GEOG Feb 20 (L13) Medieval Warm Period and Little Ice Age PDF

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Reading Questions: 1. Approximately when did the medieval warm period and Little Ice Age occur? 2. What evidence is there for each event (including where)? 3. What processes have been proposed to be responsible for the climatic changes? 4. How do volcanic eruptions affect climate? 5. How long does t...

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Reading Questions: 1. Approximately when did the medieval warm period and Little Ice Age occur? 2. What evidence is there for each event (including where)? 3. What processes have been proposed to be responsible for the climatic changes? 4. How do volcanic eruptions affect climate? 5. How long does the impact of a volcanic eruption last and what factors affect the duration? 6. What are sunspots and how long are sunspot cycles? 7. How are sunspot cycles thought to have affected climate? 8. What can cause climate variation over the time scale of centuries? 9. Under what social or economic conditions would minor climate change have impacts on society? (Think about where food came from for people living during the Little Ice Age.) The Medieval Warm Period - Mild temperatures, agriculture in Europe flourishes - Called Little Optimum - Called Medival Warm Period - Vineyards existed in Britain and were 3-5 degrees more northern latitude - Also 100-200 meters up hillsides - Historical records of agriculture existed in china→ te lychee was north of the current range -

Warmer climate encouraged the Vikings to explore more Vikings expanded to Newfoundland and formed small settlements in Iceland and Greenland - Perhaps as far back as the 9th century AD - Harbors of the northern Atlantic were ice-free more often for longer periods

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Tree rings (dendroclimatology) and ice cores - Proxy indicates - Produce annual records of past climate - Medieval Warm Period was not warmer than the 1950s to 2000s - Milder winter temperatures

The Little Ice Age - A colder period that followed the Medieval Warm period - More widely recognized but still debated - Time interval spans anywhere from 14th to 16th century AD - Ends uring the 18th or 19th century - Paintings and drawings show there was an intense period of cooling - Colder winters and summers - Increased storminess - Great negative impact on agrarian society as there was crop failure→ famile→ malnutrition and need to find a scapegoat→ , witches

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- This triggered early witch hunts - People needed to blame someone In britain,→ the vineyards were pushed back south In Europe (Alps) - Mountain glaciers advanced causing damage→ the swiss requested tax relief!

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In Switzerland, the Aletsch moved over an aqueduct In Norway, there was also an increased occurrence of avalanches, landslides… people asked for tax relief which gives us a historical record Bad weather Colder winters and summers → resulted in colder winters and summers

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Average temperature decreased about 0.5 degrees Celcius In Greenland - The last record of marriage happening in this church was 1408 AD - Then the Viking settlement was abandoned - No bodies have been found on the surface - Currently, the ground is too cold to dig into and bury people - Back then, during the warm age, the weather was warm enough to do so - This indicates there was a cooling period following a warmer period Crowley - A range of sources of evidence do initiate a cooler period during the Little Ice Age preceded by a warmer period but followed by the warmest period the Earth has seen in the last 1200 years

Valid Question: If the earth’s climate is always changing, then why is our climate warming so much now? - Answer in the movie What can cause climate change over the scale of centuries? - Initially, witches were blamed - Causes of the Medieval Warm Period and the Little Ice Age - Solar Radiation and its “amplification” - Volcanic Activity Solar Radiation - See link to NASA: Solar Cycle - https://www.youtube.com/watch?v=sASbVkK-p0w Solar Radiation - Sunspots - Dark patches on the surface - Strong magnetic forces which block solar plasma - So they are cooler - Faculae - Bright blotches that surround sunspots - Put out more radiation that normal sun surface - Their effects beat out that of sunspots - Thus, the frequency of sunspots correlates to periods of higher solar radiation - A 1% decrease in the solar constant could lower global average temperatures by 1-2 degrees Celcius - Sunspot activity follows an 11-year cycle - Magnetic fields of the solar wind deflect cosmic [articles which lead to a reduction fo cosmogenic nuclide production in the the earth’s atmosphere. (high 14C content in tree rings formed during hte Maunder Minimum a period of law sunspot activity that corresponds ot the little Ice Age) Solar radiation - 2 indications (one calculated 2 ways) of solar energy are plotted (expressed as “net radiative forcing in watts per square meter over time)

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All 3 records show that radiative forcing (solar energy) received from 1100-1400 AD was generally greater than the period following Support for warmer conditions during the MWP and cooler in the LIA

Volcanic activity as a cause of climate change - Volcanic eruptions produce - Dust that blocks the sun’s rays and causes cooling - The dust (particulates) can also serve as nuclei for cloud formation - Increased cloud cover woudl also reduce temepratures - HOWEVER, the impact is dependent upon - how broadly the dust is dispersed - How long it stays int he atmosphere → residence time -

What is more important is the release of sulfur into the atmosphere In the atmosphere, sulfuric acid causes backscattering of incoming solar radiation, thus cooling It also may encourage cloud formation It is more widely dispersed than dust and has a longer residence time (1-5 years)

Evidence: annual records in ice cores - When snow falls it collects insoluble dust particles, soluble compounds, and water in the snow itself - Some places have more snow fall than metling or sublimation - Annual layers of snow pile up and atmospheric gases fill the open pores between snow crystals - The weight of accumulating snow compresses the pores in the snow turning the snow to ice and trapping the atmpshereic gases - Layers in ice can be seen becuase the concentration of sea slats, nitrate, mineral dust and gas content differn than in summer snow - Can determine ice age by coutnign the layers - The gas trapped gives an idea of what the ancient atmosphere was Volcanic activity as a cause of climate change - Volcanic eruptions are recorded in ice cores

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As increased concentrations of dust and as increased acidity Through measurements of electrical conductivity, we can create “acidity profiles” such as the one to the right Acidity of Greenland Ice Sheet shown on the right - Low acidity means few or minor eruptions - High acidity indicates intensive and persistent volcanic activity around this time - Note the general correspondence of low volcanic activity to the Medieval Warm Period and high persistent acidity during the Little Ice Age - There is also good correspondence to the lowering of snow caps on mountains - Considerable mountain glacier depressions - Acidity decreased as well - What do these both indicate? Why these units?

Cowley (2000) - Calculated the relationships of volcanism and solar radiation over time to the paleotemperature estimates derived from proxy data, such as historical records, ice cores, and tree rings - His results varied depending upon his choice of records and the time period (as statistics can) - Some of these analyses showed that 49% of the temperature variability can be explained by volcanism and 45% by solar radiation - Thus both factors probably played an important role in climate change over the last 100 years - NOTE - The two processes (called forcings by medlers) have OPPOSITE effects - More volcaism → cooling -

More solar raditation → warming Thus they reinforce each other ro meoderate each other Which combinations were likely during the MWP and LIA?

What makes a society sensitive to climate change? - Limited external resources - Dependent upon agriculture - Already “living on the edge”, marginal regions Are annual averages an appropriate means to assess all climate changes? - Cold the Medieval Warm Period or Little Ice Age have been recognized in certain regions either - Because the process causing the climate change was partially restricted OR because the Sensitivity of regions varied

Valid Question: Order oldest to youngest 1. Last interglacial 2. Last Glacial Maximum 3. Younger Dryas 4. Hypsithermal 5. Medieval Warm Period 6. Little Ice Age Valid Question - Can you describe the evidence of each and climate processes associated with them?...