Lecture 8: what is climate and palaeoclimates? 2

Question 1

WHY SHOULD WE BE BOTHERED ABOUT CLIMATE CHANGE?

Answer 1

Climate change is the most serious environmental problem today because of the harm it may bring.
• Our way of life (e.g., building, travelling, working, recreation) is dependent on a fairly narrow range of climatic conditions, even though industrial & technological developments have slightly reduced this dependence.
• Natural climate variability (e.g. El Niño or local multi-year droughts) has caused great economic loss and human suffering – climatic changes for 21st century are predicted to be much larger.
• Climate change does not only affect humans but also ecological processes and ecosystems as a whole.

Question 2

TEMPERATURE VARIABILITY DURING THE PHANEROZOIC EON

Answer 2

Influencing factors in the natural variability in Earth’s global average surface temperatures include
• Changes in incoming solar radiation (e.g. orbital changes, solar output)
• Continental drift (e.g. affects thermohaline circulation, rate of chemical weathering)
• Changes in Earth’s albedo (e.g. volcanic winter, change in extent of polar ice caps)
• Changes in the outgoing terrestrial radiation (e.g. increased greenhouse effect)

Question 3

THE LONG-TERM AND SHORT-TERM CARBON CYCLE

Answer 3

Long-term “thermostat” between emissions from solid Earth and chemical weathering of rock (time scale millions of years)

Question 4

MILANKOVITCH CYCLES

Answer 4

• The 3 most common orbital changes are referred to as “Milankovitch Cycles”
• Changes in the eccentricity of the elliptic orbit around the sun vary with a period of about
100,000 years
• Variations in the obliquity (angle of tilt) of the Earth’s axis (between 21.6o and 24.5o (currently
it is 23.5o) have a period of about 41,000 years
• Changes in precession (direction axis tilt) and point of perihelion (closes proximity to the sun)
change with a period of about 23,000 years
• Currently the Earth is closest to the sun in January, in 11,000 years the perihelion point will be in July (resulting in more summer sunshine affecting ice caps)

Question 5

INFERRED TEMPERATURE DATA FROM ICE CORE RECORDS

Answer 5

• Proxy data is available from ice cores, typically from the ice caps in Greenland or Antarctica where some of the ice is several hundred thousand years old.
• Ice caps of several thousand metres thickness have been created by compacted snow deposits which turned to solid ice, trapping air bubbles of the time in the process
• Over time the ice moves downwards and flows outwards at the bottom of the ice sheet
• Ice cores of 3500 m depth have provided atmospheric records dating back 400,000 years (Petit et al., 1999) and more recent experiments have yielded records dating back to almost 700,000 years BP (Siegenthaler et al., 2005).