Download - Understanding Climate Change
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Basics …
• Climate change is not the same as the greenhouse effect !
• but greenhouse is global and it’s being amplified by human activity
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Temperature
• Continued greenhouse gas emissions at or above current rates would cause further warming - very likely larger than those observed during the 20th century.
20052006
2007
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What causes greenhouse ?
• Carbon dioxide
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Basic science
• Warming of the climate system is unequivocal– atmosphere – Oceans (to at least 3000m)– Snow and ice are melting, flora and
fauna are changing
• There are no observations that suggest the planet is not warming.
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Basic science• Continued greenhouse gas emissions will cause further
warming
• They would cause changes in the global climate during the 21st century– very likely larger than those during the 20th century
• 21st century emissions will contribute to warming and sea level rise for more than a millennium– due to the long timescales required to remove this gas
• We are committed to at least several more decades of warming and associated changes in temperature, sea level and other impacts
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… what does the greenhouse do ?
• Earth has warmed 0.74oC in the last 100 years – unusual and very unlikely to be entirely natural in origin.
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Sea level rise
• Global sea levels rose at an average rate of 1.8 mm y-1 over 1961 to 2003 - faster over 1993 to 2003, about 3.1 mm y-1.
• total 20th century rise is estimated to be 0.17m.
• Projected globally-averaged sea level rise at the end of the 21st century in metres is between 0.18 m and 0.59 m.
• if increases in melt from Greenland and Antarctic continue, these projections may increase by a further 10 to 25%.
• Warming of 1.9 to 4.6°C would elimination the Greenland ice sheet and result in 7m rise in sea level if sustained for millennia.
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Global warming - Impacts
• For the next two decades a warming of about 0.2°C per decade is projected.
• Projected globally-averaged surface warming for the end of the 21st century (2090–2099) ranges from 1.8 to 4.0°C
• Possibility of positive feedbacks accelerating this
• Projected warming will eliminate the Greenland ice sheet and result in 7m rise in sea level if sustained for millennia.
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Impacts – less well known
• no trend in the frequency of tropical cyclones, but hint of an increase in intensity since about 1970
• frequency of cyclones projected to decrease, intensity expected to increase
• No idea no changes in tornadoes, hail, lightning and dust-storms etc.
• it is virtually certain that acidification will continue and will lead to dissolution of carbonates
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Regional projections …
• What should we expect over Australia ?
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Temperatures: mean and extremes
Low emissions
High emissions
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Changes in mean precipitation
Low emissions
High emissions
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What about Woollahra?• Climate strongly influenced by:
– El Nino-La Nina– East coast lows– Storm activity
– We cannot project how east coast lows may change yet
– We cannot project changes in storm activity
– Considerable effort on El Nino – but remains the greatest uncertainty in projecting the future climate of eastern Australia
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What about Woollahra?
• Not really vulnerable to flood (cf. Lismore)– Likely more driven by catchment management
that climate change
• Not vulnerable bush fires
• Fresh water reasonably secure (cf Wagga)– But invest now to preserve resource
• Temperature– unlikely to be the key problem due to moderation
by ocean and location
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Why is it always seem to be bad news ?
• Humans have “tuned” their crops, water use, settlements, storm water, ports etc assuming climate does not change
• Of course we can adapt – but that costs time and money
• Climate change may [rarely] exceed the adaptive capacity of a society
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What can we do about it ?
• Adapt to projected changes– Planning– Build robustness into social, economic and
environmental systems
• Buy time– Cut emissions– Renewables, gas replacing coal …– Increase sinks (plant forests)– Protect sinks (protect forests)
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Conclusions
• Climate change, driven by humans, is a reality
• The science underpinning this reality is well understood, robust and reliable - large scale impacts of global warming are well understood, robust and reliable
• Hard to be precise about what will happen in a specific location
• Solutions – build robustness into your existing environment …
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But satellites don’t show warming
Satellite Surface