Climate change is altering winter precipitation across the Northern Hemisphere

Climate change is altering winter precipitation across the Northern Hemisphere
This map shows the influence of human-caused climate change on wintertime precipitation in the Northern Hemisphere from 1921 to 2015. The warming climate has spurred significant increases in precipitation across much of northeastern North America and northern Eurasia. The stippled regions show precipitation trends that are statistically insignificant. Credit: Simmi Sinha, UCAR, redrawn from map by Ruixia Guo of Lanzhou University and NCAR

A team of scientists has successfully teased out the influence of human-caused climate change on wintertime precipitation over much of the last century, showing that the warming climate is significantly altering wintertime rainfall and snowfall across the Northern Hemisphere.

The study, led by scientists at the National Center for Atmospheric Research (NCAR), used an innovative approach that relied on observations of and large-scale atmospheric circulation patterns, along with statistical techniques and computer climate simulations. This enabled the research team to identify the amount of average monthly precipitation in specific regions of North American and Eurasia that fell as a result of human impacts on the climate, rather than natural variability.

"I thought this was quite revealing," said NCAR senior scientist Clara Deser, a co-author of the study. "Our research demonstrates that human-caused climate change has clearly affected precipitation over the past 100 years."

The results show that warming temperatures associated with human emissions of greenhouse gases spurred a noticeable increase in wintertime precipitation across widespread regions of northern Eurasia and eastern North America since 1920.

The work may point the way to more into the influence of climate change on precipitation changes year-round. Precipitation globally is projected to increase by an average of 1-2% per additional degree Celsius because a warmer atmosphere holds more water vapor. But local changes may be highly variable, with some regions becoming dryer and others far wetter.

The study, by scientists at NCAR, Lanzhou University in China, and the University of Toulouse in France, was published in the AGU journal Geophysical Research Letters. It was funded in part by the National Science Foundation, which is NCAR's sponsor.

Subtracting the influence of natural variability

Scientists for years have conducted attribution studies to determine the extent to which changes in weather patterns can be attributed to human influence on climate. Using computer models and observations, national and international teams of researchers have repeatedly demonstrated that globally warming temperatures since the 1950s are largely due to societal emissions of carbon dioxide and other heat-trapping greenhouse gases.

But determining the role of greenhouse gases in century-long precipitation trends across continents is highly challenging, because precipitation is affected by localized and variable weather conditions, making it difficult to discern the long-term changes amid the noise of day-to-day and year-to-year changes in weather. Scientists have previously relied on large numbers of climate model simulations to try to detect the signal of long-term precipitation trends.

In the new study, the researchers used observations, rather than climate models, to determine the influence of a changing climate on precipitation. They essentially reduced the question to a subtraction problem: if you take away the amount of precipitation that's caused by natural variability, then the difference between that and what actually fell can likely be attributed to society's impact on climate.

The scientists turned to an innovative approach known as dynamical adjustment. This consisted of applying statistical techniques to observations of large-scale circulation patterns in the atmosphere for every winter month from 1920 to 2015. These circulation patterns, such as the location of high- and low-pressure systems over North America and Eurasia, occur independently of the build-up of heat-trapping greenhouse gases.

By aggregating all the circulation patterns, the researchers could estimate the typical amount of precipitation that would fall when a particular circulation pattern occurs. The team then compared the results to measurements of the precipitation that actually fell. The difference between the two—the amount of precipitation that would be associated with the large-scale circulation patterns under natural conditions and the actual precipitation trends—revealed the influence of climate change.

The results showed that the has led to increased wintertime precipitation across northeastern North America, as well as a small region of northwestern North America. Climate change also has contributed to an increase in precipitation across much of northwestern and north central Eurasia.

In contrast, the study indicated that climate change may have had had a drying influence on parts of central and southwestern North America—although not enough to offset natural variability—and on much of southern Eurasia. However, the authors cautioned that the results for those regions were less pronounced and not statistically significant.

Deser and her colleagues focused on winter because precipitation during that time of year is driven by broad atmospheric patterns that are easier to see in the data than localized conditions that affect summer precipitation, such as soil moisture and individual thunderstorms. They concentrated on the Northern Hemisphere because it contains far more measurements of precipitation than the Southern Hemisphere.

The results were in good agreement with climate simulations of human-induced changes in precipitation, providing an independent verification of the models.

"Scientists previously turned to climate models for answers. Here, the climate models come in only at the end to confirm what we teased out of observations independently," said NCAR scientist Flavio Lehner, a co-author of the study. "I think this is the major scientific breakthrough of this work."

Lehner and Deser used the same technique in a separate study, published in Geophysical Research Letters last year, to show that recent drying in the U.S. Southwest is largely attributable to natural variability.

Supporting evidence from international studies

The new study relied on detailed, international datasets of historic precipitation measurements and atmospheric circulation patterns. It also drew on two datasets of global climate simulations. One, known as the Large Ensemble, used the NCAR-based Community Earth System Model (CESM) to create 40 simulations of global climate beginning in 1920—each one with slightly different starting conditions. The other consisted of simulations from 37 world-leading climate models, including the CESM, that were used for an international climate research project known as the Coupled Model Intercomparison Project 5 (CMIP5).

The findings lend support to international studies that have used powerful climate models to try to discern the influence of greenhouse gases. For example, the CMIP5 project showed a similar pattern of precipitation trends due to climate change. That research relied entirely on computer simulations, and its results were less detailed than the new study.

"When we saw how well our approach, which is based entirely on observational data, agreed with the models, we were surprised because these are two independent ways of looking at ," Deser said. "The degree of agreement with both the amplitude and the spatial patterns of precipitation change was really impressive."


Explore further

Model development is crucial in understanding climate change

More information: Ruixia Guo et al. Human Influence on Winter Precipitation Trends (1921–2015) over North America and Eurasia Revealed by Dynamical Adjustment, Geophysical Research Letters (2019). DOI: 10.1029/2018GL081316
Journal information: Geophysical Research Letters

This story is republished courtesy of AGU Blogs (http://blogs.agu.org), a community of Earth and space science blogs, hosted by the American Geophysical Union. Read the original story here.

Citation: Climate change is altering winter precipitation across the Northern Hemisphere (2019, August 27) retrieved 22 October 2019 from https://phys.org/news/2019-08-climate-winter-precipitation-northern-hemisphere.html
This document is subject to copyright. Apart from any fair dealing for the purpose of private study or research, no part may be reproduced without the written permission. The content is provided for information purposes only.
953 shares

Feedback to editors

User comments

Aug 27, 2019
Scientists now believe in magical thinking more than wizards do.

Aug 27, 2019
Scientists believe in what is real and science is real, your delusional understanding of reality defies even stupidity

Aug 27, 2019
The hockey stick is Fake News. Warming is occurring, Holocene Thermal Maximum is no where in sight.

If you're concerned;
Plant trees
Paint all artificial sky facing surfaces a reflective color
Tell you political and social betters to stop flying chartered jets.

Carry on.

Aug 27, 2019
@shootist Its good you point out the hypocracy of many in the previleged west. I myself am guilty as charged. As well as the switch to sustainable practices, we all must take on a large reduction in our personal energy use, including ironicly use of the internet. As for placing the science in the false news category you're off target. Science willingly puts itself up for disproving, but you've got to do the sums - opinions just get in way and must be put aside.

Aug 27, 2019
The inability to understand science and giving alternative pseudo-scientific explanation of the natural phenomena led to the evolution of religions and cults.

Aug 27, 2019
''high- and low-pressure systems over North America and Eurasia, occur independently of the build-up of heat-trapping greenhouse gases.''

wow i thought EVERYTHING was affected by climate change , guess u get to pick and choose to get your result.

'build-up of heat-trapping greenhouse gases.''

in the 1950'S ?

Aug 27, 2019
has successfully teased out the influence of human-caused climate change


Lol, Teased out? What total crap science.

Aug 27, 2019
Scientists believe in what is real and science is real, your delusional understanding of reality defies even stupidity
says Menelo

Scientists believe in whatever is testable. If it isn't testable then it isn't provable or disprovable.
And SOME scientists will continue testing until the tests come out to their satisfaction. After which those scientists will write a math formula to explain their results. And if they don't like the results, they will start all over again with a slight difference.

Aug 28, 2019
@snoosebaum.
From above article: ''high- and low-pressure systems over North America and Eurasia, occur independently of the build-up of heat-trapping greenhouse gases.''
wow i thought EVERYTHING was affected by climate change , guess u get to pick and choose to get your result.
AS usual for you 'bots', you miss that the BROAD pattern of highs and lows is not the point; it's the moisture/precipitation accompanying same that is CHANGING. Hence the increasing disastrous flood events around the globe now....while the drying of atmosphere in other parts is causing record droughts. It's the scientifically predicted transitional dangers coming to pass.
From above article: 'build-up of heat-trapping greenhouse gases.''
in the 1950'S ?
Yes, it started with Industrial Revolution; got worse due to World Wars I & II (when armaments, ships/planes and chemicals etc production skyrocketed); and getting worse ever since due to vastly expanded agriculture/industry/population.

Aug 29, 2019
''
Yes, it started with Industrial Revolution; got worse due to World Wars I & II (when armaments, ships/planes and chemicals etc production skyrocketed); and getting worse ever since due to vastly expanded agriculture/industry/population. ''

implying an extreme sensitivity to a tiny amount of CO2

Aug 29, 2019
@snoosebaum.
Yes, it started with Industrial Revolution; got worse due to World Wars I & II (when armaments, ships/planes and chemicals etc production skyrocketed); and getting worse ever since due to vastly expanded agriculture/industry/population.
implying an extreme sensitivity to a tiny amount of CO2
It all adds up, mate. And the increase since then is slowly producing heating which is reaching levels that will trigger even more extreme outgassing of CO2 and Methane from clathrates/hydrates and ocean water no longer cool enough to hold all that CO2 it has been absorbing since the atmospheric CO2 concentration increases which are continuing. If we allow that to happen, then all bets are off and it will only get worse not better. Let's hope your kind of stupidity and betrayal of humanity does not prevail, @snoose; else you and your family will pay the price along with the rest of the world. Good luck to us all.

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more