LIVERMORE, Calif. — The rain in Spain may lie mainly on the plain, but the location and intensity of that rain is changing not only in Spain but around the globe.
A new study by Lawrence Livermore National Laboratory scientists shows that observed changes in global (ocean and land) precipitation are directly affected by human activities and cannot be explained by natural variability alone. The research appears in the Nov. 11 online edition of the Proceedings of the National Academy of Sciences.
Emissions of heat-trapping and ozone-depleting gases affect the distribution of precipitation through two mechanisms. Increasing temperatures are expected to make wet regions wetter and dry regions drier (thermodynamic changes); and changes in atmospheric circulation patterns will push storm tracks and subtropical dry zones toward the poles.
“Both these changes are occurring simultaneously in global precipitation and this behavior cannot be explained by natural variability alone,” said LLNL’s lead author Kate Marvel. “External influences such as the increase in greenhouse gases are responsible for the changes.”
The team compared climate model predications with the Global Precipitation Climatology Project’s global observations, which span from 1979-2012, and found that natural variability (such as El Niños and La Niñas) does not account for the changes in global precipitation patterns. While natural fluctuations in climate can lead to either intensification or poleward shifts in precipitation, it is very rare for the two effects to occur together naturally.
“In combination, manmade increases in greenhouse gases and stratospheric ozone depletion are expected to lead to both an intensification and redistribution of global precipitation,” said Céline Bonfils, the other LLNL author. “The fact that we see both of these effects simultaneously in the observations is strong evidence that humans are affecting global precipitation.”
Marvel and Bonfils identified a fingerprint pattern that characterizes the simultaneous response of precipitation location and intensity to external forcing.
“Most previous work has focused on either thermodynamic or dynamic changes in isolation. By looking at both, we were able to identify a pattern of precipitation change that fits with what is expected from human-caused climate change,” Marvel said.
By focusing on the underlying mechanisms that drive changes in global precipitation and by restricting the analysis to the large scales where there is confidence in the models’ ability to reproduce the current climate, “we have shown that the changes observed in the satellite era are externally forced and likely to be from man,” Bonfils said.
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Identifying external influences on global precipitation
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Edited by Kerry A. Emanuel, Massachusetts Institute of Technology, Cambridge, MA, and approved October 18, 2013 (received for review July 30, 2013)
Significance
This study provides evidence that human activities are affecting precipitation over land and oceans. Anthropogenic increases in greenhouse gases and stratospheric ozone depletion are expected to lead to a latitudinal intensification and redistribution of global precipitation. However, detecting these mechanisms in the observational record is complicated by strong climate noise and model errors. We establish that the changes in land and ocean precipitation predicted by theory are indeed present in the observational record, that these changes are unlikely to arise purely due to natural climate variability, and that external influences, probably anthropogenic in origin, are responsible.
Abstract
Changes in global (ocean and land) precipitation are among the most important and least well-understood consequences of climate change. Increasing greenhouse gas concentrations are thought to affect the zonal-mean distribution of precipitation through two basic mechanisms. First, increasing temperatures will lead to an intensification of the hydrological cycle (“thermodynamic” changes). Second, changes in atmospheric circulation patterns will lead to poleward displacement of the storm tracks and subtropical dry zones and to a widening of the tropical belt (“dynamic” changes). We demonstrate that both these changes are occurring simultaneously in global precipitation, that this behavior cannot be explained by internal variability alone, and that external influences are responsible for the observed precipitation changes. Whereas existing model experiments are not of sufficient length to differentiate between natural and anthropogenic forcing terms at the 95% confidence level, we present evidence that the observed trends result from human activities.
paper: http://www.pnas.org/content/early/2013/11/05/1314382110.full.pdf
Imagined interview with the authors:
Authors (A): We cannot explain it any other way. It must be human emissions.
Interviewer (I): Did you look for another way to explain it?
A: Well…no.
I: Did you consider that your model, which has yet to demonstrate any significant level of skill, might account for your findings?
A: Well…no.
I: Did you consider the impact of natural climate cycles like the AMO and PDO in your calculations and what impact they might have had?
A: What are those?
I: Do you think it is odd that you found evidence of warming in the precipitation patterns when there is no evidence of warming in the temperature record? Doesn’t that simple fact actually disprove your entire thesis?
A: That is worthy of more research. We have applied for additional funding in order to clarify the calamity of climate change. No more questions. It is obvious that you do not know a thing about climate or science in general. It is a waste of our important and precious time to talk with you flat-earthers! Good day!
We are well into the era you just have to laugh at this stuff. I wonder how much differently schools will teach the scientific method in coming decades as the mythology of Cagw falls apart.
Janice Moore says:
November 13, 2013 at 10:27 am
(Trivia: of course, this little bit of climatology wasn’t completely honest, either…. that’s not Audrey Hepburn singing….. it’s Julie Andrews)
Actually…it was Marni Nixon that sang for Audrey Hepburn in the movie, although Audrey did sing a few of the songs that did not require a great deal of range, like ‘I could have danced all night.’ I have a crush on Julie Andrews and I didn’t think that was her voice…so I looked it up.
“where there is confidence in the models’ ability to reproduce the current climate”
Really.
So just another load of old donkey droppings.
Hmm. Higher temperatures enhance precipitation?
What do they say about lake-effect snow? Quite a bit of precipitation occurs even when the water temperature is just above freezing. Try living in Buffalo, NY. Maybe the phenomenon has more to do with temperature differences than higher absolute values. And don’t the typical models of global warming suggest the temperature differences in air masses are reduced? The only hope for their model seems to be in tropical cyclones driven by warmer water. And we see how that’s playing out despite Yolanda.
Jim Clarke,
Fine script at 11:20am, lol. (sigh) Too bad it isn’t fiction.
Thank you for correcting my mistake about Julie Andrews’ voice.
Janice
“…and cannot be explained by natural variability alone.”
Oy! Where have I heard that one before?
The models have AGW built into them. They don’t have built into them ENSO, AMO, PDO, IOD, or any natural factors that could be of any significance over the study period. The models are parameterised to match what has been going on in the real world in the recent past. The period studied is 1979 to 2012, ie. the recent past. Therefore the models will necessarily find that everything and anything that they choose to look at in this or any other study over the recent past was caused by AGW and could not have been caused by natural factors. No other result is possible. It’s called circular logic.
Since the forcing doesn’t exist, neither do the effects.
As I have been trying to convey the atmospheric circulation has been behaving the opposite of what this article maintains. The atmospheric circulation has been becoming more meridional (toward the equaote),less zonal (retreat toward the pole.).
Anthony ‘s website puts up or post an article like this which has no validity, and then does not post my sensible commentary about this article.
What makes this situation sad is we agree on much ,and yet because I was rough with Leif ,more often then not my commentary is not going through, and yet we are close in all of our opinions Anthony.
.
“They claim, that earthlings screw everting up.. This is true from observation. What is not said,. but also obvious, is that this planet was “not’ designed nor constructed by earthlings.. The designers anticipated all of the stupidity of earthlings and constructed this planet with all that in mind! What a wonderful planet. Perhaps it is only a zoo. It is high time
that earthlings recognize “what they are”, rather than “what they think they are!
Will Janoshchka (8:05pm) — Excellent comment. One of the best I’ve ever read (and the Scandihoovian accent in the first line only adds to its overall appeal).
Just a thought…
I look into the sky and see great columns of nimbus or is it cumulonimbus clouds, anyway they look great on the skyline back-lit by a rising sun. Nature is beautiful.
But then my thoughts wonder again – those great clouds are the conveyors of heat energy around the globe. And an essential for human life too, each of us is about 55% water, and with the human population getting on for 10 billion, that’s an awful lot of stuff we have in those many bodies. We also more water around to where we need it, sometimes large quantities of it.
Of course nearly all humans in the course of a day, burn some type of fuel and all of these release yet more water into the atmosphere. I wonder if any of these things have an effect on the biosphere we inhabit?
I’m sure lots of research must have been done on it by someone somewhere…
tom;
Locate the UN Population Survey, and open the Low Band page. It’s the only one ever close to accurate. Peak in 30 years, at about 8bn, declining thereafter, indefinitely. De-pop will be the real crisis, just as cooling will hit all the warmist-planners crossways.
To be explicit, we are being pushed to prepare for an overheated and overcrowded planet and are going to get the reverse. Which will be REALLY bad news, not pretend and imaginary bad news like we are playing with currently, for thrills and jollies.