Environmental change during the last 10,000 yrs - "The Little Ice Age"

Over last 10ka the scale of climate change has been much more subdued - Holocene has characteristics of low magnitude events showing a more stable period

Stability clearly indicated by ice core records - occasional events such as 8.2 yrs BP

Best evidence for climate change from last 1-2,000 yrs - based in ecological and geomorphic evidence combined with historical records

• Periods linked to human identification:
  • Roman warm period (250 BC-450 AD)
  • Dark ages (cool period) (450-950 AD)
  • Medieval warm period (950-1400 AD)
  • Little ice age (1400-1850 AD)

Holocene had pronounced warming between 11-5ka; after this regular oscillations between cooling and warming

Climate change recorded in oscillations of Alpine Glacier margins 

• In the Alps, ice advance occurs during periods of increased precip and cooler temps therefore is a proxy for climate change

Sierra Nevada - glaciers existed until about 120yrs ago - shows that Southern Spain was the maximum extent of the little ice age = glacial extent matched that from the LGM and hence shows importance of preicp and not just temps

Can study climatic events using pollen for vegetation records and geomorph evidence and seds for the geomorphic response

Also people kept diaries of weather, crops grown at the time and maps e.g. of ice sheet limit = good documentary information of recent climate change - over past few hundred yrs

• Longest instrumental records date back to 1600s - covers a major part of the Little ice age but not all
• Average trends show generally a warming climate - temp changes only 1 or 2 degrees difference form the mean

Recent cliamte changes are very short lived (100yrs) and often only a few degrees in climate (1 or 2oC) - most probably due to variations in precip = if it occurs and glaciers survive throughout summer months, they will advance in winter

The Little Ice Age

Covers period from 1300-1850

Glaciers during this period were most extensive from 1400-1800 and have undergone progressive retreat since then

• Main periods of advance = 1300-1400, 1580-1650, 1690-1760, 1800s
• Understood due to early work in the Alps - also landforms such as moraines and outwash fans in Iceland and Norway also show advance of ice sheets and are well preserved

Little ice age consists of four short lived periods of ice advance separated by ice margin stability or retreat

Multiple causes have been proposed, most common:

• Volcanic eruptions - 1400-1900 was a period of pronounced global volcanic activity
• Sunspot activity - periods of Alpine glacier advance correspond with a minima in sunspot activity

Little ice age was characterised by increased precip (snow) and cooler winters and summers

Identifying the Little ice age

Vegetation systems can't respond over such short time periods

% pollen composition shows no oscillations corresponding to Little ice age - tiem period and degree of change in climate is too small

Desprat et  al (2003) - compiled a detailed pollen diagram over the last 3000 yrs in Iberia:

• Showed no large wholescale changes in any vegetation type - indicates a relatively stable climate as changes are very…