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Comment by Hammershaft | Hacker News Reader

Interesting... judging from this pic the 1960s seemed to be unusually cool. I wonder why.

https://www.climate.gov/sites/default/files/30yrNormal_Temp_...

Only slightly educated guess forthcoming.

Air pollution was pretty bad in the United States from the 1950s through the late 1980s, and we know that https://en.wikipedia.org/wiki/Global_dimming has kept temperatures down a bit.

So basically from the early 1970s through the 1990s in the United States, the amount of 'global dimming' type air pollution decreased tremendously, because of a number of factors, including all sorts of clean air mandates and regulation.

The dimming factor seems a bit frightening.

I don't know how sound the theory is, but i remember listening to the climate podcast Radio Ecoshock where a scientist talked about aerosols in general and that there could be a negative feedback loop that would disappear if we stop polluting heavily, ironically then raising temperatures significantly - this could mean that an extremely agressive decrease towards 2030 could increase temperature weirdly enough.

The effect was seen over the US after 9/11 as far as i remember.

A damned if you do and don't situation.

> The effect was seen over the US after 9/11 as far as i remember.

There was a study that claimed that but there's a second study that claims general cloud cover was a confounding factor not controlled for that explains the actual result:

https://en.wikipedia.org/wiki/Global_dimming#Contrails_and_c...

Even with a full set of airplanes in the air contrails are a tiny minority of the cloud cover. Seems pretty hard for them to have any visible impact. Aerosols in general are another matter all together. Those are all over the atmosphere and it wouldn't be surprising if they had a large effect as they accumulate.

Thanks for the clarification. Always seemed a bit too quick and neat a causation.

But as you say the bigger picture is still worrying - and i am not sure that disregarding cloud formation there isn't still certain aerosols hanging around changing things for the worse after heavy air traffic - it's hard to gauge from the Abstracts of papers i just skimmed, but something seems to be happening : https://link.springer.com/article/10.1023/A:1006600107117 https://www.researchgate.net/publication/279155481_Impact_of...

Related to cloud cover: one of the biggest uncertainties in climate models is how to cater for the albedo effect also known as cloud feedback. It goes something like this:

1) The most potent greenhouse gas is water vapor (not CO2) 2) Increased temperatures result in more water vapor (simple evaporation) 3) Water vapor forms clouds 4) Clouds are white and reflect incoming solar radiation

A lot of models have to make big assumptions about the strength of this negative feedback loop, and the assumptions have a big impact on the output of the models.

https://en.wikipedia.org/wiki/Cloud_feedback

Conversely, further increased evaporation > even more water vapor > increased precipitation > fewer clouds.

Also, clouds reflect sunlight > less warming, but clouds reflect IR > less cooling.

It’s a really complex interaction that doesn’t have a clear global maximum as each region has a slightly different impact and they all interact. Atmosphere dust is one of the biggest drivers here and dust alone involves a lot of non linear feedback loops.

"further increased evaporation > even more water vapor > increased precipitation > fewer clouds." No. You can't get fewer clouds from more water vapor, that's not how equilibria work.

Clouds are dependent upon the particulate matter in the air, which is reduced by precipitation. You still get cloud formation without that, but the air ends up very supersaturated.

https://en.wikipedia.org/wiki/Cloud_condensation_nuclei

Well, we can always spray sulphur aerosols in the stratosphere without all the CO2 and acid rain.

My best guess is some natural cycle tied to the https://en.wikipedia.org/wiki/Atlantic_multidecadal_oscillat... is involved. You'll note that the 1960s correspond to the point where the Atlantic was cooling most rapidly, which would be suggestive that the air above the Atlantic was relatively cold at that time.

That said I'm not a climatologist, nor do I play on on TV.

It's worth pointing out that there likely is no such thing as the AMO. The scientist who coined the term in some pioneering work in 2000 has, over the past few years, been extremely outspoken that it was probably an errant interpretation of the data available at the time (e.g. https://michaelmann.net/content/rise-and-fall-atlantic-multi...) and even just a year ago published an article in Nature which more or less thoroughly eliminates the possibility of such a mode of multi-decadal variability actually existing (https://www.nature.com/articles/s41467-019-13823-w).

Whether or not the variation is a predictable cycle notwithstanding, there is a substantial natural variation, and the 1960s coincided with a drop in Atlantic sea temperatures of the right order of magnitude. Which suggests that natural variation could have caused the 1960s to be unusually cool relative to overall warming trends.

Interesting to note that in the 1970's the talk of another ice age was really more of a conversation about a rapidly changing planet. The real anxiety was over pollution and its effect on the climate - not that the planet was cooling naturally or going through a cooling phase:

1974 TIME "Another Ice Age?" https://www.sott.net/article/271592-Time-magazine-1974-Anoth...

As they review the bizarre and unpredictable weather pattern of the past several years, a growing number of scientists are beginning to suspect that many seemingly contradictory meteorological fluctuations are actually part of a global climatic upheaval.

They thought it was due to pollution (man made) even back then:

Man, too, may be somewhat responsible for the cooling trend. The University of Wisconsin's Reid A. Bryson and other climatologists suggest that dust and other particles released into the atmosphere as a result of farming and fuel burning may be blocking more and more sunlight from reaching and heating the surface of the earth.

Interesting to note they speculate the trend might be temporary - which makes sense because as we've reduced pollution by leaps and bounds since then, you've started to see more of a warming trend:

Climatic Balance. Some scientists like Donald Oilman, chief of the National Weather Service's long-range-prediction group, think that the cooling trend may be only temporary. But all agree that vastly more information is needed about the major influences on the earth's climate.

This article was never an indictment on the scientists believing we were heading for another ice age. Quite the opposite. They started seeing rapid changes in the planet's climate and wanted to try and explain what the consequences were. They even say they need more data and more research to figure out exactly what's going on.

> 1960s seemed to be unusually cool

Note that the set of thermometers and temperatures that make it into the GHCN comprise repeated convenience samples. The techniques used to smear individual observations over vast swathes of territory tend to leave much to be desired.

Here's an animation[1] I made way back when I thought maybe thinking scientifically about how to evaluate the existing climate record for the recent past was acceptable.

I have not touched the GHCN recently nor have I updated the analyses, but it did not take much time to produce the videos many years ago. Anyone curious should be able to repeat the same thing of plotting coordinates of temperature stations with fresh data with no trouble.

So, for the original question, the answer is we do not know. However, data are subject to selection bias and that affects what kind of inferences you can make.

But do compare the distribution of observation sources in the 60s to periods before and after.

[1]: https://www.youtube.com/watch?v=h95uvT67bNg GHCNv3 (20141118 qca) Temperature Station Locations 1702-2014

>The techniques used to smear individual observations over vast swathes of territory tend to leave much to be desired.

I am by no means an expert, but after farting around with climate data, even today I'm curious how they smear data across comparatively smaller swathes of territory.

I've noticed, in my area (south west), that many of the stations are located in seemingly unique microclimates--like the tops of mountains, on the shores of rivers, etc.

It roadblocked my layman research because distance to a given station was not very indicative of how that area's climate is.

For one example, note https://data.giss.nasa.gov/gistemp/graphs_v4/ which leads to http://www.columbia.edu/~mhs119/Temperature/ which leads to https://data.giss.nasa.gov/gistemp/ which leads to https://data.giss.nasa.gov/gistemp/sources_v4/ which should give you some non-source controlled Python code translated from Fortran code which tried to use a weighted average from stations in something like a 1250 mile radius based on the unproved assertion that deviations from a 30-year mean were correlated well even though levels were not.

Representative comment:

    In Step 5: 8000 subboxes are combined into 80 boxes, and ocean data is
    combined with land data; boxes are combined into latitudinal zones
    (including hemispheric and global zones); annual and seasonal anomalies
    are computed from monthly anomalies.

I can't believe I missed this: https://data.giss.nasa.gov/gistemp/sources_v4/gistemp.html:

> In 2007, David Jones' team, Climate Code Foundation, reprogrammed the whole procedure in python, as a product of the Clear Climate Code project and the Climate Code Foundation, http://clearclimatecode.org/

That's all the source control you'll ever get. Don't bother clicking on that link.

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