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 cannot 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
FOR IMMEDIATE RELEASE
CCL applauds 21 Republicans for supporting clean energy tax credit support
March 12, 2025 – Citizens’ Climate Lobby is very encouraged to see 21 House Republicans sign onto a letter in support of America’s clean energy tax credits.
Jennifer Tyler, CCL’s Vice President of Government Affairs, said, “More and more Republican House members are recognizing that clean energy tax credits are benefiting their districts — and that constituents and businesses don’t want to lose them. It’s clear that these policies are delivering real economic value in communities nationwide.”
The letter, led by House Climate Solutions Caucus co-chair Rep. Andrew Garbarino (R-NY-02), was signed by 20 of his fellow House Republicans: Reps. Amodei, Bacon, Bresnahan, Carter, Ciscomani, Evans, Fong, Houchin, Hurd, James, Joyce, Kean, Kiggans, Kim, LaLota, Lawler, Mackenzie, Miller-Meeks, Newhouse and Valadao.
“We have 20-plus members saying, ‘Don’t just think you can repeal these things and have our support’” for the larger budget reconciliation package, Rep. Garbarino told Politico.
That’s a bigger group than the 18 Republicans who sent a similar letter last fall.
In last week’s Conservative Climate Leadership Conference and Lobby Day, 50 right-of-center climate advocates from CCL visited 47 Republican offices on Capitol Hill to reinforce that message.
These grassroots volunteers “found that Republican offices are receptive to the case that these tax credits have spurred unprecedented private investment, driven innovation, and created well-paying jobs across the country,” Tyler added.
CONTACT: Flannery Winchester, CCL Vice President of Communications, 615-337-3642, flannery@citizensclimate.org
###
Citizens’ Climate Lobby is a nonprofit, nonpartisan, grassroots advocacy organization focused on national policies to address climate change. Learn more at citizensclimatelobby.org.
The post CCL applauds 21 Republicans for supporting clean energy tax credit support appeared first on Citizens' Climate Lobby.
CCL applauds 21 Republicans for supporting clean energy tax credit support
FOR IMMEDIATE RELEASE
50 grassroots conservatives visit Capitol Hill to support clean energy tax credits
March 10, 2025 – Last week, conservatives from across America gathered in Washington D.C. for Citizens’ Climate Lobby’s fifth annual Conservative Climate Leadership Conference and Lobby Day.
After receiving communications training from CCL staff, 50 right-of-center volunteers visited 47 Republican offices on March 5.
“I think this is one of the most impactful things that we do,” said Drew Eyerly, CCL’s Action Team Director, in CCL’s national volunteer call sharing highlights and reflections from the event.
Eyerly remarked on Republican offices’ enthusiasm for speaking with CCL volunteers, often giving them more time than originally planned. “They’ll say 10 minutes, and those meetings will turn into 20 to 30 minutes,” he reflected. “Just really, really great conversations.”
Those conversations centered on one main ask: For Republican lawmakers to protect America’s clean energy tax credits.
“As we talk about how competitive American businesses can be in clean energy and how many jobs it can bring to their district, the members are much more open to that discussion,” said Jennifer Tyler, CCL’s Vice President of Government Affairs.
This week, Citizens’ Climate Lobby launched a new action for volunteers around the country to call Republican members of Congress about the clean energy tax credits, reinforcing our recent lobby day message.
Volunteers will be back on Capitol Hill this summer for CCL’s annual Summer Conference and Lobby Day in late July.
CONTACT: Flannery Winchester, CCL Vice President of Communications, 615-337-3642, flannery@citizensclimate.org
###
Citizens’ Climate Lobby is a nonprofit, nonpartisan, grassroots advocacy organization focused on national policies to address climate change. Learn more at citizensclimatelobby.org.
The post 50 grassroots conservatives visit Capitol Hill to support clean energy tax credits appeared first on Citizens' Climate Lobby.
50 grassroots conservatives visit Capitol Hill to support clean energy tax credits
Greenhouse Gases
DeBriefed 21 March 2025: Germany’s climate win; Conservatives’ net-zero row-back; Key messages from major UK climate conference
Welcome to Carbon Brief’s DeBriefed.
An essential guide to the week’s key developments relating to climate change.
This week
Germany’s €100bn climate funding
BILLIONS IN FUNDING: Germany’s parliament on Tuesday voted to create a €500bn defence and infrastructure fund and relax “constitutionally-protected debt rules”, the Guardian reported, with “the last-minute backing of the Greens” in return for “guarantees that €100bn of the funds destined for infrastructure would be allocated for climate and economic transformation investments”. The deal came following “clumsy” initial negotiations from Germany’s chancellor-in-waiting, Friedrich Merz, Bloomberg said. It reported that the Greens “finally came around” after Merz’s negotiators “conceded to their key demands”, which also included adding Germany’s 2045 climate-neutrality target into the constitution.
TAKING CLIMATE ‘SERIOUSLY’: The Greens said in a statement on social media that the agreement “finally takes the challenges of the future seriously”, according to the New York Times. Paula Piechotta, a member of the Greens in the German Bundestag, told the German newspaper Tagesspiegel that the deal was a “great success for democracy in our country, for sustainability and intergenerational justice”. The newspaper added that the far-right Alternative for Germany (AfD) and the Left party, “unsurprisingly”, criticised the agreement.
UK opposition breaks cross-party climate consensus
BREAKING AWAY: In a speech, Kemi Badenoch, leader of the UK opposition Conservative party, said it was “impossible” for the UK to meet its net-zero target by 2050, marking a “sharp break from years of political consensus”, BBC News reported. She did not offer an alternative target for the goal, the broadcaster said, quoting her telling reporters that if the Conservatives “do find a target is necessary, then yes we will have one”. Badenoch “failed to cite any evidence in support” of her arguments, according to a factcheck published by Carbon Brief, which concluded that much of the existing evidence “contradicts” her claims.
TORY BACKLASH: In response, Conservative former prime minister Theresa May, who was responsible for passing the 2050 target into law, warned the move “will hurt future generations and cost Britons”, the Times reported. The Confederation of British Industry (CBI) also criticised the speech, warning that “now is not the time to step back from the opportunities of the green economy”, according to the i newspaper. In the Daily Telegraph, Ambrose Evans-Pritchard said Badenoch’s “rant comes close to political tragedy”.
Around the world
- CARNEY CUTS: New Canadian prime minister Mark Carney removed the country’s “consumer carbon tax”, CBC News reported, adding that the policy had been a “potent point of attack” for his political opponents.
- GREENPEACE BILL: Greenpeace has been ordered to pay $660m in damages over its protests against the Dakota Access pipeline in 2016, which could “bankrupt its US operations” if upheld, the Financial Times said.
- UK-CHINA FORUM: The UK and China agreed to establish an “annual climate dialogue”, with the first meeting to be held in London later this year, the Times reported.
- CHEQUES AND BALANCES: A US judge has “temporarily barred” attempts by the Trump administration to recoup at least $14bn in “grants issued by the Biden administration for climate and clean-energy projects”, the Washington Post said.
- EXTREME HEAT: “Severe heatwave conditions” have begun affecting several areas across India “unusually early in the season”, the Hindustan Times reported.
- SOUTH AFRICAN SUPPORT: The EU will fill a “$1bn hole” in South African’s “just energy transition partnership” left by the US, the Financial Times reported. The US is also “stalling” $2.6bn of climate finance for South Africa, Bloomberg said.
152
The number of “unprecedented” extreme weather events that occurred in 2024, according to the World Meteorological Organization’s State of the Climate 2024 report. Heatwaves were the most common type of unprecedented events – defined as events “worse than any ever recorded in the region” – followed by “rain or wet spells” and floods.
Latest climate research
- New research in Climate and Development explored how environmental justice featured in the climate action plans of rust-belt cities in the US, finding that few “provided enough details” to determine if it was a priority.
- A new Science Advances study identified “increasing storminess” in the south-western Caribbean, which was attributed to “industrial-age warming”.
- Marine heatwaves are now 5.1 times more frequent and 4.7 times more intense since records began, new research in Communications Earth & Environment found.
(For more, see Carbon Brief’s in-depth daily summaries of the top climate news stories on Monday, Tuesday, Wednesday, Thursday and Friday.)
Captured
The UK’s high electricity prices are primarily driven by gas prices, according to an analysis published by Carbon Brief, with the UK typically seeing gas set electricity prices 98% of the time – compared to an average in the EU of 40%.
Spotlight
Chatham House talks climate and resilience
Carbon Brief outlines key takeaways from Chatham House’s climate and energy summit.
Chatham House, the UK’s leading international affairs thinktank, held its annual summit on climate and energy on 18-19 March. This year’s theme was: “Securing a resilient future.”
Carbon Brief attended the conference, where speakers including COP30 CEO Ana Toni, UK climate envoy Rachel Kyte and Moroccan minister for energy transition and sustainable development Leila Benali shared their thoughts on encouraging and enacting climate action.
Climate backlash
A sense of urgency permeated discussions at the summit, underpinned by concerns over growing anti-climate narratives.
Toni argued climate scepticism proves climate action is on the right track.
She said: “First people ignore you, then they laugh at you, then they fight you – and this is where we are – then we win.”
Other speakers said that increasing support for climate action by building new norms and creating overlapping interests could also be effective strategies.
Former US climate envoy Todd Stern pointed to increasing adoption of electric vehicles, while ClientEarth CEO Laura Clarke raised the example of community-owned renewable power.
Fretting over finance
Clean Earth Gambia founder Fatou Jeng warned that climate finance, as ever likely to be an important issue at COP30, has “not progressed much”.
“Blended finance” – using public money to leverage private funds – was heavily criticised in several panels. Ben Parsons, a partner at consultancy firm Oaklin, noted that only 72 such deals were agreed in 2024.
Speakers agreed that innovative mechanisms to derisk climate finance were needed, with Morocco’s Benali critiquing “exclusive” and inflexible private financing options.
Ndongo Samba Sylla, head of research and policy at International Development Economics Associates, argued that using local currencies would significantly boost climate finance.
Resilience through renewables
A key benefit of the UK’s “climate leadership”, Kyte argued, is that the energy transition will “make British people more secure”.
Parsons said the argument – recently deployed by Conservative leader Badenoch – that the energy transition replaced reliance on Russian fossil fuels with reliance on Chinese technology was incorrect.
“Fossil fuels are fuel – they require constant replenishment. Renewables are infrastructure,” he said, adding that arguably the UK should be accelerating its deployment of clean-energy technology.
On cybersecurity challenges in renewable power systems, Alex Schoch, vice president and group director of flexibility and electrification at Octopus Energy, argued that the key issue is how renewable energy “hardware” is managed, rather than where it is sourced from.
Parsons agreed, noting that the UK’s current power system has “plenty of cybersecurity vulnerabilities in it today”.
He said: “We have to make sure we’re putting [cybersecurity strategies] in place…But I don’t think that goes hand in hand with thinking we should avoid buying renewables from certain parts of the world.”
In a session on energy security in war-time Ukraine, held under the Chatham House rule, participants noted that the country was a case study for the importance of energy security.
Speakers said that since Russia’s invasion of Ukraine, attacks on thermal power plants have seen growing use of low-carbon energy – particularly distributed solar.
Watch, read, listen
ELEPHANT IN THE ROOM: The Columbia Energy Exchange podcast explored how the new Trump government underpinned discussions at the energy industry event CERAWeek.
‘CONFLICT BLINDSPOT’: A new report by ODI found that “less than 10% of international climate finance” in 2022 went to fragile and conflict-affected countries.
METHANE INACTION: Leading supermarkets in the global north are “failing to address the methane pollution in their supply chains”, according to a study covered by Desmog.
Coming up
- 24-26 March: 16th Petersberg Climate Dialogue, Berlin, Germany
- 24-26 March: IPCC lead author meeting for methodology report on inventories for short-lived climate forcers, Bilbao, Spain
- 24-28 March: 20th session of the UN FAO commission on genetic resources for food and agriculture, Rome, Italy
- 25 – 28 March:First G20 climate and environment sustainability working group meeting, online
Pick of the jobs
- ClientEarth, lawyer or legal consultant, energy systems, Asia | Salary: 455m-585m Indonesian rupiah. Location: Jakarta
- European External Action Service, policy officer for green diplomacy | Salary: Unknown. Location: Brussels
- Bloomberg, climate reporter | Salary: Unknown. Location: Hong Kong
- The Grantham Research Institute on Climate Change and the Environment, project manager | Salary: £42,679-£51,000. Location: London
DeBriefed is edited by Daisy Dunne. Please send any tips or feedback to debriefed@carbonbrief.org.
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The post DeBriefed 21 March 2025: Germany’s climate win; Conservatives’ net-zero row-back; Key messages from major UK climate conference appeared first on Carbon Brief.
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