A year after Australia was hit by its first-ever major heat wave, climate scientists are still trying to nail down the precise cause of the unusually strong heat.
What they do know is that the past decade has seen a dramatic shift in the pace of global warming.
A new paper by scientists from the University of Queensland, the University and Australian National University, looks at what climate scientists have been saying for years.
The paper, published in the Proceedings of the National Academy of Sciences, looks into the potential of new methods for studying climate change, and how this could inform policy.
The authors say that climate change is not a ‘relatively simple problem’ Climate change is, and has been, complex, says co-author Dr Simon Williams from the Department of Geography at the University.
“Climate change is a complex process that is complex, but it has a number of distinct, well-defined pathways,” he says.
For instance, scientists are using the term ‘interannual variability’ to describe how climate change can affect rainfall patterns.
The key to understanding how the climate is changing is understanding the relationship between the timing of natural events, such as droughts and heatwaves, and the amount of CO2 in the atmosphere.
But for a lot of years, the models used to model this are not calibrated to reflect the actual rate of change, so the scientists have relied on computer models to do the calibration work.
Dr Williams says that, while the models have improved over the past 15 years, they still lack a “critical mass” of climate models that are capable of simulating the actual climate.
The modelers are also struggling to understand how the current El Niño weather pattern, which occurs when a warmer Pacific ocean warms the planet, can be explained by the influence of greenhouse gases on the atmosphere and ocean. The El Niño model is a very powerful tool in climate change modelling.
It works by measuring how much CO2 the atmosphere releases when it’s warmed, and comparing that to what’s happening on Earth.
In the past, climate models have relied heavily on computer modelling to calculate how much warming and cooling each region would get from the CO2 they were simulating.
But because CO2 levels are rising faster than the rate of global temperature change, this is not very useful for climate models.
“In many ways, we are just stuck with what we’ve got,” Dr Williams said.
“We can’t use the model that has the best estimates of the CO3 and the temperature.
And we don’t know how it works.
We’re really struggling to come up with a good alternative.”
He said climate models were already showing that the current trend in warming is more likely to continue, rather than be stopped.
“It is very unlikely that we will stop warming at all, because that would mean we are heading into a very hot future and we have no way to predict how much the climate will change in that future,” he said.
The researchers say that if we don ‘t do anything’ to reduce greenhouse gases in the future, we will get “a very hot and dry future”.
Dr Williams and his colleagues used an approach called ‘natural climate variability’, which tries to understand what happens when a climate system is forced to change.
He said the research showed that “we have not fully accounted for all of the natural climate variability that could be involved”.
They used simulations of the Pacific Ocean, the atmosphere, and a combination of these to model the response of the climate system to the changing climate.
They found that climate models do not fully account for the response to the El Niño of 2015-16, which occurred between June and September of that year.
“So the model can’t account for all the natural variability that’s in the system,” Dr Simon said.
Dr Simon’s team looked at a wide range of scenarios for the future.
The first scenario they used involved “zero greenhouse gas emissions by the end of the century, with emissions continuing to decline through 2100”, while the second involved emissions declining from 2020-21 until the end in 2030.
This means that there would be no net effect of CO3 emissions from the greenhouse gas reductions they proposed.
The third scenario, which included a reduction in greenhouse gas emission, included emissions continuing until 2030-21.
The team found that there was an overall warming effect from 2030-22 onwards, but that this effect was “largely independent of the effects of greenhouse gas reduction”.
The researchers also looked at whether or not the effect of climate change on the Earth system could be explained with models that could simulate it.
They concluded that, in principle, “the model results would be consistent with the natural and observed response of climate systems to climate change”.
But it is important to stress that these models cannot account for every possible response, such that they cannot predict all possible future climates, Dr Williams explains.
“When you’re modelling a system that is constantly changing, you don’t want to rely on model simulations alone to explain the climate, because