natural climate change prior to 1850 ad geography 1050, memorial university

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