ENSO

An Illustrated Guide to El Nino and La Nina and how they control climate

Bob Tisdale, author of Who Turned on the Heat?, has produced an excellent explanation of the solar-driven El Nino-La Nino events that arise in the Pacific Ocean and control global weather and climate on annual, decadal, and multidecadal time frames.

His long post contains 29 illustrations that take you through the process (three illustrations are reproduced below). Tisdale also provides explanatory text. I have read many papers on El Nino-La Nina (collectively called ENSO) and think Tisdale’s presentation is the most lucid and understandable explanation of the interplay between trade winds and ocean currents and their effects on ocean and air temperatures. It is aimed at the layman. Give it a look, read the whole post here.
A free preview of Tisdale’s book, in pdf format, is available here. The whole book is available for purchase here.

El Nino

ENSO neutral

La Nina

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Droughts in the Southwest put in perspective

The severe drought in Texas this year has fueled speculation that alleged human-caused global warming has somehow caused “unprecedented” conditions. But real research data show that the current drought is not unprecedented and is part of a natural cycle. There have been much more severe and persistent droughts in the past before humans began emitting signification amounts of carbon dioxide into the atmosphere. This post focuses on research from the University of Arizona and the Lamont-Doherty Earth Observatory of Columbia University.

From the University of Arizona and Arizona State University we have “A 1,200-year perspective of 21st century drought in southwestern North America.”

The Abstract reads in part:

A key feature of anticipated 21st century droughts in Southwest North America is the concurrence of elevated temperatures and increased aridity. Instrumental records and paleoclimatic evidence for past prolonged drought in the Southwest that coincide with elevated temperatures can be assessed to provide insights on temperature-drought relations and to develop worst-case scenarios for the future. In particular, during the medieval period, AD 900–1300, the Northern Hemisphere experienced temperatures warmer than all but the most recent decades. Paleoclimatic and model data indicate increased temperatures in western North America of approximately 1 °C over the long-term mean. This was a period of extensive and persistent aridity over western North America. Paleoclimatic evidence suggests drought in the mid-12th century far exceeded the severity, duration, and extent of subsequent droughts. The driest decade of this drought was anomalously warm, though not as warm as the late 20th and early 21st centuries. The convergence of prolonged warming and arid conditions suggests the mid-12th century may serve as a conservative analogue for severe droughts that might occur in the future. The severity, extent, and persistence of the 12th century drought that occurred under natural climate variability, have important implications for water resource management. The causes of past and future drought will not be identical but warm droughts, inferred from paleoclimatic records, demonstrate the plausibility of extensive, severe droughts, provide a long-term perspective on the ongoing drought conditions in the Southwest, and suggest the need for regional sustainability planning for the future.

This paper goes on to discuss the role of El Niño-La Niña cycles and sea-surface temperature, but the paper does not really address cause of the droughts. The theme of this paper is that past droughts are associated with warm periods and that continued warming may portend more severe droughts in our future. However, the authors partly contradict themselves by saying that the more severe droughts of the Medieval period occurred when the temperatures were cooler than the current warm period.

It seems we have a complex interplay of natural cycles which are not completely understood.

From Cornell, we have “The characteristics and likely causes of the Medieval megadroughts in North America.” and a very interesting graph:

Droughts in the west

  This graph shows that while the current drought is severe, it is much less severe than droughts during the Medieval Warm Period, a time before humans were emitting much carbon dioxide into the atmosphere.

The paper presents three conclusions:

1) The similarity of the spatial patterns suggests that the physical processes that caused the modern droughts also caused the medieval megadroughts.

2) The global atmosphere ocean conditions that currently cause modern droughts for a few years at a time were the prevailing ocean climate during the medieval period.

2) Despite the shift in the mean tropical ocean climate ENSO variability continued as now but oscillating about a colder mean state.

The authors also present an archaeological speculation:

The medieval megadroughts may also have left their signature on the human environment of the West. The great cliff cities in the four corners region of the West such as at Chaco Canyon and Mesa Verde were all abandoned towards the end of the drought. These societies were based on irrigated agriculture. Although there remains much debate about why these highly organized Indian societies collapsed, archaeologists are revisiting the idea that decades of dry conditions were part of the reason.

With both papers we see that data collection is one thing, interpretations are another.

See also:

Drought in the West

El Niño, bristlecone pines, and drought in the Southwest

EL NINO behavior, climate models predict opposite of what really happens

EL NINO behavior, climate models predict opposite of what really happens

The El Nino/La Nina cycle, more formally known as the El Nino/Southern Oscillation (ENSO) is an irregular cycle of sea surface temperature, atmospheric pressure, and wind direction in the tropical Pacific Ocean which has a profound affect on global weather. Both floods and droughts are associated with phases of ENSO.

ENSO2

 El Nino (warm phase)

In South America, this warm phase suppresses the normally cold upwelling currents that bring fish to the coasts of Peru and Ecuador. This phase brings unusually warm and wet weather during the South American winter.

In North America, El Nino brings warm, dry winters and wet summers to the northern region, and much wetter winters to the southwestern U.S. and northern Mexico.

Australia can experience droughts.

La Nina (cool phase)

In South America, La Nina brings drought to Peru and Chile but more rain to northern Brazil. In North America, La Nina brings above average precipitation to the north (hence our heavy snowfall during the winter of 2010-2011) and average to much below average precipitation to the southern U.S.

The influence of La Nina reaches Africa and produces more precipitation in south Africa and dryer conditions in equatorial Africa.

Climate models fail

Climate models, which are based on the assumption that carbon dioxide has a positive feedback, i.e., that carbon dioxide causes significant warming, make predictions on the behavior of ENSO. An analysis of those predictions versus what actually happened shows that the climate models predicted almost the exact opposite of what really happened.

Citation: McPhaden, M. J., T. Lee, and D. McClurg (2011), El Niño and its relationship to changing background conditions in the tropical Pacific Ocean, Geophys. Res. Lett., 38, L15709, doi:10.1029/2011GL048275

The abstract reads:

This paper addresses the question of whether the increased occurrence of central Pacific (CP) versus Eastern Pacific (EP) El Niños is consistent with greenhouse gas forced changes in the background state of the tropical Pacific as inferred from global climate change models. Our analysis uses high-quality satellite and in situ ocean data combined with wind data from atmospheric reanalyses for the past 31 years (1980–2010). We find changes in background conditions that are opposite to those expected from greenhouse gas forcing in climate models and opposite to what is expected if changes in the background state are mediating more frequent occurrences of CP El Niños. A plausible interpretation of these results is that the character of El Niño over the past 31 years has varied naturally and that these variations projected onto changes in the background state because of the asymmetric spatial structures of CP and EP El Niños.

In another paper:

Wolter, K. and Timlin, M.S. 2011. El Niño/Southern Oscillation behavior since 1871 as diagnosed in an extended multivariate ENSO index (MEI.ext). International Journal of Climatology 31: 1074-1087.

The researchers were able to extend analysis of ENSO events back to 1871 and found: “none of the behavior of recent ENSO events appears unprecedented, including duration, onset timing, and spacing in the last few decades compared to a full century before then.” Climate models predict that ENSO events should become more frequent and intense with global warming.

In other words, the climate model assumption of a positive feedback for carbon dioxide is wrong. And once again there is evidence that our carbon dioxide emissions have little actual effect on global temperature, and, there is still no physical evidence that carbon dioxide does have a significant effect. We, therefore, should not be basing policy decisions on flawed model scenarios.

ENSO is just one of several recognized oscillations driven by the sun and the earth’s position relative to the sun. To see other oscillations go here.

See Tisdales guide: An Illustrated Guide to El Nino and La Nina

See also:

A Basic Error in Climate Models

Climate Model Projections vs Real World Observations

Climate Data, Fact or Fiction

Natural Climate Cycles

NASA satellite data show climate models are wrong – again

Carbon Dioxide and the Greenhouse Effect

Humans and the Carbon Cycle

El Niño, bristlecone pines, and drought in the Southwest

While the Southwest is experiencing drought conditions, unusual flooding is occurring along the Mississippi River.  This is part of the natural La Niña cycle.

Research from the University of Hawaii’s International Pacific Research Center  has found an 1100-year correlation between El Niño-La Niña cycles and tree rings in bristlecone pines in the American Southwest.  This may allow better prediction of the cycles and a better understanding of past cycles and their implications.

El Niño and its partner La Niña, the warm and cold phases in the eastern half of the tropical Pacific,  play havoc with  climate worldwide. Predicting El Niño events more than several months ahead is now routine, but predicting how it will change  in a warming world has been hampered by the short instrumental record. An international team of climate scientists has now shown that annually resolved tree-ring records from North America, particularly  from  the US Southwest, give a continuous representation of the intensity of El Niño events over the past 1100 years and can be used to improve El Niño prediction.

Tree rings in the US Southwest, the team found, agree well with the 150-year instrumental sea surface temperature records in the tropical Pacific. During El Niño, the unusually warm surface temperatures in the eastern Pacific lead to changes in the atmospheric circulation, causing unusually wetter winters in the US Southwest, and thus wider tree rings; unusually cold eastern Pacific temperatures during La Niña lead to drought and narrower rings. The tree-ring records, furthermore, match well existing reconstructions of the El Niño-Southern Oscillation and correlate highly, for instance, with [oxygen 18] isotope concentrations of both living corals and corals that lived hundreds of years ago around Palmyra in the central Pacific.

The graph below shows the correlation.

El nino amplitude from tree rings

The tree rings reveal that the intensity of El Niño has been highly variable, with decades of strong El Niño events and decades of little activity. The weakest El Niño activity happened during the Medieval Climate Anomaly in the 11th  century, whereas the strongest activity has been since the 18th  century.

These different periods of El Niño activity are related to long-term changes in Pacific climate. Cores taken from lake sediments in the Galapagos, northern Yucatan, and the Pacific Northwest reveal that the eastern–central tropical Pacific climate swings between warm and cool phases, each lasting from 50 to 90 years. During warm phases, El Niño and La Niña events were more intense than usual. During cool phases, they deviated little from the long-term average as, for instance, during the Medieval Climate Anomaly when the eastern tropical Pacific was cool.

While correlation does not necessarily prove causation, these results are compelling.  Many factors such as temperature and amount of precipitation affect the width of tree rings.  The researchers say in this case, that precipitation is the controlling factor.  They rely on Liebig’s Law  which states that yield is proportional to the amount of the most limiting nutrient, and in the desert southwest, water is the limiting factor.

We are currently experiencing the La Niña phase which means a dry southwest and colder, wetter conditions in the north and mid-west.

For more background on drought see: Drought in the West.

Drought in the West

Pima County and the City of Tucson have a cooperative project to study the regional water supply and demand. “The ultimate goal of this effort is to assure a sustainable community water source given continuing pressure on water supply caused by population growth.”

Water is vital to life, so there is concern about the current drought in the Western U.S. and its impact on our water supply. In Arizona, our supply from the Lower Colorado River system stands at just 56% capacity as of Jan. 19, 2010, according to the Bureau of Reclamation. The Salt River system, supplying Phoenix, stands at 79% capacity, and the Verde River system is at 34%.

Some claim that the current drought is the result of human-induced global warming; others blame the ozone hole. However, droughts are naturally occurring and cyclic.

According to NOAA, “Droughts occur throughout North America, and in any given year, at least one region is experiencing drought conditions.” “Droughts similar to the 1950s, in terms of duration and spatial extent, occurred once or twice a century for the past three centuries (for example, during the 1860s, 1820s, 1730s). However, there has not been another drought as extensive and prolonged as the 1930s drought in the past 300 years. Longer records show strong evidence for a drought that appears to have been more severe in some areas of central North America than anything we have experienced in the 20th century, including the 1930s drought.”

In the Pacific northwest, Knapp et al, found that widespread and extreme droughts were concentrated in the 16th and early 17th centuries when the planet was considerably colder than the 20th century.

In a separate study of mean water-year flow on the Columbia River, Gedalof et al. found that “persistent low flows during the 1840s were probably the most severe of the past 250 years,” and that “the drought of the 1930s is probably the second most severe.” They say also that ” recent droughts were not exceptional in the context of the last 250 years and were of shorter duration than many past events.”

In Montana and Idaho, Gray et al. (2004) found that “both single-year and decadal-scale dry events were more severe before 1900,” and that “dry spells in the late thirteenth and sixteenth centuries surpass both the magnitude and duration of any droughts in the Bighorn Basin after 1900.”

Researchers working in the Pyramid Lake area of Nevada found that for the past 2,740 years “intervals between droughts ranged from 80 to 230 years; while drought durations ranged from 20 to 100 years.” Another study in the same area found that the longest of these droughts occurred between 2,500 and 2,000 years ago and between 1,500 and 1,250, 800 and 725, and 600 and 450 years ago, with none recorded in more recent warmer times.

In the Rocky Mountains, Gray et al. (2003) found a pattern of droughts that they say “may ensue from coupling of the cold phase Pacific Decadal Oscillation with the warm phase Atlantic Multidecadal Oscillation.”

Research on the Upper Colorado River Basin shows “a near-centennial return period of extreme drought events in this region.” The major drought of 2000-2004 was not as severe as 1844-1848, and was similar to droughts in the early 1500s and early 1600s. They conclude, “these analyses demonstrate that severe, sustained droughts are a defining feature of Upper Colorado River hydroclimate.” And the results show that more severe droughts are associated with colder cycles.

Work in Arizona and New Mexico shows that “sustained dry periods comparable to the 1950s drought occurred in “the late 1000s, the mid 1100s, 1570-97, 1664-70, the 1740s, the 1770s, and the late 1800s.”

Drought cycles are most closely correlated with various solar cycles of 1,533 years (the Bond cycle), 444 years, 170 years, 146 years, and 88 years (the Gleissberg cycle). Asmerom,et al. report that periods of increased solar radiation correlate with periods of decreased rainfall in the southwestern United States (via changes in the North American monsoon). These solar cycles control the Pacific Decadal Oscillation and the El Nino system which control weather and climate in the southwest. We are just entering solar cycle 24 and it seems very sluggish. That could mean that we will be spared from an intensifying drought.

For specifics on Tucson’s water supply see:

https://wryheat.wordpress.com/2009/06/21/water-supply-and-demand-in-tucson/

For a primer on drought see:

http://www.ncdc.noaa.gov/paleo/drought/drght_home.html

To understand the proxies used in paleoclimate research see:

http://www.ncdc.noaa.gov/paleo/primer_proxy.html

References:

Papers reviewed by http://www.co2science.org/subject/d/summaries/droughtusawest.php

Asmerom, Y., Polyak, V., Burns, S. and Rassmussen, J. 2007. Solar forcing of Holocene climate: New insights from a speleothem record, southwestern United States. Geology 35: 1-4.

Benson, L., Kashgarian, M., Rye, R., Lund, S., Paillet, F., Smoot, J., Kester, C., Mensing, S., Meko, D. and Lindstrom, S. 2002. Holocene multidecadal and multicentennial droughts affecting Northern California and Nevada. Quaternary Science Reviews 21: 659-682.

Gedalof, Z., Peterson, D.L. and Mantua, N.J. 2004. Columbia River flow and drought since 1750. Journal of the American Water Resources Association 40: 1579-1592.

Gray, S.T., Betancourt, J.L., Fastie, C.L. and Jackson, S.T. 2003. Patterns and sources of multidecadal oscillations in drought-sensitive tree-ring records from the central and southern Rocky Mountains. Geophysical Research Letters 30: 10.1029/2002GL016154.

Gray, S.T., Fastie, C.L., Jackson, S.T. and Betancourt, J.L. 2004. Tree-ring-based reconstruction of precipitation in the Bighorn Basin, Wyoming, since 1260 A.D. Journal of Climate 17: 3855-3865.

Hidalgo, H.G., Piechota, T.C. and Dracup, J.A. 2000. Alternative principal components regression procedures for dendrohydrologic reconstructions. Water Resources Research 36: 3241-3249.

Knapp, P.A., Grissino-Mayer, H.D. and Soule, P.T. 2002. Climatic regionalization and the spatio-temporal occurrence of extreme single-year drought events (1500-1998) in the interior Pacific Northwest, USA. Quaternary Research 58: 226-233.

Mensing, S.A., Benson, L.V., Kashgarian, M. and Lund, S. 2004. A Holocene pollen record of persistent droughts from Pyramid Lake, Nevada, USA. Quaternary Research 62: 29-38.

Ni, F., Cavazos, T., Hughes, M.K., Comrie, A.C. and Funkhouser, G. 2002. Cool-season precipitation in the southwestern USA since AD 1000: Comparison of linear and nonlinear techniques for reconstruction. International Journal of Climatology 22: 1645-1662.

Woodhouse, C.A., Gray, S.T. and Meko, D.M. 2006. Updated streamflow reconstructions for the Upper Colorado River Basin. Water Resources Research 42: 10.1029/2005WR004455.

El Niño Drives Temperature

Here is a story you won’t see in the Arizona Daily Star.  Three Australasian researchers have shown that natural forces are the dominant influence on climate, in a study just published in the Journal of Geophysical Research. The research finds that finds that the El Niño -Southern Oscillation (ENSO) is a key indicator of global atmospheric temperatures seven months later.

The abstract of the paper says in part: “The results showed that SOI (Southern Oscillation Index) accounted for 81% of the variance in tropospheric temperature anomalies in the tropics. Overall the results suggest that the Southern Oscillation exercises a consistently dominant influence on mean global temperature, with a maximum effect in the tropics, except for periods when equatorial volcanism causes ad hoc cooling. That mean global tropospheric temperature has for the last 50 years fallen and risen in close accord with the SOI of 5–7 months earlier shows the potential of natural forcing mechanisms to account for most of the temperature variation.”

Citation:

McLean, J. D., C. R. de Freitas, and R. M. Carter (2009), Influence of the Southern Oscillation on tropospheric temperature, J. Geophys. Res., 114, D14104, doi:10.1029/2008JD011637.

To see a broader view of natural climate change, see my article: Natural Climate Cycles.