natural climate change prior to 1850 ad geography 1050, memorial university
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Natural Climate Change prior to 1850 ad
Geography 1050,
Memorial University
Outline
• The need to measure past climates
• The nature and type of proxy data for measuring past climates– Historical (written, painted)– Archaeological– Biological– Geomorphic (landforms)– Sediments– Fossil soils (palaeosols)
How do we know climate is changing?
• Ongoing Monitoring– ~ 200 years of numerical data
• Proxy data - records of natural conditions or events that are strongly controlled by climate
• Best to use a series of records and look for similar patterns
INSTRUMENTAL DATA
Measuring Past Climate Changes• Identifying climate change requires long-term, dated records of
climate conditions
Numerical weather records only extend back to early-1800sat best…
Global temperature record from 1860 to 2000 AD based on corrected instrumental data
……assessing change assessing change and variation is and variation is complicated by complicated by human created human created effectseffects
a)a) Stations Stations active active since 1900since 1900
b) Stations b) Stations active at active at some time some time before before 19001900
R & H-S, p. 7
PROXY DATA
• Historical Records
Harvest dates, e.g., wine
Biwa-Ko area, Japan
Historical: Harvest Data
To use proxy data, we need …
• To understand the proxy
• To understand how the proxy relates to either specific aspects or climate in general
• To understand how the spot under study relates to broader regional conditions
• To date the events accurately & precisely
Harvest data
• Assumption: agricultural yield linked to weather conditions
– good weather, good yield
• Potential problems: – improvements over time (genetic-hybrids; farming practices)
– Loss of efficiency – soil degradation, pathogens
– Changes in farming effort
– External factors (war, plague)
– Governance & market factors (taxation, demand)
Cape Spear
Mariners’ logs, recording dates and positions of iceberg sightings
Lutra Canadensis © Rupert Matthews
Hudson Bay Company records can also be used. How many furs, when were they brought in, and what condition was the fur in?
PROXY DATA
• Historical Records• Archaeological
Murray Springs, Arizona
Archaeological (Human) DataArchaeological (Human) Data
Infilled irrigation ditch was infilled after flooding & mudflows associated with El Nino activity ca. 900
Pueblo Bonito, New Mexico, USA
Attributed (at least in part) to severe drought in 1100s
Macchu Piccu, Peru
Abandoned as a consequence of political conflict
Archaeological (Human)
• Assumption: human activity is linked to climate
• Change in practice response to change in climate
• Problems: – To what degree does environment control human activity ? – Is climate the ….“Driving force, supporting player, or
background noise”?
PROXY DATA
• Historical Records• Archaeological• Biological
Biological
• Assumptions: – An organism requires specific environmental conditions for survival
– Presence of an organism indicates those conditions are (were) met
– Human efforts are not responsible for survival or distribution of organisms
– Distribution of organisms is conditioned primarily or solely by climate
– Fossil record is an accurate measure of distribution
Opossum, Didelphis virginianus, © Rupert Mathews
Mammuthus jeffersoni tooth
Tooth structure and type indicates what the mammoths were eating (e.g., tree/shrub vs. tundra / steppe vegetation)
BiologicalBiological
ProxiesProxies
Generally, as proxies …
• Plants are better than animals. Why?
• Herbivores are better than carnivores. Why?
• Look for ones not of ‘interest’ to humans (but humans are very eclectic and ingenious)
• Small plant fossils (seeds); plankton & pollen are good choices
Palynological Coring,
Lake O’Hara, Yoho NP
Pollen
Principles of fossil pollen analysis (palynology)
• Plants produce pollen (or spores) in large numbers
• Preserved pollen serves as proxy for plant species
• Total assemblage of pollen indicates vegetation assemblage
• Vegetation assemblage indicates climate
http://www.poughkeepsiejournal.com/sections/environment/stories/en111404s1.shtml
Results of a palynology core sample
http://sofia.usgs.gov/publications/ofr/2004-1312/images/fig12.gif
Point LaHaye
St. Mary’s Bay, shows peat containing pollen dated to 7600 YBP
Pollen shows succession…
… with more Red Pine in past.
Today Red Pine confined to warmest (summer) and driest areas of province.
Therefore, what was past climate like?
Problems with pollen evidence
• Each species … – Produces different amounts– At different times – Which are transported differently– Have differences in form and structure,– And have different degrees of survivability– And are subject to different processes after deposition.
Pines
• Produce large amounts• Transported effectively• Durable• Preserve well, especially in
acidic soil• Easy to recognize (although
some species are hard to distinguish)
• Over-represented
Jack Pine, Pinus banksiana
http://reserve.charfac.umn.edu/gallery/images/ig_pine_pollen_30kv.jpg
Poplar
• Produces small amounts• Very fragile• Not transported far• Do not preserve well• Highly under-represented
http://www.tvcclinic.com/allergy/pollen/balsampoplar.jpg
• Produce moderate amounts• Moderately robust• Effective wind transport• But, most grass pollens look
very similar, therefore difficult to identify species
Grasses
PROXY DATA
• Historical Records• Archaeological• Biological• Geomorphic and Sedimentological
Pangnirtung Pass, Baffin Island
Geomorphic & Sedimentological
Western Brook Pond, Gros Morne
Hearts Delight
Cirque, Berg Lake, Waterton Lakes NP, Alberta
Athabasca Glacier, Jasper NP
Recession of glaciers today indicates ongoing climate change
Geomorphic & Sedimentological
http://earthobservatory.nasa.gov/Newsroom/NewImages/images_topic.php3?topic=land&img_id=8268
Pangnirtung Pass, Baffin Island
Geomorphic & Sedimentological
• Assumption: – landforms and sediments are the product of climate
conditions
• Difficulties: – require longer to form (hence, measure of ‘average’
conditions)– More difficult to date precisely– Time lag may exist between formation and exposure (dating)– Dating may be indirect
PROXY DATA
• Historical Records• Archaeological• Biological• Geomorphic and Sedimentological• Palaeosols
Hearts Delight
Parabolic Dune, Spruce Woods PP, Manitoba
Soils & wind-blown deposits. Soils (dark band with shovel, second dark band above) can be 14C dated.
Here, soils are about 13,000 and 12,000 years old respectively, developed under pine f
orests. Dune sand forms during drier (colder sometimes) periods.
Crotovina (rodent burrow): Korostelova, Russia
Palaeosols
• Assumption: – Soils reflect climate
• Difficulties: – Soils also reflect parent material, vegetation assemblages,
human interaction– Dating difficulties (must have preserved organic material)– Soils take time to develop (100s of years)– Soils have long memories (1000s of years)
Summary
• The need to measure past climates
• The nature and type of proxy data for measuring past climates– Historical (written, painted)– Archaeological– Biological– Geomorphic (landforms)– Sediments– Fossil soils (palaeosols)
Geomorphic & Sedimentological
http://umainetoday.umaine.edu/Issues/v3i4/iceage.html