AMS Releases Report on Extreme Weather of 2012 and its Relation to Climate Change

[LocoAko]

Article on the subject: http://america.aljazeera.com/articles/2013/9/7/scientists-link-2012extremeweathertomanmadeclimatechange.html

 

Summary of key conclusions: http://www.wunderground.com/blog/weatherhistorian/comment.html?entrynum=191

 

Full report: http://www.ametsoc.org/2012extremeeventsclimate.pdf (still reading through this)

 

 

Man-made climate change was factor in 2012 extreme weather, study finds

by Renee Lewis

 

September 7, 2013  2:00PM ET

Scientists say atmospheric pollution contributed to half of the extreme weather-related events of last year

 

Man-made climate change may have contributed to half of the extreme weather events of 2012, scientists said in a new report in the Bulletin of the American Meteorological Society (AMS).

The report (PDF), published Friday by scientists with the National Oceanic and Atmospheric Administration (NOAA), is based on studies of about a dozen extreme weather events from around the world in 2012 -- from northern Europe’s unusually wet summer to Hurricane Sandy.

 

The scientists were aiming to answer the question from which their field of study, known as “climate attribution science,” was born: How many of these events were caused by man-made climate change as opposed to natural variability?

 

Their conclusion, based on factors such as sea-surface temperatures, changes in incoming solar radiation and many others, is that human influence varies from one event to another. But in about half of the extreme events studied, they found that man-made climate change was a contributing factor.

 

Attempting to decipher whether or not climate change is the dominant factor in these events is a complex process.

 

Using an analogy, the AMS report explained: “Adding just a little bit of speed to your highway commute each month can substantially raise the odds that you’ll get hurt some day. But if an accident does occur, the primary cause may not be your speed itself: it could be a wet road or a texting driver.”

 

Likewise, while climate models indicate that compounded human effects increase the frequency of extreme-weather events -- “much like speeding increases the chances of having an accident” -- natural variability may still be the primary factor in any individual event.

 

Hurricane Sandy's intensity, for example, was reportedly compounded by both human effects and natural variability.

 

Global warming caused by human atmospheric pollution makes storms more frequent and intense, the report said. Hurricane Sandy happened to hit the East Coast at peak storm-tide levels and close to local high tide -- what researchers behind the report call natural variability. Further aggravating the intensity of the storm was Sea Level Rise (SLR), which has been shown to make flooding events worse.

 

'Century scale events'

 

In 2012 the United States experienced its most severe drought in decades, with more than half of all counties in the country listed as natural-disaster areas by the Department of Agriculture.

“For much of the central U.S., such conditions of combined scarcity of precipitation and elevated temperature had not been experienced since the Dust Bowl years of 1934 and 1936,” the report said.

 

The drought resulted in low or even zero crop yields, reduced livestock inventory, increases in food prices and at least 123 direct human deaths, according to the report, which called it a “century scale event.”

 

The report attributed the drought to a combination of factors, including increased surface heating due to human pollution -- more specifically, greenhouse-gas emissions.

A recently convened Intergovernmental Panel on Climate Change (IPCC) examining extreme weather events said it was confident that the central United States would experience an increase in duration and intensity of droughts in the coming years.

 

The report seemingly supports IPCC’s claim, finding that such large-scale droughts are four times as likely amid current temperatures than at pre-industrial levels. A model scenario developed by the NOAA scientists found that increases in temperature resulted in decreases of overall precipitation.

 

Higher temperatures have also been blamed for extensive ice loss in the Arctic, but the report found that it is not that simple. Melting ice, the report says, cannot be wholly attributed to human effects, but to a natural, gradual warming of Earth.

 

Yet global warming from man-made atmospheric pollution did contribute to a large storm which transited over the Arctic, breaking up the ice and sending a significant amount to warmer waters.

Some climate models project that theArctic will be ice-free in summer within a decade -- spelling disaster for low-lying countries such as Bangladesh and Pacific Island nations already feeling the effects of SLR.

 

Future of climate change

 

NOAA scientists behind the report say they hope to help provide “information that governments, organizations, and individuals can use to manage climate risks and opportunities.”

According to the Environmental Protection Agency (EPA), global average temperatures have already increased more than 1.4 degrees Fahrenheit over the last 100 years. Scientists project the Earth’s average temperatures to rise between 2 and 12 degrees Fahrenheit by 2100.

 

Increasing the average global temperature by a degree or two can have serious global consequences.

 

For every 2 degrees Fahrenheit of warming, the EPA says it expects a 5 to 15 percent reduction in crop yields; a 3 to 10 percent increase in rain during heavy precipitation events which can lead to flooding; a 5 to 10 percent decrease in stream flow and some river basins; and a 200 to 400 percent increase in the area burned by wildfire in parts of the western United States.

 

The magnitude and frequency of future climate change depends on the rate at which levels of greenhouse gas emissions increase in the atmosphere, and how strongly temperature, precipitation and sea levels respond to expected increases in emissions, the report said. 

 

Al Jazeera

 

[LocoAko]

Also, I figured this could serve as a catch-all thread for attribution studies and their discussion, since this is quickly becoming more and more of a subfield. 

[tacoman25]

So they are more than willing to at least partially blame the 2012 U.S. drought on AGW...and yet has there been an overall increase in U.S. droughts over the course of warming the past 100+ years? Are severe droughts actually becoming more frequent, or are they just singling out a very recent event as evidence?

 

Is AGW to blame for the quick recovery/reversal from drought conditions over much of the plains/midwest this year?

 

 

[LocoAko]

So they are more than willing to at least partially blame the 2012 U.S. drought on AGW...and yet has there been an overall increase in U.S. droughts over the course of warming the past 100+ years? Are severe droughts actually becoming more frequent, or are they just singling out a very recent event as evidence?

 

Is AGW to blame for the quick recovery/reversal from drought conditions over much of the plains/midwest this year?

 

 

drought.png

Where are you getting that from? I haven't had time to read the full report yet, but I got this from the Results & Discussions section:

 

...

The implication is that human alteration of the atmospheric composition may have had little effect on the frequency of low-precipitation periods. This leads us to hypothesize that if there are consequential changes to the hydrological cycle driving extreme dryness at seasonal scales, they will not be to rates of input, but to rates of output, via evaporative demand with increased surface warming. However, a recent GCM-based study using improved land surface representation suggests the effects of warming on drought in the central United States will be modest (Hoerling et al. 2012a).

Our findings are generally consistent with two studies of the severe drought/heat wave that occurred in the region of Texas and Oklahoma in 2011 (Hoerling et al. 2013a; Rupp et al. 2012). Using methods different from those used in this study, both found little or no change in precipitation likelihood due to anthropogenic GHGs. It is also worth pointing out that observational records indicate long-term trends of slight increases in annual precipitation over the central United States since the beginning of the 20th century (McRoberts and Nielson-Gammon 2011)

[ORH_wxman]

 

So they are more than willing to at least partially blame the 2012 U.S. drought on AGW...and yet has there been an overall increase in U.S. droughts over the course of warming the past 100+ years? Are severe droughts actually becoming more frequent, or are they just singling out a very recent event as evidence?

 

Is AGW to blame for the quick recovery/reversal from drought conditions over much of the plains/midwest this year?

 

 

drought.png

 

 

Its a typical attribution assessment. They say that climate models tell us that drought is more likely in a warming world, so that means that droughts have had a slightly higher chance of happening versus a colder world. It really doesn't tell us anything substantial though, and they note that observations do not show any attribution yet.

 

In fact, the 2012 drought was not attributable to GHGs according to the report. The relevant part of the study here:

 

 

 

[forkyfork]

i'll add bluewave's post from january to the discussion

http://www.americanwx.com/bb/index.php/topic/38999-714-year-return-period-for-hurricane-sandys-track-in-a-static-climate

my issue with sandy is thus: if humans are at least partially to blame for sea ice loss, and jennifer francis' conclusions about reduced sea ice leading to more blocking patterns are correct, couldn't you attribute some of sandy to AGW?

[ORH_wxman]

 

i'll add bluewave's post from january to the discussion

http://www.americanwx.com/bb/index.php/topic/38999-714-year-return-period-for-hurricane-sandys-track-in-a-static-climate

my issue with sandy is thus: if humans are at least partially to blame for sea ice loss, and jennifer francis' conclusions about reduced sea ice leading to more blocking patterns are correct, couldn't you attribute some of sandy to AGW?

http://www.pnas.org/content/early/2013/08/28/1308732110.abstract?sid=64a8d333-0e49-4595-a084-2f858e346c55

[forkyfork]

http://www.pnas.org/content/early/2013/08/28/1308732110.abstract?sid=64a8d333-0e49-4595-a084-2f858e346c55

"climate models consistently project a decrease in the frequency and persistence of the westward flow that led to Sandy’s unprecedented track"

do they mean blocking related westward flow? they make it sound like there was a jet blowing due west when it was really a strong block which forced a phase

[ORH_wxman]

 

"climate models consistently project a decrease in the frequency and persistence of the westward flow that led to Sandy’s unprecedented track"

do they mean blocking related westward flow? they make it sound like there was a jet blowing due west when it was really a strong block which forced a phase

 

Yes. They find less wave-breaking and blocking episodes in the future due to GHG warming.

This is actually consistent with the theory of a poleward jet increasing the AO. Obviously the recent blocking episodes and extreme negative AO do not fit the climate model theory, but that also does not mean they are wrong going forward.

Its just another reason to be careful of climate model based studies.

[TerryM]

"Some climate models project that the Arctic will be ice-free in summer within a decade -- spelling disaster for low-lying countries such as Bangladesh and Pacific Island nations already feeling the effects of SLR"

 

I suspect this was a journalists slip, not in the report itself.

Terry

[tacoman25]

Where are you getting that from? I haven't had time to read the full report yet, but I got this from the Results & Discussions section:

 

 

I didn't read the full report either, but the article said this: The report attributed the drought to a combination of factors, including increased surface heating due to human pollution -- more specifically, greenhouse-gas emissions. A recently convened Intergovernmental Panel on Climate Change (IPCC) examining extreme weather events said it was confident that the central United States would experience an increase in duration and intensity of droughts in the coming years.

 

So we are once again dealing with an inaccurate news article?

[ORH_wxman]

I didn't read the full report either, but the article said this: The report attributed the drought to a combination of factors, including increased surface heating due to human pollution -- more specifically, greenhouse-gas emissions. A recently convened Intergovernmental Panel on Climate Change (IPCC) examining extreme weather events said it was confident that the central United States would experience an increase in duration and intensity of droughts in the coming years.

 

So we are once again dealing with an inaccurate news article?

 

 

Relying on news journalists to report science accurately is like relying on the NAM to give you an accurate snow forecast in the winter.

 

Its better to read the papers for yourself rather than trust their analysis of it to be correct and/or unbiased.

[tacoman25]

Relying on news journalists to report science accurately is like relying on the NAM to give you an accurate snow forecast in the winter.

 

Its better to read the papers for yourself rather than trust their analysis of it to be correct and/or unbiased.

 

Yup. It's just frustrating because most of the time it wouldn't be that hard to get it right. Seems that pre-existing biases play a big role in how the message is delivered. Even in science sometimes, not just journalism. When the expectation is that AGW will increase certain types of events, of course researchers will look for attribution in those types of events. Fortunately, in this case it looks like the researchers did not attribute the drought to AGW when the evidence did not support it, regardless of what their expectations were.

 

It's interesting that the article says the IPCC is "confident" that the central U.S. will see increasing drought, but the paper indicates the opposite and points to little evidence of increasing drought over the past 100+ years.

[forkyfork]

 

 

Yes. They find less wave-breaking and blocking episodes in the future due to GHG warming.

This is actually consistent with the theory of a poleward jet increasing the AO. Obviously the recent blocking episodes and extreme negative AO do not fit the climate model theory, but that also does not mean they are wrong going forward.

Its just another reason to be careful of climate model based studies.

 

in that case i disagree with the climate models.  complex land/ocean interactions haven't been modeled well (the PDO comes to mind)

[bluewave]

in that case i disagree with the climate models.  complex land/ocean interactions haven't been modeled well (the PDO comes to mind)

 

It's interesting that other recent studies support the idea of increased blocking and patterns slowing down

or getting stuck in a warmer climate.

 

http://solberg.snr.missouri.edu/gcc/EarthSci1304014MokhovKOR.pdf

 

http://www.pik-potsdam.de/~stefan/Publications/Nature/Petoukhov+PNAS_2013.pdf

[forkyfork]

It's interesting that other recent studies support the idea of increased blocking and patterns slowing down

or getting stuck in a warmer climate.

 

http://solberg.snr.missouri.edu/gcc/EarthSci1304014MokhovKOR.pdf

 

http://www.pik-potsdam.de/~stefan/Publications/Nature/Petoukhov+PNAS_2013.pdf

having a water covered north pole surrounded by land really complicates things

[bluewave]

having a water covered north pole surrounded by land really complicates things

 

And having a longer observational record over the next 100 years should help to put some of these questions to rest:

 

 

http://www.washingto...xtreme-weather/

 

 

Here are Jennifer Francis’ comments in full…

Comments on Barnes 2013: Revisiting the evidence linking Arctic amplification to extreme weather in midlatitudes. GRL. by J.A Francis

I am pleased that Dr. Barnes, a respected and talented atmospheric dynamicist, has taken an interest in the topic of linkages between the rapidly changing Arctic and the large-scale circulation. The emerging influence of Arctic amplification (AA) on mid-latitude weather patterns is complex, and her expertise will help resolve some fundamental dynamical questions that are relevant to understanding mechanisms driving these linkages as the Arctic continues to warm faster than elsewhere.

What perplexes me, however, is that her intent in interpreting the new results in Barnes (2013) seems less than objective and is a direct attempt to disprove the work presented in Francis and Vavrus (2012; hereafter FV12). A very different interpretation of the results could be made. While her overarching conclusion is that the connections between AA and mid-latitude extreme weather are unfounded, I see a great deal of support for our results in her new work. For example:

Figure 2 presents time series of wave amplitudes (or extents) measured using two methods: one similar to ours and an alternative based on seasonal latitude differences. In all cases the trends are positive, suggesting an increase in amplitude during fall and summer, albeit only some of the trends are statistically significant. Because AA has emerged from the noise of natural variability only in the last 15 year or so, it is not surprising that its influence would not drive 30-year trends in a statistically significant way. Note that her new method does exhibit significant trends. This supports FV12.

My interpretation of the results in her Figure 3 is that in the ranges of 500 hPa heights that typically occur in mid-latitudes during summer (5.6 to 5.8 km) and autumn (5.5 to 5.7 km), the wave amplitudes are increasing from the early to the later part of the record. This, once again, supports FV12. She claims that because warming is shifting a particular height contour northward, it is incorrect to conclude that wave amplitudes are increasing. In fact, it is this northward shift – in particular the larger shift in high latitudes where warming is greatest – that we hypothesized would be a factor causing the waves to elongate.

Figure 4 presents measures of wave phase speed. While FV12 did not present wave speeds, we speculated that larger amplitude waves should have slower wave speeds. Her measure of phase speed for waves at 500 hPa slows with time, supporting our speculation. She then measures speeds at the 250 hPa level and finds no change in speed. This much higher level is near the tropopause, often above the jet stream, and can be affected by dynamics of the stratosphere. The stratosphere is cooling with increasing greenhouse gases, leading to very different dynamical changes. Why did she choose to analyze this level? My only guess is to deliberately cast doubt on FV12.

The mechanisms linking Arctic amplification with large-scale circulation patterns are clearly not simple and we still have much to learn. These new results provide additional insight into those linkages, but it appears that the interpretation of these results in Barnes (2013) was conducted with a particular intent. I welcome and appreciate Dr. Barnes’ contribution to the community’s efforts to understand the effects of AA on large-scale circulation changes, but perhaps a more balanced approach to interpreting the results could be applied going forward.

[ORH_wxman]

 

And having a longer observational record over the next 100 years should help to put some of these questions to rest:

 

Agreed. Unfortunately that is a long time to wait.

Trying to attribute trends of blocking based on 4-5 years of low sea ice is somewhere between difficult to impossible.

[bluewave]

 

 

Agreed. Unfortunately that is a long time to wait.

Trying to attribute trends of blocking based on 4-5 years of low sea ice is somewhere between difficult to impossible.

 

Yeah, that is a long wait.

 

Even shortly before the big 2007 decline, researchers found the 2005-2006 Eurasian winter was impacted

by the KB blocking pattern with lower sea ice coverage.

 

http://oceanrep.geomar.de/8738/1/2009JD013568-pip.pdf

 

I think that the AGW signal combined wit the +AMO shift in 1995 and the super El Nino in 1998

was an important part of the timing. It may have got us just warm enough to begin to see these 

potential effects.

[LocoAko]

The report for 2013 is out. Should make for good discussions. I look forward to reading it.

Full report: http://www2.ametsoc.org/ams/assets/File/publications/BAMS_EEE_2013_Full_Report.pdf

http://www.ncdc.noaa.gov/news/explaining-extreme-events-2013 (emphasis mine):

 

A report released today investigates the causes of a wide variety of extreme weather and climate events from around the world in 2013. Published by the Bulletin of the American Meteorological Society, “Explaining Extreme Events of 2013 from a Climate Perspective (link is external)” addresses the causes of 16 individual extreme events that occurred on four continents in 2013. NOAA scientists served as three of the four lead editors on the report.

Of the five heat waves studied in the report, human-caused climate change was found to have clearly increased the severity and likelihood of those events. On the other hand, for other events examined like droughts, heavy rain events, and storms, fingerprinting the influence of human activity was more challenging. Human influence on these kinds of events—primarily through the burning of fossil fuels—was sometimes evident, but often less clear, suggesting natural factors played a far more dominant role.

“This annual report contributes to a growing field of science which helps communities, businesses and nations alike understand the impacts of natural and human-caused climate change,” said Thomas R. Karl, L.H.D., director of NOAA’s National Climatic Data Center. “The science remains challenging, but the environmental intelligence it yields to decision makers is invaluable and the demand is ever-growing.”

Confidence in the role of climate change about any one event is increased when multiple groups using independent methods come to similar conclusions. For example, in this report, five independent research teams looked at specific factors related to the record heat in Australia in 2013. Each consistently found that human-caused climate change increased the likelihood and severity of that event. However, for the California drought, which was investigated by three teams from the United States, human factors were found not to have influenced the lack of rainfall. One team found evidence that atmospheric pressure patterns increased due to human causes, but the influence on the California drought remains uncertain.

When human influence for an event cannot be conclusively identified with the scientific tools available today, this means that if there is a human contribution, it cannot be distinguished from natural climate variability.

“There is great scientific value in having multiple studies analyze the same extreme event to determine the underlying factors that may have influenced it,” said Stephanie C. Herring, PhD, lead editor for the report at NOAA’s National Climatic Data Center. “Results from this report not only add to our body of knowledge about what drives extreme events, but what the odds are of these events happening again—and to what severity.”

The report was edited by Herring, along with Martin P. Hoerling, NOAA’s Earth System Research Laboratory; Thomas Peterson, NOAA’s National Climatic Data Center, and Peter A. Stott, UK Met Office Hadley Centre and written by 92 scientists from 14 countries. View the full report online (link is external).

Also, view the slides for the media briefing on the "Explaining Extreme Events of 2013 from a Climate Perspective" report.

Edit: Didn't see the other thread on this already made. Feel free to delete/merge if need be.

[LocoAko]

Is this still the threat to post all attribution studies? 

 

Anyway, new study out in Nature Climate Change: http://www.nature.com/nclimate/journal/vaop/ncurrent/full/nclimate2617.html

 

Abstract: 

 

 

Climate change includes not only changes in mean climate but also in weather extremes. For a few prominent heatwaves and heavy precipitation events a human contribution to their occurrence has been demonstrated^{1, 2, 3, 4, 5}. Here we apply a similar framework but estimate what fraction of all globally occurring heavy precipitation and hot extremes is attributable to warming. We show that at the present-day warming of 0.85 °C about 18% of the moderate daily precipitation extremes over land are attributable to the observed temperature increase since pre-industrial times, which in turn primarily results from human influence⁶. For 2 °C of warming the fraction of precipitation extremes attributable to human influence rises to about 40%. Likewise, today about 75% of the moderate daily hot extremes over land are attributable to warming. It is the most rare and extreme events for which the largest fraction is anthropogenic, and that contribution increases nonlinearly with further warming. The approach introduced here is robust owing to its global perspective, less sensitive to model biases than alternative methods and informative for mitigation policy, and thereby complementary to single-event attribution. Combined with information on vulnerability and exposure, it serves as a scientific basis for assessment of global risk from extreme weather, the discussion of mitigation targets, and liability considerations.