Contrails and Aerosols effects on the melt season

[marcel_g]

Taking this topic from the melting season thread and starting a new thread:

From BeesKnees in message https://forum.arctic-sea-ice.net/index.php/topic,3017.msg275564.html#msg275564

From your link
"Like regular cirrus clouds, contrail cirrus clouds have two competing effects on climate. They shade us by reflecting incoming sunlight back into space. But they also trap heat radiating from the earth’s surface, so causing warming in the air below.
During the day, cooling compensates part of the warming. But at night, with no sunlight, only the warming effect operates. "

Suggests that in the Arctic, contrails would cool the summer and warm the winter, with the net effect being warming.

Yes, I agree, the net effect for reduced contrails should be the Arctic Sea Ice should get more sunlight, and since it's the insolation that affects the melt season the most, rather than air temperature (reflected longwave radiation), the reduced contrails should make a significant difference for the amount of melting we're seeing.

As far as aerosols go, they were definitely reduced for March and April, but I'm not sure how much they were reduced in May and June and July, so I have no idea how much they'll affect the melt season.

[marcel_g]

From guygee in the melting thread:

Apologies for the OT on clouds, but I've seen the same error here repeatedly regarding the effect of high altitude clouds. These clouds raise temperatures both day and night, since  they are relatively transparent to incoming short wave radiation but tend to reflect outgoing long wave radiation. So their effect on warming is positive both in the day, and, like all clouds, at night. See, for example,
https://earthobservatory.nasa.gov/features/Clouds/clouds3.php

yes, the contrails, if they act like clouds, might have a net warming effect on air temperatures, so if they're gone, then it should cool air temperatures. However, the strength of the melt season is driven primarily by insolation, not air temps, so the great reduction of the clouds should increase the melting, because it allows more sunlight to hit the ice.

[Burnrate]

I did mention this once before in the ice thread but haven't seen anyone else mention it.  The ban on burning high sulfur fuels in shipping began in January of this year.  It was expected to reduce global sulfur dioxide output by nearly 10%.

I don't know of any current analysis of the new rules efficacy but I would imagine even reaching half of that would have a significant impact.

This chart shows that the SO2 is pretty significant.


http://www.imo.org/en/MediaCentre/HotTopics/Pages/Sulphur-2020.aspx

I imagine this has a larger effect than the pandemic.

[jens]

What is the average amount of cloudiness in the Arctic historically? Because back in 1980 there were definitely less economic induced-aerosols than in 2019 due to the smaller human economic activity back then.

[Freegrass]

What is the average amount of cloudiness in the Arctic historically? Because back in 1980 there were definitely less economic induced-aerosols than in 2019 due to the smaller human economic activity back then.

True, but we've also cleaned up a lot bad shit from the air since then. Do we still have acid rain?

[ajouis]

My post from another thread on aerosols in Arctic background

What we know about aerosol reduction
It will probably worsen heatwaves, especially in the northern hemisphere which is bad news if it penetrates into the arctic circle, like with last year’s Siberian and Canadian heatwave, or for arctic centred heatwaves like we had in northern Greenland
https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2019GL082269

It can strengthen the jet stream in winter, when localized in eurasia, because of warming, lessening extreme weathers outside the arctic, so probably good news for the refreeze given that most aerosol is concentrated away from the arctic.
https://www.nature.com/articles/s41558-020-0693-4t
There is further evidence that aerosols could inhibit thermal contrast between land and sea, in east Asia, as well as further evidence that they reduce insolation
https://agupubs.onlinelibrary.wiley.com/doi/full/10.1002/2015RG000500

In contrast of the decreased surface insolation, aerosols increase air Temperatures, which seems less important on melting ice, but they also are the cause of more stormy events as opposed to light rain, which will have a definite differentiated impact on the melting season, though I cannot guess which, and on the freezing season with probably earlier refreeze due to less storm events but lesser refreeze due to more ubiquitous snow cover. As the study concentrates on a blackspot for aerosols, it will probably be a much lesser impact in the arctic.
https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2019JD030758

Finally there is a feedback loop that increases aerosol concentration, stabilizing it in place, along with the atmosphere, with the creation of a heat gradient. It being broken could paradoxically mean more aerosols in the arctic for a little while (so opposite effects to those discussed above) and more chaos in an already volatile weather and climate system.
https://academic.oup.com/nsr/article/4/6/810/4191281
Additionally another feedback loop between reduced precipitation and higher aerosol concentration, also tributary to the same atmospheric stabilization, strengthens the case for increased precipitations and chaos in the system with reduction in aerosol, although locally
https://opensky.ucar.edu/islandora/object/articles%3A7038/datastream/PDF/download/citation.pdf

Overall, simulations tend to agree that its macro effect is additional melt within the arctic
https://agupubs.onlinelibrary.wiley.com/doi/full/10.1002/2015GL065504?campaign=wlytk-41855.6211458333
And, warming in various world regions
https://iopscience.iop.org/article/10.1088/1748-9326/ab6b34

Additional links
https://eos.org/editors-vox/intensified-investigations-of-east-asian-aerosols-and-climate
https://ftp.cpc.ncep.noaa.gov/hwang/Papers_pdf/Publication_2007-present/2008_Zhang_JGR.pdf (Could mean a change in moisture repartition in a reduction event if taken along with the feedback article)

[marcel_g]

I did mention this once before in the ice thread but haven't seen anyone else mention it.  The ban on burning high sulfur fuels in shipping began in January of this year.  It was expected to reduce global sulfur dioxide output by nearly 10%.

I don't know of any current analysis of the new rules efficacy but I would imagine even reaching half of that would have a significant impact.

This chart shows that the SO2 is pretty significant.
...

http://www.imo.org/en/MediaCentre/HotTopics/Pages/Sulphur-2020.aspx

I imagine this has a larger effect than the pandemic.

This is a good point, nice find on that one.

[guygee]

From guygee in the melting thread:

<snip>

yes, the contrails, if they act like clouds, might have a net warming effect on air temperatures, so if they're gone, then it should cool air temperatures. However, the strength of the melt season is driven primarily by insolation, not air temps, so the great reduction of the clouds should increase the melting, because it allows more sunlight to hit the ice.

As to the effect of some difference due the number of contrails this year as opposed to previous years, I  lack sufficient information to have any informed opinion. Considering all other factors, I doubt the lack of contrails has a large effect.

I don't mean to belittle your statement on insolation, but rather point out that it is not only insolation that drives summertime sea ice melting, but rather a large number of factors including increased warm air intrusion from continental warming, breaking the near-surface inversion over the ice by strong subsidence under the persistent high pressure this year, increased water temperatures both from continental sources and early melting, increased exchange of waters between the Arctic, Atlantic and Pacific, breaking of the halocline due to increased upwelling and strong atmospheric pressure gradients, and probably other positive ongoing feedbacks not mentioned.

In particular, this year, strong subsidence under the center of the high pressure, and strong pressure gradients around the periphery of the high have served to reduce the predominance of the usual near-surface temperature inversion over the ice. Also, over the open water, the inversion lifts. This increases the importance of air temperature in ice melt as opposed to 'more usual' conditions that have prevailed during the satellite era. Granted the persistent high this year also greatly increased direct insolation. As to the relative importance of all of these factors in this melting season, I would welcome any further information you can provide.

[marcel_g]

My post from another thread on aerosols in Arctic background

What we know about aerosol reduction

Wow, thanks, those provide a lot to think about.

[ArcticMelt2]

As I said on another topic, satellite measurements in recent months behind global temperature give strict limits on the possibility of large cooling due to anthropogenic aerosols.

If there were a strong effect, then the global temperature would surely become a record high due to the global quarantine and easily overcome the 2016 records. But this is not observed:

http://images.remss.com/msu/msu_time_series.html



On the contrary, the global temperature anomaly has dropped significantly since February 2020.

So it looks like the warming effect of black soot is actually much stronger than the cooling effect of aerosols.

If there is any significant cooling due to aerosols, it is Canada with an increasing production of bitumen oil with a high sulfur content. In recent years, winters have really cooled down there, and an excess of ice and snow is often observed. But again, no significant warming has been observed in Canada this spring. On the contrary, there is still anomalously much ice and snow here.

[igs]

Kind of a redundant thread:


Check here: [size=78%]https://forum.arctic-sea-ice.net/index.php/topic,3181.msg275471/topicseen.html#new[/size]


Just keep going, i have no issues with that, just sharing an observation and at times it could be difficult to chose between several therads.


That aside, an interesting topic indeed.

[guygee]

Any analysis of global temperatures without including an analysis of the current ENSO state is incomplete, for example see:

https://www.osti.gov/pages/servlets/purl/1511151

https://journals.ametsoc.org/jcli/article/7/11/1719/36167/The-Signature-of-ENSO-in-Global-Temperature-and

[ajouis]

ArcticMelt, whether drop in production caused a temperature increase is unknowable because, 1 China restrarted early, 2 lockdowns went into effect in a successive manner or not at all not all at once, 3 while consumption was down, production did not dip as low (change in production type) resulting in a lower decrease of aerosol, 4 very importantly china and other countries rolled back environmental regulations, and finally, 5 aerosols usually take several weeks to breakdown and exit the atmosphere, leaving the bulk of the difference between lockdown emissions and usual emissions in the atmosphere before emissions returned back to normal. This means that the absence of further heating this year is not evidence that the studied effect of aerosol dimming is false.

[ajouis]

Guygee, the correlation between melt and surface temperature is very weak, insolation through high pressure, lower cloud cover and less storms, in the central seas, is responsible for the bulk of it https://agupubs.onlinelibrary.wiley.com/doi/full/10.1002/2014JD022608#jgrd52033-fig-0006

[guygee]

Thank you for the reference, ajouis, that is a very interesting study. The authors use an extensive data set "standardizing the sea ice melts over the 140 MJJA months from 1979 to 2013", ..."with composites of 23 high (HMR) and 17 low (LMR) melt months."

Most of the discussion on the weak correlation with surface temperature is connected with the author's Figure 10. Below that figure they state:

The temperature signal over the Arctic Ocean in HMR months is nevertheless small compared to the warming along its coastal boundaries (average of 0.3°C compared to up to 2.0°C over the Taymyr Peninsula at 100°E). This is due to the fact that sea surface temperature will always be close to the freezing point in a partly ice covered ocean.

With the record melt-out of the Siberian Arctic seas and attendant record high SSTs I wonder how the above might be modified this year? Areas that were previously "partly ice covered ocean" are now ice-free.

I also found these two paragraphs in their conclusion very interesting, as a possible prediction of how the rest of this melt season will unfold:

In the Arctic, HMR months coincide with an anticyclonic tendency (up to 7 hPa; Figure 3a), which enhances the incoming SW radiation at the start of the summer (average of 9 W/m2 over the Arctic Ocean; Figure 8a) and warms the region in general (0.3°C over the Arctic Ocean, up to 2.7°C over Greenland; Figure 10). This atmospheric circulation is associated with a tendency of storms to veer away from the Arctic on a more zonal path (Figure 6a), leaving the Arctic drier  (average reduction of 0.1 mm/d over the Arctic Ocean; Figure 7a) with lowered albedo (represented by the equally sized reduction in snowfall in Figure 7b). A positive snow-albedo feedback emerges.

In August, the enhanced ocean surface evaporation from the retreating sea ice promotes cloud development (represented by the 7 W/m2 reduced incoming SW radiation in Figure 8b and 9 W/m2 increased incoming LW radiation in Figure 9b). Coming into late summer, re-emission of LW radiation surpasses incoming SW radiation at the surface [Curry et al. , 1996]. Hence, the clouds trap heat, providing a mechanism for a positive cloud feedback.

[oren]

Very good thread.
Is anyone aware of any ground stations in the Arctic that measure actual insolation? Comparing such measurements to previous years could settle the question of the overall effect of the Arctic skies this year (less/no contrails, less aerosols, less soot?). Maybe somewhere in Svalbard or the CAA an answer is waiting.

[Hefaistos]

There is also this thread:
"Topic: Temperature signals from Covid-19"
https://forum.arctic-sea-ice.net/index.php/topic,3078.msg262481.html#msg262481

I crosspost the last post in that thread, regarding a possible temperature signal in USA, due to lockdown effects:

Clearly, we see no positive temperature signal from the Covid lockdowns.
Anomalies are continuing down, both globally, and for SH and NH, see the chart with GFS weekly forecast (from Karsten Haustein).

I also checked to temperature data for USA, as one country where the lockdown would assumedly bring a more pronounced signal due to high emissions.
But USA also displays a decline in anomalies.
This is UAH6 satellite data for the LT.

[Hefaistos]

And this, illustrating lockdown effects on air traffic and thus contrails in USA (from another thread).

Previous research on aerosols in connection with major volcanic eruptions (Agung, Pinotubo, etc), show that the (cooling) effect from increased aerosols happens with very little delay in the area first affected.
But we really see no such (warming) effect from the collapse in air traffic in USA.

[Hefaistos]

ArcticMelt, whether drop in production caused a temperature increase is unknowable because, 1 China restrarted early, 2 lockdowns went into effect in a successive manner or not at all not all at once, 3 while consumption was down, production did not dip as low (change in production type) resulting in a lower decrease of aerosol, 4 very importantly china and other countries rolled back environmental regulations, and finally, 5 aerosols usually take several weeks to breakdown and exit the atmosphere, leaving the bulk of the difference between lockdown emissions and usual emissions in the atmosphere before emissions returned back to normal. This means that the absence of further heating this year is not evidence that the studied effect of aerosol dimming is false.

No, but the total absence of a temperature effect due to Covid lockdowns also doesn't support a strong aerosol dimming effect.
Just to give a classic reference on the importance of aerosols, and the Faustian bargain:
"The importance of knowing the aerosol forcing is shown by considering the following two cases: (1) aerosol forcing about -1 W/m2, such that the net climate forcing is ~ 2 W/m2, (2) aerosol forcing of -2 W/m2, yielding a net forcing ~1 W/m2. Both cases are possible, because of the uncertainty in the aerosol forcing. Which alternative is closer to the truth defines the terms of a "Faustian bargain" that humanity has set for itself."

Hansen, see figs 3 and 4
https://www.giss.nasa.gov/research/briefs/hansen_16/

This also is well worth studying:
"Rethinking the Lower Bound on Aerosol Radiative Forcing" by Bjorn Stevens
J. Climate (2015) 28 (12): 4794–4819.
doi.org/10.1175/JCLI-D-14-00656.1
open access

[ajouis]

Hefaistos, obviously absence of warming is absence of evidence of lack of aerosol warming, however other studies, especially on the regional scale, have found significant effect of aerosol reduction on temperature, lower air temperature but higher insolation so ground temperature, just not during the covid, and data is even more clear on precipitation.

Also aerosol effect is much quicker than aerosol reduction because in the latter aerosols first need to breakdown which often takes several weeks

[kassy]

But we really see no such (warming) effect from the collapse in air traffic in USA.

The graph is about passenger numbers which is not the same as the number of flights (there were more planes flying in the US then in Europe in march/april).

[marcel_g]

As I said on another topic, satellite measurements in recent months behind global temperature give strict limits on the possibility of large cooling due to anthropogenic aerosols.

If there were a strong effect, then the global temperature would surely become a record high due to the global quarantine and easily overcome the 2016 records. But this is not observed:
...

So it looks like the warming effect of black soot is actually much stronger than the cooling effect of aerosols.

...

I didn't intend this thread to be about global increase in air temperatures due to changes in aerosols and contrails, but more specifically it was supposed to be about how those two elements affect the current melt season.

Since the primary driver of the melt season is insolation, how aerosols and contrails affect air temperatures is less important than how much more or less solar energy is getting through to the ice this year, compared with recent non-covid years.

The arguments that posters are making here seems to say that there might not be a huge difference in aerosols between 2020 and previous years, as Asian industrial production didn't slow down for that long and coal plants didn't really slow down at all, and aerosols take some time to dissipate.

My guess is there's some difference due to the major decrease in road traffic, and due to the previously mentioned change in global shipping fuel. Maybe a small % difference in solar energy allowed through to the ice?

Contrails on the other hand, have an immediate effect on solar radiation hitting the ice. Those are have been greatly reduced for the entire melt season.

If those two effects allow even 5-10% (just guessing) more solar energy through compared to previous years, this would have a significant melting effect when combined with the 3 weeks of high pressure clear skies during peak insolation.

[Burnrate]

...

Since the primary driver of the melt season is insolation, how aerosols and contrails affect air temperatures is less important than how much more or less solar energy is getting through to the ice this year, compared with recent non-covid years.
...

You are right.  People constantly point to temperature anomalies and other things as evidence that the aerosols aren't changing the insolation.  As Oren said this can probably be confirmed or not by a ground station in the arctic that is measuring insolation.  It would be great to compare cloud free days from different years.

Another aspect of the reduced aerosols could be reduced cloud cover which has been a big factor this season.  With global warming in general you would expect to see increased cloud cover and precipitation over the arctic but the huge reduction could be partly due to the reduced aerosols (and mostly due to the huge stuck high pressure system I would imagine).

[Burnrate]

If those two effects allow even 5-10% (just guessing) more solar energy through compared to previous years, this would have a significant melting effect when combined with the 3 weeks of high pressure clear skies during peak insolation.

I don't really know how to quantify the change but if we imagine the negative radiative forcing of aerosols have been reduced 10-20% that still only creates a change of about .1-.3 W/m2.  Even with a more extreme estimate it would increase the insolation by less than a tenth of a percent.  Over time this matters but I don't think it would have drastic effects in a single year.

I do think it could have a much bigger impact by reducing cloud formation and as you said it is just another part of all the bad things happening to the ice this year.  Every little bit counts.

(Of course I could have had some drastic misunderstanding about something here.)

[glennbuck]

I think Aerosols will have a big effect from the Lockdown and Flight grounding/reduced industrial activity, MSM and IPCC will then blame 2020 as an anomoly if we have a 1.75 million km^2 to 2.75 km^2 million minimum this year and say it will not happen again until 2050 etc. The Aerosol masking effect reduction from the Lockdown will cause a permanent 0.5C to 1C increase in global temperatures within months, so around this time June, July, August, this will cause record melting for the Arctic in July and August which can not be compared to past data  on ASIF, bringing forward a BOE event to 2021 to 2024.

[Burnrate]

...
bringing forward a BOE event to 2021 to 2024.

I remember someones tongue in cheek prediction using 2007, 2012, 2016, 2019 (years 5, 4, 3) so the next bad year was supposed to be 2021 but the pandemic and shipping changes pushed it forward one year.  If you follow it forward 2021 was bad then 2022 or 2023 was BOE.  We can bump it up one year to 2021 or 2022.

[ArcticMelt2]

This year is unique with record-breaking wildfires in the Arctic that nullify talk of a clean atmosphere.

[Hefaistos]

I think Aerosols will have a big effect from the Lockdown and Flight grounding/reduced industrial activity, MSM and IPCC will then blame 2020 as an anomoly if we have a 1.75 million km^2 to 2.75 km^2 million minimum this year and say it will not happen again until 2050 etc. The Aerosol masking effect reduction from the Lockdown will cause a permanent 0.5C to 1C increase in global temperatures within months, so around this time June, July, August, this will cause record melting for the Arctic in July and August which can not be compared to past data  on ASIF, bringing forward a BOE event to 2021 to 2024.

"The Aerosol masking effect reduction from the Lockdown will cause a permanent 0.5C to 1C increase in global temperatures within months"?

First of all, the aerosol effect initially will be a local/regional effect, and then spreading to a global effect.
We should have seen the local/regional effect already in the data.
So where are your data for your claim of such a big and permanent temperature increase?
Attach two graphs of current developments in different data sets, as far as I can see we have a pronounced negative trend in the temperature anomalies.

[ajouis]

are those ground temps or air temps? because aerosol reduction increase the earlier and decrease the latter, which is logical, there is no additional insolation from the sun, it is just no longer stopped in the atmosphere

[glennbuck]

I think Aerosols will have a big effect from the Lockdown and Flight grounding/reduced industrial activity, MSM and IPCC will then blame 2020 as an anomoly if we have a 1.75 million km^2 to 2.75 km^2 million minimum this year and say it will not happen again until 2050 etc. The Aerosol masking effect reduction from the Lockdown will cause a permanent 0.5C to 1C increase in global temperatures within months, so around this time June, July, August, this will cause record melting for the Arctic in July and August which can not be compared to past data  on ASIF, bringing forward a BOE event to 2021 to 2024.

The global land and ocean surface temperature for May 2020 tied with 2016 as the highest in the 141-year record at 0.95°C (1.71°F) above the 20th century average of 14.8°C (58.6°F).

https://www.ncdc.noaa.gov/sotc/global/202005

Averaged as a whole, the global land and ocean surface temperature for April 2020 was 1.06°C (1.91°F) above the 20th century average of 13.7°C (56.7°F) and the second highest April temperature in the 141-year record. Only April 2016 was warmer at +1.13°C (+2.03°F). The eight warmest Aprils have occurred since 2010.

https://www.ncdc.noaa.gov/sotc/global/202004

Averaged as a whole, the global land and ocean surface temperature for March 2020 was 1.16°C (2.09°F) above the 20th century average of 12.7°C (54.9°F) and the second highest in the 141-year record.

https://www.ncdc.noaa.gov/sotc/global/202003
"The Aerosol masking effect reduction from the Lockdown will cause a permanent 0.5C to 1C increase in global temperatures within months"?

First of all, the aerosol effect initially will be a local/regional effect, and then spreading to a global effect.
We should have seen the local/regional effect already in the data.
So where are your data for your claim of such a big and permanent temperature increase?
Attach two graphs of current developments in different data sets, as far as I can see we have a pronounced negative trend in the temperature anomalies.

[glennbuck]

The shape of current anomalies is very similar to the peak reached around 2016. This is alarming because the peak around 2016 was reached under El Niño conditions, whereas the current temperatures are reached under conditions that are leaning toward La Niña, as illustrated by the images below.

[glennbuck]

 

[glennbuck]

 

[Burnrate]

This year is unique with record-breaking wildfires in the Arctic that nullify talk of a clean atmosphere.
...

Carbon emissions from wildfires has nothing to do with aerosols.  It would be interesting to know how much and what kinds of aerosols are being released by the wildfires and how that compares to the changes in human emissions.

[bbr2315]

This year is unique with record-breaking wildfires in the Arctic that nullify talk of a clean atmosphere.
...

Carbon emissions from wildfires has nothing to do with aerosols.  It would be interesting to know how much and what kinds of aerosols are being released by the wildfires and how that compares to the changes in human emissions.

Carbon emissions from wildfires are aerosolized.... i.e. they are aerosols....

[glennbuck]

I think Aerosols will have a big effect from the Lockdown and Flight grounding/reduced industrial activity, MSM and IPCC will then blame 2020 as an anomoly if we have a 1.75 million km^2 to 2.75 km^2 million minimum this year and say it will not happen again until 2050 etc. The Aerosol masking effect reduction from the Lockdown will cause a permanent 0.5C to 1C increase in global temperatures within months, so around this time June, July, August, this will cause record melting for the Arctic in July and August which can not be compared to past data  on ASIF, bringing forward a BOE event to 2021 to 2024.

Every latitude band observed above average temperatures in June 2020...


"The Aerosol masking effect reduction from the Lockdown will cause a permanent 0.5C to 1C increase in global temperatures within months"?

First of all, the aerosol effect initially will be a local/regional effect, and then spreading to a global effect.
We should have seen the local/regional effect already in the data.
So where are your data for your claim of such a big and permanent temperature increase?
Attach two graphs of current developments in different data sets, as far as I can see we have a pronounced negative trend in the temperature anomalies.

Every latitude band observed above average temperatures in June 2020...

[glennbuck]

What is most remarkable (and troubling) is that 2020 is so warm without the benefit of a Super El Niño. The 132 month running mean taking a decidedly nonlinear tick up.

[glennbuck]

For three days after September 11, the Federal Aviation Administration grounded commercial aircraft in the U.S., stranding travelers, hindering mail delivery and interrupting courier service, but for scientists at Penn State and the University of Wisconsin–Whitewater, the three-day shutdown provided a rare glimpse of the climate effects of jet contrails.

The change in the temperature difference was plus 1.1 degree Celsius, equal to plus 2 degrees Fahrenheit, above the 30-year long-term mean diurnal temperature range. The researchers compared the temperature ranges on these three days to those of the three days directly before Sept. 11 and the three days after Sept. 14, finding that the days before and after were similar, but that the three days in question differed by 1.8 degrees Celsius or 3.2 degrees Fahrenheit.

https://www.sciencedaily.com/releases/2002/08/020808075457.htm

[Amarok]

This is my fist posting .Thank you all for this web site.

I remember reading about the cooling effect of contrails  in the days after 911.
I have seen articles that claim heating effects at night  counteracts the daytime cooling ,
Since most air traffic is during the day contrails would not persist into the night.
Most contrails only last 4 to 6 hours
In the arctic summer there isn't very much night to worry about anyway.
During WW2 the the temperature below the high altitude bombers and fighters was over 2 deg. F. cooler.

Would it be possible to use flights over the arctic to slow down the loss of ice cover during the summer . I know the CO2  would be a  long term negative.
 



 

[oren]

Welcome, Amarok.
Do uou have a source for the WW2 info?

[El Cid]

I took a look at 2020 monthly temperature anomalies vs 2015-19 average at GISS Temp.

here are the results :
Jan +0,21 C
Feb +0,19 C
Mar +0,07 C
Apr +0,20 C
May +0,17 C
Jun +0,13 C

We had an "amazing", unprecedented and likely unreplicable experiment this year when globally many many factories closed off, airplanes were grounded, cars stoped, etc from roughly mid-march to mid-May, so aerosol emission fell by a lot.

If there were a big aerosol effect then April (and partly March and May) temperatures should have been much higher than  Jan, Feb and June. They are not. And this somewhat proves to me that aerosol effects are not as strong as estimated.

[ajouis]

I took a look at 2020 monthly temperature anomalies vs 2015-19 average at GISS Temp.

here are the results :
Jan +0,21 C
Feb +0,19 C
Mar +0,07 C
Apr +0,20 C
May +0,17 C
Jun +0,13 C

We had an "amazing", unprecedented and likely unreplicable experiment this year when globally many many factories closed off, airplanes were grounded, cars stoped, etc from roughly mid-march to mid-May, so aerosol emission fell by a lot.

If there were a big aerosol effect then April (and partly March and May) temperatures should have been much higher than  Jan, Feb and June. They are not. And this somewhat proves to me that aerosol effects are not as strong as estimated.

For one aerosol reduction as already been studied, notably the difference after air pollution measures,
and more importantly the covid is not a good event to study aerosol reduction, it has had countries opening and closing at different times, production didn’t take that huge a hit where it matters, and environmental laws were relaxed, compensating aerosol reduction. Besides they take several weeks to decompose, so they might have stayed long enough to be replaced.

[El Cid]

... more importantly the covid is not a good event to study aerosol reduction, it has had countries opening and closing at different times, production didn’t take that huge a hit where it matters, and environmental laws were relaxed, compensating aerosol reduction.

The above are basically all false.

1) Almost ALL countries shut down during March and reopened from the end of April/beginning of May. Except for China: they closed down at the end of January.
2) As for "production didn't take a huge hit". Industrial Production in April in Europe fell 27% yoy, India 55% (btw, India is now the world's biggest emitter of So2: https://www.nature.com/articles/s41598-017-14639-8 ), US 11%, even China was still negative in April yoy. This hit is bigger than any time since WW2. April was the absolute, extreme low point in global industrial production and car use.
3) Environmental laws were relaxed? I don't know about that. Where?

[Hefaistos]

For three days after September 11, the Federal Aviation Administration grounded commercial aircraft in the U.S., stranding travelers, hindering mail delivery and interrupting courier service, but for scientists at Penn State and the University of Wisconsin–Whitewater, the three-day shutdown provided a rare glimpse of the climate effects of jet contrails.

The change in the temperature difference was plus 1.1 degree Celsius, equal to plus 2 degrees Fahrenheit, above the 30-year long-term mean diurnal temperature range. The researchers compared the temperature ranges on these three days to those of the three days directly before Sept. 11 and the three days after Sept. 14, finding that the days before and after were similar, but that the three days in question differed by 1.8 degrees Celsius or 3.2 degrees Fahrenheit.

https://www.sciencedaily.com/releases/2002/08/020808075457.htm

That research has later been debunked. The temperature jump during those days was due to a change of low cloudiness.

" Abstract
One of the most visible anthropogenic phenomena in the atmosphere is the occurrence of contrails. The direct effects of contrails on surface temperature are investigated on the basis of the data sets for the cloud cover and surface temperature over the conterminous United States for the period 1971–2001. It is shown that the increase of the average daily temperature range (DTR) over the United States during the three‐day grounding period of 11–14 September 2001 cannot be attributed to the absence of contrails, a subject was debated in several previous studies. The present analysis suggests that the DTR is attributed to the change of low cloudiness."

"We conclude that the increase of the diurnal temperature range over the United States during the three‐day grounding period of 11–14 September 2001 cannot be attributed to the absence of contrails. While missing contrails may have affected the DTR, their impact is probably too small to detect with a statistical significance. The variations in high cloud cover, including contrails and contrail‐induced cirrus clouds, contribute weakly to the changes in the diurnal temperature range, which is governed primarily by lower altitude clouds, winds, and humidity. "

https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2008GL036108

[ajouis]

el cid, the fact that china was not lockeddown at the same time is major, and several countries only locked down in april-may (south america), very little or not at all (the US), and as I said there would be a delay anyways due to the time it takes for aerosols to degrade.
that’s even more damning

Comparisons among the simulations altering emissions, chemistry, and meteorology reveal that the unprecedented NOx reduction during the COVID 19 does not significantly reduce aerosol formation because of the non-linear ozone and aerosol chemistry

https://science.sciencemag.org/content/early/2020/06/16/science.abb7431

for production I meant compared to the overall gdp loss and on a yearly basis, because aerosols take time to degrade (3 months https://pubs.acs.org/doi/10.1021/acs.est.6b02313# )

yeah environmental law relaxation happened, and look at the date https://www.google.com/amp/s/mobile.reuters.com/article/amp/idUSKBN20X0AG
https://www.google.com/amp/s/www.bloomberg.com/amp/news/articles/2020-03-18/china-may-help-struggling-carmakers-by-relaxing-emission-curbs

All in all, it is logical that the aerosol reduction has not been strongly felt globally temperature wise

[El Cid]

The following are from IPCC Chapter 7 on Clouds and aerosols to refute your above claims. They show you that

1) it does not take months but instead only days for aerosols to breakdown (see troposheric lifetime)
2) the net effect of aerosols is not at all final and we are not yet sure whether it is positive or negative

In light of the above I still say that the April lockdown "experiment" showed that the net effect of aerosols is likely not significant

[Burnrate]

10 minutes.  It goes into a lot of the history of the research and what to expect.

[ajouis]

el cid, look at the study, they have divergent findings from that. Besides the other source that the reduction of primary aerosols didn't necessarily mean a net reduction in aerosol because of the increase of secondary product aerosols

[oren]

While the counterarguments presented by ajouis are quite convincing regarding the timing of lockdowns and some inherent delays, it still seems quite true that the effect of aerosol reduction is not huge (as often feared), given the lockdown "experiment". I don't think the data is enough to say it is not significant, as the lockdowns were not prolonged and deep enough, except the Chinese one, and there is also natural variability in the global temp data.

[oren]

I just noted this thread was intended to discuss effects on the melting season. Discussion of aerosols reduction in general should be held in another thread, which if I recall correctly exists already.