Understanding Climate Change

Basics …

• Climate change is not the same as the greenhouse effect !

• but greenhouse is global and it’s being amplified by human activity

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

What causes greenhouse ?

• Carbon dioxide

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.

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

… 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.

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.

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.

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

Regional projections …

• What should we expect over Australia ?

Temperatures: mean and extremes

Low emissions

High emissions

Changes in mean precipitation

Low emissions

High emissions

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

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

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

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)

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 …

But satellites don’t show warming

Satellite Surface