Climate change in North Dakota

This post is in response to Darin, who left a good comment on my previous post concerning flooding in North Dakota.  Darin said:

Something is going on. I have lived here all my life and experienced two of the record level floods prior to the 1997 flood. That was the flood of 1975 and 1979.

Since then we’ve had 97-2001-2006-2009 that have each bumped all other years in the previous 110 years of record keeping down the list.

Now 7 of the top 10 flood levels come in the last 25 years.

You don’t have to have a masters in statistics to see a correlation to SOMETHING? I don’t know if it is global warming changing weather patterns, but they are changing.

Darin’s observations are legitimate and he has asked some good questions.  I would say that perhaps a master’s in statistics would, in fact, be useful in this situation.  But references to paleoclimatological records would be even more useful.  Why?  Because the real question is whether or not the climate in North Dakota and surrounding areas in the last several decades (while CO2 levels have gone up significantly) has varied in an obvious way from the magnitude of fluctuations seen during the “normal times” over the last several millennia (before CO2 levels rose).   

Consider recent history first. 

Pre-industrial CO2 levels are typically pegged at 280 ppm (parts per million).    Levels rose slowly during the 19th century and reached about 290 ppm by around 1930 and 310 ppm around 1950.   Today the number is at about 385 ppm, as shown below.  So I think that we can agree that the CO2 level started rapidly increasing when the world started becoming highly industrialized in the 40s and 50s. 

So when did the most extreme measured temperatures occur in North Dakota?  Answer: in the 1930s (-60 and +121 degrees F), when CO2 levels were much closer the pre-industrial levels.  When was the previous measured record crest of the Red River?  Answer: 1897, at 40.1 feet, when atmospheric CO2 levels were almost at pre-industrial  levels.

Paleoclimatological history

Drought is the most commonly sited risk of CO2 induced anthropogenic global warming for North Dakota.  For example, the Center for Integrative Environmental Research at the University of Maryland reports in their paper “Economic Impacts of Climate Change on North Dakota”:

“Atmospheric models predict that North Dakota will become drier in the future, with drought patterns becoming more intense as a consequence of global warming.”

Additionally the argument is made that rising levels of atmospheric CO2 will result in “climate change,” as opposed simple “global warming,” with greater extremes in temperature, precipitation, etc.  Using this terminology any changing climate conditions can be attributed to anthropogenic CO2, right?  Well, no.  This argument only works if it can be shown that the range of weather extremes in the era of increasing CO2 is statistically greater than the range of weather extremes during at least several thousand years while CO2 held steady at about 280 ppm.   What does the paleoclimatological record say about North Dakota climate for the last several thousand years?

In 1999, in the Proceedings of the North Dakota Academy of Sciences, Allan Ashworth pointed out that:

North Dakotan’s know only too well the effects of climate change. From 1988 to 1992 the State experienced drought conditions but since then North Dakota has been in a wet cycle. North Dakotans are stoical when it comes to weather but even so there is a concern about what the future will bring. Most of our knowledge of climate change comes from an instrumental record that is only 100 years in length. This record has been extended by dendroclimatology and by high resolution paleontologic and geochemical studies of lake sediments. What these studies are showing is that 100 years is far to short a time to show the variability in the climate record. (emphasis added)
 

 Ashworth points out some interesting details.  For example, at Rice Lake “maximum drought conditions during the mid-Holocene occurred between 7-6” thousand years ago.  Similarly, “maximum drought conditions at Elk Lake, Itasca Park, Minnesota, occurred between 6.2 to 6” thousand years ago.  At Moon Lake the presence of Iva pollen (which at the present “does not extend north of Nebraska…is thought to represent warmer conditions”  in the mid-Holocene.  Ashworth gives details of lake salinity and level changes during the mid-Holocene and notes “The general assumption is that significant changes in the lake levels are the result of climate change” during the last several thousand years, before CO2 levels rose.  He further notes:

“Individual records show a lot of variation, but there appears to be a cyclicity to drought, with intense droughts occurring on a frequency of 40 – 60 years. What is particularly striking is the Moon Lake salinity record is the magnitude of a series of droughts prior to AD 1200: at AD 200-370, AD 700-850 and AD 1000 -1200. These droughts were all of a greater magnitude than the intense drought of the 1930’s.”

In a 1997 Quaternary Research paper concerning climate variability, as measured by a variety of markers at Moon Lake, North Dakota,  Blas L. Valero-Garces, et al. wrote:

Seismic stratigraphy, sedimentary facies, pollen stratigraphy, diatom-inferred salinity, stable isotope (δ¹⁸O and δ¹³C), and chemical composition (Sr/Ca and Mg/Ca) of authigeniccarbonates from Moon Lake cores provide a congruent Holocene record of effective moisture for the eastern Northern Great Plains. … A change at about 7100¹⁴C yr B.P. inaugurated the most arid period during the Holocene. Between 7100 and 4000¹⁴C yr B.P., three arid phases occurred at 6600–6200¹⁴C yr B.P., 5400–5200¹⁴C yr B.P., and 4800–4600¹⁴C yr B.P. Effective moisture generally increased after 4000¹⁴C yr B.P., but periods of low effective moisture occurred between 2900–2800¹⁴C yr B.P. and 1200–800¹⁴C yr B.P. The data also suggest high climatic variability during the last few centuries.  (emphasis added)

 If Valero-Garces, et. al., are correct then is seems that recent variability in North Dakota is not unusual, and cannot be blamed on anthropogenic CO2.

Sherilyn C. Fritz of the University of Nebraska – Lincoln Department of Geosciences and her co-authors considered the “Hydrologic Variation in the Northern Great Plains During the Last Two Millennia“, and claim that

“The data show that the last 2,000 years have been characterized by frequent shifts between high and low salinity, suggesting shifts between dry and moist periods. Long intervals of high salinity suggest periods of multiple decades when droughts were intense and frequent, thus indicating times when drought was more persistent than in the 20th century. ..[T]he climate of the last 2000 years was hydrologically complex, with large oscillations between low-salinity wet phases and high-salinity dry phases.” (emphasis added)

Fritz gives details from three North Dakota lake sites showing constant variation…

“All records show an interval of prolonged drought between ca. A.D. 40 and 130, followed by a wetter period, and also a dry period about A.D. 250, which two of the records (Moon [Lake]and Rice [Lake]) suggest was sustained for more than a century. Shorter periods of drought are evident at ca. A.D. 400 and 530, and the data suggest a period of major and sustained drought from ca. A.D. 620 to 790. The time from A.D. 1020 to 1150 was also characterized by major drought and was followed by a distinct wet interval to at least A.D. 1300. …. All sites show intervals of very fresh conditions, suggesting high precipitation, sometime between A.D. 1330 and 1430 and in the early decades of the 1800s. The data also suggest periods of drought in the decades surrounding A.D. 1500, 1600, and 1800, and in the latter decades of the 19th century.”

Kathleen Laird of the Department of Ecology at the University of Minnesota writes in Nature  that

“Extreme large-scale droughts in North America, such as the “Dust Bowl” of the 1930s, have been infrequent events within the documented history of the past few hundred years, yet this record may not be representative of long-term patterns of natural variation of drought intensity and frequency. .. Here we present a reconstruction of drought intensity and  frequency over the past 2,300 years in the Northern Great Plains…” (emphasis added)

Laird studied the salinity record of Moon Lake, North Dakota, as an indicator changing hydrological conditions and said…

“Our working assumption is that periods of positive water balance (precipitation > evapotranspiration) are reflected by higher lake levels and lower salinities, whereas when the water balance is negative, lake levels are lower and salinity higher …”

and found the following fluctuating signal:

Figure 2. Salinity of Moon Lake, North Dakota, from Laird, et. al., Nature

My conclusion is that the precipitation variation seen over the last 100 years in North Dakota is not unusual when compared to previous centuries, when CO2 levels remained near 280 ppm