Climate Code Red

Claims that climate scientists have abandoned their most dire scenario have been widely misunderstood. While the highest emissions pathway is now considered unlikely, evidence suggests the climate system may still be tracking toward dangerously high levels of warming.

by David Spratt, first published at Pearls&Irritations

Figure 1: RCPs and SSPsOccasionally, climate science is big news. On 26 May, the New York Times headlined: “Why scientists retired the dire climate scenario used for over a decade”. A good story!

The Australian, true to form, went with “Climate doomsday scenarios just got a major rewrite”, and in Jeff Bezos’s Washington Post it was  “The climate apocalypse? Don’t count on it”. There were a host of similar headlines.

Climate deniers and Donald Trump used an old playbook to claim scientific fraud (surprise!), but were called out, with ‘Trump twisted a climate debate beyond recognition’ and ‘Factcheck: Trump’s false claims about the IPCC and ‘RCP8.5’ climate scenario’.

So what’s the real story? Did scientists get it wrong, and is warming now likely to be less severe than previously thought?

As in engineering and business and government, scenarios are used by climate scientists to think about plausible alternative futures and their risks. The commonly-used climate scenarios are based on different possible trajectories for human greenhouse gas emissions and the social path humanity takes, and the consequences. And remember, scenarios in the end are simply a product of the minds that imagined them.

Fifteen years ago, four scenarios called representative concentration pathways (RCPs) were developed for the fifth IPCC assessment report in 2014, with RCP2.6 the lowest and RCP8.5 the highest. The numbers are radiative forcing (RF) values in 2100 for each scenario, where RF is the difference between the incoming radiation energy and the outgoing radiation energy in a given climate system, which is an indicator of total expected warming.

In conventional climate science terms, each one unit of RF (in watts per square metre) would in the long run be expected to result in around 0.75°C of warming. This relationship between change in radiative forcing and change in temperature is known as climate sensitivity.

RCP8.5 was sometimes called a ‘business as usual’ scenario, but this was a misnomer, and it was based on an assumption of little or no curbing of  greenhouse gases. Modellers estimated it would result in the end of warming of 5 to 6°C, with a range of 3.0 to 12.6°C.

The sixth IPCC report in 2022 focused on a modified system called Shared Socioeconomic Pathways (SSPs), where the scenarios more explicitly considered social, economic, and technological trends. The SSPs were again expressed as RF values. Figure 1 illustrates both the RCP and SSP scenarios as they relate to total emissions.

Now, in preparation for the modelling project for the next IPCC report due in 2029, known as ScenarioMIP,  scientists have suggested that the highest, ‘worse-case’ RCP8.5 scenario be dropped, because emissions were tracking more in line with one of the middle scenarios, RCP4.5. Hence all those headlines.

So, the ‘worse-case’ global warming case is no longer realistic. Big sighs of relief!

Not so quick. The big question in the end is not the amount of emissions but how hot it gets: the temperature. The focus on emissions in RCPs/SSPs is a bit to one side.

And on the future temperature, here’s the bomb. In a recent post, Ryan Katz-Rosene showed CERES data where the effective radiative forcing (ERF) at the moment is tracking above RCP8.5:

Effective radiative forcing and SSP scenarios.

 CERES is a NASA project that uses satellite and other data to measure the amount of sunlight absorbed by Earth and the amount of infrared energy emitted to space. As Katz says “current forcing observations from CERES really do appear to show a high current ERF value, which (at least at this point in time) does seem to be above the mean ERF expected in RCP8.5.”

[Technically, RF measures the immediate change in energy balance at the top of the atmosphere due to an external driver, while ERF accounts for adjustments in temperature and other factors after the initial change. ERF gives a more comprehensive understanding of the climate response to these changes.]

With the actual radiative forcing higher than the worst-case scenario, all those headlines about things getting better look like a lot of hot air.

So how can actual and future warming, indicated by RF, be tracking the worst case when the emissions trajectory is a middle-of-the-road scenario? The RCP/SSP scenarios were built around greenhouse gas emissions, not around the full suite of forcings and climate feedbacks that determine what the climate system actually does in terms of heating.

The assumptions about the relationship between emissions and temperatures have been too conservative. For example, what is not getting said is that the best estimate of the climate sensitivity has been rising, with perhaps the world’s most eminent climate scientist, Jim Hansen, taking it beyond the IPCC upper-range estimate. In fact, even the current range of modelling, known as CMIP6, produces a higher climate sensitivity than previously thought.

Other factors include reduced aerosol masking, ice-reflection loss, the release of permafrost carbon, and weakening ocean sinks that are not adequately captured by the IPCC or in model assumptions about future warming. Yet they’re showing up in the real-world numbers right now.

What is happening is way beyond IPCC projections. The rate of warming has accelerated by half over the last two decades, driven by reduced aerosols emissions and diminishing cloud cover. Warming has reached 1.5°C, and with an approaching strong El Nino, 2026-27 is likely to be around 1.7°C. Earth’s Energy Imbalance, an indicator of future warming, has doubled in the last 15 years and continues to increase, suggesting a warming trend of 2°C by 2040 is likely. Even global warming of 1°C, a threshold already passed, risks triggering some tipping points. At 1.5°C, six out of 10 studied climate subsystems already show large-scale abrupt shifts across multiple models.

Katz says: “We have such large uncertainty by end of century on climate sensitivity and carbon feedbacks, such that we can’t preclude mean warming of up to 4°C by 2100 even if we successfully pursue an emissions pathway resembling that in RCP4.5. So, again, if sensitivity or carbon feedbacks are not in our favour, there are plenty of scientific findings based on RCP8.5 which could turn out to be right on the mark in meteorological terms later this century, despite being way off on anthropogenic fossil emissions assumptions.”

Any reputable climate scientist over a drink at the bar will tell you that by far the majority of the human population would likely not survive 4°C. And that sounds like a worst case to me.

 by David Spratt, first published at Pearls&Irritations

Acknowledgment rather than denial of a crisis’s reality is the key to coping with it, but the 2026 Australian Government budget is a continuation of the Labor Government’s denial of the urgent need to reduce carbon emissions before the climate reaches a tipping point.

The 2026 budget speech was titled ‘Resilience and reform’. ‘Resilience’ – a very fluid term favoured by political communicators these days – was deployed 13 times, but the word ‘climate’ failed to appear even once.

This glaring omission reaffirms the government’s reluctance – seemingly intentional – to discuss climate change risks, as I have previously discussed in P&I.

The budget continued the tax-friendly treatment of the fossil fuel industry and failed to reform tax loopholes and subsidies. The diesel Fuel Tax Credit scheme at a cost of $13 billion a year in 2026–27 was left untouched, and the broadly-supported proposal for a 25 per cent gas exports levy that would have delivered $17 billion annually was ignored. $2.2 billion over the next 14 years of the climate department funding was redirected.

How can we understand the government’s energy – and what’s left of its climate – policy? There are clear actions to support the transition from expensive gas and ageing coal plants to now cheaper and more reliable renewables and storage. But this has not so far significantly dented Australia’s greenhouse gas emissions because other sectors’ emissions continue to rise.

And the government is still giving licenses and tax advantages to new coal and gas exports, keeping Australia ranked in the top three in the world for gas and coal exports. Wherever possible, it promotes its ‘good-news’ domestic renewable energy policy, while avoiding discussion of future climate impacts.

Thus, Australia’s first climate and security risk assessment delivered in December 2022 by the Office of National Intelligence remains under lock and key. Even the Parliament, charged with making policy on the subject, is left in the dark. And the domestically focused National Climate Risk Assessment was proscribed from considering climate mitigation. It ended up low-balling on crucial issues.

This leaves Australians ill-prepared for what is to come. In his book, Upheaval, geographer and anthropologist Jarod Diamond concluded that the key predictors of success in responding to crisis and change are “acknowledgment rather than denial of a crisis’s reality; acceptance of responsibility to take action; and honest self-appraisal”, plus the “presence or absence of a shared national identity”, which can help a nation’s people recognise shared self-interest and unite in overcoming a crisis.

Four brief examples demonstrate that Australia is more at the denial than the acknowledgement end of the spectrum.

The first is the fate of the Office of National Intelligence report.

The second is the issue keeping climate scientists awake at night: the coming collapse of the Atlantic Meridional Overturning Circulation (AMOC), which transports tropical ocean heat to the northeast of North America and western Europe. AMOC is slowing down and now rapidly approaching a tipping point for its collapse over a hundred years.

This would be a going-out-of-business scenario for northwest European agriculture. Monsoons that typically deliver rain to West Africa and South Asia would become unreliable. Huge swathes of Europe and Russia would be devastated by drought. As much as half of the world’s viable area for growing corn and wheat could dry out. The southern hemisphere, including Australia, would become warmer and more prone to flooding. A regional food crisis could lead to large-scale people displacement and contribute to state breakdown and regional conflict.

Does that sound relevant to future food security for Australians – and regional security, too?

Yet there is barely a flicker of recognition about this from Australia’s political parties. A search of Hansard for the current parliamentary term (since May 2025) finds no reference to AMOC in either house.

The third example is the coming El Niño. Scientists are increasingly concerned that  conditions now developing in the eastern Pacific will result in a ‘super’ El Niño later this year, perhaps the strongest ever recorded. In T_he_ New York Times, David Wallace-Wells writes it will:

… almost certainly [be] stronger than the ‘Super’ El Niño of 2015–16, and perhaps the most intense since the epochal El Niño of 1877… It’s almost certain that this El Niño will make 2027 the hottest year on record by some margin…A monster El Niño will give us at least a brief preview of a hotter and more chaotic world — a 2027 like we might’ve expected to see in 2035, and which not that long ago didn’t seem likely before 2050. ‘Prepare for bedlam’, the environmental writer Bill McKibben wrote earlier this year in anticipation.

For Australia, an El Niño means less rainfall and higher temperatures (drought) and less cooling cloud cover, including over the Great Barrier Reef. If this super El Niño eventuates, it will likely destroy swathes of the Great Barrier Reef, and produce record-breaking heat waves and severe fire risk, drought and lower crop yields and adverse health impacts on vulnerable Australians.

A check of Hansard for the current Parliament shows that no minister, or indeed Labor backbencher, in either house in the last year uttered a single sentence about the El Niño threat. Not a word! There are four mentions only by other parties: one by shadow minister Chester criticising the budget cuts to the Future Drought Fund; one by Greens Senator Whish-Wilson highlighting the issue in a short speech; and twice by Barnaby Joyce in what can only be described as wide-ranging rants.

The fourth example are the climate derailment and transition risks the government should have centre of mind. Transition risks are those associated with the move to a post-carbon economy. A recent study concluded the scale of the net-zero transformation means that reaching net zero will fundamentally overhaul vast parts of the global economy:

The transition is not simply a matter of swapping one energy source for another; it requires rebuilding infrastructure, retraining workers and redirecting trillions of dollars in investment…This uneven distribution of winners and losers will create difficult economic and political challenges, particularly during the transition period.

Even more pressing and most pertinent is derailment risk, where society becomes too distracted by escalating immediate crises to address the root causes of climate change by reducing emissions. A recent report by the UK Institute and Faculty of Actuaries, Parasol Lost, says an immediate step up in pace and preparedness can significantly reduce the impact of accelerated climate hazards, but warns that “global catastrophic risks, including economic shocks, are proximate”. And above 1.5°C:

We enter the danger zone where multiple climate tipping points may be triggered, such as the collapse of ice sheets in Greenland and Antarctica, permafrost melt, Amazon dieback and changes in ocean circulation. Some tipping points accelerate climate change…meaning there is a point of no return, after which it may be impossible to stabilise the climate close to conditions that we are able to adapt to.

The world reached 1.5°C in 2023, 2024 and 2025, and likely will again in 2026 and 2027.

Is our parliament capable of coming to grips with climate risks of these magnitudes? Or is it easier to abide by a new maxim, “Don’t mention the climate!”