by Catriona Nguyen-Robertson MRSV
Science Engagement Officer

This article follows a presentation on 23 July, 2020 titled “Climate Change: Managing the Unavoidable, Avoiding the Unmanageable” by Professor David Karoly, Leader of the Earth Systems and Climate Change Hub in the Australian Government’s National Environmental Science Program, to a joint meeting of the Royal Society of Victoria and the Australian Academy of Technology and Engineering, via Zoom videoconference.

That climate change is happening and that it is influenced by human activity are undeniable facts. Professor David Karoly, an internationally recognised expert on climate change, warns that it is a growing threat to human wellbeing, environmental ecosystems, and the entire planet. ‘There is much damage to come in the future,’ but we can limit it to avoid complete catastrophe.

Foreshadowing David’s excellence in science and leadership, his early education was at Mountain View Elementary School in Silicon Valley. When his family moved back to Australia, his teacher was worried that his seven times tables were not up to scratch and wanted to move David down a grade. David’s mother vouched for him and drilled him until he learned them – years later, he became the Head of the School of Mathematical Sciences at Monash University.

During his Bachelor of Science at Monash University, David enjoyed outdoor activities. Every weekend he would be off bushwalking, rock climbing, kayaking, or cross-country skiing. After stumbling across geophysical fluid dynamics later in his degree, he realised that he could combine his passions for maths and physics with the environment. He then pursued a PhD in meteorology and is currently Leader of the Earth Systems and Climate Change Hub in the Australian Government’s National Environmental Science Program, based in CSIRO.

The World Meteorological Organisation reported that the global average temperature in 2019 was 1.1°C above pre-industrial levels. But global land temperatures are often neglected, despite the fact that they impact us most. As David pointed out, ‘most people are not fish – we live on land’. According to the IPCC Special Report on Climate Change and Land, average global land temperatures have already risen by 1.7-1.8°C. In Australia, average land temperatures have risen by 1.5-1.6°C in only 70 years. The warming of land is considerably faster than the warming of the planet as a whole. The UNFCCC Paris Agreement aims to global limit warming to under 2°C, but if we reach that, temperatures on land may have already risen by more than 3°C.

Rainfall is another important factor to consider in climate change. 2019 saw Australia’s lowest recorded rainfall yet extreme rainfall events are likely to be more intense. Long-term trends show a great reduction in rainfall in southern Australia during April-October, while rainfall in the northern wet season has increased. Together with high temperatures, these dry conditions contribute to unprecedented fire danger across much of Australia, particularly in south eastern Australia. The fire danger index in December 2019 was the highest on record, partly due to global warming and partly due to natural yearly variation – either way, the results were catastrophic.

Trends in rainfall and temperature may appear small when compared to daily, monthly, or seasonal climate variability, however, the changes accumulated over decades have a large influence on ecosystems, agriculture and our community. CSIRO projects an increase in the frequency and or intensity of extreme weather events such as tropical cyclones, heavy rainfall, drought, and fire danger.

The increase in average global temperatures since pre-industrial levels correlates with an increase in atmospheric greenhouse gas concentrations. Carbon dioxide levels have been measured, dating over the past millennium, and while they remained relatively stable at about 280 ppm for centuries, they have sharply risen to over 400 ppm since the industrial revolution. Carbon exists in two forms: a lighter ¹²C isotope and a heavier ¹³C isotope. Plants preferentially take up the lighter ¹²C for photosynthesis and is it hence associated with plant matter. The relative abundance of the heavier form in the atmosphere has decreased, which is accounted for by a large release of ¹²C from the burning of fossil fuels (composed of plants that lived millions of years ago) and decaying trees caused by land clearing. This shift in carbon ratios, with an increase in atmospheric greenhouse gases coinciding with the emissions from the industrial revolution, provides powerful evidence that human actions are contributing directly to climate change.

CSIRO uses the Australian Community Climate and Earth System Simulator (ACCESS) to model future climate scenarios based on our possible carbon emissions. There are two paths that we can take: either emissions continue as they are and global warming continues, or we reduce them to stabilise the average global temperature. The very low emissions scenario gives a greater than 50% chance of limiting warming to less than 2°C. But if we do not make changes to reduce emissions, the global average temperature could climb by 5°C. Concerningly, even if temperatures do stabilise by 2050, sea levels will continue to rise for the next 300 years because it will take long time for Arctic and Antarctic ice to melt due to the current conditions. ACCESS presents us with two possible future worlds: one where carbon emissions are reduced, and another where carbon emissions continue to grow and the global mean temperature shoots 6.2°C above pre-industrial levels by the next century.

The future climate is in our hands – our actions now will decide that future. Energy production remains the primary driver of greenhouse gas emissions, followed by agriculture, forestry and other land uses, then industry and transport. Countries in the Southern Hemisphere are expected to experience the largest economic impacts from global warming, and it is therefore imperative that Australia takes both leadership and responsibility for making change. There are possible solutions for these sectors to reduce their production of greenhouse gasses. We need more efficient use of energy, a transition to zero carbon energy sources, improvement of carbon sinks (e.g. uptake of carbon dioxide by soil and algal farms in oceans) and, on both individual and community scale: lifestyle and behavioural changes.

The UNFCCC Paris Agreement to combat climate change requires commitment and action towards a sustainable, low carbon future. The target set was to limit global warming to 1.5°C – and we are only 0.4°C away. Global carbon emissions peaked in 2019 but have already dropped down this year due to limited air travel and other factors. While the circumstances that brought about these changes are less than ideal, it is a start and hopefully lays the foundation for sustained reductions.

‘We’ve got to limit global warming,’ says David. ‘We can do it. We can be sustainable. The choices we make will create different outcomes.’ Climate scientists have provided us with a choice for which planet we want based on our carbon emissions. The future is in our hands. Which will you choose?

Videos

Livestream of Joint Meeting

YouTube Presentations

In Brief:

Full Presentation: