My Top-10 pick of insightful climate papers of 2025
For my last article of 2025, I thought I’d look back over the climate change, paleoclimate, impacts, solutions and science papers that I found most fascinating this year. Here are my Top-10.
A 485-million-year history of Earth’s surface temperature.
Emily Judd et al.
Starting with the paper that looked back the furthest, Emily Judd et al.1 carried out a robust analysis of the global mean surface temperature and atmospheric carbon dioxide (CO2) concentration since the end of the Cambrian Period, 485 million years ago. This stretch of time, almost impossible to comprehend, contained the whole spectrum of climate states from Coldhouse (where we are now), Coolhouse (where we’re heading), Transitional, Warmhouse and Hothouse. It included three long periods of ice age as well as super hot climates where forests thrived in Antarctica.
It also includes the five mass extinction events of the past, all coinciding with major sudden climatic changes, at least on geological timescales. Our current rate of change is orders of magnitude faster of course.
Two particular outputs from the paper for me are firstly, and perhaps obviously, atmospheric CO2 has always driven temperature. That much has been understood for well over a century, but the precision the paper brings is to set the concentration boundaries for each climate state. For example the median concentration for a coldhouse regime is 307ppm and a coolhouse 608ppm. Surprisingly a full hothouse regime has a median level of just 870 - 1,200ppm although values as high as 3,000ppm have been recorded. We are currently passing 425ppm growing at ~3ppm a year, so very likely leaving the coldhouse period. Interestingly coldhouses are relatively rare on geological timescales. They occupy the lowest proportion of time in the 485 million year record at just 13%.
The second key output from the paper for me is the consistency of the Arctic Amplification phenomena. Today the Arctic is warming 3-4 times faster than the global mean and this process happens across every climate state. The warmer the planet, the less temperature difference between the poles and the equator. Panel D in their graphic below shows this nicely. This confirms that the warming poles being observed today is not temporary and will not slow down as we continue to warm. This has implications for sea level rise as well as permafrost melt and ecological change in the high latitudes.
Arctic speleothems reveal nearly permafrost- free Northern Hemisphere in the late Miocene.
Anton Vaks et al.
Staying with the paleoclimate of the deep past, the second paper by Anton Vaks et al.2 jumps to just 8.7 million years ago. This time period is interesting since the continents were positioned similarly to today. This is especially true for the trial site of this work which was the caves of northern Siberia which have not changed latitude since then. Speleothems are carbonate deposits that grow as freshwater flows and drips through caves. You may know them better as stalactites and stalagmites, with stalactites hanging from the ceiling and stalagmites growing on the floor. (Stalagmites might have been stalactites if they had held on tight enough - I remember from a childhood visit to Cheddar Gorge).
Speleothems grow with water flow, so if the ground above consists of deep frozen permafrost there is no flowing water and so no growth at all. Within the caves however there are such deposits and through radiometric dating, it’s possible to discover when they last able to grow.
The results show that the ground above these caves were last ice free 8.7 million years ago in the Tortonian stage of the Miocene epoch. Paleo-temperatures reconstructed from these speleothems show that mean annual air temperatures in the Arctic region were +6.6°C to +11.1°C higher than pre-industrial, which given Arctic Amplification suggests a mean global temperature of about +4.5°C. However CO2 at the time was in the region of 350ppm, significantly less than today, which suggests we are heading in this direction if concentrations are not brought back down.
If we let temperatures rise to this level again, it shows that the arctic will be permafrost free once more, releasing huge amounts of carbon into the atmosphere in the process. That additional carbon would drive even more warming in a feedback loop as it is released, regardless of our emissions.
Emerging evidence of abrupt changes in the Antarctic environment.
Nerilie Abrams et al.
Bringing us up to date, but sticking with the ice theme, the Nature review paper by Nerilie Abrams and 20 colleagues3 highlighted the rapid changes underway in Antarctica and the future global implications they will cause. I wrote a review of this paper which you can access in the footnotes4, but in summary, significant changes are affecting the ice sheets that cover the continent, the sea-ice that surrounds it, the overturning circulation within the ocean system which has global impacts, and not least the unique ecology and wildlife that inhabit this special environment.
Antarctic sea ice experienced a significant regime shift in 2016. Having been stable, even expanding slightly since satellite measurements began in the 1970s, it suddenly saw a huge drop which has been sustained ever since. The decline is so significant that it has matched the total decline in the Arctic sea ice since 1979, but in a quarter of the time. Variability and seasonal persistence has also increased which suggests the system is fundamentally unstable, with knock-on effects for ice sheet stability and ecology.
The Antarctic overturning circulation, which is similar to the more famous AMOC, is significantly declining. Measurements suggest a loss of deep water formation of 40%. This is partly through the decline in sea ice formation but also from significant freshening of the waters through glacial and ice sheet melting. This has implications for carbon storage in the Southern Ocean which currently accounts for 40% of all ocean carbon absorption.
The ice sheets are also retreating. The West Antarctic Ice Sheet is the most vulnerable and has been known to collapse in previous interglacials when temperatures were similar to todays. The ice shelves that float on the ocean and buttress the glaciers and ice sheets behind them are being melted from beneath as warmer water penetrates the coastline. Mass loss has increased by 6x since the 1990s.
Rapid changes to the environment are always detrimental to endemic species. Antarctica has been relatively stable for more than 100,000 years and when changes have occurred, they have been gradual, over centuries and millennia. Changes over mere decades, when added to by other human pressures such as pollution, fishing and disease introductions are very hard to adapt to.
The paper cites three main stressors that are changing rapidly. Habitat transformation, reproductive failures and the exceedance of physiological thresholds. Penguin colonies have made the headlines, but even krill, the shrimp at the base of the food chain, are in trouble. Despite its importance, it targeted by commercial fishing vessels for pet food!
These pressures cascade and drive each other to make the situation both more complex and serious.
The State of the Cryosphere report is also worth a read on this topic. I did a review of this too which is linked in the footnotes - this doesn’t count as one of my 10 papers though.5
Equatorial Atlantic mid-depth warming indicates Atlantic meridional overturning circulation slowdown.
Qiuping Ren et al.
Following on from the subject of abrupt change, tipping elements are the most concerning since they mark a point of no return as they are driven by self-reinforcing feedbacks. The Atlantic Meridional Overturning Circulation or AMOC is the one that is causing increasing concern. The AMOC is the natural process that brings warm salty water from the tropics and Southern Ocean all the way north into the Atlantic. It is the reason why western Europe is so temperate for its latitude and it also controls the position of the tropical rain belts.
Mounting evidence suggests that the AMOC has already lost about 15% of its strength in recent decades. It is also well established that it has a tipping point at which it can collapse completely into an alternative off state. In fact it has done so many times in the past.
This paper6 is very important as it adds a new way of measuring the decline of the current, and one that is less noisy with natural variations. The fingerprint identified is the temperature increase in mid depth waters between 1,000 and 2,000 meters deep across the Atlantic Equator. The warming signal , and hence AMOC slowdown, is detectable since the 1960s and emerges from the natural variability by the early 2000s showing that the current is indeed in decline.
Since the implications of AMOC slowdown and collapse are so severe, this is an area that requires a great deal of attention both from science and policy makers. I wrote an overview article on the AMOC which you can also find in the footnotes7.
Quantifying the acceleration of multi-decadal global sea surface warming driven by Earth’s energy imbalance.
Chris Merchant, Richard Allan & Owen Embury
The Earth’s Energy Imbalance (EEI) is the difference between the energy entering the system from the sun and the amount of energy being reflected and re-radiated back out into space. It is the fundamental measure that shows if the climate system as a whole is cooling, stable or warming. A positive EEI means more energy is entering the system than is leaving, leading inevitably to warming. Since 2000 this has been measured with the CERES satellite system and the results are alarming. Not only is the EEI positive, it is increasing, more than doubling in fact over the period if 10 year averages are compared. The trend line has increased by 7x in the 25 years.
The current value is about 1.4 watts per square meter of Earth’s surface. Earth’s surface has a lot of square meters. The energy being accumulated is roughy equivalent to the heat from 11 Hiroshima bomb blasts every second!
This paper8 is interesting since it then uses this EEI data to also calculate and plot the Energy Accumulation curve. This is the first time I have seen the data in this way and it provides direct proof that warming is accelerating since the accumulated energy curve is clearly rising as the EEI increases. There is some scientific debate about whether warming is accelerating, but this approach and data clearly shows that it is. You can’t add more and more energy at ever increasing levels and not have acceleration.
The paper goes on to use the data to explain the rapid recent warming in sea surface temperatures observed over the last decade, especially the peaks of 2023/24. The paper makes the point that policy makers and wider society should be aware that the rate of global warming over recent decades is a poor guide to the faster change that is likely over the decades to come, underscoring the urgency of deep reductions in fossil-fuel burning.
Reduced aerosol pollution diminished cloud reflectivity over the North Atlantic and Northeast Pacific.
Knut von Salzen et al.
Analysis of the EEI data shows that not only are greenhouse gases trapping in heat that would otherwise be radiated out into space from the warming surface, but the reflectivity of the Earth to incoming solar radiation is also in decline. The Earth reflects just under a third of the incoming short wave radiation, but since 2000 this has dropped by 0.7% from 29.4% to 28.7%. This may not sound a lot but it makes a huge difference to the energy imbalance and accumulation. It equates to about 0.8 watts per meter squared of the earth surface and is roughly the equivalent of adding a further 135ppm of CO2 to the atmosphere.
The big question in climate science is what is driving this dimming of the Earth. It’s clear that clouds are declining and this is the major cause, but why are they in decline? Two scenarios are proposed. One is that cloud reduction is a natural feedback of global warming itself. The other is that reductions in air polluting aerosols, which have been artificially brightening clouds, is returning clouds to their natural state and unmasking warming that was essentially hidden by this air pollution cooling effect.
The reality is probably a combination of the two, but the extent of pollution brightening is important to pin down to better model future warming, especially as air pollution is reduced further.
A great global experiment has been carried out to help answer this question, albeit accidentally. In 2020 the International Maritime Organisation mandated that all shipping fuels, which were notoriously dirty, be cleaned up resulting in an 80% reduction in their sulphur aerosol emissions. This was done for good reason, air pollution from fossil fuel emissions kills millions of people every year. A host of papers were published examining the effects of this change on the global temperature warming rate, which has accelerated since 2020.
This paper9 looks at the effect of the changes on the north Pacific and Atlantic Oceans where a majority of the shipping lanes exist. They found that since 2003 marine cloud reflectivity has reduced by 2.8% in these regions and that 69% of the change is due to aerosol declines.
This work, and others like it are very important since the, now aging, CMIP6 climate models that the IPCC rely on, simulate a much weaker cloud response. This means that they also underestimate future energy accumulation, warming and climate impacts as a result.
Natural sequestration of carbon dioxide is in decline: climate change will accelerate.
James and Samuel Curran
Of course the principle driver of warming is the accumulation of greenhouse gases in the atmosphere. Even reflectivity decline would not be an issue without it, since the long wave radiation coming from the warmer surface would escape to space and reverse the trend, halting the feedback and returning the status quo.
Every year we pump an ever increasing amount of CO2 and other gases into the atmosphere, knowing that about half of it will remain, but half will be absorbed through natural take-up in the oceans and on land. After all, carbon dioxide is plant food, they will take all they can get. At least that was the assumption.
This analysis and paper from James and Samual Curran10 states otherwise. Every year the atmospheric CO2 goes through a cycle. In the northern hemisphere summer it drops and in the winter it rises. The reason is that land based photosynthesis is dominated by the northern hemisphere and during the growth season, CO2 is absorbed from the atmosphere to be replaced in the winter through biodegradation. By plotting the regression of the annual maximum and minimum concentrations, they showed that up until 2008, plants indeed absorbed more and more CO2, but they then peaked and since that time, they have absorbed less and less. 2024 saw a record atmospheric growth despite near stable human emissions.
Natural land based photosynthesis is therefore in decline, absorbing less of our emissions each year. This leads to an acceleration in accumulation and therefore warming. The causes are complex and include droughts, deforestation, wildfires and other pressures. This is despite the fact that increases in global greening area are being reported. Its the quality, not the quantity of the biosphere that’s important.
This paper inspired some of my own work this year looking more closely at the shape of the annual concentration curve using machine learning11.
The 2025 report of the Lancet Countdown on health and climate change: climate change action offers a lifeline.
Marina Romanello et al.
The papers so far have described the predicament and evidence of global warming and climate change this year. That’s all very interesting but what does that mean for people today? The Lancet Countdown paper12, written by 128 specialists and scientists pulls no punches. I wrote a review which you can access here13, but in summary:
Heath hazards, exposures and impacts are assessed, including heatwaves, extreme weather events, infectious disease transmission and food insecurity. All are worsening and account for hundreds of thousands to millions of deaths annually.
Many of the issues can cascade together. Heat stress preventing outdoor working affects food production but also lowers incomes for people, which lowers their health outcomes. Recovery from extreme weather events also puts long lasting pressure on health systems leading to substantially more deaths in the following years than the event caused itself. This has been confirmed by a study of American Hurricanes which showed that although on average only 24 people died during each storm, 7,000-11,000 additional deaths were recorded on average over the following 15 years.
The paper concludes with some messages of hope. There are some glimpses of light at the end of this dark and deadly tunnel. The growth of the clean energy sector is underway. It’s fair to say the massive expansion of renewable energy is yet to displace legacy fossil energy, but it’s a start and the economics greatly favour continued adoption and expansion. Just how much longer can the world afford to subsidise fossil fuels by $7 trillion a year (IMF estimate)? That figure does not include immunity for the millions of deaths the industry causes each year.
A prudent planetary limit for geologic carbon storage.
Gidden, M.J., Joshi, S., Armitage, J.J. et al.
Decarbonising the economy is the number one priority for humanity in the coming decades. The papers above all show very clearly why this is necessary. Even nature cannot cope with our increasing emissions and its literally killing us.
Step two however is reducing the levels of CO2 in the atmosphere. Some of this can be achieved with nature based solutions, but probably only about 10% of what is required in the time available. Carbon capture and long term storage is going to be inescapable if the world is to avoid 3ºC or more of warming.
This paper14 is the first of two I’ve picked on the subject of long term storage and it caused a bit of a sensation when it first came out. It looked at the storage space available for future carbon capture, which had previously been thought to be near limitless. They used a set of safety constraints to re-calculate the available space in depleted oil and gas fields and found the total to be much lower. So much lower in fact that it ought to be restricted to hard to abate sectors and saved for future atmospheric capture. Running the numbers they estimated that if it was all used for carbon removal from the atmosphere it would only be sufficient to reduce temperatures by 0.7ºC, nowhere near enough to return the planet to a safe state.
Since the vast majority of country’s commitments and all the ‘safe’ IPCC scenarios rely on huge amounts of carbon removal, this paper was a major concern.
From carbon to climate action: harnessing basalt for geological carbon dioxide (CO2) storage onshore and offshore.
Conor M. O’Sullivan et al.
Fortunately a second paper15 was published a month later which pointed towards an alternative solution. The earlier paper had only considered sedimentary rocks which consist of porous, normally sandstone rock formations. These are typically pumped with liquid CO2 for storage. This second paper looked at the potential for chemically locking the carbon into basalt rock formations.
The study was carried out in Ireland and follows trial work in Iceland and other regions. It found that there was significant and sufficient scope for permanent carbon storage in country and by extension globally for the carbon removal requirements left for us by decades of free waste disposal in the atmosphere.
The study was also interesting from a geological complexity perspective and illustrated the degree of work required at each site to search for and quantify safe storage sites. There is no long term alternative to permanently return the released carbon to the lithosphere and this paper shows what is involved to even stretch the surface.
Closing thoughts
I hope you have found this selection of papers interesting. It’s been an active year for climate science. I also hope you have found my other articles and notes useful and interesting too. If you’d like me to cover a particular topic, please make a suggestion in the comments.
I’ll be back in the New Year. Thank you all.
Emily J. Judd et al. ,A 485-million-year history of Earth’s surface temperature.Science385,eadk3705(2024).DOI:10.1126/science.adk3705
Vaks, A., Mason, A., Breitenbach, S.F.M. et al. Arctic speleothems reveal nearly permafrost-free Northern Hemisphere in the late Miocene. Nat Commun 16, 5483 (2025). https://doi.org/10.1038/s41467-025-60381-5
Abram, N.J., Purich, A., England, M.H. et al. Emerging evidence of abrupt changes in the Antarctic environment. Nature 644, 621–633 (2025). https://doi.org/10.1038/s41586-025-09349-5
Ren, Q., Xie, SP., Peng, Q. et al. Equatorial Atlantic mid-depth warming indicates Atlantic meridional overturning circulation slowdown. Commun Earth Environ 6, 819 (2025). https://doi.org/10.1038/s43247-025-02793-1
Christopher J Merchant et al. Quantifying the acceleration of multidecadal global sea surface warming driven by Earth’s energy imbalance, 2025 Environ. Res. Lett. 20 024037 DOI 10.1088/1748-9326/adaa8a https://iopscience.iop.org/article/10.1088/1748-9326/adaa8a
von Salzen, K., Akingunola, A., Cole, J.N.S. et al. Reduced aerosol pollution diminished cloud reflectivity over the North Atlantic and Northeast Pacific. Nat Commun 16, 9433 (2025). https://doi.org/10.1038/s41467-025-65127-x
James C. Curran, Samuel A. Curran. Natural sequestration of carbon dioxide is in decline: climate change will accelerate, 2025, Weather Volume 80 Issue 3, https://doi.org/10.1002/wea.7668
Romanello, Marina et al. The 2025 report of the Lancet Countdown on health and climate change: climate change action offers a lifeline, The Lancet, Volume 406, Issue 10521, 2804 - 2857 https://www.thelancet.com/journals/lancet/article/PIIS0140-6736(25)01919-1/fulltext
Gidden, M.J., Joshi, S., Armitage, J.J. et al. A prudent planetary limit for geologic carbon storage. Nature 645, 124–132 (2025). https://doi.org/10.1038/s41586-025-09423-y
Conor M. O’Sullivan et al. From carbon to climate action: harnessing basalt for geological carbon dioxide (CO2) storage onshore and offshore, 2025, Earth Science, Systems and Society Volume 5 https://doi.org/10.1144/esss2024-016
So if this is your top 10, which is your favorite??
Thank you for the write up! I am interested in new projections of food availability (especially ones that include the time for farmers to learn new crops). Also interested in any papers that look at impacts trade networks or widespread economic impacts (most out there seem like they leave so much out they are useless)