Australian Academy of Science:
If emissions continue unabated, current mid-range estimates are for 4-5°C higher global average temperatures by 2100, which would mean that the world would be hotter than at any time in the last few million years. …
The further climate is pushed beyond the envelope of relative stability [the greater] the risk of passing tipping points that will result in profound changes in climate, vegetation, ocean circulation [and/or] ice sheet stability.
(The Science of Climate Change: Questions and Answers, 2010, p 15)
Contents
What is climate change?
How has the climate changed in the distant past?
How has the climate changed in the recent past?
Are human activities causing climate change?
How do we expect climate to evolve in the future?
What are the consequences of climate change?
How do we deal with the uncertainty in the science?
Would you like to know more?
The Australian Academy of Science
- Australian Academy of Science: Funding and direction of Australian climate science research needs an overhaul, Breakfast, ABC Radio National, 3 August 2017.
Graeme Pearman: Professorial Fellow, School of Earth Sciences, University of Melbourne; Former Chief, CSIRO Division of Atmospheric Research 1992 to 2002. - The Science of Climate Change: Questions and Answers, Canberra, August 2010.
What is climate change?
Climate change is a change in the average pattern of weather over a long period of time
Greenhouse gases play an important role in determining climate and causing climate change
(p 4)
How has Earth's climate changed in the distant past?
Climate has varied enormously through Earth's history
Evidence from the past shows that global climate is sensitive to small influences
Past records also show that climates can shift abruptly
Although the millennium before the industrial revolution was relatively stable, there were variations in climate over that period
(p 6)
How has climate during the recent past?
Global average temperatures have increased over the past century
(p 7)
Temperature observations are not the only evidence of recent climate change
(p 8)
Australia's climate has changed along with the global climate
(p 9)
Are human activities causing climate change?
Human activities are increasing greenhouse gas levels in the atmosphere
It is very likely that most of the recent observed global warming is caused by increasing greenhouse gas levels
(p 10)
Some recent Australian climate changes have been linked to rising greenhouse gases
(p 11)
How do we expect climate to evolve in the future?
Climate models and studies of past climates indicate that global warming and associated changes will continue if greenhouse gas levels keep rising as they are now
While these two approaches — modelling and studying the past — rely on markedly different methodologies, they both yield broadly similar indications of where global climate is headed.
[Both] methods project a long-term warming of global air temperature of around 3°C … in response to a doubling of the concentration of CO2 in the atmosphere.
Evidence from Earth's past … indicates that changes of this magnitude can have major long-term ramifications, such as sea level rise of many metres.
Continued increases in greenhouse gas levels are expected to lead to significant warming through the 21st century and beyond
If society were to shift rapidly away from using fossil fuels, there would be little reduction in the rate of global warming in the first couple of decades, but warming later this century and beyond would be significantly reduced.
(p 12)
Some climate change will continue for centuries, and some change will be essentially irreversible on a 1,000-year timescale
Even if human societies completely ceased greenhouse gas emissions at some time in the future, atmospheric temperatures would not be expected to fall significantly for a thousand years, as CO2 and heat are only gradually absorbed by the deep oceans.
Sea level rise is also expected to continue for many centuries due to the ongoing melting of ice sheets and the gradual thermal expansion of the oceans …
Global warming above … about 2°C and 4.5°C, would lead to an ongoing melting of the Greenland ice sheet.
If sustained for thousands of years, this [raise] sea level by about seven metres. …
It is possible that increased snowfall over Antarctica may partially offset other contributions to sea level rise …
[Accelerated] outflow of ice has been observed from Greenland and West Antarctica [which] could make these ice sheers more vulnerable to future warming.
Reduction of greenhouse gas emissions could significantly reduce long-term warming
To have a better than even chance of preventing the global average temperature from eventually rising more than 2°C above pre-industrial temperatures, the world would need to be emitting less than half the amount of CO2 by 2050 than it did in 2000.
To do this on a smooth pathway, global emissions … would need to peak within the next 10 years and then decline rapidly.
(p 13)
What are the consequences of climate change?
Climate change will have significant impacts on our society and environment
By around 2030, Australian temperatures are likely to be a half degree or more higher than 1990 and the frequency of hot days and nights will have increased.
Sea level is expected to be about 15 cm higher and there is some evidence to suggest that tropical cyclones will become more severe, but less frequent. …
[Some] future trends are projected fairly consistently, including increases in rainfall in northern Australia and decreases in Victorian and southwest WA coastal regions. …
It is likely that higher temperatures and changing patterns of wind and rainfall will change the patterns and frequency of extreme fire weather, and also lead to more heat-related deaths and fewer cold-related deaths. …
Higher CO2 levels, fewer frosts and changed rainfall patterns may be beneficial to agriculture in some parts of Australia, but decreases in rainfall in other Australian regions are likely to have a detrimental effect on agriculture.
As a result of increased CO2 in the atmosphere, oceans will become more acidic and, in combination with the higher temperatures, coral bleaching events are likely to become more frequent and severe around northern Australia.
Sea level will increase, inundating parts of the Kakadu freshwater wetlands and causing increased coastal flooding, with consequent change to sandy coastlines. …
Tourism may be adversely affected, in part due to the sector's dependence on natural assets and the built environment, both of which are vulnerable to the physical impacts of climate change. …
[The] inability of many species to migrate as a result of both land use change and habitat fragmentation means that biodiversity is likely to decline overall, in line with observed global trends.
Higher temperatures on the forested mountaintops of north-east Queensland, for example, may exceed the heat tolerance of some endemic species in the wet tropics, resulting in their extinction.
Climate change will exacerbate the impacts of other stresses
The world's population is … expected to increase [from seven] to around nine billion by mid-century …
[Half] of all readily available fresh water is already appropriated for human use. …
[The] additional potential burdens of climate change impacts could lead to social unrest across large parts of the world.
[There] is now little room for many populations to relocate in response to climate change.
These factors are likely to affect developed as well as developing nations.
(p 14)
All of these factors demonstrate the need for an integrated approach to understanding how a sustainable planet can be attained in the presence of population pressures, risks from climate change, and other stresses.
Future impacts are expected to be more severe
If emissions continue unabated, current mid-range estimates are for 4-5°C higher global average temperatures by 2100, which would mean that the world would be hotter than at any time in the last few million years. …
The impacts of such changes are difficult to predict, but are likely to be severe for human populations and for the natural world.
The further climate is pushed beyond the envelope of relative stability [the greater] the risk of passing tipping points that will result in profound changes in climate, vegetation, ocean circulation [and/or] ice sheet stability.
(p 15)
How do we deal with the uncertainty in the science?
No scientific conclusion can ever be absolutely certain
There is a high degree of confidence in the broad conclusions of climate science
Some aspects of climate science are still quite uncertain
Despite the uncertainties, climate science has an important role to play in informing public policy on climate change
(p 16)
