Professor David Karoly, climate scientist at the School of Earth Sciences at the University of Melbourne, writes: It is beyond reasonable doubt that the global climate has warmed over the last fifty years. Our climate is getting hotter — it is developing a fever. This is a symptom of the underlying cause.

It also beyond reasonable doubt that most of this global warming is due to human activity, to the increase of carbon dioxide and other greenhouse gases in the atmosphere from burning fossil fuels, land clearing, agriculture and industrial activity. Continued emissions of greenhouse gases will lead to much greater warming this century, together with social, economic and environmental impacts from the changing climate.

Most discussion and debate at national and international levels on addressing the global problem of climate change has focussed on two different approaches: mitigation and adaptation.

Adaptation is like dealing with the symptoms of a fever. It involves the development of systems and activities that reduce the adverse impacts of climate change, without directly reducing the causes.

Mitigation aims to address the causes of the problem, by reducing emissions of greenhouse gases associated with human activity. It involves the transition to low carbon energy sources and the reduction in energy use through efficiency measures, as well as reduction in land clearing and changes in agricultural practices.

A third approach may exist for addressing climate change, called geoengineering. It involves deliberate manipulation of physical, chemical, or biological aspects of the Earth system to reduce human-caused climate change.

There are two main types of geoengineering options that are being discussed. One involves enhanced removal of carbon dioxide from the atmosphere, either into vegetation and soils or into the oceans. The other involves reducing the amount of sunlight that warms up the Earth, through increasing the reflection of sunlight either from the surface or from clouds or particles in the atmosphere.

If we stretch the fever metaphor, geoengineering is a bit like a new experimental treatment that doesn’t deal directly with the symptoms of the fever or its causes. Instead, geoengineering could be thought of as introducing a new disease that makes you colder, offsetting the fever. If it works well, it will exactly counteract the fever and its symptoms. If it doesn’t work well, it might make things a lot worse.

Geoengineering is increasingly being discussed as providing possible strategies to counteract some of the effects of anthropogenic greenhouse gas emissions. While not advocating geoengineering, both the Royal Society in the UK and the US National Academy of Sciences over the last two years have called for research to explore how geoengineering approaches may impact on the Earth system – undesired as well as desired.

In response to such northern hemisphere calls for geoengineering research, it is important to develop a southern hemisphere perspective on possible geoengineering interventions. To engage responsibly in any future high-level international discussion or agreements relating to geoengineering options, Australia needs to be well informed of the ideas being explored and their potential effects and repercussions.

On Monday and Tuesday this week, a symposium “Geoengineering the Climate? A Southern Hemisphere perspective” is being held at the Australian Academy of Science in Canberra.  This symposium addresses some of the implications of different approaches to geoengineering the climate, including their relative opportunities and risks, and the possible impacts in the Southern Hemisphere. Importantly, in addition to scientific and technological aspects of geoengineering, it also includes consideration of ethical and governance aspects. It is the first major meeting in Australia to provide a forum for cross-disciplinary discussions on geoengineering the climate.

Some examples of different technologies for enhanced carbon dioxide removal that will be discussed include:

• Changes in land-cover management e.g. growing more trees
• Changes in agriculture to increase uptake of carbon in soils
• Ocean fertilisation by adding iron or nitrogen to stimulate growthof marine plankton
• Engineered capture of carbon dioxide directly from the atmosphere

Examples of technologies that might be used to increase reflection of sunlight that will be discussed include:

• Increasing reflection at the surface by growing crops or vegetation of high reflectance, or reflective painting of human-built structures
• Cloud reflectivity enhancement or cloud brightening
• Injection of sulphate aerosols into the stratosphere

Each of these geoengineering options has its advantages and disadvantages. It is only through open public discussion that informed decisions on the use of any of these options can be achieved. The last thing that we want in Australia is for a scientific solution to cause more problems than those it was supposed to fix. We certainly have enough experience of that with cane toads already!

David Karoly is a member of the National Committee for Earth System Science of the Australian Academy of Science and a Professor of Meteorology in the School of Earth Sciences at the University of Melbourne.