Unit 18: Natural Climate Change

OBJECTIVES:• Explore the origin and nature of climate

change• Present Earth’s climatic history prior to

the industrial era• Explain the natural mechanisms that

cause climate change• Discuss important indicators and evidence

of climate change

Banded iron formations reveal an early atmosphere with little oxygen. Multiple lines of evidence indicate Earth’s climate has been punctuated by ice-house conditions numerous times, with huge ice caps like those we find at high latitudes today (blue bars).

The early atmosphere had little oxygen and no protective ozone layer

There has always been climate changeTypes of Evidence• geological-glacial features & distribution; sediments (varves)

• biological-pollen, midden, coral, foraminefera, tree rings

• isotopes-O18/O16 ratio, C-14

• historical-diaries, logs, legends, crop yields, art

• “proxy” data

Antarctica ice core. Source: http://earthobservatory.nasa.gov/Features/Paleoclimatology_IceCores/

Under a microscope the distinctive shapes of plant pollen grains emerge (a) and can be used to identify the type and relative abundance of vegetation for layers within a lake core (b).

A

B

Coral ring record. Source: http://serc.carleton.edu/images/microbelife/topics/proxies/.gif

Tree rings giving annual data. Source: http://www.dailykos.com/story/2007/12/28/427429/-Marine-Life-Series-Bivalve-Dendrochronology

Proxy data used as evidence of climate change

Bristlecone pine of the Great Basin region of western North America are the oldest known living trees, up to 5,000 years old.

DENDROCHRONOLOGY

Positive and Negative Feedbacks

Positive: Temperature-icemelt Negative: volcano-cooling-more snow

Source: http://www.sciencedaily.com/releases/2007/09/070927090341.htm

Rising temperatures increase melting of snow and sea ice, reducing surface reflectance, thereby increasing solar absorption, which raises temperatures, and so on. The feedback loop can also work in reverse. For instance, if climate cools, less snow and ice melts in summer, raising the albedo and causing further cooling as more solar radiation is reflected rather than absorbed. The temperature—albedo feedback is positive because the initial temperature change is amplified.

Source: http://www.eo.ucar.edu/Dark_Skies_2.ppt

Volcanic ash and gas block energy from the Sun. Earth's temperature drops.

The CO2-weather feedback resists both warming (a) and cooling (b).

Carbon dioxide weathering feedback

Earth’s Climate History• Ice-house Earth: Ice Ages, snowball Earth

Ice age has lasted the last 15 million years

• Hot-house Earth: Ice-free (95% of Earth’s history was iceless)

PETM (Paleocene-Eocene Thermal Maximum) 55mya

Climate of the last 70 million years as indicated by oxygen isotope records. The curve reflects changes in both ice amount and temperature.

Ice core record for the last 600,000 yearsPeaks of temperatures and carbon dioxide occur approximately every 100,000 years

Northern hemisphere ice extent during the last glacial maximum about 20,000 years ago.

Temperature and snow accumulation for central Greenland.

Temperature departures from the long-term mean for the last 2000 years as estimated by various proxy measures (colored curves) and by thermometers (black) since 1854.

Little Ice Age: 1400 to 1850 AD

Ruins of a medieval Norse village in Greenland. Relatively mild climatic conditions meant traditional farming practices could succeed, at least initially.

Hunters in the Snow by the Flemish painter Pieter Bruegel the Elder (1525–1569). Completed in February 1565, during the first of the many bitter winters of the Little Ice Age.Source: http://www.wikipaintings.org/en/pieter-bruegel-the-elder/hunters-in-the-snow-1565