Continued warming and wild weather: State of the Climate 2020

Continued warming of Australia’s climate, an increase in extreme fire weather and length of the fire season, declining rainfall in the south, increasing rainfall in the north and rising sea levels are some of the key trends detailed in the latest State of the Climate report.

‘State of the Climate 2020’ is the sixth report in a series published biennially by the Bureau of Meteorology (BoM) and CSIRO, which together play an integral role in monitoring, measuring and reporting on weather and climate. Drawing on the latest climate observations, analyses and projections, the report provides a comprehensive and scientifically rigorous analysis of Australia’s changing climate, today and into the future.

Available now on the CSIRO and BoM websites, key observations from the report are as follows:

• The warming trend outlined in previous State of the Climate reports is continuing.
• Australia’s climate has warmed on average by 1.44°C (±0.24°C) since 1910, leading to an increase in the frequency of extreme heat events.
• Oceans around Australia are acidifying, and have warmed by around 1°C since 1910, contributing to longer and more frequent marine heatwaves.
• The rate of sea level rise varies around Australia’s coastlines, but overall sea levels are rising in line with global trends.
• There has been an increase in extreme fire weather, and in the length of the fire season, across large parts of the country since the 1950s, especially in southern Australia.
• Rainfall between April and October has declined across parts of southern Australia.
• Rainfall has increased across parts of northern Australia since the 1970s.
• Fewer tropical cyclones are projected for the future, but a greater proportion will be of high intensity, with large variations from year to year.
• Global CO₂ concentrations in the atmosphere reached 410 ppm in 2019 and the CO₂-equivalent of all greenhouse gas reached 508 ppm. The rate of CO₂ accumulation in the atmosphere has increased with every passing decade since atmospheric measurements began.
• Emissions from fossil fuels are the main contributor to the observed growth in atmospheric CO₂. Around 85% of global CO₂ emissions in the decade from 2009 to 2018 were from fossil fuel sources.
   

“Our science clearly shows that, due to increasing greenhouse gases, such as carbon dioxide, in the atmosphere, Australia’s climate is continuing to warm, and the frequency of extreme events such as bushfires, droughts and marine heatwaves is growing,” said CSIRO’s Climate Science Centre Director, Dr Jaci Brown.

Furthermore, it is questionable as to whether or not these projections can be avoided, with a new study claiming that global temperatures may continue to rise for centuries — even if human-induced greenhouse gas emissions can be reduced to zero.

That’s according to BI Norwegian Business School’s Jorgen Randers and Ulrich Goluke, who used a reduced complexity earth system model (ESCIMO) to study the effect of different greenhouse gas emission reductions on changes in the global climate from 1850 to 2500 and created projections of global temperature and sea level rises. Their results were published in the journal Scientific Reports.

The modelling suggests that under conditions where anthropogenic greenhouse gas emissions peak during the 2030s and decline to zero by 2100, global temperatures will be 3°C warmer and sea levels 3 m higher by 2500 than they were in 1850. Under conditions where all anthropogenic greenhouse-gas emissions are reduced to zero during the year 2020 the authors estimate that, after an initial decline, global temperatures will still be around 3°C warmer and sea levels will rise by around 2.5 m by 2500, compared to 1850.

The authors suggest that global temperatures could continue to increase after anthropogenic greenhouse gas emissions have reduced, as continued melting of Arctic ice and carbon-containing permafrost may increase the levels of water vapour, methane and CO₂ in the atmosphere. Melting of Arctic ice and permafrost would also reduce the area of ice reflecting heat and light from the sun.

To prevent the projected temperature and sea level rises, the authors suggest that all anthropogenic greenhouse gas emissions would have had to be reduced to zero between 1960 and 1970. To prevent global temperature and sea level rises after greenhouse gas emissions have ceased, at least 33 Gt of CO₂ would need to be removed from the atmosphere each year from 2020 onwards through carbon capture and storage methods.

With Randers and Goluke now encouraging other researchers to explore their results using alternative models, we can only hope that others may come to a more optimistic conclusion, and that the world has not yet passed the point of no return.

Image credit: ©stock.adobe.com/au/sarawutnirothon

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