GeoLog

history

Geosciences Column: How climate change put a damper on the Maya civilisation

Geosciences Column: How climate change put a damper on the Maya civilisation

More than 4,000 years ago, when the Great Pyramid of Giza and Stonehenge were being built, the Maya civilisation emerged in Central America. The indigenous group prospered for thousands of years until its fall in the 13th century (potentially due to severe drought). However, thousands of years before this collapse, severely soggy conditions lasting for many centuries likely inhibited the civilisation’s development, according to a recent study published in EGU’s open access journal Climate of the Past.

During their most productive era, often referred to as the Classic period (300-800 CE), Maya communities had established a complex civilisation, with a network of highly populated cities, large-scale infrastructure, a thriving agricultural system and an advanced understanding in mathematics and astronomy. However, in their early days, dating back to at least 2600 BCE, the Maya people were largely mobile hunter-gatherers, hunting, fishing and foraging across the lowlands.

Around 1000 BCE, some Maya communities had started to transition away from their nomadic lifestyles, and instead were moving towards establishing more sedentary societies, building small villages and relying more heavily on cultivating crops for their sustenance. However, experts suggest that agricultural practices didn’t gain momentum until 400 BCE, raising the question as to why Maya development was delayed for so many centuries.

By analysing two new palaeo-precipitation records, Kees Nooren, lead author of the study and a researcher at Utrecht University in the Netherlands, and his colleagues were able to gain insight into the environmental conditions during this pivotal time, and the impact that climate change could have had on the Maya society.

To determine the regional climate conditions during this period of time, the authors examined a beach ridge plain in the Mexican state of Tabasco, off the Gulf of Mexico, which contains a long-term record of ridge elevation changes for much of the late Holocene. Since precipitation has a large influence on the elevation of this beach ridge, this record is a good indicator of how much rainfall and flooding may have occurred during Maya settlement.

A large part of the central Maya lowlands (outlined with a black dashed line) is drained by the Usumacinta (Us.) River (a). During the Pre-Classic period this river was the main supplier of sand contributing to the formation of the extensive beach ridge plain at the Gulf of Mexico coast (b). Periods of low rainfall result in low river discharges and are associated with relatively elevated beach ridges. Taken from Nooren, K et al., 2018

Additionally, the researchers also assessed core samples taken from Lake Tuspan, a shallow body of water in northern Guatemala that is situated within the Central Maya Lowlands. Because the lake receives its water almost exclusively from a small section of the region (770 square kilometres), its sediment layers provide a good record of rainfall on a very local scale.

The image on p. 74 of the Dresden Codex depicts a torrential downpour probably associated with a destructive flood (Thompson, 1972). Taken from Nooren, K et al., 2018

The research team’s analysis suggested that, starting around 1000-850 BCE, the region shifted from a relatively dry climate, to a wetter environment. Such conditions would have made a farming in this region more difficult and less appealing compared to foraging and hunting. The researchers suggest that this change in climate could be one of the reasons why Maya agricultural development was at a standstill for such a long time.

The researchers also propose that this long-term climate trend could have been brought on by a shift of the Intertropical Convergence Zone (ITCZ), a region near the equator where northeast and southeast winds intermingle and where most of the Earth’s rain makes landfall. The position of this zone can move naturally in response to Earth’s changes in insolation, and a northerly shift of the ITCZ could help account for some of the morphological changes the authors observed in the precipitation records.

After more than 450 years of excessive rainfall and large floods, the records then suggest that the region experienced drier conditions once again. By this time period, the Maya populations began to rapidly intensify their farming efforts and develop major cities, further suggesting that the wet conditions may have helped delay such efforts.

This is not the first time the Nooren and his colleagues have found evidence of major environmental influence on the Maya civilisation. For example, earlier research led by Nooren suggests that, in the 6th century, the El Chichón volcano in southern Mexico released massive amounts of sulfur into the stratosphere, triggering global climate change that likely contributed to a ‘dark age’ in Maya history for several decades. During this time, often referred to as the “Maya Hiatus,’ Maya societies experienced stagnation, increased warfare and political unrest. The research results were presented at the 2016 General Assembly and later published in Geology.

The results of these studies highlight how changes in our climate have greatly influenced communities and at times even shaped the course of societal history, both for better and for worse.

By Olivia Trani, EGU Communications Officer

References

Ebert, C. et al.: Regional response to drought during the formation and decline of Preclassic Maya societies. Quaternary Science Reviews 173:211-235, 2017

Nooren, K., Hoek, W. Z., Dermody, B. J., Galop, D., Metcalfe, S., Islebe, G., and Middelkoop, H.: Climate impact on the development of Pre-Classic Maya civilization. Clim. Past, 14, 1253-1273, 2018

Nooren, K.: Holocene evolution of the Tabasco delta – Mexico : impact of climate, volcanism and humans. Utrecht University Repository (Dissertation). 2017

Nooren, K. et al.: Explosive eruption of El Chichón volcano (Mexico) disrupted 6th century Maya civilization and contributed to global cooling, Geology, 45, 175-178, 2016

Press conference: Volcanoes, climate changes and droughts: civilisational resilience and collapse. European Geosciences Union General Assembly 2016

Caltech Climate Dynamics Group, Why does the ITCZ shift and how? 2016

April GeoRoundUp: the best of the Earth sciences from the 2018 General Assembly

April GeoRoundUp: the best of the Earth sciences from the 2018 General Assembly

The 2018 General Assembly took place in Vienna last month, drawing more than 15,000 participants from 106 countries. This month’s GeoRoundUp will focus on some of the unique and interesting stories that came out of research presented at the Assembly.

Mystery solved

The World War II battleship Tirpitz was the largest vessel in the German navy, stationed primarily off the Norwegian coastline as a foreboding threat to Allied armies. The ship was 250 metres in length and capable of carrying around 2,500 crewmates.

Despite its massive size, the vessel’s presence often went unnoticed as it moved between fjords, masked by a chemical fog of chlorosulphuric acid released by the Nazi army.

Ultimately the ship sank and the war ended, but evidence of the toxic smog still lingers today, in the tree rings of Norway’s nearby forests.

Claudia Hartl, a dendrochronologist from the Johannes Gutenberg University in Mainz, Germany, made this discovery unexpectedly while sampling pines and birches near the Norwegian village Kåfjord. She and her research team presented their findings at the General Assembly in Vienna last month.

The German battleship Tirpitz partly covered by a smokescreen at Kaafjord. (Image Credit: Imperial War Museums )

Hartl had been examining wood cores to draw a more complete picture of past climate in the region when she noticed that some trees completely lacked rings dating to 1945,” reported Julissa Treviño in Smithsonian Magazine.

The discovery was odd since it is rare for trees to have completely absent rings in their trunks. Tree ring growth can be stunted by extreme cold or insect infestation, but neither case is severe enough to explain the missing tree rings from that time period.

“A colleague suggested it could have something to do with the Tirpitz, which was anchored the previous year at Kåfjord where it was attacked by Allied bombers,” explains Jonathan Amos from BBC News.

The researchers indeed found physical and chemical evidence of the smokescreen damage on the trees, demonstrating the long-lasting impact warfare can impart onto the environment.

 

What you might have missed

Seismicity of city life

Researchers use seismometers to record Earth’s quakes and tremors, but some seismologists have employed these instruments for a different purpose, to show how humans make cities shake. “This new field of urban seismology aims to detect the vibrations caused by road traffic, subway trains, and even cultural activities,” reports EGU General Assembly Press Assistant Tim Middleton on GeoLog.

With seismometers, Jordi Díaz and colleagues at the Institute of Earth Sciences Jaume Almera in Barcelona, Spain have been able to pick up the seismic signals of major football games and rock concerts, like footballer Lionel Messi’s winning goal against Paris Saint-Germain and Bruce Springsteen’s Barcelona show.

Seismic record captured by the seismometer during the Bruce Springsteen concert. The upper panel shows the seismogram, while the lower panel shows the spectrogram where it is possible to see the distribution of the energy between the different frequencies. (Image Credit: Jordi Díaz)

Díaz’s project first began as an outreach campaign, to teach the general public about seismometers, but now he and his colleagues are exploring other applications. For example, the data could help civil engineers with tracking traffic and monitoring how buildings withstand human-induced tremors.

Antarctica seeing more snow

Meanwhile in Antarctica, snowfall has increased by 10 percent in the last 200 years, according to new research presented at the meeting. After analysing 79 ice cores, a research team led by Liz Thomas from the British Antarctic Survey discovered that Antarctica’s increased snowfall since 1800 was equivalent to 544 trillion pounds of water, about twice the volume of the Dead Sea.

It has been predicted that snowfall increase would be a consequence of global warming, since a warmer atmosphere can hold more moisture, thus resulting in more precipitation. However, these ice core observations reveal this effect has already been happening. The new finding implies that Earth’s sea level has risen slightly less than it would have otherwise, but only by about a fifth of a milimetre. Though overall, this snowfall increase is not nearly enough to offset Earth’s increased ice loss.

Ocean’s tides create a magnetic field

Also at the Assembly, scientists presented new data collected from a team of ESA satellites known as Swarm, In particular, the satellite observations recently mapped magnetic signals induced by Earth’s ocean tides. As the planet’s tides ebb and flow, drawn by the Moon’s gravitational pull, the salty water generates electric currents. And these currents create a tiny magnetic field, around 20,000 times weaker than the global magnetic field.

Scientists involved with the Swarm project say the magnetic view provides new insight into Earth’s ocean flow and magnetic field, can improve our understanding of climate change, and help researchers build better Earth system models.

When salty ocean water flows through Earth’s magnetic field, an electric current is generated, and this in turn induces a magnetic signal. (Credit: ESA/Planetary Visions)

 

Other noteworthy stories:

 

To stay abreast of all the EGU’s events and activities, from highlighting papers published in our open access journals to providing news relating to EGU’s scientific divisions and meetings, including the General Assembly, subscribe to receive our monthly newsletter.

Imaggeo on Mondays: Iceland’s original birch forest

Imaggeo on Mondays: Iceland’s original birch forest

Iceland is a country of dramatically rugged landscapes. The region is home to sweeping valleys and mountain ranges, dotted with lava fields, large glaciers, hot springs and impressive waterfalls.

The territory is also notoriously treeless. As of 2016, forests only made up 1.9 percent of Iceland, according to the Icelandic Forest Service. However, about a thousand years ago the country’s landscape was far more vegetated, and remnants of Iceland’s original woodlands still exist today.

It is a common misconception that Iceland is too cold to sustain a forest. “On the contrary, it has been observed that, at the time of human settlement, birch woods and scrubs have covered large parts of Iceland,” said Marco Cavalli, a researcher at the Research Institute for Geo-Hydrological Protection in Italy and the photographer of today’s featured image. In fact, Iceland’s fossil evidence suggests that, before human settlement, 25-40 percent of the island was dominated by woodlands and thickets.

When humans migrated to the island about 1100 years ago, much of Iceland’s natural forests were chopped down to make way for fields and pastures. In the centuries following human settlement, intensive sheep grazing and volcanic eruptions prevented forests from regenerating. By 1950, less than one percent of the country was covered by trees.

Iceland’s vegetation-devoid state presents an environmental problem to local Icelanders, since the lack of trees, combined with the island’s volcanic activity, has left the land vulnerable to severe soil erosion. Since the soil conditions prevent vegetation from taking root, erosion has limited farming and grazing efforts. Iceland’s loose soil and strong winds are also responsible for damaging sandstorms.

Soil conservation and forestry services have made substantial efforts to repopulate the Icelandic environment with trees, just about doubling Iceland’s tree cover since the mid-20th century. However, there is still a long road ahead to reach the Icelandic Forest Service’s goal to see 12 percent of Iceland afforested by 2100.

This picture was taken by Cavalli while on a field trip in Rangárvellir, a southern region of Iceland near Gunnarsholt, the headquarters of the Soil Conservation Service of Iceland (SCSI). The workshop focused on the area’s severe degradation from both human activities and natural causes, and efforts to restore the ecosystem.

During the workshop he spotted this particular grove of dwarf birch trees. “I was impressed to see a small remnant patch of the Icelandic original birch forest resisting all these adverse conditions,” said Cavalli. “I would say this is a good example of nature fighting to survive.”

References

Forestry in a Treeless Land, Icelandic Forest Service

Changes in vegetation cover from the time of Iceland’s settlement, Icelandic Institute of Natural History

Vikings Razed the Forests. Can Iceland Regrow Them?, The New York Times

Imaggeo is the EGU’s online open access geosciences image repository. All geoscientists (and others) can submit their photographs and videos to this repository and, since it is open access, these images can be used for free by scientists for their presentations or publications, by educators and the general public, and some images can even be used freely for commercial purposes. Photographers also retain full rights of use, as Imaggeo images are licensed and distributed by the EGU under a Creative Commons licence. Submit your photos at http://imaggeo.egu.eu/upload/.

A brief history of science communication

Science communication has become a common focus of many aspects of academic research and teaching. Despite becoming more prevalent in recent years it has a long and deep rooted history, which goes hand in hand with scientific discovery. In this blog post, Sam Illingworth, gives a brief outline of the history of science communication.

Science Communication is a phrase that seems to permeate into many facets of our lives as scientists and educators, and indeed it has featured prominently in many of these posts. However, what is it and where did it come from?

Debating, Ancient Greece style (Photo Credit: Raphael [Public domain], via Wikimedia Commons)

Debating, Ancient Greece style (Photo Credit: Raphael [Public domain], via Wikimedia Commons)

 The word ‘science’ itself derives from the Latin word ‘scientia’, meaning knowledge. So to communicate science is effectively to communicate knowledge, and at its most basic level science communication can be thought of as those in the know informing those that are not. In Ancient Greece this imparting of knowledge took place in public debates, where understanding and thought were deliberated by the masses. This democratisation of knowledge and inquiry ultimately led to the dawn of experimentation and to the advancement of philosophy and science.

This early wooden printing press could spit out 240 impressions per hour (Photo Credit: Jost Amman [Public domain], via Wikimedia Commons)

This early wooden printing press could spit out 240 impressions per hour (Photo Credit: Jost Amman [Public domain], via Wikimedia Commons)

Sadly, in Western Europe the dark ages quickly put an end to this period of scientific enlightenment, with knowledge now transferred via the written word, and often hoarded by the privileged few. The masses were now either unable to process any knowledge because of their illiteracy, or else the vast expense associated with hand-copied books and manuscripts prevented them from learning anything of scientific merit. Thankfully, the invention of the printing press by Johannes Gutenberg in 1456 eventually made the printed word more accessible, meaning that knowledge could now be much more easily spread. Yet, despite the ensuing scientific revolution that the printing press sparked, it wasn’t until much later on that scientists began to consider their responsibility to communicate knowledge to the general public.

The British Science Association (BSA) was set up in at the beginning of the nineteenth century, mainly to address the fact that science in the UK was in a somewhat laconic state. The first meeting was held in York on the 26 September 1831, where one of the aims of the society was declared to be: “to obtain a greater degree of national attention to the objects of science.” The association also inspired the formation of similar associations for the advancement of science in other countries, and have continued to have annual meetings ever since. Perhaps the best remembered of all these meetings was at Oxford in 1860, where the English biologist Thomas Huxley debated Darwinism with the then Bishop of Oxford, Samuel Wilberforce. Huxley’s speech ended with him stating that he was not ashamed to have a monkey for his ancestor, but that he would be ashamed to be connected with a man who used great gifts to obscure the truth; a reference to the oratory skill, yet perhaps clouded judgement, of his religious opponent.

Thomas Henry Huxley: Communicating for Science  (Photo Credit: Lock & Whitfield [Public domain], via Wikimedia Commons)

Thomas Henry Huxley: Communicating for Science (Photo Credit: Lock & Whitfield [Public domain], via Wikimedia Commons)

In more recent times, European science communication can essentially be thought of as having gone through three stages of development. The first generation of science communication centred on a deficit approach, which aimed to fill in the gaps in the knowledge of the general public. The second-generation approach favoured a more two-way dialogue, in which the scientists engaged with the general public, and in which the general public began to have an influence on informing scientific practice and policy. Currently the third-generation approach aims to continue this two-way dialogue, but also transfers greater ownership to the general public, by encouraging them to define exactly what knowledge it is that they want to have communicated.

With the advent of citizen science, and crowdsourcing (more of which can be read about here), the general public are now in a position where they are not only choosing what they want to be informed about, but are taking an active role in the pursuit of this knowledge. As scientists, we have to ensure that it is not now us that are left behind.

By Sam Illingworth, Lecturer in Science Communication, Manchester Metropolitan University