A report by by the World Weather Attribution (WWA) looks at climate change and the likelihood of wildfire disaster in LA.
Shirin Ermis, Researcher in Climate Damages Analysis at the Smith School of Enterprise and the Environment, and DPhil candidate in Atmospheric Physics at the University of Oxford; and Dr Sarah Sparrow, Associate Professor in Environmental Impact, University of Oxford, both said:
“The study by World Weather Attribution is a very rigorous one and acknowledges the complexities of the event. In Los Angeles, multiple factors played together to create perfect conditions for a devastating fire. WWA analysed the drought preceding the fires, the lengthening of the drought season, and the onset of the Santa Ana winds before winter rain started. All of these were crucial to make the fire as impactful as it was. Previous studies have found that Fire Weather is made more likely by global warming, especially because climate change intensifies both dry and wet extremes in what is called ‘climate whiplash’. This study tightens the evidence further.
“The method that WWA use is well tested and peer-reviewed. Crucially, it combines multiple sources of data such as observations and climate models which all point in the same direction. Questions remain on the effect of climate change on the Santa Ana winds which include local features that are hard to resolve in climate models. Future studies will certainly analyse these aspects further.
“With the evidence of increasing fire risks in black and white, the question remains of how we can protect vulnerable members of society from the increasing risks of climate change. Here, WWA point to crucial adaptation measures to protect people from future fires.”
Dr Rupert Stuart-Smith, Senior Researcher in climate science and attribution, Oxford Sustainable Law Programme and Smith School of Enterprise and the Environment, University of Oxford, said:
“This study shows that the scale of the devastation caused by the LA wildfires is yet another outcome of human-driven climate change. While it hasn’t yet been through peer-review, WWA’s study uses widely-employed methods in climate change attribution, considers long-term and immediate causes of the fire, and draws on multiple lines of evidence from weather observations and climate models to buttress their findings. Fires in California are far from unprecedented, but, be it in the extremely dry autumn that created tinderbox conditions, or the fire weather that drove the rapid spread of the flames, the authors find fingerprints of human-caused climate change throughout this event. The financial consequences of climate change are already substantial and, until we stop emitting greenhouse gases, will be increasingly severe.”
Prof Tim Palmer, Royal Society Research Professor Emeritus in Climate Physics, University of Oxford, said:
“Climate change at the global level is comparatively straightforward and shows unambiguously that the Earth is warming due to our emissions of greenhouse gases. At the regional level, the impact of these emissions is more complex, involving the interaction of human-induced warming with the natural internal modes of variability of climate. The LA fires are no exception. Most important concerns the trends in temperature in the equatorial East-Central Pacific (far from Southern California!). The relatively cool sea temperatures in the equatorial East-Central Pacific that existed at the time of the fires are consistent with a long-term cooling trend in this region. La Nina-like atmospheric teleconnections from this region to Southern California cause both dry weather and Santa Ana winds as has been well documented over the years. Put another way, human-induced climate change notwithstanding, these fires would likely not have occurred if the climate system had transitioned to a warm El Nino event in January, which some seasonal forecast models were suggesting would happen. The key question is whether the multi-year cooling trend in the East-Central equatorial Pacific is itself anthropogenically forced. Most of the CMIP (IPCC-class) models suggest the cooling trend in the East-Central Pacific does not have an anthropogenic origin since they predict a slow warming in the equatorial East-Central Pacific, along with most of the rest of the world. However, this is an area where results from high-resolution climate models (with 1/10th degree ocean grid for example) are starting to suggest the opposite: that the East-Central Pacific cooling might be anthropogenic. So, in short, currently we don’t know and await further clarifying research.
“The climate models used in this rapid attribution study are either limited-area models over North America forced with CMIP5 data at their boundaries, or data from HighResMip whose models are not coupled ocean-atmosphere models, but have prescribed sea surface temperatures. After 2014, the sea temperatures in HighResMip are based on CMIP5 output (which, as mentioned above, don’t predict the recent cooling trend in the equatorial East-Central Pacific). Hence, neither of these modelling datasets is adequate to address the question of whether the observed La Nina-like cooling trend in the equatorial East-Central Pacific is anthropogenic in nature. This in my view is a serious shortcoming of the present study and hence of its conclusions, particularly about the role of human climate change in reducing rainfall.
“I note also that in the study’s observational analysis, El Nino and Global Mean Surface Temperature are treated as separate independent predictors of Californian weather. In reality, El Nino impacts on Global Mean temperature dynamically (and conceivably there is a backwards dynamical reaction), so it is unclear how, even when the timeseries of El Nino is linearly detrended, they can be treated as physically independent predictors (i.e. one anthropogenic the other not).
“Whilst the evidence suggests quite clearly that climate change is impacting on the severity of heat waves and flooding events around the world, we need to better understand the dynamical impacts of climate change at the regional level to be able to attribute specific events, like these LA fires, to climate change. So far, the climate science community has rightly focussed on the thermodynamic effects of a warmer moister climate, as these are much more straightforward to understand. Importantly, we need a new generation of much higher resolution climate models to have confidence in the dynamical impacts of climate change – the current CMIP datasets are simply not reliable enough for this purpose. These dynamical effects can be as large as the thermodynamic effects as this case study suggests.
“I believe rapid attribution studies such as this need to be more open about these key areas of uncertainty and possible model shortcoming. Highlighting such uncertainties and shortcomings is the only way to get the resources needed to improve our modelling capability. And this will be vital if society is to adapt wisely to future climate change.”
Prof Gabi Hegerl FRS, Professor of Climate System Science, University of Edinburgh, said:
“Given the short timeline that WWA aims for this is a very thorough analysis of the role of climate change and also El Nino conditions contributing to the fires in Los Angeles. The authors determine several factors that have contributed to this disaster, from severely dry conditions to high fire weather indices, late arrival of winter rains etc. Several of these factors point to high fire risk, both due to El Nino conditions and global warming. Overall the paper finds that climate change has made the Los Angeles fires more likely despite some statistical uncertainty. This is a carefully researched result that should be taken seriously. El Ninos come and go, but as long as the climate warms we will continue to see increasing risk of this hazard. Adapting to it will help, and the authors make some suggestions, but this example is one of many of how climate change increases the risk of deadly and costly disasters.”
Dr Karsten Haustein, Climate Scientist, Leipzig University, said:
“I remember a stark and dire warning of an US-based weather forecaster just before the fires. Sadly, he was absolutely spot on. The extremely hazardous mix of dry and windy conditions led to unprecedented destruction, displacing tens of thousands of people and costing billions of dollars. Naturally, folks want to know what role climate change played in this catastrophic disaster.
“Following two very rapid attribution studies by teams from UCLA (California) and IPSL-CNRS (France), now WWA has released their comprehensive rapid attribution study. The former two have already highlighted that climate change did play a role and made the fires more likely. Especially the so-called ‘hydroclimate whiplash’, where wetter than average years are followed by drier than average years, contributed to the devastating outcome. While these year-to-year variations are normal given the strong ENSO teleconnection in the region (El Niño leads to wetter conditions and vice versa for La Niña), now wet gets wetter and dry gets drier for longer.
“Hence one of the key messages of the WWA study is that the dry season in the region lasts longer than it used to be (23 days), increasing the risk for very dry conditions to overlap with strong (St Ana) winds, which occur mainly in winter. While WWA does not find increasing wind speeds during St Ana events, they do find that the risk for such a dry season has already increased by 35%, with a 6% increase in fire intensity.
“WWA highlights that a more in-depth analysis is required to make conclusive statements about changes in atmospheric circulation that favour such cut-off lows. But the thermodynamic climate change fingerprint (drier and warmer) is clearly present. So is the problem of exposure in the region. Houses are not build to withstand fire. Instead, they are fuelling the fires. A tinderbox when combined with built up vegetation from the preceding two wet seasons. All these aspects are meticulously discussed in WWA’s new attribution study.
“Their press release accurately summarises the scientific findings. The team involved was larger than ever, including the UCLA colleagues mentioned above. All methods used to conduct the analysis are peer-reviewed. The results do confirm prior research such as, for example, the hypothesised ‘hydroclimate whiplash’. The team also mentions the deficits of global climate models to simulate such wind events, which is why no attribution statement regarding the frequency of occurrence or magnitude of the St Ana winds is made.”
‘Climate change increased the likelihood of wildfire disaster in highly exposed Los Angeles area’ by Clair Barnes et al. was published by World Weather Attribution at 22:00 UK time on Tuesday 28 January 2025.
Declared interests
Shirin Ermis: “No interests to declare.”
Dr Rupert Stuart-Smith: “No conflicts of interest to declare.”
Prof Tim Palmer: “No interests to declare.”
Prof Gabi Hegerl: “No competing interests, occasional collaboration with some of the study’s authors.”
Dr Karsten Haustein: “No conflict of interests.”
For all other experts, no reply to our request for DOIs was received.