By Dr Catriona Nguyen-Robertson,
Senior Editor, Science Victoria
with Prof David Karoly,
Professor Emeritus (Honorary), The University of Melbourne

The climate is changing, and it is influenced by human activity. These 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,” he says, “but we can limit it to avoid complete catastrophe”.

The changes that come with “climate change”

Last year (2023) was the warmest year on record, with the global average temperature 1.44°C above the pre-industrial levels (prior to ~1850).¹ We often discuss “global average temperature”, but global land temperatures are often neglected, even though they impact us most. As David points out, “most people are not fish – we live on land”.

On land, 2023 was also the warmest year on record, reaching 2.10°C above the pre-industrial average.² The warming of land is considerably faster than the warming of the planet as a whole, as water in the oceans is slower to increase in temperature. With land warming nearly double the warming of the entire globe, even if we limit global warming to 2°C, by the time we reach that, temperatures on land may have already risen by about 3.5°C.³

Rainfall is another important factor to consider in climate change. Long-term trends show less rainfall in southern and eastern Australia, while rainfall in much of the north has increased. Australia’s lowest recorded rainfall was recent – in 2019 – yet extreme rainfall events are likely to be more intense. In addition, the 2023 August to October period was Australia’s driest three-month period recorded since 1900.⁴

Together with high temperatures, these dry conditions contribute to unprecedented fire danger across much of Australia, particularly in south-eastern Australia. The forest fire danger index in December 2019 was the highest on record in most parts of the country, and for Australia as a whole.⁵ This was partly due to global warming and partly due to natural yearly variation, combining for catastrophic results.

In Victoria, the average temperature in 2023 was 0.69 °C above the 1961-1990 annual average, while rainfall was 5.3% below average.⁴ Changes in rainfall and temperature trends may appear small when compared to daily, monthly, or seasonal climate variability, however, the changes accumulated over decades have a large influence on the health and wellbeing of communities and ecosystems.

CSIRO’s most recent State of the Climate report projects an increase in the frequency and/or intensity of extreme weather events such as tropical cyclones, heavy rainfall, drought, and fire danger.⁶ Australia needs to plan for and adapt to the changing climate now and in the years ahead. With this knowledge, we can make informed decisions and be better prepared.

We’re heating things up

There is an undeniable correlation between the increase in average global temperatures and an increase in greenhouse gas emissions from human sources. The annual rate of increase in atmospheric carbon dioxide (CO₂) over the past 60 years is about 100 times faster than previous natural increases.⁷ Atmospheric CO₂ levels remained relatively stable for centuries (with natural, cyclic variation), but over the millions of years that we can trace, levels never exceeded 300 parts per million.

Until now.

CO₂ levels have been climbing since the mid-1700’s, and reached a new record high in 2023 of 419.3 parts per million.⁷

The increase in atmospheric greenhouse gases, coinciding with the emissions from the industrial revolution and land clearing, provides powerful evidence that human actions are contributing directly to climate change. This rapid, human-driven increase gives ecosystems less time to adapt to changing climates. We are introducing a sudden shock into the system.

Earth’s “last chance”

The latest Intergovernmental Panel on Climate Change (IPCC) report makes it clear that we are almost out of time to change the planet’s trajectory.⁸ In its sixth iteration, there are few surprises: the alarming warming trends continue and the scientific evidence of the influence of human activity on the climate is only becoming stronger. The decisions that we make now, and the actions of this decade will determine the future.

Our window to avoid the worst of climate change is rapidly closing – by the time the Seventh Assessment Report is released, and if we work towards targets in 2050 as opposed to earlier time frames, a better or worse future will be locked in.

CSIRO uses the Australian Community Climate and Earth System Simulator (ACCESS) to model future climate scenarios based on our possible carbon emissions.⁹ According to the models, 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 us a chance of limiting warming to around 2-2.5 °C.⁹ But if we do not make changes to reduce emissions, the global average temperature could climb by over 6 °C by next century.⁹

Concerningly, even if temperatures do stabilise by 2050, sea levels will continue to rise for the next 300 years. This is because the melting of Arctic and Antarctic ice sheets and glaciers is difficult to stop, as they will no longer be stable.¹⁰

ACCESS presents us with two possible future worlds: one where carbon emissions are reduced, and another where carbon emissions continue and the global mean temperature shoots in the order of 6 °C and global land temperatures in the order of 10 °C higher – “that is a very different planet,” says David.

It is not all doom and gloom, however. The climate has been set on a warming path – the long-lived greenhouse gases that are now in the atmosphere and the extra energy soaked up by oceans have guaranteed that warming will continue for the next few decades. But the sooner we act, the sooner we will see reduced impacts, and the greater our chance of avoiding the ‘worst case scenario’ projections in climate models and simulations.

Choosing our future

The future climate is in our hands. Energy production remains the primary driver of greenhouse gas emissions, followed by agriculture, forestry and other land uses, followed by 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 leadership and responsibility for making change.

There are possible solutions for these sectors to reduce their production of greenhouse gases. We need more efficient use of energy, a transition to zero carbon energy sources, improvement of carbon sinks (e.g., uptake of CO₂ by soil, and algal farms in oceans), and lifestyle and behavioural changes on both individual and community scale.

The United Nations Framework Convention on Climate Change (UNFCCC) Paris Agreement to combat climate change requires commitment and action towards a sustainable, low carbon future.¹¹ The original target set was to limit global warming to 1.5 °C – and we have nearly surpassed that.

“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.” The climate will continue to change if we do not change. 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 future will you choose?

References:

1. Met Office. (2024). Climate Dashboard. climate.metoffice.cloud/temperature.html
   
2. Rohde, R. (2024, January 12). Global Temperature Report for 2023. Berkeley Earth. berkeleyearth.org/global-temperature-report-for-2023
   
3. Masson-Delmotte, V., et al. (2019). Climate Change and Land. IPCC. ipcc.ch/site/assets/uploads/2019/11/SRCCL-Full-Report-Compiled-191128.pdf
   
4. The Bureau of Meteorology. (2023, 8 February). Annual Statement 2022. bom.gov.au/climate/current/annual/aus/#tabs=Key-points
   
5. Australian Institute for Disaster Resilience. (2020). Bushfires – Black Summer. Australian Disaster Resilience Knowledge Hub. knowledge.aidr.org.au/resources/black-summer-bushfires-vic-2019-20
   
6. CSIRO. (2022). State of the Climate. CSIRO. csiro.au/en/research/environmental-impacts/climate-change/state-of-the-climate
   
7. Lindsey, R. (2023, May 12). Climate Change: Atmospheric Carbon Dioxide. NOAA Climate.gov. climate.gov/news-features/understanding-climate/climate-change-atmospheric-carbon-dioxide
   
8. IPCC. (2023). AR6 Synthesis Report: Climate Change 2023. IPCC. ipcc.ch/report/ar6/syr
   
9. CSIRO. Australian Community Climate and Earth System Simulator (ACCESS). csiro.au/en/research/environmental-impacts/climate-change/access
   
10. Mengel, M., et al. (2018). Committed sea-level rise under the Paris Agreement and the legacy of delayed mitigation action. Nature Communications, 9(1). doi.org/10.1038/s41467-018-02985-8
    
11. UNFCCC. (2015). The Paris Agreement. unfccc.int/sites/default/files/resource/parisagreement_publication.pdf