Primitive climate models dating back to the 1970s have turned out to be ‘impressively accurate’, helping scientists rebut sceptics
- Researchers assessed 17 models created between the years 1970 and 2000
- These were now created long enough ago compare their predictions with reality
- 14 models were reliable, once unexpected emissions levels were accounted for
- The findings provide reassurance that modern models are also trustworthy
Primitive climate models dating back to as early as the 1970s have turned out to be largely accurate, rebutting the long-running doubts of sceptics, a study has found.
Experts assessed 17 old models — including one that brought the issue of climate change to public light — to see how accurate their temperature predictions were.
Time must pass before model predictions can be compared with the actual average global temperatures, as short-term variations can obscure the real trend.
The team found that most of the discrepancies between the studies and real-word figures came not from errors in the models but from unexpected emissions levels.
The findings, the researchers conclude, provide reassurance that models being used today are likely to be reliable as well.
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Primitive climate models dating back to as early as the 1970s have turned out to largely accurate, rebutting the long-running doubts of sceptics, a study has found
Energy systems analyst Zeke Hausfather of the University of California, Berkeley and colleagues assessed 17 climate models published between 1970–2000.
They found that the majority — 14 — proved to be quite accurate in their forecasts of the changing average global temperature in the years after their publication.
‘We often hear that ‘models always overestimate warming’ from those sceptical of climate change,’ Mr Hausfather told CBS News.
‘The real message is that the warming we have experienced is pretty much exactly what climate models predicted it would be as much as 30 years ago,’ he added in a press release.
‘This really gives us more confidence that today’s models are getting things largely right as well.’
Each of the models predicted the future average global temperature based on the levels of carbon dioxide, methane and other greenhouse gases released into the atmosphere.
Since the 1880s, greenhouse gas emissions — primarily sourced from the burning of fossil fuels — have been responsible for a rise in the average global temperature of nearly 1.4°F (around 0.8°C).
Two-thirds of this increase has come in the last four decades alone.
Alongside looking at future global temperature predictions, the researchers also evaluated how well the models matched the relationship between warming and greenhouse gas levels after they were published.
This allowed the team to account for how climate modellers cannot be expected to accurately predict future emission level, which are driven by human behaviour.
‘We did not focus on how well their crystal ball predicted future emissions of greenhouse gases, because that is a question for economists and energy modellers, not climate scientists,’ explained Mr Hausfather said.
‘It is impossible to know exactly what human emissions will be in the future. Physics we can understand […] future emissions depend on human systems.’
One model the team analysed was the work that first brought the issue of climate change into the public eye in 1988, published by NASA climatologist James Hansen — pictured here testifying before the US Senate Committee on Energy and Natural Resources in the same year
One model the team analysed was the work that first brought the issue of climate change into the public eye in 1988, published by NASA climatologist James Hansen.
Dr Hansen’s predictions for average global temperatures after 1988 were 50 per cent higher than the actual figures for those years, they noted.
According to Mr Hausfather, this discrepancy was due in part to the model having not been designed to account for the Montreal Protocol on Substances that Deplete the Ozone Layer.
This 1989 treaty that banned chlorofluorocarbons, a potent greenhouse gas then used in aerosol sprays and refrigerators.
In addition, Dr Hansen’s model had been given incorrect estimates of future methane emissions.
‘If you account for these and look at the relationship in his model between temperature and radiative forcing, which is CO2 and other greenhouse gases, [Dr Hansen] gets it pretty much dead on,’ he added.
‘So the physics of his model was right. The relationship between how much CO2 there is in the atmosphere and how much warming you get was right. He just got the future emissions wrong.’
The team also found that — when provided with the real greenhouse gas levels to work with — most of the other models could also accurately predict global temperature changes.
Dr Hansen’s predictions for average global temperatures, pictured here in comparison with the actual figures, were 50 per cent higher after 1988 than the actual figures for those years
Our models of the Earth’s changing climate will continue to improve, Mr Hausfather noted, as we build into them increasingly refined understandings of the chemistry and physics of the atmosphere, clouds, oceans and land.
However, he added, it is too early to assess more recent models, as the natural variation in the average global temperature can serve to mask the overall trend.
These models can, however, be put to the test in other ways — such as looking at how well they would have predicted temperatures in the past.
‘We often hear that ‘models always overestimate warming’ from those sceptical of climate change,’ Mr Hausfather told CBS News. Pictured, protesters in Wellington, New Zealand, march against proposed new climate policies
‘New research replicating and reaffirming what we already knew – that models are trustworthy – is both welcome and needed,’ climate change communication expert John Cook of the George Mason University in Virginia told CBS News.
‘Climate misinformation can be divided into 5 categories: it’s not real, it’s not us, it’s not bad, there’s no hope, experts are unreliable,’ he added.
‘Attacks on the trustworthiness of science are the most common form of climate misinformation.’
The full findings of the study were published in the journal Geophysical Research Letters.
Such will also form part of the opening chapter of the next climate assessment by the Intergovernmental Panel on Climate Change, which is due to be released in 2021.
WHAT IS THE PARIS AGREEMENT?
The Paris Agreement, which was first signed in 2015, is an international agreement to control and limit climate change.
It hopes to hold the increase in the global average temperature to below 2°C (3.6ºF) ‘and to pursue efforts to limit the temperature increase to 1.5°C (2.7°F)’.
It seems the more ambitious goal of restricting global warming to 1.5°C (2.7°F) may be more important than ever, according to previous research which claims 25 per cent of the world could see a significant increase in drier conditions.
In June 2017, President Trump announced his intention for the US, the second largest producer of greenhouse gases in the world, to withdraw from the agreement.
The Paris Agreement on Climate Change has four main goals with regards to reducing emissions:
1) A long-term goal of keeping the increase in global average temperature to well below 2°C above pre-industrial levels
2) To aim to limit the increase to 1.5°C, since this would significantly reduce risks and the impacts of climate change
3) Goverments agreed on the need for global emissions to peak as soon as possible, recognising that this will take longer for developing countries
4) To undertake rapid reductions thereafter in accordance with the best available science
Source: European Commission
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