Monsoons & Megadroughts
Large portions of the globe rely on the seasonal monsoon for water. Across much of Asia, agriculture depends on the coming of the monsoon rains. One scare tactic employed by global warming extremists is to claim that human caused climate change will keep the monsoon from coming, causing drought, failed crops and famine. In truth, science does not fully understand the complex interactions of ocean, atmosphere, and land that influence the monsoon, or how it impacts climate in other parts of the world. Now, a new Monsoon Asia Drought Atlas (MADA) provides reconstructions of summer moisture for the region going back to 1300 AD. It documents a long sequence of droughts so persistent that scientists call them “megadroughts.” These megadrought events, the worst of which may have toppled ancient kingdoms, show that unreliable monsoon seasons have afflicted mankind throughout history—long before the clamor over climate change arose.
Drought is not an unusual occurrence. For several years, the American South had suffered under a long-lasting severe drought, until this year's wet El Niño driven winter and spring. Half a world away, the southwestern corner of Australia was in the grip of a devastating drought since the 1970s. These events have naturally been blamed on global warming by publicity seeking researchers.
Sheep search for feed on a dry and dusty property in rural New South Wales, January 2010.
In the April 23, 2010, edition of Science, Edward R. Cook et al. present a large-scale, spatially explicit, long-term data set they are calling the Monsoon Asia Drought Atlas (MADA). Based on tree rings from more than 300 sites across the forested areas of Asia, the authors claim the long-term perspective it provides is essential for comparisons with other proxy, historical, and archaeological data. It is also needed to help validate those notoriously inaccurate computer models that climate scientists are so fond of. In an accompanying perspective article, “Toward Understanding and Predicting Monsoon Patterns,” Eugene R. Wahl and Carrie Morrill place the complexity of the monsoon this way:
It results from an interplay between the ocean, atmosphere, and land surface (see the figure). Many factors thus affect its strength, including sea surface temperatures (SSTs) in the Indian and Pacific Oceans; variations in solar output; land snow cover and soil moisture over the Asian continent; and the position and strength of prevailing winds. The links between these factors and the monsoon appear to wax and wane over time, and the observational record is too short to explain this longer-term variability.
Precipitation and surface wind maps over Asia during summer (June to August) show the average spatial patterns of monsoon circulation and moisture. Yellow areas and schematic of westerly winds indicate some factors that influence monsoon variability. Precipitation data are from the Global Precipitation Climatology Project v. 2.1, and wind data are from the NCEP/NCAR Reanalysis. Both are averaged over the period from 1979 to 2009. All data were obtained from the National Oceanic and Atmospheric Administration (NOAA). Image Wahl & Morrill/Science.
As described by Cook et al., in “Asian Monsoon Failure and Megadrought During the Last Millennium,” MADA offers an absolutely dated, annually resolved reconstruction of Asian monsoon variability over the past thousand years. Most interesting is the seasonal- to centennial-scale window into the Asian monsoon’s repeated tendency for extended dry and wet extremes. It was found that the El Niño–Southern Oscillation (ENSO) and the Pacific Decadal Variability, display distinct “spatial flavors” of response.
The article shows how both Asian and North American megadrought patterns in the late 19th and early 20th centuries are linked to Pacific SST patterns of the El Niño-Southern Oscillation (ENSO). Note that a megadrought can last for decades or centuries. The methodology employed also makes it possible to identify rigorous mathematical subcomponents from the MADA data. This is crucial for showing that different types of Pacific SST patterns, including ENSO and the Pacific Decadal Oscillation (PDO), are associated with different drought patterns.
“We used the MADA to identify the regional footprints and severity of four well-documented historical droughts: the Ming Dynasty drought (1638 to 1641), the Strange Parallels drought (1756 to 1768), the East India drought (1790 to 1796), and the late Victorian Great Drought (1876 to 1878),” report Cook et al.. Each of these periods is well documented by historical observation. According to some historical records, the drought in China during the late 1630s and early 1640s was the most severe drought in the past five centuries. Historians speculated that the drought led to a peasant uprising that hastened the fall of the Ming Dynasty in 1644.
Spatial drought patterns during four historical Asian droughts.
The East India and the Late Victorian droughts, which strongly impacted India, coincided with two severe El Niño events. The first one had an impact on the East India Company's plans for permanent settlement, while the second megadrought led to the Great Madras Famine that killed thousands. That famine affected South and Southwestern India for two years, primarily in the areas around Madras, Mysore, Hyderabad, and Bombay. In its second year, the famine also spread north to the Central Provinces, the United Provinces and a small area in the Punjab.
The study appears to provide an explanation for the so-called “strange parallels” described by Victor Lieberman, an historian at the University of Michigan, in his award winning book Strange Parallels: Southeast Asia in Global Context, c. 800-1830. For the millennium spanning the period 800-1830, Lieberman identified four roughly synchronized cycles of political consolidation in mainland Southeast Asia, as well as in France and Russia.
In 1756-1786, kingdoms in what are now Vietnam, Myanmar and Thailand collapsed. In each realm, new, more dynamic leaders came to power, leading to a series of wars in the late 18th and early 19th centuries. As a result, the number of independent states in Southeast Asia shrank and competition between major powers increased.
In 1792, the French monarchy collapsed. Between 1799 and 1815, a new regime dramatically expanded French military power and triggered a number of wars of conquest. Lieberman asked the question “How shall we explain these parallels between Europe and Southeast Asia?” Some historians have speculated that climate must have played a role for such sweeping political changes to have happened simultaneously. Indeed, scattered accounts suggest that periods of drought may have been punctuated with devastating floods.
The 1756-1768 drought, the Strange Parallels drought, is not documented in historical records—scientists first identified it in teak rings from Thailand, and later in Vietnamese cypress trees. The tree ring data indicate that western India was also severely affected. “It provides confirmation that there are very strong climate links between monsoon regimes in India, Southeast Asia and southern China,” said Lieberman in an interview.
The East India drought came in 1790-1796 and affected events worldwide. Civil unrest and socioeconomic turmoil spread around the globe: In Europe, drought led to crop failures that preceded the French Revolution; Famines hit India, again; and in Mexico, water levels at Lake Pátzcuaro fell so much they gave rise to ownership disputes over the land that emerged.
Perhaps the worst of the big 4 droughts was the Victorian-era “Great Drought” of 1876-1878. Again social unrest and political upheaval were triggered by crop failure and famine. According to the tree-ring evidence, the effects were especially acute in India, but extended as far as China and present-day Indonesia. Driven by famine and cholera outbreaks, a peasant revolt against the French broke out in colonial Vietnam. By some estimates, resulting famines killed as many as 30 million people across tropical Asia.
Tree ring scientists Ed Cook (left) and Paul Krusic trekked for nearly two weeks to reach this 1,000 year old hemlock in the Himalayas of Nepal. Photo: Brendan Buckley.
For more about the effects of these droughts check the Earth Institute press release. There you will find a recording of principle investigator Edward Cook, from Columbia University’s Lamont-Doherty Earth Observatory, discussing the study. There is also an audio slideshow about tree-ring work in Asia on that page.
Asian megadroughts, the researchers concluded, are as big in “magnitude and persistence” as the megadroughts in the southwestern US, which are linked to sea surface temperature anomalies in the Pacific. “This will hopefully lead to more accurate monsoon forecasts,” Cook, the principal investigator, told the Deccan Herald. “This atlas should provide monsoon modelers with new insights into how and why the summer monsoon varies the way it does and also how to improve their models.”
According to Wahl and Morrill, “Making sense of the dynamic processes underlying the large amount of spatial and temporal detail in the MADA will be a challenge for climate modelers, but is a key goal on the road to improved predictions of monsoon precipitation.” Of course, the biggest challenge for climate modelers it getting anything remotely like a correct answer.
Even the worst droughts come to an end, as in the case of Australia. “After a decade of drought, said to be Australia’s worst in a century, the plains that were brown and parched just weeks ago are now smiling green,” reported The Economist. “Waves of water from two magically timed floods, in northern NSW and southern Queensland, are slowly making their way south towards the Murray and Darling rivers, bringing the desert back to life with birds, frogs and plants that many outback folk had given up hope of ever seeing again.”
Forbes Lake had been completely empty before the rains.
Since Christmas, parched areas of New South Wales, Australia's most populous state, have received their best rains in a decade, fueling hopes the Happy Land's worst drought in a century may finally be over. The area of New South Wales in drought has dropped dramatically, falling from 81% in January to just 7.3% in March, a nine year low. If the drought was being caused by global warming and the drought goes away, does that mean global warming has gone away?
Of course, there are other reports that claim global warming should lead to greater precipitation. In particular, the IPCC's own Climate Change 2007: The Physical Science Basis, Contribution of Working Group I to the Fourth Assessment Report, predicts a heightened hydrologic cycle, resulting in a stronger, not weaker, monsoon. According to the AR4 FAQ:
In particular, over NH land, an increase in the likelihood of very wet winters is projected over much of central and northern Europe due to the increase in intense precipitation during storm events, suggesting an increased chance of flooding over Europe and other mid-latitude regions due to more intense rainfall and snowfall events producing more runoff. Similar results apply for summer precipitation, with implications for more flooding in the Asian monsoon region and other tropical areas.
We find ourselves in a familiar situation, with climate science coming down firmly on both sides of the question. Some scientists say more drought, others say more precipitation—competing theories abound, all incorrect or untested. There is strong evidence that pre-climate change times saw multi-decade periods of persistent El Niño and La Niña conditions. You can bet if such conditions arose today that they would be loudly proclaimed a result of global warming, even though such events are perfectly normal. My future climate prediction is for possibly wet weather except in areas of drought—the way things have been since the beginning of the Holocene. Truly, there is nothing new under the Sun.
Be safe, enjoy the interglacial and stay skeptical.
Recent floods caused by heavy spring rains have caused $1.5 billion in damage around Nashville, Tennessee. Three years ago the Southern US was experiencing its worst drought in more than a century.