A Vanishing Sea of Toxic Dust Storms

In the last Climate Change MSc lecture of 2015, a case study was presented regarding the changes that have happened in a relatively short space of time in the Aral Sea, on the border between Kazakhstan and Uzbekistan. Figure 1 below clearly shows the reduction in the area covered by water in the sequence which runs from 2000 to 2015.

Figure 1: Aral Sea satellite image sequence from 2000 to 2015 (looping). The black outline is the approximate lake shoreline in 1960. Source: Constructed animating gif from NASA Earth Observatory images.

Otherwise known as the ‘Sea of Islands’, this endorheic sea was once the fourth largest inland sea in the world, and allowed fishing communities and agriculture to sustain themselves for decades in the early half of the 20^th century. As an endorheic sea (meaning no outflow to the ocean) it acts as a terminus for surrounding hydrological systems, also termed as a terminal lake. Terminal seas and lakes such as this are very sensitive to changes in climate, for example through changes in evaporation rates. In fact, the Aral Sea has undergone a cycle of drying out and filling up over the past 10 thousand years (Micklin 2007).

Another picture, Figure 2 (sourced cited by an article on the Aral Sea Crisis by Columbia University) shows some older images than Figure 1, which highlight the longer term reduction.

Figure 2: Clear reduction in Aral Sea. When combined with Figure 1 we see the extremes of the reduction in water surface area. Source: http:/www.envis.maharashtra.gov.in and cited by Thompson 2008

The main cause for this reduction was the development of the Karakum Canal, built for agricultural irrigation, shipping and fisheries allow for economic development of Turkmenistan. It was started in 1954 and completed in 1988. It has enabled huge areas of Turkmenistan to be committed to high intensity agriculture, essentially draining the Aral Sea of water.

The reason for this huge engineering endeavour was the farming of cotton. The cotton, nicknamed ‘white gold’, requires a huge amount of water. To make matters worse the engineering practices used to construct the canal allow around 50% of the water to be lost into the ground and to evaporation.

Impact

Micklin noted the reduction in water surface area to be around 75%, and the lake level reduction to be around 23 to 30 meters (Glantz 2007), which led to a volume reduction of 90% and an increase in salinity of over an order of magnitude, from 10 g/l to over 100 g/l. This lead to tragic and severe impacts to the local ecosystems, mainly fish species, as well as enhancing the frequency of dust storms to roughly ten per year (Glantz 1999, cited by an article by Thompson in 2008 on the Columbia University website). These impacts deveastated local communities and made the area extremely inhospitable. 

Knock on impacts on local communities and industries are numerous. Obviously, the fishing industry in the sea has been decimated due to increasing salinity and agricultural practices are now hampered by the loss of water resources. Mammals and birds have also seen sharp decline in species diversity: from 1960 to 2007, the area lost roughly half of the number of species (Micklin 2007).

The other major impact of over 36,000 km² (Wiggs et al. 2003) of dusty seabed being created is that there is now a large source of extra dust available to be picked up by the winds and on occasion whipped into dust storms (Figure 3). Roughly ten dust storms occur in the region per year (Glantz 1999, cited by an article by Thompson in 2008 on the Columbia University website).

Figure 3: Dust storms on the coast of the Aral Sea in May 2007 (Source: NASA)

Agricultural waste products containing pesticides, insecticides, herbicides and fertilisers have drained into the sea, accumulated over time, and then once the sea dried, they became baked into the exposed sediments. The desiccated land surface also potentially contains remnants from Soviet Union's biological warfare testing in the 1950’s, including Antrax, which is just waiting to be transported around by the aeolian processes. Vozrozhdeniye island, also known as Resurrection island, remained a controversial subject as it was one of the chief locations for such testing.

Wiggs et al. (2003) studied the link between aoelian dust and child health in the populations close to the Aral Sea, and found some associations to local respiratory illness in local populations, although there are significant long-distance sources of dust in the region too. Micklin (2007) also confirmed this negative impact on human health and agriculture in the wider area from dust storms that can grow to be 500km in size.

Climate perspective

Although the case of the Aral Sea’s reduction is an extreme example, it seems fair to assume that endorheic lakes will see pressure due to global climate change (Timms 2005), whether there is significant human influence or not. The Aral Sea has suffered from a two-pronged attack as the region undergoes warming, and agricultural exploitation and over-use. Strategies to preserve the remaining water in the North Aral Sea through damming projects after the sea split in to two basins in 1987, seem to be successful, which will enable the communities in the area to hold on to their way of life to an extent.

The former majesty of the larger portion of Aral Sea (the Big Aral), now seems to resemble no more than a salty (and toxic) dust bowl, with former islands now parched monuments to the impact of cotton farming and climate change, although to a lesser but still significant extent, (Aus Der Beek et al. 2011). The region will only come under more pressure if water resources become scarcer in the area linked to global warming and high evapotranspiration rates. 

Small et al. (2001) examined how the desiccation of such a large area through excessive irrigation has modified the sea surface temperatures, precipitation regimes and the hydrological cycle in the area. I wonder if the original plans to build the Karakum Canal took any of these knock-on effects in to consideration.

To end, I’ll post this interactive storymap hosted by Esri which highlights some human induced change since 1990 using the Landsat satellite imagery from NASA. The first example is the Aral Sea and, you can see again, by swiping the dividing line, how the lake has undergone a dramatic and rapid drying out in the last 25 years. The other pages of the map, also show cases of anthropogenic land use change from urban expansion, damming, land reclamation, and agricultural uses.

*UPDATE*
My brother's comment below makes a very good point regarding the fact that such a sad story, now serves as a an evocative reminder of the impact of human over exploitation of the environment. This reminder should be documented as it happens, not only in scientific literature, but in art too. We are both keen photographers, and so I thought I'd add this link to herwigphoto.com's Aral Sea project. Some amazing and poignant images.

Palaeotempestology: Tree rings

In my last blog, I explored how the layers of calcium carbonate, which build up as a coral skeleton grows, can be used as a climate proxy. We can find a similar process by looking at tree rings. One of the more established practices in palaeoclimatology is dendroclimatology (the use of tree rings to study the past climates). Like other palaeoclimatological proxies, it allows us to extend the range of our observational record beyond that of conventional weather recording instrumentation.

Just as corals live for hundreds of years (sometimes over a thousand years), trees can keep on recording the composition of the atmosphere in their layers of cellulose for many hundreds of years, and beyond when fossilised. Figure 1 below shows an example of Huon pine samples ready for analysis, each dark line denoting a season of growth.

Figure 1: Huon Pine ready for analysis. Source: Edward Cook, Lamont-Doherty Earth Observatory, Columbia University, Palisades, NY

Isotopic differences

Ancient pines are often the favoured study subjects due to their longevity. They can give annual or seasonal information on atmospheric composition. To extend the record beyond a single sample, a variety of sources can be combined together using distinctive signatures as shown in Figure 2 below.

Figure 2: Sources of tree ring data showing how various samples can be linked together. Source: Laboratory of Tree-Ring Research, The University of Arizona

The main process that allow us to look at past storms is the fractionation of stable oxygen isotopes through condensation and evaporation. I touch upon this in my previous blog about corals, it is the difference atomic weight between the heavier oxygen-18 isotope and oxygen-16 isotope that allows us to glean clues about past climate events from tree cores.

The difference in atomic weight of oxygen isotopes is derived from the number of neutrons in the atomic structure. The most common natural isotope is oxygen-16 (over 99% of atmospheric oxygen) which has 8 protons and 8 neutrons (electrons are virtually weightless by comparison), but stable oxygen atoms can also have 9 or 10 neutrons to make up the different isotopes that we find useful for palaeoclimatology. As mentioned before, the water molecules with the lighter oxygen isotopes (oxygen-16) are preferentially evaporated in warm temperatures, while conversely the water molecules with heavier isotopic values (oxygen-18) tend to condense and form clouds or precipitation more easily. It is this property that allows us to identify different sources of precipitation in tree ring samples.

In extreme precipitation events associated with tropical cyclones, the level of oxygen-18 depletion in the rain water is high due to the highly efficient process of forming precipitation via condensation in the core of a tropical cyclone (Lawrence in 1998, Monksgaard et al. 2015). In Lawrence’s paper, five tropical cyclones that made landfall in Texas, U.S, were studied. They showed much lower oxygen-18 to oxygen-16 ratios (or δ¹⁸O) from tropical cyclones than normal summer convective storms.

This finding was further corroborated by a study of Hurricane Olivia by Lawrence et al. in 2002. Tropical cyclones are also large and long-lived and create vast areas of precipitation that can stay in the water system for weeks, giving different isotopic characteristics associated with the location of the heaviest rain bands and storm centre (Monksgarrd et al 2015). Deep soil water can remain unaffected by normal summer rainfall, and in the absence of further heavy rain events, it is allowed to be taken up by trees (Tang and Feng, 2001).

It seems clear that oxygen isotope analysis seems to be the favoured form of tree ring analysis for palaeotempestology.

Tapping the potential

Upon learning about these methods it also seems reasonable to assume that different intensities and characters of storms will result in different levels of oxygen-18 depletion. It seems likely that there would be much uncertainty in making assumptions of a storm’s intensity based on isotope fractionation (but I’ll keep looking for more research on this). At the moment, it seems that the uncertainty may preclude a reliable intensity measure of past storms using this approach.

The oxygen isotopes uptake into the tree’s structure will depend on many factors, including biological processes that are dependent on species, tree age, exposure to the storm, soil composition. Growth cycles are also taken into account. By doing so we can try to limit the degree to which uncertainty derived from the mismatch between growth season and storm season, can cloud useful information.

In the North Atlantic basin for example, hurricane season runs from early June to late November and as such overlaps mainly with latewood (as opposed to earlywood) growing phase. Therefore it is these sections of the layers of tree rings which are focussed upon for palaeotempestological studies.

Miller et al. 2006 presented the emerging case for using oxygen isotopes more widely after the devastation left behind by the busy 2004 and 2005 hurricane seasons, by building a 220-year record to identify past storms from unusually low oxygen-18 isotopes in pine forests. This is potentially very useful for engineering and loss modelling concerns.

“Can’t see the wood for the trees”

There are many uncertainties in the application of tree ring data to palaeoclimatology, let alone palaeotempestology, as summarized in the review paper by Sternberg et al. in 2009, including complex cellulose uptake biology, changes in isotopic composition of soil water, assumptions based on the relationship between leaf temperature and ambient temperature.

However, every study adds to the wealth of information and since each site represents a single location slice through time, it seems as though the science of dendroclimatology will only continually benefit from new data. And there still seems to be push to collect and analyse more data. The National Climatic Data Center, hosted by NOAA, is a font of old and recent tree ring datasets.

A recent review of the data by Schubert and Jahren published in October this year (2015) takes a wide view. It aims to unify tree ring data sets, to bring together a global picture of past extreme precipitation events based on low oxygen-18 isotope records. They conducted 5 new surveys and used 28 sites from the literature to create a relationship using seasonal temperature and precipitation, which can explain most of the isotopic oxygen ratio in tree cellulose. This seems to be a step up in resolution, as looking at seasonal variations rather than annual cycles may provide a step closer to identifying individual storms or storm clusters using tree ring data. It is interesting to see a comment in the conclusion of this paper about the fact that much of the uncertainty that still remains in this link, is derived from disturbances, such as storms.

Figure 3: Comparison between measured δ¹⁸O in the cellulose of studies trees and the calculated δ¹⁸O using the model developed by Schubert and Jahren which uses known climate characteristics. It shows a good correlation on relating seasonal temperature and precipitation to oxygen-18 isotope ratios. Source: Schubert and Jahren, 2015

It seems clear that it would be much more difficult to develop a simple equation to explain the extremes of the isotopic ratio chronologies to identify extreme storms. However, Schubert and Jahren seem to have taken a step forward while remaining focussed on average seasonal conditions. Nevertheless, I can’t help but wonder if there is a way for extreme events to be linked in to somehow.

Alternatives to isotopes

When looking specifically at past storms in trees rings, I did find a couple of other approaches to using tree ring data that may also be worth a mention.  

Firstly, an interesting couple of papers by Akachuka in 1991  and another in 1993, used a method where trees that have been forced to lean after a hurricane. This phenomenon is examined for any extra clues that it may provide by assessing how these trees recover from such disturbances. Although the papers do not look specifically at characterising the storms themselves (i.e. there is no wind speed to bole displacement relationship), I couldn’t help but wonder if there is some extra information to gather from these trees and whether we could build a relationship to specific storms or storm seasons.

Another paper by Sheppard et al. in 2005 looks at the effect of a tornado in 1992 on a specific dendrochronology and re-evaluates the pre-historical records from wood samples retrieved from an 11^th century ruin in Arizona. He looks for similar patterns in wood growth (see Figure 2 for conceptualisation). Unfortunately, the patterns found in the tree rings which were caused by the tornado in 1992 were not replicated in the ring patterns of the 11^th century sample. This is certainly interesting work, but I imagine that finding enough data for trees that are damaged but still survive tornadoes is not easy, especially when comparing to single older samples.

Conclusions

Although individual studies using tree lean or damage from specific events like tornados, are interesting and worthwhile academic endeavours to help us understand the ways in which storms of various scales impact certain tree growth, they do seem somewhat less applicable to thinking about climate change and how frequency and severity of storms are changing over a wide area.

With so many subtleties based on factors such as tree species or topography of a study site, I feel that the broader synthesis approaches (as per Schubert and Jahren above) using stable oxygen isotopes offer greater immediate potential for aiding our understanding of past changes in storm activity with possibility for application to risk assessments and projecting impacts of future climate change. 

Palaeotempestology: Beach ridges, corals and sclerosponges

After looking in depth at lake sediment layers as a proxy for hurricane activity, I’ll now turn my attention to the marine environment, as we head the seaside in our investigation. As we move off shore into the ocean, there are some other proxies as we broaden our options for looking at past tropical cyclones. For example, large scale storm surge or precipitation events can lead to rapid erosion or landslides which may become trapped in sediment records in the ocean. Corals can be smashed and broken in a storm and deposited or trapped in mud substrates.

Rubble Ridges

A ridge that is largely made up of broken coral or shell in mud layers is called a chenier. The subtle differences between a beach ridge and a chenier are described in the introduction of a paper by Taylor and Stone in 1996. Basically, it describes a chenier as having muddy swales in between ridges of sand, coral and shell deposits over the layers of sediment from the normal active geomorphological processes. Beach ridges however, are long ridges aligned with the general approach of the waves and confined by the limits of tidal depositing. 

Taylor and Stone (1996) describe how beach ridges and cheniers have formative processes during normal tidal and swell events, but ridge formation above the high tide level is likely to be due to extreme tropical cyclone action via extra deposition of sand, coral or shell. It is also likely that in the tropics, most or even all, cheniers are built by tropical cyclones (or the rare tsunami). It is this fact that allows them to add to the jigsaw of palaetempestological data, when appropriate examples are found.

Coral rubble ridges can also provide eveidence of storm history. If the bathymetry allows, we can see ridges of left behind by storms, which will likely contains larger proportions of coral debris. An excellent example of this is again found in Taylor and Stone 1996 where they have examined Curacao island in the Great Barrier Reef in Austalia (Figures 1 and 2). Figure 1 is a view to show the sheltered side of the island which suffers less wave action (and so mainatains a historical record) and therefore can accumulate beach and coral ridges during storm surge events. These ridges can be radiocarbon dated to provide the chronology in Figure 2 (labelled as Figure 3 in Figure 1).

Figure 1: Curacoa Island in the Great Barrier Reef, Australia showing coral rubble ridges. Source: Taylor and Stone 1996

Figure 2: Coral rubble ridges from transect denoted in Figure 1, showing radiocarbon dates of each mound.Source: Taylor and Stone 1996

These data can be misleading however, and although provide a clear demonstration of large surge events, in periods of high storm frequency, multiple storms will be superimposed on top of one another as it takes time for the sediments to become resistant to further storm erosion. This resistance is through carbonate cementation via weathering of coral material. This is an example of the one of the sources on uncertainty in using this data.

Frequency is studied by looking at the interval between ridges, but Nott and Hayne in 2003, also developed a proxy for intensity of storms. It links the height of the ridge with the minimum flood depth due to storm surge, which is above the highest tide level. The paper suggests their identified ‘super cyclones’ are much more frequent than previously considered along the Great Barrier Reef.

However, a key and more stable marine proxies in the near-coasts zones affected by tropical cyclone landfalls, is found through drilling cores both in corals and sclerosponges. A combination of coral core data and examination of beach and coastal zone sediments can be a powerful duo when assessing coastal impacts.

Correlating with corals

Normally, these cores are taken from old specimens in the areas most frequently affected by tropical cyclones. Many studies have been conducted on corals and sclerosponges in the Caribbean and across the North Atlantic coast of the U.S. prone to tropical cyclone activity, as well as pacific basins also prone to tropical cyclones. A list of datasets on coral and sclerosponges is compiled by NOAA’s National Climate Data Center and shows the range of study undertaken.

Layers of growth can be examined for stable isotopes or metal deposits which can tell us much about the past characteristics of the uppermost levels of the marine environment. One of the key pieces of information relevant to tropical cyclone formation that we can gain from coral cores, is the proxies for sea surface temperature (SST). SST is one of the main near-coast environmental components for generating storms that make landfall i.e. if the waters are warmer in the North Atlantic, perhaps during a La Nina phase of the El Nino-Southern Oscillation, then conditions are more favourable for cyclogenesis (birth of a cyclone) which gives a higher likelihood of landfall if occurring near to the coast. Information from corals is highly relevant and adds to the gamut of data that are used to build palaeotempestological records.

Diving for data

This has to be one of the more appealing ways to gather climate data: Dive in to the warm tropical waters, search around the ocean floor looking for suitable corals or sponges, retrieve your sample (Figure 3) followed by some lab analysis over a rum cocktail – sign me up! Of course, as with any worthwhile endeavour, there is only a very small amount of time spent in the field doing the fun stuff, compared to the lab work and analysis to follow.

Figure 3:  Coring large Porites coral, Rowley Shoals, Western Australia (Photo credit: Eric Matson, AIMS)

The equipment used (as shown in Figure 3) is custom built and after finding a suitable specimen, based on age, size, shape and species. It is often difficult to find multiple samples for verification purposes - a particularly tricky element of this type of study.

Due to limitations in the field, it is difficult to know whether a sample is of high or low quality, as it is not always obvious where interruptions in growth cycles, infestations, or damage from marine life are present. Samples are returned to the lab to have X-ray images taken and for chemical analysis. Two main factors are derived from corals. Firstly, there is the growth rate based on samples with clear banding, and secondly the information via the geochemical composition of  various layers of the coral skeleton which represent different times in its life cycle.

Figure 4 shows a slice of a Porites coral illuminated by ultraviolet light to show luminescent banding associated with freshwater inputs from heavy precipitation events which lead to local flooding and therefore more terrestrial-based organic material being made available.

Figure 4: Coral slice illuminated by UV light showing luminescent banding which indicated freshwater input after flood events. Source: Lough, 2010 John Wiley & Son s, Ltd

A good NOAA summary of how sclerosponges are used to reconstruct past climate can be found when the practice was still quite young in 1998 can be found here in the proceedings from a workshop held in Miami.

Another method used with sponges and corals is to analyse stable oxygen and carbon isotopes. Rather than luminescence, this examines the stable oxygen isotopes within their carbonate skeletons, which are formed according to their surroundings and 'locked-in' as a record. The ratio between Oxygen-18 (heavy and abundant in sea water) and Oxygen-16 (lighter and abundant in clouds and water vapour), can tell us a lot about sea surface temperatures. This ratio depends on temperatures since the fractionation between the isotopes occurs via evaporation and condensation. Since most evaporation occurs in the tropics, we see less and less oxygen-18 in the atmosphere as we head towards the poles as the heavier isotopes tends to condense out first. 

Using coral cores, one of the most important factors to consider is that the process by which corals and sponges incorporate oxygen into their skeletons (as Calcium Carbonate mainly) also prefers the heavier oxygen-18 isotope. This is corrected for using other biochemical characteristics. Once calibrated, the coral core can reveal information about past temperatures as corals  tend to preferentially utilise the heavier isotope in colder water. This therefore allows us to infer sea surface temperature from coral cores and link our data to past events such as strong La Nina conditions or fluctuations in the Pacific Decadal Oscillation (PDO). For more detail, this NASA Earth Observatory educational web page on Oxygen isotopes.

So after coral and sponge samples have been retrieved and analysed how do we actually gain some useful information?

How do corals tell us about tropical cyclones?

There are a number of studies that use coral luminescence. This sounds like a fairly abstract concept at first but the rationale is fairly straight forward so let me try to explain:

Luminescence can be a strong indicator of flooding in rivers near to the sample sites. It is this property of coral records that becomes very useful for palaeotempestology in that flood events that affects a large area, are likely to be caused by severe storms, monsoonal changes. This begins to tell us about the extremes of any given climatic conditions in the coral’s history. Climate variability is known to shift rainfall patterns, such as during ENSO phases or monsoon rains, and so this can lead to modulation of rainfall amounts over land, which correlate well with coral luminescence. These luminescent lines also act as ground for comparison for other coral records. 

Work by Johan Nyberg (2002) and Barnes et al. (2003) are examples of using coral luminescence to infer tropical cyclone activity in certain parts of the world. These papers explain the process of measuring luminescence and how the data can be applied to various fields of study surrounding past climates and climate variability.

The method of using UV light to identify terrestrial run off events in coral was first identified by Peter Isdale in 1984, Isdale identified that strong banding did not occur in corals greater that 20km from the coast and that the brighter bands correlated with periods of high precipitation and therefore enhanced riverine outflow to the sea.

Coral information combined with studies of tree rings can provide good cross validation and increase confidence in building past chronologies of climatic events such as monsoon droughts as studied by D’Arrigo et al. 2008, and so I wonder if there is anything that can help us find out about past wet seasons, or climate modes, such as the PDO, as in Rodriguez-Ramirez et al. 2014,or ENSO as in D’Arrigo et al. 2006, and therefore link to storm activity.

In my next blog, I will explore the use of tree rings to find out about past storms.

Palaeotempestology: Lake sediment records

Digging in to sediment records

With continued debate among scientists on exactly how future climate change will affect storm frequency and severity, it seems logical to see if we can find out more about variability in storm activity from the past.

Lake sediments are extremely useful in studying past climates, for which we have no observational record (through conventional weather recording equipment). They provide a slice through time to look at the changes in lake chemistry and environmental activity affecting the make up of suspended particles in the lake that eventually settle at the bottom.

Radiocarbon dating, thickness of layers of different sediments, analysis of diatoms and inference from the occasional break in the record (a hiatus, perhaps due to the drying out of a lake), are various ways in which lake sediments can give us clues about the past.

Within this range of different approaches there are a few ways in which sediments from lakes can be used to look at past storm events. In my previous blog, I highlighted a paper by Dr Jeff Donnelly et al. in 2015 entitled “Climate forcing of unprecedented intense-hurricane activity in the last 2000 years”. It presents a history of storm events over the past two thousand years, using an analysis of sediment grain size in their collected samples, with a resolution of around 1 year. The work uses evidence gathered from field work during the project (and previous studies) to determine the presence of two distinct periods of higher activity in severe hurricanes for the west North Atlantic coastline of North America: one between 1400 and 1675 C.E.; and another period of high frequency storms further back in time between 250 and 1150 C.E.

The study location is a place called Salt Pond, in Massachusetts. It has a tidal inlet linking it to the ocean, making it full of brackish waters. This proximity to the ocean means that the pond is exposed to ‘overwash’ during storm surge events associated with large storms heading northwards along the Eastern seaboard of the United States. These salt water incursions occur when the storm surge level is higher than any natural or man-made defences. This ‘overwash’ leads to ‘coarse grain event beds’, and so these can be used as an indicator of severe storm activity. This process is vaidated using known hurricanes landfalls, which are represented in the sediment records and act as ‘anchors’ to verify that the samples are valid.

The study builds on a number of papers that were produced after the convening of a workshop on Altlantic palaeohurricane reconstructions in 2001 at the University of South Carolina. The workshop aimed to identify new opportunities in the field of palaeotempestology. A summary of the workshop can be found here. Dr Jeff Donnelly and colleagues studied a number of lakes in the Northeast of the US, in the states of New Jersey and New England, and so to learn a bit about the methodology, I dug into some of the papers in some more depth.

Getting your hands dirty

It seems the only way to get at clues available from sediment records is to get your hands dirty. I found an earlier paper by Donnelly at al. from 2001 which built a 700 hundred year sediment record of severe storms in New England. This paper (and a couple more in Boldt et al. 2010, Liuand Fearn, 2000) started to show me that each project strategy is subtly different. 

Various schemes are planned based on the conditions of the study sites, to find the best locations for sampling overwash areas in a consistent manner. The aim is to try to consistently capture the process by which more intense storms erode more sand from the coastal beach and bring this coarse sediment into the brackish lakes and ponds, larger storms being assumed to produce wider fans of overwash sand deposits, being thicker near the shore and thinner near the centre of the study lake. A range of
samples should be taken to try to represent the range of possible characteristics of past intense storms. Figure 1 (below) is a hypothetical diagram from Liu and Fearn (2000) to show various patterns of deposition. Note the radial patterns associated with the various directions of storm approach, with the larger fans associated with more intense storms.

Figure 1: Hypothetical coarse grain deposition fans in severe storm surge events. Source: Liu and Fearn, 2000 

The coarse sand creates a layer over the more usual organic-based deposits that settle on the bottom of a lake as a stratified layer. This happens most effectively in anoxic lake beds (lacking dissolved oxygen) since any mixing from plant of animal life will be minimal.

Having never been in the field to collect sediment samples, I found it interesting to see how Donnelly et al. (and other teams) maintained a consistent chronology in the sediment records. They took multiple samples and use the variety of methods above to build their chronology.

Markers in time

Isotopic radio carbon dating and stratigraphic markers used to mark certain control points to validate the data. Pollution horizons are useful in this respect, for example lead concentrations mark the beginning of the industrial revolution as it quickly made it's way into the water systems and lakes and then 'fixed' by anoxic sediments. The presence of lead pollution is an indicator of the late 1800's (Donnelly et al. 2001) and then another change occurs when lead was removed from gasoline in the 1970's and 1980's. This is a good example as it shows how these markers are useful for calibrating sediment records, in a way that is easily understood and recognised.

Pollen records can also mark certain points in history, for example the European colonisation of the eastern U.S. led to large scale clearance of the vegetation for farmland meaning that the pollen composition changes drastically (Russell et al. 1993).

Once these markers are established, previous storms are used to calibrate storm events, and then previous coarse grain even layers are identified and carbon dated.

Clear as mud?

So having learned a lot more about sediment analysis in relation to palaeotempestology, I now have a greater respect for what these cores of old mud and sand can tell us about the past. However, it does seem to me that there is still a large degree of uncertainty in the data when trying to discern an idea about individual storms. For example, what if two storm occur in quick succession as a cluster, before a sediment layer has had a chance to settle and ‘lock in’ the information? This may end up looking look like one larger or more intense storm, when actually it is the frequency of storms in that season which is varing. Donnelly et al. 2001 give an example from their study location of a lack of agreement between historical accounts of two intense storms in 1635 and 1638 which likely created overwash signatures, but in the sediment proxy data, only one event was indicated. This means that the estimated frequencies may have significant uncertainty.

Also, responses of lake or pond to overwash events may change over time due to changes in natural or man-made barriers. However, even with these uncertainties in mind, it is still clear that there is great value in understanding the past clues left behind by storms in our coastal lake sediments. 

Without any alternative information, the best that we can do is to piece together palaeotempestological proxies and glean snippets of information to build a longer record of storms.

It also provides grounds for comparison in using climate models to try to understand past variability,
another subject I intend to explore in a future blog.

For now, I’ll leave you with an informational video by Ocean Today in conjunction with the Smithsonian Institution and NOAA, just after Hurricane Sandy in 2012 which will hopefully make a clear demonstration of what overwash looks like and how the coastal beach material can be dragged in across to end up in lakes or ponds that lay close to the ocean to give us these markers of past events.

My next blog will be on the evidence that can be derived from coral cores.

Palaeotempestology series: Introduction

In a previous blog, I talked about the various ways in which historical documents, records and anecdotal evidence are used in climatology. I mentioned briefly some of environmental proxies used to derive information about the climate throughout the whole of the Earth’s history using palaeoclimatological techniques. Studying past climates is an essential part of any debate on climate change and there has been a huge amount of science produced in this field both in terms of improved methods and developing datasets.

Depth of data

Ice cores, lake sediments, tree rings records, coral analyses and more, have been conducted around the world for the last few decades to build the picture of past climates that we have today. The National Oceanic and Atmosphere Administration (NOAA) in the U.S. has an online portal and interactive map (Figure 1) that shows the geographical spread of data. I knew there was a lot of data out there but this map really puts into perspective the amount of work that has been done to gather information around the world, but also shows that there are still many gaps and much more that could be done. Check out the Climate Data Online interactive map of palaeo records here.

Figure 1: Screen shot on NOAA's Paleoclimatology interactive map at Climate Data Online. Source: NOAA (https://gis.ncdc.noaa.gov/map/viewer/#app=cdo&cfg=paleo&theme=paleo)

Depth of study

As a snapshot to show the amount of research into palaeoclimatology, a useful list of just one year’s worth of research is compiled here by the team at the 'Skeptical Science' website.

Palaeoclimatological proxies are signatures left behind in the natural environment that can tell us something about the climate in the past. They require detective work and often sophisticated laboratory analysis, but can provide windows into the past to show us data that are otherwise not available.

They are often used to derive at temperature trends over thousands of years from which drought periods can be inferred, or to develop records of past atmospheric composition (useful for revealing changes in greenhouse gas concentrations) but certain proxies can also used to investigate past storm activity.

Pre-historical storm evidence

Since I am obsessed with storms, when thinking about pre-historical records, I couldn’t help but be drawn towards Palaeotempestology (a term coined by Professor Kerry Emanuel at MIT) which is the study of pre-historic storms. In this context 'pre-history' refers to the time before the beginning of observed instrumental record of weather and climate data, which is generally no more than 100-150 years long at best, shorter still if you consider that observations and full representation of all storms that occur has only really been possible since weather has been observed using satellites.

The first satellite used to observe weather conditions was TIROS I, launched on April 1^st 1960 and initially could only tell us some basics about locations of clouds, as analysed by hand. This image below (Figure 2) shows the very first image from this satellite.

Figure 2: The first image sent back from the first satellite used to observe the weather. SOURCE: NOAA/NESDIS

Satellite technology and application has come a long way since then (I’ll likely cover this in a future blog).

Palaeotempestology aims to look back hundreds or even thousands of years, so I’ll take a bit more time on this subject. In my next few blogs, I shall aim to investigate, and share, more on the various sources of data used to drill down in to using sediments (Figure 3), 

Figure 3: Heavy duty sediment core retrieval. Source: NOAA image by Ane Jennings. (ftp://ftp.ncdc.noaa.gov/pub/data/paleo/slidesets/heinrich/heinrich08.jpg)

swim through the information on coral cores (Figure 4),

Figure 4: SCUBA scientists extracting a core from coral. Source: NOAA image by Maris Kazmers. (ftp://ftp.ncdc.noaa.gov/pub/data/paleo/slidesets/coral/coral12.jpg)

and circle around the subject of tree rings (Figure 5).

Figure 5: Scientist preparing to take a sample from a Giant Sequoia tree. Source: NOAA image by Peter Brown. (ftp://ftp.ncdc.noaa.gov/pub/data/paleo/slidesets/treering/tree01.jpg)

Notes on COP21 - follow up interactive infographic

While thinking about the COP21 negotiations in under two weeks, I came across this excellent interactive infographic produced by the World Resources Institute. It shows the various greenhouse gas contributions from different countries, split by sector sources too. 

It's a good quick reference guide when comparing countries that I couldn't resist sharing, as a quick follow up to my previous blog post about the critical meeting in Paris.





I found it at the bottom of an interesting article regarding China's INDC, the article comments on the boldness on China's commitments to a low carbon future. My favourite comment from the article is how the INDC's should be seen as a 'floor' rather than a 'ceiling' on ambition! Hopefully, this advice is heeded at the negotiations.

Notes on COP21

A couple of weeks ago, on the 5^th of November, I attended an evening presentation on COP21. There weren’t any fireworks but it was an illuminating talk, so I thought it would be useful to turn my notes into a blog and discuss the various points raised.

Source: Official COP21 logo

The presentation was by Jesse Scott, from the International Energy Agency (IEA). She's an ex-campaigner and lobbyist who has also worked in civil service in Paris before moving to the IEA.

Initially, she charmed us with her passion for the subject of climate change by describing how, with so many different issues, interests and stakeholders, climate change is simply too interesting to ignore from a political perspective.

She spoke to the audience with authority, about what COP21 actually is, and what it is trying to do. She gave an overview of the science, technology and economic linkages, and then moved on to discuss how COP will work in practice.

She explained it in real terms, and so this worked very well as a primer on 21st conference coming up soon. In this blog, I have used her presentation as the basis of my discussion on the COP21 meeting.

Firstly, a brief overview and history is as follows:

• The Conference of the Parties (COP) meets roughly annually since 1995 (the first held in Berlin - the full list of meetings can be found here) to assess progress dealing with climate change under the UNFCCC and is the decision making body of the framework.
• It was the driving force behind the Kyoto protocol (COP3 in Japan) in which was the first major example of legally binding obligation for developed countries to reduce the greenhouse gas emissions.
• The UNFCCC is comprised of 196 countries and is committed to stabilising greenhouse gas emissions to a level that presents as little danger as possible to the global community.
• Since Kyoto there have been attempts to update the legal obligations, the biggest and most recent attempt was in Copenhagen in 2009 (COP15) which was deemed to be a failure, and unilateral agreements could not be reached.
• Paris is the next big concerted effort to reach binding legal agreements, based on the commitments outlined from each country ahead of the conference in their Intended Nationally Determined Contributions (INDC) of which most have already been submitted.
• In COP20 and COP19 the decision was taken that these INDCs would be declared before the conference to promote clarity, transparency and understanding of each country’s position and idea of the methods they will chose to tackle adaptation and mitigation strategies.

Recommended Reading

Jesse Scott recommended an article on Christina Figueres inthe New Yorker as an excellent primer on COP21. Ms Figueres is the Executive Secretary of the UNFCCC. A transcript of Christina Figueres' speech to the 1st Global Climate Legislation Summit a couple of years ago, expresses how focussed she is on delivering the goals of the UNFCCC and the strength of her advocacy for climate change legislation. She will be blogging through the COP21 so it is worth following her articles. A recent article in the Guardian also shows her optimism for these talks here.

During the presentation, Ms Scott gave us a whistle stop tour of the science (via IPCC) as a precursor to a dialogue on broader governance and political aspects.

A few initial areas she touched upon include:

Procrastination: She also discussed examples of action today being more valuable than responsive action in the future. This reminded me of a often quoted figure regarding resilience which is replicated in various reports but in one case, the UNDP state that for every one dollar spent on disaster preparedness, we save seven dollars on emergency response as highlighted in their #Actnow campaign. This is relevant in a warmed world that may see greater extremes of climate. It also reminds me of the old saying: 'a stitch in time saves nine'. Act now to stop a worse situation in the future.

Technological advances: In recent years, technological advancements have allowed companies to start to realistically consider how to maintain their economic growth trajectories, while investing in sustainable and energy efficient technologies.

Communication: She also talked about the difficulty in communicating risk and uncertainty and described a game developed by Pablo Suarez and his team have designed a game that allows us to experience the difficulty with managing climate risk. Gamification can be an effective way to communicate complex processes.

Climate Justice

Climate Justice is an important and complex principle in the debate on climate change. Climate change doesn't deal out its impacts evenly from a human-centred perspective, as Ms Scott describes, the poor and the young tending to be most vulnerable. Historically, there is also a disparity in that those countries that have a long history of high carbon dioxide emissions, are those who have benefited most, and are most resilience to future impacts. Furthermore, in terms of where the changes are required, the biggest emitters of greenhouse gasses in the past, present and future are argued to be those that need to take most responsibility.

The question of who should do what to mitigate anthropogenic climate change (as we understand it) is a question of science, politics and responsibility, while being reliant largely on metrics. In some respects, it depends how emissions are compared and the political sway of those in power. 

When looked at in the context of the 17 UN sustainability goals, we can consider how different countries and regions will have differing priorities for many of the 17 goals, but with climate change, everyone is a stakeholder and everyone has some exposure to the risk.

Being a trans-boundary and inter-generational challenge means that it requires the concerted and long term commitments and efforts the COP21 is aiming towards.

Mary Robinson (former President of Ireland) was quoted on Climate Justice and human rights summing up that 'Climate Change impacts are biggest on those who have does least to produce them'. Using IPCC parlance, it is extremely likely that this is the case. 

The inter-generational aspects also highlight that those who have made no past contribution to greenhouse gas emission levels (those as yet unborn) will be those feeling impacts of climate change for the longest. 

Some small island nations are starting to plan for the displacement that will be caused by climate change. The Bikini Atoll, a site of nuclear testing in the 1940s and 1950s (and famous for swimwear design) has applied for land in the U.S. to relocate the population due to rising sea levels. 

Source: Getty Images via BBC (http://www.bbc.co.uk/news/science-environment-34642692)

Ms Scott affirms, from the perspective of the IEA, that the main solution is to find a way to provide 'clean energy' for everyone. Allowance must be made for the ever-increasing demand for energy in developed countries and the needs for increasing energy to foster development in poorer countries.

Good COP, Bad COP

The talks in Copenhagen in 2009 (COP15) were largely seen as a failure, in that they could not reach binding commitments for countries that have the highest emissions. However, there is reason to be optimistic. Ms Scott describes herself as being ‘very cautiously optimistic’. A lot has changed since 2009:

• The science has moved on, especially through another round of IPCC research.
• Technology is offering new solutions for renewable and efficient energy at a dramatically reduced cost. 
• The U.S. and China governments have steadily shifted towards addressing climate change during the last half a decade, with recent confirmation of their positive intentions on the climate (joint presidential White House statement on September 25th).
• G7 countries addressing climate change in a practical manner, and expressing a feeling of responsibility, as seen here in a White House press summary in June.
• Lessons have been learnt from the difficulties in Copenhagen. There is generally a much brighter outlook on the potential for meaningful and binding agreements being reached, based on the INDCs.
• The Pope has issued a number of statements regarding climate change.
• Mark Carney of the Bank of England has delivered recent speeches regarding climate change and the role of the insurance industry in managing future risks. The ‘1-in-100 initiative’ is an example of how the methods used in insurance industry can benefit both the public and private sectors if adopted more widely in the risk management processes.
• Military interests (e.g. NATO) are concerned regarding their resources in a warmer world. If they need to use their troops for disaster relief after severe events, both home and abroad, then how does that affect their ability to maintain national security - an issue amplified if we can expect changes for the worse in frequency and/or severity of extreme events like floods and storms, as well as migrations and likelihood of conflict through severe droughts. 
• On the public front, celebrity endorsements (for example Leonardo DiCaprio who spoke eloquently at the UN climate change summit last year) have continued and activism continues to put pressure on companies and governments to invest on environmentally responsibly technologies.

INDC - Are all of the cards on the table?

As of last week, 85% of the INDC had been submitted. Hopefully these will be much more robust than previous efforts, focusing of the three elements that are required for any mitigation strategy to work: Monitoring, Reporting, Verification.

It should be noted that these INDCs are self-defined, and so the cynic in me suspects that they may be quite lenient, but equally, there is probably little alternative to this approach as every country will have different processes and issues that need to be understood so they can action their obligations. The sum of the INDCs should add up to one global agreement that is achievable within the context of each nation - not easy to achieve.

If the details of the INDCs were not country specific it would be very difficult to find common ground. For example, in terms of monitoring, there is the question of which metric to use. Per capita CO2 emission may favour China, with such a large population, but would this be representative with such a huge disparity between the high and low (rich and poor respectively) emitters?

Would using per capita metrics put countries other countries at a disadvantage? Using absolute (total) emissions would conversely perhaps put China at a disadvantage, being top of the worst offenders list?

This type of conversation will no doubt be had during the negotiations.

Disclaimer

I'm still getting to grips with the angles of the politics of climate change (luckily I'll be studying it more specifically next term), but this talk certainly helped me gain deeper appreciation of the complexity and importance of the COP21 meeting. If there is anything in this blog with which you disagree or looks to be misunderstood, then feel free to comment and let me know.  Most likely, it is due to me being new to thinking about these negotiations in depth so I'm eager to learn more.

Everyone is a stakeholder in looking after our climate and developing a sustainable environment, and that also means that there are lots of different opinions and views. I agree with Jesse Scott that it really is a fascinating topic to study.

A final word
I wrote most of this blog last week, but between then and posting, the tragic events in Paris have unfolded. My thoughts are with the families and friends of those directly affected and the people of Paris as they recover from this despicable and horrific act. The Foreign Minister of France, Laurent Fabius, has a short quote on the home page of COP21 today, saying simply:

“The COP is maintained”