Climate warming is increasing the frequency and intensity of extreme events, including heat waves, intense storms, heavy rainfall and wildfires. However, our ability to predict and mitigate the worst of these effects is challenging for several reasons. Planning robust monitoring schemes in advance of short-duration or unpredictable events is logistically difficult, which makes before–during–after comparisons rare. Different taxa may also exhibit differential sensitivity to extreme events, depending on factors such as thermal vulnerability and access to refugia; for example, a meta-analysis on the impacts of the 2019–2020 Australian megafires found that almost half of all effects on species were positive, even though overall the effects across more than 2,000 species were weakly negative1. Evolutionary and ecological legacy effects of extreme events may also persist in the form of recruitment failures, genetic diversity loss, habitat recovery or changes in biotic interactions, which requires assessments of their long-term impacts alongside immediate effects.

In this Focus issue, we bring together research and opinion pieces that shed light on how different facets of biodiversity and ecosystem functioning are affected by extreme events across a range of species and ecosystems, and explore conservation strategies to mitigate these effects.

In a global analysis of over 30,000 species of amphibians, birds, mammals and reptiles, Heinicke et al. find that under a medium–high emissions scenario, by the end of the century 74% (on average) of the area within species’ current geographical ranges is projected to be exposed to heatwaves, and 16% to wildfires, 8% to droughts, 3% to river floods and 36% to multiple event types. These risks were substantially lower under low emissions scenarios.

What does such exposure mean ecologically? Two different analyses of contrasting recent extreme weather events give some insight into their complex effects. Baum et al. document impacts from the 2021 western North American heatwave on terrestrial and marine taxa, including insects, birds, mammals, intertidal invertebrates, fish, algae and plants. This event, commonly known as the ‘heat dome’, ranked globally as the sixth most extreme heatwave recorded since 1960 (with temperatures that reached as high as 49.6 ºC). Their synthesis finds that more than three quarters of all taxa were negatively affected, particularly sessile taxa such as mussels (which experienced 92% mortality).

Earlier in the same year as the heat dome, two severe winter storms brought high rainfall and historically cold temperatures to the south-central USA; this represented a compound climate event that caused widespread mortality of plants and animals, including mass mortality of purple martins (a species of migratory songbird). Stager et al. combine long-term citizen-science data with whole-genome sequencing to reveal severe demographic consequences for this species. Comparing populations before and after the storm, they reveal shifts in allele frequency among survivors, negative carry-over effects into subsequent breeding seasons, and increased breeding failures that are likely to persist for decades.

Jacobson et al. find that climate extremes linked to El Niño and La Niña events may also modify within-species behavioural interactions. Compiling more than 33 years of data on groups of white-faced capuchin monkeys in Costa Rica, they find that environmental variation alters the constraints that group size imposes on foraging and competition during unusually wet or dry years.

The effects of climate extremes on species are further evidenced in two analyses on forest responses. Clipp et al. analyse 20 years of data on pest damage to native trees across the USA in relation to bioclimatic variables that represent acute, extreme climate conditions, and find that pest damage is exacerbated in areas with the greatest rates of warming. Wu et al. map spatial patterns of resilience before and after extreme multiyear droughts; they find that multi-year droughts have occurred on all continents except Antarctica over the past 40 years, which has led to decreased resilience in more than 70% of global forests, with managed forests exhibiting lower resilience than undisturbed ones.

Another paper in this issue highlights the vulnerability of marine fish populations to increasing temperatures and heatwaves. Analysing more than 33,000 fish populations across almost 30 years, Chaikin et al. find that although chronic warming had little effect on cold-edge and warm-edge populations, acute heatwaves had distinct effects across species ranges: large biomass losses at the warm edge but biomass gains at the cold edge.

The variability demonstrated in these papers presents substantial challenges for strategies aimed at mitigating the impacts of extreme events, especially where they create cascading effects such as heatwaves increasing the likelihood of severe wildfires occurring (as happened with the 2021 North American heat dome). Only drastic cuts to global carbon emissions over the near term will ultimately be enough to reduce the frequency of extreme events and their effects on species and ecosystems, and efforts should be focused primarily on achieving that goal. In the meantime, conservation strategies such as species translocations, assisted evolution and anticipatory habitat management are being developed to help at-risk populations.

An iconic example of such planning is outlined in a Species Spotlight from Berin MacKenzie, which describes efforts to save the critically endangered Wollemi pine during the 2019–2020 megafires in Australia. The success of these efforts has now led to the development of similar wildfire action plans for a further 76 threatened plants and animals across Australia.

Similarly, a Comment by Valle et al. outlines ongoing discussions about integrating extinction risks from cyclones into conservation planning. Cyclones often affect island species disproportionately and where islands harbour endemic species, the risk of extinction is particularly severe. The authors propose a general framework for generating coordinated, proactive and evidence-based strategies for managing these species in the event of extreme events.

These and other studies highlight that substantial knowledge gaps remain in predicting and managing the immediate and long-term ecological consequences of extreme events, particularly on the effects of compound events. Improving our mechanistic understanding of these impacts will go some way towards improved mitigation, but ultimately the most effective safeguard for biodiversity will be not in managing the aftermath, but in reducing the frequency of their occurrence, and their severity, via a rapid reduction in greenhouse gas emissions.