UNIB10007 Lecture Notes - Lecture 1: Ocean Heat Content, Radiative Forcing, Northern Hemisphere
16 May 2018
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TOPIC 1: CLIMATE VARIABILITY
• Climate feedbacks (water vapour, ice albedo, clouds, carbon cycle) can increase natural climate variability
FEEDBACKS
• Dominant stabilising force on the planet: as temp varies, amount of outgoing IR varies, keeping a balanced
temp
Carbon Cycle Feedback
Short Time Period Climate Variability
• Climate changes over short periods due to natural internal variations of ocean + atmosphere
• Cannot be predicted beyond 5-10 days reliably, however recurring patterns occur
• Some variability associated with variations of sea surface temperatures – longer predictability
El Nino-Southern Oscillation
• Warming of the equatorial eastern Pacific Ocean, changes in ocean currents, changes rainfall
• Largest influence on year-to-year variations in climate around the globe
• Less rainfall over Australia
• Occurs once every 2-7 years
• La Nina (opposite): cooling of the eastern equatorial Pacific Ocean
• Associated with suppression of upwelling from deep (cold) water
La Nina (Normal)
El Nino
• Strong SE trade winds cause cool SST
upwelling off S. America – establishing
strong equatorial current
• Low pressure over N. Aus (enhanced
rainfall), high pressure in east Pacific
• SE trades weaken, equatorial SST warms
• High pressure over N. Aus (supressed
rainfall), low pressure in e. Pacific
• Inconsistent onset, duration, spatial extent +
propagation
TOPIC 2: OBSERVED CLIMATE CHANGE
• Increasing trend month to month from 1970 to present
• Indicators of a warming climate over last 50 years
o Increases: air temp, marine air temp, sea surface temp, ocean heat content, sea level, temp over
land
o Decreases: glacier volume, sea ice area, snow content
Intergovernmental Panel on Climate Change (IPCC)
• Joint body of UN, established in 1988, representatives from all countries
• Comprehensive assessment reports every 5-6 years, of c.c science, impacts + approaches for mitigation +
adaptation
• Conclusions on observed c.c:
o “Warming of climate system is unequivocal, + since 1950’s many of observed changes are
unprecedented”
o “Each of last 3 decades has been successively warmer than any preceding decade since 1850”
o “The atmosphere + ocean have warmed, ice + snow diminished, sea level risen + GHG
concentration increased”
o “The largest contribution to total radiative forcing is caused by the increase in atmospheric
concentration of CO2
Global Mean Temperature Changes
• Global av. temp variations are calculated as average of temps from various locations around world (land +
ocean)
• Instead of using real temps, average is taken of the anomalies from the average for a base period
Document Summary
Topic 1: climate variability: climate feedbacks (water vapour, ice albedo, clouds, carbon cycle) can increase natural climate variability. Feedbacks: dominant stabilising force on the planet: as temp varies, amount of outgoing ir varies, keeping a balanced temp. La nina (normal: strong se trade winds cause cool sst upwelling off s. america establishing strong equatorial current, low pressure over n. aus (enhanced rainfall), high pressure in east pacific. El nino: se trades weaken, equatorial sst warms, high pressure over n. aus (supressed rainfall), low pressure in e. pacific. Increasing trend month to month from 1970 to present. Indicators of a warming climate over last 50 years: increases: air temp, marine air temp, sea surface temp, ocean heat content, sea level, temp over land, decreases: glacier volume, sea ice area, snow content. Global mean temperature changes: global av. temp variations are calculated as average of temps from various locations around world (land + ocean)
