Australia appears to be already experiencing the worst-case climate scenarios that were projected to occur eight years from now.
It’s a sobering finding, revealed by world-renowned climate scientist David Karoly’s analysis of how closely projections released in 2015 by the Bureau of Meteorology and CSIRO align to actual temperatures and rainfall experienced by 12 major Australian cities, including the capitals.
He presented his data titled “Evaluation of near-term climate change projections for selected Australian cities using recent observations” at the recent Australian Meteorological and Oceanographic Society conference.
“Unfortunately, things like temperature extremes – days over 35 and 40 degrees Celsius – and decline in rainfall in southern Australia… were tracking at or above what was projected for the 2030s,” Professor Karoly tells Cosmos.
Cities further north were also seen to experience climate changes consistent with 2030 projections, though not worst-case rainfall scenarios.
So, how do these climate models project possible futures?
Climate models simulate plausible climate futures.
They are the most accurate and useful tools available to anticipate and estimate the Earth’s future climate, and extend the calculations used by meteorologists to predict short-term weather. In this way, climate projections look beyond this week, this month and even this year.
Models use complex data inputs and mathematical calculations to simulate possible climate outcomes. To give a sense of the effort to ensure accuracy, hundreds of scientists and substantial supporting resources are required to build a model.
Not all models are the same, but each use mathematical equations to represent complex processes and interactions in the atmosphere, oceans and land surface.
Basically, lots of time, money and brain power go towards making these incredibly useful models.
“There are multiple representations of those ‘plausible futures’, and typically the projections don’t look at just one – they look at range of plausible futures,” Karoly says.
“Coordinated experiments have been run with these global models to evaluate their performance and to allow their results to be combined for future climate projections.”
To determine their precision, climate models are run over historical periods to see how closely their simulations align with past weather records.
The closer the alignment, the greater confidence in the model’s ability to simulate future scenarios.
Climate futures are uncertain, and scientists are quick to emphasise there are many variables that will influence the climate. But these uncertainties are small, and have become smaller and smaller as the reliability of climate models has improved.
Once models are verified, they’re then used to project forward scenarios.
In simple terms, this process is repeated by climate scientists around the world to inform decision-makers, businesses and individuals on what changes might look like years into the future.
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“In the most recent decade, it’s hitting us faster and harder.”
Farmers are one group particularly interested in the changing climate.
They rely on having accurate data to inform their operations – when and what to plant – based on expected temperature, rainfall, storm activity and more.
And it was discussions with farmers that prompted Karoly to look back on how accurate the Bureau of Meteorology and CSIRO’s past climate projections were.
These farmers and others who rely on accurate weather had noticed their climate expectations hadn’t married up with reality.
“I thought I’d better evaluate,” Karoly says.
“For many people, they’ve been noticing climate and weather changing around them.”
Karoly’s findings are troubling: already, 12 Australian cities are experiencing climate conditions that were projected to occur a decade from now. While specific to these locations, the findings could be considered broad indicators for the rest of the nation.
“Many businesses and many people who are looking at climate impacts tend to look at the mid-range projections for the future,” Karoly says.
“What I’ve been finding is that the mid-range climate projections for 2030 already significantly underestimate the magnitude of the likely climate impacts in terms of extreme temperatures.”
“These sorts of events that were projected to be much worse in the 2030s, and 2050s, are happening already. What we’re experiencing in some sense, for many parts of Australia, is the weather of the 2030s, or the worst case of the 2030s, now.”
One thing that Karoly did not review was extreme short-term rainfall, making it difficult to consider recent events like the recent triple La Nina, which incidentally saw 2022 become the wettest Sydney year on record.
Karoly says his results may mean experts need to revise their use of climate models. At the very least, he says, worst-case scenarios using existing simulations need to be given greater consideration.
“Maybe the issue is we haven’t actually got high resolution, or high enough resolution to represent some important [climate] processes,” he says.
“It’s potentially a risk with using coarser models… using a simple downscaling approach. We’re usually tracking within the full range, but experiencing the worst case.”