Are clouds increasing?

[Jay Reynolds]

Frequently, claims are being made that there are no more days with blue skies, or that cloudiness has increased. I'd like to discuss these claims.

here are graphs which show the results of global satellite cloud percentage measurements over time:





These graphs come from this site:
http://www.climate4you.com/ClimateAndClouds.htm#LowCloudCoverVersusGlobalSurfaceTemperature

The data comes from here: International Satellite Cloud Climatology Project(ISSCP)

The graphs show the variations in low clouds and high clouds.

Generally, to assess change in a variable over time, one looks at a deviation from the mean level. Here are the deviations:





The first graph shows that averaged globally, since about 1995 low levels clouds have decreased.
The second graph shows that averaged globally, high clouds have increased since about 2007, but are not much different from levels seen in 1986.

There are many other ways to look at the ISSCP data, which you can access here:
http://isccp.giss.nasa.gov/climanal1.html

At the above link you can make your own plots to look at regional differences and other variables within the data set.

Consider for a moment an observer whose memories of totally blue skies tell him that clouds have increased.

If his memories were acquired at different times, he might have good reason to see things differently from a person whose memories came from another time.

If he moved from one place to another with different climate, memories formed at one place might predominate over those from another.

I don't have time to go further into this, but it is grist for thought.

 

[Mick West]

In this 1980 video (made before the start points on your graphs), they say "there are 30 fewer days of sunshine now in the Mid-West now, than there were in 1900"

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Based on this research:
http://www.isws.illinois.edu/pubdoc/CR/ISWSCR-236.pdf

 

[Joe]

In this 1980 video (made before the start points on your graphs), they say "there are 30 fewer days of sunshine now in the Mid-West now, than there were in 1900"

​

Based on this research:
http://www.isws.illinois.edu/pubdoc/CR/ISWSCR-236.pdf

Someday use jets on purpose to change the weather ? 1:40

 

[Don Gisselbeck]

Here in Missoula, MT I believe we have had no days without at least a few clouds in the most of the last 2 years. Previous years we would have several winter days in a row (at least) with no clouds. They were memorable to obsessed skiers searching for any hint of snow. Is it possible to confirm my impression?

 

[Mick West]

Here in Missoula, MT I believe we have had no days without at least a few clouds in the most of the last 2 years. Previous years we would have several winter days in a row (at least) with no clouds. They were memorable to obsessed skiers searching for any hint of snow. Is it possible to confirm my impression?

You can get local weather data, see
http://weatherspark.com/history/30955/2012/Missoula-Montana-United-States
click on dates in the upper right. Scroll down for cloudiness

 

[Mick West]

You can get local weather data, see
http://weatherspark.com/history/30955/2012/Missoula-Montana-United-States
click on dates in the upper right. Scroll down for cloudiness

Here's the graphs for the last 20 years



Looks like in 1996 there was an abrupt change in the way cloud cover was measured, probably new automated instruments that have a different threshold for "cloudy", and the old data has been shoehorned into the new system.

It does look like your observations of the cloud free days in winter are understandable. However, there has not really been any change, just normal variation. There were years in the past that also had no cloud free winter spells, and there will be years in the future. You just didn't have it the past two.

 

[JRBids]

Is there someplace I can look up a specific area? We had a beautiful summer and fall, hardly any clouds.

 

[Mick West]

The above link has multiple locations.

 

[Jay Reynolds]

I have sometimes been successful finding photos of specific locations showing clear days when claims were made that there were none.

 

[Mick West]

I have sometimes been successful finding photos of specific locations showing clear days when claims were made that there were none.

Yes, Flickr is good for that, you can search by date. Theoretically by location, but I find some location specific keyword works better, like "Washington"