Scientists have challenged the conclusions of a new study suggesting that the planet has already exceeded the 1.5C warming threshold set under the Paris Agreement.
Climate change is typically measured as the average global temperature increase relative to a “pre-industrial baseline”. The UN Intergovernmental Panel on Climate Change (IPCC), for example, uses the average temperature over 1850-1900 as their historical baseline. The planet has already warmed by around 1.2C compared to this period.
The new study, published in Nature Climate Change, uses proxy data from sea sponges in the Caribbean Sea to create a record of ocean temperatures from 1700 to the present day. This data suggests that warming started 40 years before the IPCC’s pre-industrial baseline period began.
Based on this new record, the authors say “warming is 0.5C higher than IPCC estimates”.
This means that “the global warming clock for emission reductions to minimise the risk of dangerous climate change has been brought forward by at least a decade”, the lead author told a press briefing.
However, many experts have warned that the framing of the study is misleading, arguing that the finding has no bearing on the Paris Agreement 1.5C limit, because it specifically “describes temperature rise relative to the late 19th century”.
Prof Richard Betts, head of climate impacts research at the UK Met Office Hadley Centre, who was not involved in the study, tells Carbon Brief that, crucially, the study “does not mean that impacts of climate change will occur earlier than expected”.
Other experts raised doubts that the 0.5C warming in the 1800s is human-caused, while many cautioned that proxy data from a single location should not be used to make assumptions about the entire planet.
The University of Oxford’s Prof Yadvinder Malhi, who was also not involved in the study, cautions that “the way these findings have been communicated is flawed, and has the potential to add unnecessary confusion to public debate on climate change”.
Shifting baselines
Humans have been releasing greenhouse gases into the atmosphere for centuries, causing global temperatures to rise.
In IPCC reports – considered the most authoritative summaries on climate science – scientists use a combination of land surface air temperatures and sea surface temperatures to assess changes in global mean surface temperatures (GMST).
The UN body reports global warming against a “pre-industrial baseline” of 1850-1900. It describes this baseline as “a pragmatic choice based upon data availability considerations” – in part because much of the observed climate data they use is only available from 1850.
For example, the Met Office’s HadSST4 dataset – one of the three datasets used in IPCC estimates of sea surface temperatures – goes back as far as 1850.
The IPCC also recognises that “both anthropogenic and natural changes to the climate occurred” before the 1850-1900 baseline. For example, in its 2021 report on climate science, the IPCC estimates that between 1750 and 1850-1900, GMST increased by around 0.1C. Of this, human activity was responsible for 0.0-0.2C, it says.
Nonetheless, researchers have typically followed suit in using the 1850-1900 average as their “pre-industrial baseline” to measure global warming.
In 2015, countries agreed under the Paris Agreement to hold the increase in the global average temperature to well below 2C above pre-industrial levels and pursue efforts to limit warming to 1.5C. “Pre-industrial” was not clearly defined in the agreement, but it has generally been taken to mean the average temperature over 1850-1900.
However, some scientists argue that the “pre-industrial baseline” period should begin before 1850.
The new study uses proxy data taken from sea sponges from the Caribbean sea, to present a timeseries of regional ocean temperatures from 1700 to the present day. Scientists collected sclerosponges from the ocean mixed layer – a region of ocean where heat is exchanged between the atmosphere and the ocean interior.
Between 1700-90 and 1840-60, the proxy data shows ocean warming of around 0.9C, according to the study. In the intervening time, there was some cooling, largely caused by volcanic eruptions, the authors say.
The plot below shows the proxy data (blue) from the year 1770, alongside the HadSST4 observed temperature record (purple), which begins in 1850, relative to a 1961-90 reference period. The authors have applied a 0.9C “offset” to their proxy data to account for pre-industrial temperature increase.
By comparing their proxy data against existing records of global temperature changes, the authors find “strong empirical evidence that the Caribbean ocean mixed layer has warmed proportionately to the average global increase in sea surface temperature, over the last ~50 years”.
The authors assume that the 0.9C offset “can be applied to land-air as well as the ocean mixed layer anomalies”, therefore concluding that GMST increased by 0.9C between 1700-1860 and 1961-90.
Meanwhile, global ocean temperatures measured using HadSST4 show only 0.4C of warming relative to the IPCC’s 1850-1900 pre-industrial period.
As such, the authors suggest that human-caused warming to date is actually 0.5C higher than IPCC estimates.
Dr Malcolm McCulloch – an emeritus professor at the University of Western Australia and lead author on the study – told a press briefing that, according to his study, the 1.5C Paris temperature threshold has already been crossed in around 2010-12.
He continued:
“It means that now, temperatures are at least 1.7C above the pre-industrial level. It also means that the 2C target will be passed in late 2020 unless there are major reductions in emissions…
“The big picture is that the global warming clock for emission reductions to minimise the risk of dangerous climate change has been brought forward by at least a decade”.
However, many scientists are concerned about this framing of the study.
Warming limits
Dr Friederike Otto, who was not involved in the study, is a senior lecturer in climate science at Imperial College London’s Grantham Institute. She says the paper “does not tell us anything about whether we have exceeded the 1.5C temperature limit set in the Paris Agreement”.
She continues:
“That limit was established as the threshold of unacceptably dangerous warming and describes temperature rise relative to the late 19th century. If this study has indeed identified warming from before the mid-1800s, that doesn’t mean the planet is any closer to breaking the 1.5C limit as it is widely understood.”
(The IPCC best estimate – in all but the highest emission scenario – is that global warming will pass 1.5C in the first half of the 2030s.)
Mahli adds:
“Our models of climate warming impacts are based on warming relative to 1850-1900 and moving the baseline definition of pre-industrial does not make these expected impacts worse…
“It is the date of the reference period that matters rather than whether it is labelled pre-industrial or not. The period 1850-1900 is a period of relatively reliable global data when industrial era human-caused climate change was likely negligible.”
Dr Andrew King is a senior lecturer in climate science at the University of Melbourne and was not involved in the study. He tells Carbon Brief that the findings of the study do not have any implications for the Paris Agreement warming limits, because these were “written in 2015 with a view to limiting further global warming from that point onwards”.
He adds:
“While the lack of clarity on what pre-industrial means was problematic, it doesn’t really affect that goal or any of the analyses on climate impacts at global warming levels that have been performed.”
King also tells Carbon Brief that the authors have not demonstrated that pre-1850s warming is due to human activity.
Malhi agrees that “this early industrial-era warming, if real, is almost certainly not human-caused”. He notes that human-caused emissions over 1750-1900 account for only 2.5% of total emissions to date, and says they are “unlikely to have caused substantial warming compared to the 1.4C of warming caused by the remaining 97.5% of cumulative emissions”.
Dr Duo Chan, a lecturer in climate sciences at the University of Southampton, also advises “caution” when interpreting the results, noting that “this new warming estimate does not align” with historical estimates of the different factors that affect the climate.
He notes that, according to Berkeley Earth temperature estimates, the land warmed by around 0.05C per decade over 1850-1900. The new proxy data from the sponges suggests that the ocean warmed almost twice as quickly as the land over this time – a “puzzling observation given the ocean warms more slowly than land”, he says.
Dr Zeke Hausfather, Carbon Brief’s contributing science writer, adds that the study authors are “conflating ocean mixed layer temperature with sea surface temperature in a way that is confusing”. He adds that “their reconstruction also seems a bit at odds with other palaeoclimate reconstructions – such as PAGES2k – that do not see large differences in pre-1900 temperatures”.
The sclerosponge record
Coralline sclerosponges are an ancient type of calcifying sea sponge which can live for hundreds of years. As they grow, chemicals called strontium and calcium build up in their skeletons. The ratio of strontium to calcium in their skeletons is higher during warm periods and lower during cool periods.
Scientists collected live specimens of sclerosponge from the Caribbean sea and analysed the ratios of strontium to calcium in their skeletons to reproduce a timeseries of ocean temperatures in the region from the year 1700 to the present day.
Dr Amos Winter is a professor of Earth and environmental systems at Indiana State University and author on the study. He told the press briefing that there is no such thing as a “perfect proxy”, but said the sclerosponge record is “as good as possible – the holy grail of reconstruction”.
He explained that the Caribbean is “the ideal location to measure global trends”. According to the paper, the region is “ideally positioned” to have a “minimal” impact from the Atlantic Meridional Overturning Circulation, while “still registering the broader effects” of the El Niño-Southern Oscillation climate phenomenon.
He adds that the sclerosponge temperature reconstruction is “very robust” when compared to other assessments of temperature trends.
Dr Gavin Schmidt, director of the NASA Goddard Institute for Space Studies, says that the new data is a “useful addition to the database” of palaeoclimate proxies. However, he adds:
“Estimates of the global mean temperatures before 1850 require multiple proxies from as wide a regional variation as possible, thus claims that records from a single record can confidently define the global mean warming since the pre-industrial are probably overreaching.”
Prof Gabi Hegerl, a professor of climate system science at the University of Edinburgh, says that the paper presents a “nice new record” of ocean temperatures, but says that “the interpretation in terms of global warming goals overstretches it”.
She warns that “a single location cannot substitute global data, as climate varies across the globe, which is why the only way to measure global temperature is to get data from across the globe”.
Similarly, Hausfather calls the finding “interesting”, but says it “should be combined with other proxy records in a larger synthesis before it will change our prevailing views here”.
The post Scientists challenge ‘flawed communication’ of study claiming 1.5C warming breach appeared first on Carbon Brief.
Scientists challenge ‘flawed communication’ of study claiming 1.5C warming breach
When the Turkish COP31 presidency presented its priorities to international business leaders for the first time in New York in September, among those invited to give the private sector’s first response was Ali Koç, scion of one of Türkiye’s wealthiest families.
On stage, the vice chair of the board of Koç Holding said the family company, which weeks earlier had been announced as one of the top sponsors for the UN climate summit, can be seen as “quite exemplary” for its climate record.
What Koç did not mention was that the group’s biggest money-making arm – Türkiye’s largest oil refiner Tüpraş – plans to keep running its refineries “at maximum potential”. Nor did he say that, in 2025, both parent company and subsidiary cut their 2030 climate targets to a level they had already nearly achieved, as Climate Home News’ analysis of company records reveals.
The decision to hand Koç Holding a prominent role at COP31 – the company is also the summit’s “Global Business Partner” – has reignited a long-running controversy over the platforming of fossil fuel interests at the annual UN climate conference.
It has also thrown into question how COP sponsors are chosen and screened. The hosting agreement between the Turkish government and the UN climate secretariat (UNFCCC) says that a partner company’s “climate integrity” should be taken into account.
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But how that test is applied is unclear and the process for picking sponsors remains largely opaque. The Turkish COP31 presidency has not published its selection criteria, nor the financial terms of any of its partnership agreements, including Koç’s. The UNFCCC declined to clarify how it advises on such deals.
Campaigners have long argued that accepting sponsorship from polluting companies is wrong because it gives them a global stage, visibility and access to policymakers at talks that are meant to move the world away from fossil fuels, and tarnishes the reputation of the COPs.
Koç’s energy division, which is dominated by oil refiner Tüpraş, accounted for three-quarters of the parent firm’s income in the first half of 2026.
“How was Koç Holding ever chosen as a COP31 sponsor? Any corporation that makes most of its money from oil refining should not qualify as sustainable,” said Pascoe Sabido, a campaigner at Corporate Europe Observatory, which exposes company lobbying. “This is hugely embarrassing for the UNFCCC and its climate integrity check, which doesn’t appear to be worth the paper it’s written on.”
Koç Holding “is not just standing still but walking backwards”, he told Climate Home News.
Koç Holding and Tüpraş did not reply to multiple requests for comment. The UNFCCC secretariat and the Turkish COP31 presidency declined to respond to questions from Climate Home News on the sponsorship agreement.
Oil refining windfall
Türkiye’s biggest industrial group, Koç Holding has stakes in several key sectors of the economy, spanning vehicle manufacturing in a joint venture with Ford to electronics, home appliances and banking.
But the conglomerate’s crown jewel is oil refiner Tüpraş, which Koç controls. Last year its four refineries turned crude oil into 26.8 million tonnes of petrol, diesel, jet fuel and other products, enough to fill about 36 Olympic swimming pools every day.
The company plans to raise its production to 29 million tonnes in 2026 – already a bumper year so far with soaring profits, thanks to sky-rocketing refining margins driven by a crunch in global oil processing capacity caused by the Middle East crisis.
The oil business boom sits awkwardly with the climate and energy transition plans Koç and Tüpraş unveiled in 2021, when both pledged to become carbon neutral by 2050. Then, Tüpraş set out its aim to become “a leading carbon-neutral energy company”.
Despite these promises, in 2025, both companies lowered their targets for cutting emissions from their own operations by 2030, from 27% to 20% below 2017 levels. Tüpraş also cut its 2035 goal from 35% to 25%. The company still technically retains its long-term target of carbon neutrality by 2050, but the new plan will require much more drastic cuts after 2035.
Lowering the climate bar
Tüpraş blamed its weakening of climate ambition on “changing market dynamics, economic conditions and technological developments”. In a presentation announcing the revision to investors, the refiner said the energy outlook had changed since 2021.
The reasons it listed included elevated geopolitical tensions, increased investment in oil and gas extraction, which it said showed refined fuels remain vital for energy security – and even the depletion of the carbon budget to keep global warming to 1.5C.
Its parent company Koç pointed the finger at the slow pace of green hydrogen development, which the group said now had a “low feasibility” of transforming the energy sector after it had previously pinned much of its transition plan on the sustainable fuel.
The Turkish company’s new 2030 targets are certainly within reach. Tüpraş had already cut its operational emissions by 17% from 2017 levels by 2025, with nearly all of that progress achieved before the transition plan was unveiled, while Koç had reduced them by 16%.
The softer targets also exclude the bulk of the group’s climate impact. Most of its emissions come not from its own refineries and factories but from the products it sells: petrol, diesel and jet fuel burned in the engines of cars or planes.
These so-called Scope 3 emissions make up about 97% of Koç’s carbon footprint. They rose by around a sixth between 2019 and 2024, and neither Koç nor Tüpraş has set a target to cut them.
Efe Baysal, Türkiye team lead at campaign group 350.org, said there is a “clear contradiction” between talking about climate action while weakening emission targets and seeing emissions from the use of petroleum products keep rising.
“If the company is serious about the transition, it needs a clear plan to wind down fossil fuel operations, rather than relying on efficiency measures and technologies that let business as usual continue,” she told Climate Home News.
‘Sustainable refining’ push
Tüpraş’s updated transition plan rules out expanding its oil refineries, but commits to “maintaining the existing capacity” and running it “at maximum potential”. Oil refining is expected to remain its main source of earnings for years to come. Koç listed “growing oil demand and diesel deficit” in Türkiye as a competitive advantage for its energy business in a pitch to investors last month.
The biggest component of the Tüpraş transition plan is what the company calls “sustainable refining”. It plans to invest $3.9 billion between 2025 and 2035 in programmes to modernise its refineries, improve their energy efficiency and bring down the direct emissions they generate. The company is also shifting some of its production to petrochemicals, which it expects to reduce its Scope 3 emissions.
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Alongside these “sustainable refining” efforts, Tüpraş is also investing in renewable power.
Four years ago, it bought Entek, which produces electricity primarily from six hydropower plants and one gas plant. Since the acquisition, Tüpraş has started building a utility-scale solar farm in Romania and a wind power plant with storage in Türkiye, alongside smaller solar energy installations at some of its refineries. A dozen more renewable energy projects are currently in the pipeline, according to its latest annual report.
In a self-declared bid to become “Türkiye’s leading producer of zero-carbon electricity”, Tüpraş wants to reach installed capacity of 1.6 gigawatts (GW) by 2030 – a target it raised in its updated plan – and 2.5GW by 2035. The Turkish government has committed to rolling out 120GW of wind and solar capacity nationwide by then.
Setback for green fuels
Tüpraş plans to supply most of its low-carbon electricity to run its future production plants for green hydrogen, an alternative fuel that can replace fossil fuels in some heavy industries and long-distance transport.
A few years ago, green hydrogen looked set to become a key pillar of the global energy transition, with companies pitching visionary projects and governments rolling out strategies for the fuel to decarbonise economies. But inflated forecasts, high costs and weak demand have led to a reality check for prospective producers like Tüpraş.
The Turkish refiner significantly scaled back its green hydrogen plans last year. While it originally hoped to start producing the clean fuel in 2025, it now targets a first pilot project by 2030 with commercial large-scale production not expected before 2035. That’s primarily because the cost of electrolysers, the machines that split water into hydrogen and oxygen, has risen fourfold since its original projections, the company said.
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Tüpraş’s ambition to become Türkiye’s leading producer of sustainable aviation fuel (SAF) has also seen a partial rethink. The firm originally said it would convert by 2026 a unit in its sprawling oil refinery in the port city of Izmir into a plant that would produce SAF from waste cooking oil into “green” jet fuel.
But it is now planning to build a dedicated plant which is expected to be commissioned towards the end of 2028. That means its SAF output will be added to its existing fossil fuel refining capacity rather than replacing any of it.
Dividends dwarf green spending
Under its updated blueprint, Tüpraş plans to invest $4.35 billion in zero-carbon power, SAF and green hydrogen by 2035. Last year, it spent $137 million on activities that qualify as green under EU rules, leaving much ground to make up in the next 10 years. Most of its green investment in 2025 went on solar and wind farms, and a quarter on a unit making propylene, a refinery by-product used to produce plastic packaging and bottle caps.
Over the same year, it paid out about five times as much – roughly $740 million – to shareholders, under a policy of distributing around 80% of its profits. About half went to Koç Holding, which in turn paid its own shareholders some $460 million. The Koç family and companies it controls hold the majority of the group.
Kelly Trout, research director at energy think-tank Oil Change International, said a company like Koç should not be the face of the COP31 climate summit as it doesn’t pass the test of “climate integrity” the UN requires of a sponsor.
The hosting agreement struck between Türkiye and the UNFCCC says that the government has to consult the secretariat of the UN body to obtain advice on which “entities of concern” it should not conclude sponsorship or partnership agreements with. The document adds that the advice should give appropriate consideration to the partner’s climate integrity, but it does not specify how that should be judged.
‘Climate integrity’ mystery
Climate Home News asked the UNFCCC and the Turkish COP31 presidency if this process was followed for the Koç Holding sponsorship, but had not received a response at the time of publication.
The same provision featured in the host country agreement for COP29 in Azerbaijan, according to a leaked copy published by Human Rights Watch.
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The clean energy arm of state-owned oil and gas company SOCAR was named “Energy Transition Partner” for that summit, alongside other firms which an investigation from the Organized Crime and Corruption Project (OCCRP) found were owned by the country’s ruling family or people associated with them.
Koç is not the first fossil fuel-linked company to bankroll a UN climate summit. At COP24 in the Polish coal-mining city of Katowice in 2018, sponsors included the state coal power company PGE and the coking coal miner JSW.
‘A real story to tell’
COP sponsors typically get the right to promote themselves inside the conference venue and appear at official events. When it unveiled the agreement, the COP31 presidency called Koç Holding a “vital partner” in its efforts to unite the public and the private sector “to demonstrate Türkiye’s unwavering commitment to global climate action”.
The presidency declined to answer Climate Home News’ questions on how Koç Holding will be involved in the summit.
Koç itself has revealed little about its plans for the Antalya talks. When the deal was announced, the group said it would use the summit to share its experience of turning climate solutions into “concrete business results” and to forge new partnerships.