Towards the future: A summary

This starting this blog back in October 2015, it has taken me on a journey. A journey through time, a journey to various corners of the world, and a journey into the colourful lives of various societies and civilisations which have inhabited this world at one point or another.

We have discussed the role played by climate change in the collapse of past civilisations including the Norse colony in Iceland (Norse colony and the climate change catastrophe), the Saharan tribes (Green Sahara), the Mayan civilisation of South America (Climate and the classic Mayan collapse), and the inhabitant of Rapa Nui or Easter Island, Pacific Ocean (Lessons from Rapa Nui).

We have explored the possibility of that humans have delayed the onset of a glaciation which would have occurred without the effect of the enhanced anthropogenic forcing on the climate system during the onset of the agricultural revolution (Rivalling the forces of nature).

We have provided an insight into the issues facing societies today as they battle against climate change including an African farmer battling against extreme precipitation events (At the front line against climate change), Greenland communities threatened by retreating sea ice (Melting away and When the sea took the land), extensive droughts in the region of the Sahel (Do they know its Christmas?), and widespread flooding which hit the UK over the Christmas period (When the floods ruined Christmas).

Future projections by climate models and the effects of societies were explore, including the blog which explored how the Middle East could become inhospitable for human life by the year 2100 (Middle East Meltdown) and the blog which explored how the Sahara is project to become increasingly vegetated (A greener future). Solutions which could provide fundamental for societies to adapt to climate change were also explored including how to reverse desertification (Reversing desertification).

Of course, we could not ignore the climate discussion in Paris which dominated the news for a couple for weeks, and we explored how much interest did the general public in the UK have in the COP21 discussions (Alleyes on Paris?).

A blog which takes a more general take by discussing if we are today causing our own destruction (Are we committing and ecocide?) summarizes our findings and highlights the  extreme complexity of the relationship between humans and the climate. Despite the success of COP21 in Paris, enhanced anthropogenic forcing are still predicted to continue increasing at an alarming rate for the next century. Understanding how changes to the climate system will impact societies today is fundamental for our species’ survival.

So I'm going to leave you with this video below - a video which manages to summarize without the need for any fancy, motivational words, exactly why Gaia is worth fighting for. 

Over and out. 

Erin  

Lessons from Rapa Nui

Figure 1. The famous statues of Easter Islands (source)

Rapa Nui (Easter Island) is a one of the most remote islands in the world.  It is a small volcanic island of 164 km², low relief, and low rainfall. It is another classic example of a complex societal collapse which is proving to be one of the most important examples with regards to holding lessons for the future. As reported by Hunt (2007), when and how the first humans discovered Rapa Nui is still highly debated. Today, cultural evidence continue to dominate the landscape as huge sculptures were erected throughout the island between AD 1200 and AD 1650. At peak, the population may have reached 10,000, yet in AD 1650, this dramatically reduced as the civilization headed for collapse. Important lessons could be learnt from this societal collapse story with regards to the future therefore this blog will explore the main drivers behind the collapse with special reference to the role of climate change. 

A classic view of the Easter Island collapse story is one of 'ecocide' as the human population drove its own destruction by exploiting its natural resources, degrading the island's lands, causing extensive deforestation, and driving the extinction of plants and animals (Diamond, 2005). Extensive deforestation has received considerable attention, as this would have prevented the society from building boats and rafts to escape from ecosystem damage. Diamond writes that ‘‘in just a few centuries, the people of Easter Island wiped out their forest, drove their plants and animals to extinction, and saw their complex society spiral into chaos and cannibalism.’’. 

This has been heavily criticised as presenting an environmental deterministic view. There exists no reliable evidence of a large population which could not sustain itself followed by an abrupt,  cataclysmic collapse (Hunt., 2007) and Rapa Nui does not appear to represent a case of ‘‘ecocide.’’. Instead, the arrival of Europeans to the island, bringing with the new species, diseases and slave-trading has been suggested to play a more crucial role (Peiser, 2005). It has been reported that the societal collapse on Easter Island is ‘‘one of the most hideous atrocities committed by white men in the South Seas" (Metraux,1957). 

Other theories suggest that the arrival of the European bought rapidly reproducing rats to the islands, and that this invasive caused considerable damage to plants and animals, dramatically changing the islands food chain and resources and driving the society towards collapse (Hunt, 2007). This theory has been heavily critisiced on the basis that the rats could not have reproduced fast enough to cause such devastating consequences (Mann et al., 2008). 

Figure 2: An identified period of intense deforestation which coincides with an El Nino-Southern Oscillation period (source)

A studies which used pollen to reconstruct vegetation chance across the island found a correlation between a period of major deforestation and an intense El Nino-Southern Oscillation period (figure 2, Cobb et al. 2003). ENSO events result in a change in sea surface temperature, which leads to the lowering of biomass production and upwhelling of nutrients. This would have reduced the availability of marine resources around the island, a key source of protein for the islanders. An abrupt ENSO event could have caused a significant decline in food resources, driving an expansion in agriculture, and reducing the availability of wood to make boats would have also made fishing ground inaccessible. The role of climate change has a more recently been confirmed by a more recent study which identified period of drought being experienced on the island prior to the collapse of the civilization at AD1180-1290 (Mann et al. 2008). Stratigraphic records from lake sediment cores looking at sediment, charcoal and pollen stratigraphy suggests that the lake dried out during this period of drought identified by a hiatus in sedimentation. The study concludes that it looks likely that latitudinal shifts of tropical storm tracks, changed to the moisture balance across the island triggered the period of drought.

As we have previously explore in many past blogs, the relationship between civilisations and the climate is highly complex! Both interlink with each other. Hence, when attempting to understand what caused past civilisations to collapse, it is difficult to isolate individual signals from the records and pin pointing a specific climatic change or societal driver. However, many key lessons can be learnt from past societies including the need to be aware of the damage that we are causing to the planet, the need to plan and prepare with adequate mitigation measures, and the need to be flexible and adaptable to change. Only then can we survive this world's dynamic climate. 
 

Rivalling the forces of nature

Figure 1. Future Earth? (source)

Global average temperatures throughout the Holocene were relatively stable in comparison to previous warm or interglacial period in the Earth's history. It was originally thought that this was the result of natural climatic drivers and that humans did not influence the climate until two centuries ago during the Industrial Revolution which saw a rapid surge of greenhouse gases into the atmosphere (figure 2). This has been challenged by a hypothesis which states that without the anthropogenic factor, the Holocene should have experienced gradual cooling under a natural state, and that anthropogenic emissions first started altering the climate 8,000 years earlier (figure 2, Ruddiman, 2003). This blogs explores the overdue glaciation hypothesis.  

Figure 2: Changes in atmospheric greenhouse gases and global average temperature over the last 8,000 years (source)

Ruddiman (2003) bases his hypothesis on two key point. Firstly, atmospheric gases stopped following the natural oscillating trend driven by Milankovitch cycles seen throughout most of the Quaternary and instead of falling, CO₂ levels began rising 8,000 years ago and CH₄ around 5,000 years ago. Secondly, numerous archaeological, historical and geological evidence exists which points towards a large social shift in Eurasia 8,000 years ago as the Neolithic Revolution drove hunter-gatherers into settled farmers. This gave rise to the domestication of plants and animals, change in landuse and an increase in population. Bringing both together, evidence shows how the rise of agriculture and extensive deforestation around 8,000 ago coincides with the gradual rise in CO₂ whilst the expanding of rice irrigation occurred around 5,000 years ago coinciding with a rise in CH₄. Together, these changes have contributed to the 0.8°C rise observed above the Holocene baseline which has been enough to stop the natural cooling trend and prevent the Earth entering a glacial period. 

The climate model GENESIS was created to test the hypothesis to see how the Earth would have responded if the greenhouse gases had not increased since the agricultural revolution (figure 3) (Ruddiman, 2005). The model showed how temperatures today would be 2°C colder and the Earth would be one third on the way to maximum glacial conditions. Other studies also support the findings showing how changes in orbital configuration and solar radiation based on oxygen isotope suggest that global ice volumes should have reached minimum 6,000 years ago (Berger and Loutre, 2003). 

Figure 3. An artists impression of the Agriculture Revolution (source)

The overdue glaciation hypothesis has received three main criticism all of which are address by Ruddiman (2007). Firstly, many have criticised Ruddiman's use of the previous three interglacials to compare against the Holocene (MIS1) since the orbital configuration of marine isotope stage 5, 7 and 9 are significantly different to the Holocene. During MIS 5, 7 and 9, eccentricity was higher than for MIS 1 resulting in more extreme solar radiation received on Earth. MIS11 has been proposed as a better analogue for MIS1 due to low eccentricity. The duration of MIS11 was significantly greater than other interglacials with marine sediments used to reveal how it lasted for 28,000 years, and this would therefore suggest that MIS1 has 16,000 years until the current interglacial come to termination (McManuset al., 2003). Ruddiman fires back with an argument that aligning the orbital configurations is flawed and that cooling had began during MIS11 at the isolation level comparable to that of MIS1 (Ruddiman, 2005). 

Secondly, many have question if humans have the capacity to increase greenhouse gases to reach such levels. To account of the 230 ppb anomaly found for methane, studies have suggested the expansion of wetlands across Eurasia but this has been rejected due to differences in the concentration between Greenland and Antarctica (Chappellaz et al. 1997). Ruddiman argues that substantial evidence from sedimentary records from deltas in the tropics show increased sedimentation and provide evidence of extensive deforestation  and widespread erosion (Roberts, 1998). Thirdly, detailed reconstruction of the Holocene temperature reveal small fluctuations around 10ppm in CO₂ in the last 1,000 years whilst human activity continues to increase. Ruddiman provides a possible explanation for this by claiming that three key major pandemics occurred over the last 1,000 years during the Roman Era (Cartwright, 1991), the Black Death pandemic during the Dark Ages, and the arrival of the Europeans in American 1942 (Denevan, 1992). 

Ruddiman provides a strong argument in favour of his overdue glaciation hypothesis. The implication of this provides important for defining the start of the Anthropocene which marks a moment in the Earth's history then humans activity becomes so profound that it rival the geological forces of the Earth and changes the course of the Earth away from its natural variation (Crutzen and Stoermer, 2000). Ruddiman's work shows how the Holocene was not free of human influence as previously believe and this has significant implications with respect to the current impact anthropogenic forcing are having on the current climate and on future climate. 

When the floods ruined Christmas

Figure 1: A rescue scene from the streets of Carlisle (source)

Over the Christmas period, large parts of the British Isles were battered by the latest 1/100 year storm event, Storm Frank, which caused widespread flooding and extensive damages across the UK. Britain saw high winds, flood defenses being breached, thousands evacuated from their homes and record breaking water levels. A large section of a bridge in the town of Todcaster collapsed under the force of the River Ouse, isolating a section of the community for hours which caused social stress and instability (see video below). Cumbria was hit badly as over 3,500 homes were evacuated according to the Observer, and Capel Currig saw 201.6mm of rain fall over 48 hour period between Christmas Day and Boxing Day. This all comes following the mildest December in the UK since records began in 1910 as an average of 9.5°C was observed for December according to the MetOffice. This was 4.8°C warmer than the average and 2.8*C higher than the second highest average set in 1938.

Can we blame global warming? Based on the fundamental laws of thermodynamics and the Clausius-Clapeyron equation, which states that warmer air can hold more water, climate models predict that in the future warmer world, dry areas will become drier and wet areas will become wetter. A recent study published in Science compared ocean surface salinity between 1950 and 2000 to establish a relationship between ocean salinity, rainfall and evaporation and used this to build hydrological climate models. Durack et al. (2012) found that over the designated 50 year period, the global cycle of rainfall and evaporation has accelerated by four per cent due to the enhancement in rainfall and evaporation. The study warns how future changes will not be uniform, and that 'changes to the global cycle and the corresponding redistribution of rainfall will affect food availability, stability, access and utilisation.'. 

It is possible that Britain is beginning to experience the direct impacts of climate change. As global warming increases in the future, the hydrological cycle is predicted to continue to increase, bringing more rain to already wet areas, and less rain to already dry areas. It is crucial that the Government invests in planning and preparation of flood defenses and coping strategies in an attempt to reduce future impacts of storm events and social instability.