Background
The year is 2018. The United States remains in a prolonged economic downturn, and pressure continues to mount on federal government agencies to reduce costs through any and all means. Despite the fact that it comprises only 0.2 percent of the total annual Budget of the United States Government, the National Science Foundation has been identified as a target for cost savings. The agency has received particularly harsh criticisms from both Democrats and Republicans for the high salaries and rich benefits it provides to staff that supervise the distribution of research funds to institutes of higher education.

In a bold and unprecedented move, the executive board of NSF has decided to fire every Program Director and Program Manager at the agency and replace them with junior scientists who are paid entry level salaries. You are one of those junior scientists. You have been selected along with five other new hires to serve as co-directors of a long-standing program called Paleo Perspectives on Climate Change, commonly abbreviated as P2C2. The overarching goal of P2C2 is support the scientific objectives of the United States Global Change Research Program by fostering understanding of the climate system at timescales longer than the instrumental record. Along with your colleagues, you are responsible for setting priorities for research conducted under this interdisciplinary initiative, and making decisions about how best to allocate nearly $10 million worth of American tax-payers' money every year.

Unfortunately, on your first day on the job, you and the other co-directors receive an urgent request from Dr. Subra Suresh, the Director of NSF and your ultimate boss. In his message, Dr. Suresh explains that NSF has been instructed by the United States Congress to report on the return on investment provided by your program. Because of a severe drought affecting their home states of Minnesota and Wisconsin, a pair of influential members of Congress have become convinced that the Earth's climate has changed and will continue to change in the future due to human activities. This shift in thinking has led them to conclude that past climate history is no longer helpful for making decisions about the future and that NSF should terminate P2C2 and put the money towards a better use. Dr. Suresh calls on you and your team to help him argue for the continuation of support to P2C2 when he testifies in front of Congress later that afternoon.

Task
Over the next two days, you and the rest of your team need to produce two resources that will help Dr. Suresh to explain the value of paleoclimatology and save your program (and your jobs).

First, compose a tightly-written, single-spaced two-page report that defines the field of paleoclimatology and outlines how it contributes to priority issues in modern climate science. Take particular care to address the central question that will be posed to Dr. Suresh at the Congressional hearing: If the climate of the future will be different from the climate of the past, what is the justification for studying paleoclimatology? Given that the two most vocal critics of your program hail from the Upper Midwest, your report should also provide at least one or two examples that illustrate how insights from climate history can help address important questions that related to future climate change, natural resources or hazards in that region.

Second, Dr. Suresh understands that members of Congress do not always read written reports and that his best opportunity to make the case for P2C2 will be through a brief oral presentation at the hearing. Please prepare a short (10-minute) presentation that explains why NSF should continue to support paleoclimatology. You will need to develop a clear central message, present strong supporting examples and assemble a set of powerful visuals to hammer home the importance of this research. Starting at 10:15AM on Friday, several of you will need to deliver a 'dry-run' of this talk to Dr. Suresh's assistant so he can understand how you intend this material to be presented to Congress.

Because both tasks must be completed in only two days, you may need to split your group into two teams and work on each resource in parallel. Good luck, junior Program Directors!

This summary comes courtesy of Catharine McCook.

Sir Walter Raleigh was granted the first English charter to establish a colony in North America. The colony was built on Roanoke Island, close to Chesapeake Bay. In 1587 the colony held 90 men, 17 women, and 11 children, including the first European born in North America. Around this time England went to war with Spain, so the governor was not allowed to bring his ship back to the colony. When he was allowed to return three years later, Roanoke was empty. Dendrochronologist David Stahle examined a tree ring record going back 1500 years and was able to determine that 1587 had had the worst drought in 800 years, causing the water to become more saline and caused sickness among the colonists. This kind of accuracy and resolution is unique to tree rings, as most proxies cannot pinpoint a single year.

The period of classic Maya civilization is typically placed from AD 300 to AD 900. The classic Maya lived in the Yucatan Peninsula, which gets most of its water from groundwater and sinkholes as there are no rivers or lakes. Because of this lack of permanent lakes the proxies are used as far away as Venezuela. Venezuela is far from the Yucatan Peninsula but they are both influenced by the ITCZ synchronously, which means they have similar climates. The Cariaco Basin is anoxic at the bottom, preventing decomposition and bioturbation from disturbing the sediment layers. Light-colored laminae are deposited in the dry season, dark-colored in the wet season. Titanium can also be detected in cores; more titanium means more rain. The cores back seventy thousand years and have decade-scale resolution. They show that the Maya collapse at AD 800 was at the same time as the lowest precipitation in the eight hundred years previously, implying a shift in the ITCZ. This was compounded by the Maya reaching their peak in civilization, and thus the carrying capacity for the environment. The distant Venezuelan proxy is somewhat correlated by calcium carbonate records in speleothems in Belize, showing a drop in δO18--less moisture--from AD 1000 to AD 1150, but this was after the collapse in AD 800.

The Anthropocene is an informal geological timescale, defined by humans impacting the environment. The boundary for where the Anthropocene started is still unclear, though conventionally it is placed somewhere around the industrial revolution. But scientists like Bill Ruddiman believe anthropogenic impact on the environment may have started thousands of years ago, from increased atmospheric methane. Methane concentrations usually follow the Milankovitch cycles, but around 5 ka the CH4 concentration began to rise while insolation was decreasing. This may have been caused by the ancient rice production found in south China and India, but the cause is still unclear.

This summary is courtesy of Yuxi Jin.

Decadal climate variability refers to the climate change of Earth on a decadal timescale considering the Pacific Decadal Oscillation (PDO) and Atlantic Multi-decadal Oscillation (AMO). This concept was developed in the 1990s. And the first relevant event was happened when an oceanographer found a specific pattern of North Pacific Salmon. After the observation of quantity catch, he found a seesaw-shape pattern between Alaska and California. Several events and disasters happened in Alaska in 1939 and 1995 corresponded to what happened in British Columbia Coastal. These phenomena triggered scientists to wonder could this pattern related to climate change.

With further research on the air temperature in Alaska, sea surface temperature in British Columbia Costal and the stream flow in Gulf of Mexico. A clear pattern with persistently high values and low values changes happened in the same time was observed and concluded. The significant part of the climate variability is the ocean which drives the climate change behavior for last several years and also serves as buffer and sink. It takes long time for oceans to heat up and cool down which explains why the surface temperature of the Pacific Ocean tends to slowly alternate between "warm" and "cold" conditions.

The Pacific Decadal Oscillation index is defined as the major element of North Pacific monthly sea surface temperature variability. It goes back to 1900 and has a long-lived El~Nino-like pattern of Pacific climate variability. And it usually maintains in warm phase for 20 years which is quite slow and stable. In this case, the shifts in salmon can be explained by the mediation by sea surface temperature. The PDO variability is vital due to its clarity on demonstrating that "normal" climate conditions can vary over time periods comparable to the length of a human's life-time, and climate anomalies that stick for one or more decades which can influence the human societies and ecosystem significantly.

Another important factor in decadal climate variability is the Atlantic Multi-decadal Oscillation which is slower and more persistent. The variability of AMO is about 20-30 years which is slower than PDO. However the observation shows it should be around 100 years. The AMO is also expressed in sea surface temperature. Therefore, the combination of PDO and AMO is telling the story about how decadal climate variability occurs, behaves and disappears.

Yesterday we discussed how paleoclimate data spanning the Holocene has been used to address outstanding questions in archeology and history. We ended our conversation talking about the 'early Anthropocene hypothesis', which suggests that early human civilizations have slowly changed the trajectory of the Earth's climate over the last half of the Holocene.

I've uploaded the main papers highlighted in yesterday's class.

Stahle et al. (1998), The Lost Colony and Jamestown Droughts. Science.PDF

Haug et al. (2003), Climate and the Collapse of Maya Civilization. Science. PDF

Ruddiman (2013), The Anthropocene. Annual Reviews of Earth and Planetary Sciences. PDF

Decadal climate variability

On Wednesday we discussed 'decadal climate variability' and reviewed its definition, its importance, and the reasons why proxies are an important (but complicated) tool to understand this behavior. I've uploaded three articles that relate to our discussion, which I hope will be useful references for you in the future.

The first article is a classic paper from the mid-1970s on 'An Overview of Climatic Variability and its Causal Mechanisms'. Instead of tracking climate variability through time, this paper provides an (early) description of how climate varies by frequency, which is a common way to summarize the behavior of climate and paleoclimate records.

The second paper introduced the concept of the 'Pacific Decadal Oscillation', and tracks the development of this idea from the Pacific fisheries to oceanography and subsequently to terrestrial climates. The PDO is often described as the 'low-frequency' equivalent of the El Nino-Southern Oscillation, so any discussion of decadal climate variability usually starts with this system.

Finally, I mentioned that although proxies provide a critical long-term perspective on decadal climate variability, it's not always clear how we should interpret paleo-records. This article by Kurt Kipfmueller compared several different proxy estimates of the PDO and argued that the strong disagreement between these reconstructions makes it very difficult (perhaps impossible) to come to any conclusions about the PDO's behavior prior to the 20th century.

This summary comes courtesy of John Munson.

The Medieval Climate Anomaly, previously referred to as the Medieval Warm Period, occurred from 1000-1200AD according to Hubert Lamb, but it is often referenced from 500-1500 even if the anomaly is unrelated to temperature. Lamb mentioned three lines of evidence for the Medieval Climate Anomaly: Viking settlements on Greenland, sea ice, and the geographic distribution of vineyards throughout Great Britain. First, the Viking settlements on Greenland occurred on the western margin from 985-1408AD. Where these settlements are found there is now permafrost that contains roots and graves, suggesting that at the time of the Viking occupation of Greenland the climate was warm enough to allow for digging and vegetation in what is now frozen ground. Secondly, Lamb uses historical data of the Arctic ice pack. There is no record of drift ice around Iceland from 1020-1194AD. Therefore, the climate was warmer than it is today which caused the ice to melt farther North than usual. Lastly, Lamb uses historical data of vineyards from 1300-1450AD and found that they were found further North and at higher latitudes during that time period than at any other time in history. However, Lamb's research only involves the Northern Hemisphere which only shows regional change. There are problems with widespread use of the Medieval Warm Period. The main issue is with chronology and synchronicity. By referring to the Medieval Warm Period as occurring from 500-1500AD, there are long temporal gaps that would be too great to just be an anomaly. There is also little evidence for a global synchronized climate over space and time.

The causes of the Medieval Climate Anomaly include decreased volcanism and increased solar irradiance. With decreased volcanism there are less than normal sulfate aerosols in the atmosphere which would result in a less solar radiation being deflected. Furthermore, the more sunspots there are on the surface of the sun, the more energy that is released. This causes an increased solar wind, a decreased in cosmic rays bombarding the upper atmosphere. The decrease in cosmic rays creates a decrease in the production of the cosmogenic nuclides, C-14 and Be-10. C-14 may be measured from tree rings and Be-10 is observed in ice cores.

The Medieval Climate Anomaly
I've uploaded two key resources in support of yesterday's discussion of the 'Medieval Climate Anomaly' (aka 'The Medieval Warm Period' aka 'The Medieval Warm Epoch'.

The first is a classic article by Hubert Lamb called 'The Early Medieval Warm Epoch and Its Sequel'. Because it was published in 1965, most of the sources used to support Lamb's argument are out of date and most of the important proxies spanning the last 2K didn't exist. Even so, as the first article to make the case for a warmer world during the 'medieval period', this paper is the starting point for nearly every discussion of the MCA.

The second is a more up-to-date summary written by Henry Diaz and several collaborators on 'Spatial and Temporal Characteristics of Climate in Medieval Times Revisited''. I used this article as the framework for yesterday's lecture, and several of the graphics we reviewed come straight out of this paper.

Finally, I'll also point you to an online post on medieval English vineyards and their interpretation as temperature proxies. The fact that the English were making wine in the early 11th century was one of the key points backing up Lamb's claim of a warmer medieval climate, but exactly what we should interpret from this evidence is somewhat controversial.

Genghis Khan
Next week (April 16), we'll be joined (via Skype) by Dr. Neil Pederson. Neil is a research scientist at the Lamont-Doherty Earth Observatory, which is affiliated with Columbia University in New York. He's primarily trained as a forest ecologist, but he is also an expert in tree rings, paleoclimatology, and natural history.

Neil was the lead author on a recent paper published by the Proceedings of the National Academy of Sciences linking climate change during the 13th century with the expansion of the Mongolia Empire. Neil has made several trips to Mongolia to develop tree-ring records for that region, and has worked closely with Mongolia scientists for nearly 15 years. Please read the article before class and come prepared to ask questions about Mongolia field work and the beautiful data he and his colleagues have extracted from some very ugly old trees.

You may also want to listen to Neil's colleague, Dr. Amy Hessl from West Virginia University, discuss this work on Minnesota Public Radio. You can check that out here.

This summary is courtesy of Jennifer Krueger.

The Little Ice Age (LIA) climate was generally colder conditions and occurred approximately between the 16th and 19th centuries. The LIA was hemisphere wide, meaning that it did not affect just Europe. There is evidence in northern Asia and it is important to note that other all regions experienced colder than normal temperatures but not in the same way. In class we discussed the LIA characteristics and causes and more specifically glacierization and climate.

Glaciers respond slowly and depend greatly on climate. Unfortunately they are non-linear causing it difficult to connect specific responses in climate. However, moraines provide us with helpful evidence as to when and to what extent glaciers have expanded and rescinded. A moraine is build-up of sediment among the margins of glaciers as they expand downward. As a glacier rescinds the sediment and debris is left behind creating a distinct landscape of a past glacier. Moraines have a potential for a high-resolution proxies however dating them can be challenging and older moraines get erased as glaciers extend. There a several different types of moraines yet lateral moraines are the main indicators of past glaciers. Tree rings can show when they were killed or tilted by a glacier. Trees growing above the lateral moraine, after the glacier stopped, can help in dating a glacier also. Other proxies available are photos, sea ice, ice cores, and moraine sediments.

Lower irradiance and volcanic eruptions are thought to be potential causes of the LIA. We now know that the sun experiences a cycle of sunspots, which produce a lower radiance causing an overall cooling of the earth. Evidence of higher intense volcanic eruptions occurred during the LIA and the sulfate aerosols released into the atmosphere condenses and reflects sunlight which reduces the amount of radiation able to get to the land surface resulting in cooler temperatures. Ice cores can be used to date volcanic eruptions and their magnitude, and these events can significantly affect climate and temperatures.

This summary is courtesy of Chris Mahr.

Paleoflood hydrology is the science of reconstructing the magnitude and frequency of large floods using geological evidence and a variety of interdisciplinary techniques. Paleofloods are events that are generally recorded outside of gaging records and can be extremely ancient. Paleoflood hydrology was developed in the 1970s as a way to understand the magnitude of extreme flooding in central Texas and has evolved considerably since then with broad scientific and social relevance. The evolution of these methods has made it possibly to overcome difficulties such as inaccuracies in estimating the ages of floods, inaccuracies in reconstructing discharges, lack of robust statistical methods for incorporating data in flood-frequency analysis, and the effects of climatic shifts. Climatic shifts are used since floods are a hydroclimatic process and their frequency may be affected by climatic variability. Flooding causes extensive damage, which removes much of the evidence of their occurrence, and can last as long as 2-6 weeks. Flood damages between 1903 and 1999 peaked with floods associated with the 1993 El Ninos, and the 25-year running mean of flood damages has risen from $.043 to $3.15 billion dollars per year! The damage including the removal of evidence can be due to erosion or simply washing material downstream. This destructive nature of floods can therefore make it a challenge to see the evidence of a flood in proxy records. The confined area of a flood (flood plain) is also a deterrent in studying paleofloods, compared to larger areas for finding evidence of temperature changes, for example. Because past floods can inform and prepare us for future floods in a given location, it is important to be able to predict and understand floods. However, floods are extremes, which makes it difficult to fully understand patterns over small interval, such as 100 years. Therefore, it is vital to find a way to build a longer record of flooding.

Paleoflood hydrology can be a challenge to study, but there are ways to do so. The most crucial step is to find real historic records, such as journals created by traders or farmers. Knowing when large floods have taken place makes it easier to be able to use proxy records, and these can include lake core samples, flood plain sediment accumulation, and tree ring records. Tree ring records may seem to be a dead end at first though, as it could be difficult to differentiate between the negative effect on the rings by both flooding and droughts. However, tree rings do tend to show a unique ring that has no dark fiber during years of large floods, and this can be proven by comparing the tree ring record to historical records. These rings can belong to modern trees, sub-fossil trees, or even trees used for the construction of buildings on flood plains. Using this method, a 350 year record of Red River flooding in Minnesota, North Dakota, and Canada was constructed. Other techniques for studying paleofloods include regime based paleoflow estimates, paleo-competence studies, paleostage estimates and bounds, and floodplain stratigraphy. Regime based paleoflow estimates use empirically derived relations to estimate the value of high-probability flow events, such as the mean annual flood. Paleocompetence studies use empirical regression or theoretical expressions to relate very large sedimentary particles to hydraulic conditions necessary for their transport or deposition. Paleostages are estimated by documenting flood-induced erosion or deposition near maximum water levels of large floods. Radiocarbon dating and mineral luminescence are useful dating methods for younger floods.

As promised, here are the two (optional) readings associated with today's lecture on paleoflood hydrology, as well as the (non-optional) reading for Friday's discussion of the 'Little Ice Age' concept. I won't assign specific questions to direct your reading of the Matthews and Briffa article, although the ideas and examples from my lecture are more likely to stick if you review it beforehand.

Paleoflood hydrology
Baker et al., 2002. The scientific and societal value of paleoflood hydrology. [PDF]
Wertz et al., 2013. Vessel anomalies in Quercus macrocarpa tree rings associated with recent floods along the Red River of the North, United States. Water Resources Research. [PDF]

The 'Little Ice Age'
Matthews and Briffa, 2005. The 'Little Ice Age': reevaluation of an evolving concept. Geografiska Annaler. [PDF]

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