carbon dioxide must be causing less warming than climate models predict

 

lol

[AvantHiatus]

Then the burden of proof falls on Ocean Heat Uptake, ECS cannot really go much lower (it was already pretty low key) and it would be unprudent to pass a judgement upon ECS based on such a short timescale.

 

There is also the possibility of steady climate warming being impossible across the board, and a perfect storm of factors such as ENSO, Solar Min, and OHC redistribution creating the illusion of a diminished forcing. We are likely to see wide stair-step behavior in the temperature trend.

 

In hindsight, the conclusions of the study are too narrow and not considerate enough about using the correct timescales and accounting for all possible climate variables in the system.

 

Using a pre-1950 timescale is kind of bizarre. It is believed that CO2 forcing stacks on itself through the stratospheric water vapor feedback. Even if the aerosol forcing is weak, 300 PPM Co2 behaves differently than 400 PPM Co2 on a per molecule basis, and besides that, you are coming off a ocean inertia that is more similar to the holocene, delaying ECS even more.

 

I conclude that ECS is about 3.0C per doubling on century timescales.

[ORH_wxman]

Then the burden of proof falls on Ocean Heat Uptake, ECS cannot really go much lower (it was already pretty low key) and it would be unprudent to pass a judgement upon ECS based on such a short timescale.

There is also the possibility of steady climate warming being impossible across the board, and a perfect storm of factors such as ENSO, Solar Min, and OHC redistribution creating the illusion of a diminished forcing. We are likely to see wide stair-step behavior in the temperature trend.

In hindsight, the conclusions of the study are too narrow and not considerate enough about using the correct timescales and accounting for all possible climate variables in the system.

The study is only talking about aerosols. It's not estimating ECS or anything else. I already linked this study in the global temp thread.

However, lower aerosol forcing would imply a lower ECS.

[AvantHiatus]

The study is only talking about aerosols. It's not estimating ECS or anything else. I already linked this study in the global temp thread.

However, lower aerosol forcing would imply a lower ECS.

Perhaps this is all more relevant to TCS dynamics.

[Hambone]

So what must be adjusted in the models if this study proves true?

[ORH_wxman]

So what must be adjusted in the models if this study proves true?

 

 

Aerosol forcing would have to be adjusted downward.

[The_Global_Warmer]

Can't they estimate it with remote sensing like they do with methane and Co2

[AvantHiatus]

Aerosol forcing would have to be adjusted downward.

Wouldn't that boost temperatures, without fixing other regions of the models? How does one dispute and change something like CO2 forcing when it is defined by a simple mathematical equation?

 

 

Radiative forcing can be used to estimate a subsequent change in equilibrium surface temperature (ΔT_s) arising from that radiative forcing via the equation:

where λ is the climate sensitivity, usually with units in K/(W/m²), and ΔF is the radiative forcing.^[4] A typical value of λ is 0.8 K/(W/m²), which gives a warming of 3K for doubling of CO₂.

[Msalgado]

Methane and CO2 absorb and emit at very specific wavelengths at are well mixed.  Aerosols have a wide variety of sizes and shapes that in turn affect their scattering, absorption and transmission profiles.  In addition, Aersols are nowhere near well mixed in the atmosphere.  Those are huge hurdles to quantifying their impact based on observations.

 

This is just their direct impact.  The larger uncertainty is their impact as CCN and in turn the changes they impart on clouds.  Solving the radiative properties of the atmosphere is incredibly complex.  

[Msalgado]

Wouldn't that boost temperatures, without fixing other regions of the models? How does one dispute and change something like CO2 forcing when it is defined by a simple mathematical equation?

 

CO2 forcing is far from the only factor regarding climate sensitivity.  That equation is far from simple.  Climate sensitivity has a ton of components having to do with all the feedbacks and forcings.

[ORH_wxman]

Wouldn't that boost temperatures, without fixing other regions of the models? How does one dispute and change something like CO2 forcing when it is defined by a simple mathematical equation?

 

If they adjusted the aerosol component downward, then they would have to lower sensitivity to GHGs or risk the GCMs not being able to reconcile the variability of the 20th century.

 

The basic equilibrium climate sensitivity formula is:

 

ECS = F (2*CO2)  * (▲T)/(▲F-▲Q)

 

Where F (2*CO2) is the radiative forcing from just the doubling of CO2 and delta T is change in temperature and delta F is change in total forcing and delta Q is the change in total heat uptake. Delta F has the aerosol component in it. So a smaller aerosol component (meaning less negative) will make delta F more positive, thus reducing the value of ECS.

[csnavywx]

I have a couple of serious misgivings about this paper, namely the way the impact of BC forcing and volcanic "rebound" forcing in the ~1910 to 1950 period is sort of waved off. I don't see anything here that would supplant AR5 or say... Wilcox et. al 2013.

[ORH_wxman]

I have a couple of serious misgivings about this paper, namely the way the impact of BC forcing and volcanic "rebound" forcing in the ~1910 to 1950 period is sort of waved off. I don't see anything here that would supplant AR5 or say... Wilcox et. al 2013.

 

Well AR5s aerosol forcing range is -0.1 to -1.9 W/M²....this paper just narrows the range to -0.3 to -1.0 W/M²

[csnavywx]

Well AR5s aerosol forcing range is -0.1 to -1.9 W/M²....this paper just narrows the range to -0.3 to -1.0 W/M²

You're right that they're technically in agreement, mostly due to the enormous aerosol forcing PDF on AR5. The important issue is the big top-end decrease, which is only justified if BC forcing and volcanic rebound in the later part of the assessment period is essentially written off as largely unimportant (especially when it comes to the N. Hem for BC aerosols). There's plenty of reason to believe otherwise, though.

 

The reason I mention Wilcox is because it gives a reasonably thorough treatment of the subject.

 

It's aggravating that Glory exploded, we might be talking about a range half as big as AR5 right now.

[csnavywx]

Since we're on the aerosol topic again, here's a paper that's in draft (please note that this is preliminary) that could be valuable in helping calculate aerosol RF without so much GCM input.

[skierinvermont]

Can't they estimate it with remote sensing like they do with methane and Co2

 

CO2 and methane forcing can't be measured using remote sensing. They are calculated based on radiative transfer codes using measured changes in concentration.

 

I believe remote sensing can tell that there has been a change in CO2 forcing but it can't tell you how much exactly.

[AvantHiatus]

 

 

Sun-blocking aerosols around the world steadily declined (red line) since the 1991 eruption of Mount Pinatubo, according to satellite estimates. Credit: Michael Mishchenko, NASA

[Msalgado]

CO2 and methane forcing can't be measured using remote sensing. They are calculated based on radiative transfer codes using measured changes in concentration.

 

I believe remote sensing can tell that there has been a change in CO2 forcing but it can't tell you how much exactly.

 

Local observations can measure changes in downward radiation from CO2 and other GHG.  There was just a recent paper that did this to show the increase radiation from CO2 emissions.  Satellites can't do that, but they can measure the changes in outgoing IR due to CO2.  There's obvious overlap in some bands, though, so its not the easiest accounting.

[chubbs]

In response to the reaction in the skeptic blogospere, the author has written a letter stating that the paper does not justify a significant change in ECS.

 

http://www.mpimet.mpg.de/fileadmin/grafik/presse/News/AerosolForcing-Statement-BjornStevens.pdf

 

"In my new paper I did not speculate as to the implications of my findings for estimates of Earth’s
Equilibrium Climate Sensitivity, which is perhaps the simplest measure of the response of the Earth
System to a change in concentration of atmospheric carbon dioxide. However others have used my
findings to suggest that Earth’s surface temperatures are rather insensitive to the concentration of
atmospheric CO2. I do not believe that my work supports these suggestions, or inferences."

[ORH_wxman]

In response to the reaction in the skeptic blogospere, the author has written a letter stating that the paper does not justify a significant change in ECS.

 

http://www.mpimet.mpg.de/fileadmin/grafik/presse/News/AerosolForcing-Statement-BjornStevens.pdf

 

"In my new paper I did not speculate as to the implications of my findings for estimates of Earth’s

Equilibrium Climate Sensitivity, which is perhaps the simplest measure of the response of the Earth

System to a change in concentration of atmospheric carbon dioxide. However others have used my

findings to suggest that Earth’s surface temperatures are rather insensitive to the concentration of

atmospheric CO2. I do not believe that my work supports these suggestions, or inferences."

 

 

By the math, the lower aerosol forcing would make the higher ECS values unlikely. But it is still within the bounds of ECS values in the literature.

[The_Global_Warmer]

Its pretty sad that he had to do that.

The first assumption should be that the oceans have cycles of retaining heat anomalously in both directions.