It has been half a century since governments around the world, faced with overwhelming evidence, started banning early generations of what we now call forever chemicals. Industrial chemicals known as polychlorinated biphenyls, or PCBs, and the notorious pesticide DDT had been widely used – DDT is credited with saving millions of lives from insect-borne disease, while PCBs were vital in electrical safety – before it was understood that they were serious environmental toxins.
“The problem with these legacy contaminants,” environmental scientist Chantel Foord says, “is that they’re amazing in our products because they don’t break down, but they’re equally devastating in our environment because they don’t break down.”
Last year, Earth experienced its hottest year on record ? for the fourth year in a row. Rising temperatures are changing the way water moves around our planet, wreaking havoc on the water cycle.
The 2024 Global Water Monitor Report released today shows how these changes are driving extreme events around the world. Our international team of researchers used data from thousands of ground stations and satellites to analyse real-time information on weather and water underground, in rivers and in water bodies.
We found rainfall records are being broken with increasing regularity. For example, record-high monthly rainfall totals were achieved 27% more frequently in 2024 than at the start of this century. Record-lows were 38% more frequent.
Water-related disasters caused more than 8,700 deaths and displaced 40 million people in 2024, with associated economic losses topping US$550 billion (A$885 billion). The number and scale of extreme weather events will continue to grow, as we continue pump greenhouse gases into an already overheated atmosphere. The right time to act on climate change was about 40 years ago, but it’s not too late to make a big difference to our future.
Humanity in hot water
Warmer air can hold more moisture; that’s how your clothes dryer works. The paradoxical consequence is that this makes both droughts and floods worse.
When it doesn’t rain, the warmer and drier air dries everything out faster, deepening droughts. When it rains, the fact the atmosphere holds more moisture means that it can rain heavier and for longer, leading to more floods.
Ferocious floods
Torrential downpours and river floods struck around the world in 2024.
In Papua New Guinea in May and India in July, rain-sodden slopes gave way and buried thousands of people alive. Many will never be found.
In southern China in June and July, the Yangtze and Pearl Rivers flooded cities and towns, displacing tens of thousands of people and causing more than US$500 million (A$805 million) in crop damages.
In Bangladesh in August, heavy monsoon rains and dam releases caused river flooding. More than 5.8 million people were affected and at least one million tonnes of rice were destroyed.
Meanwhile, Storm Boris caused major flooding in Central Europe in September, resulting in billions of euros in damage.
Across western and central Africa, riverine floods affected millions of people from June to October, worsening food insecurity in an already vulnerable region.
Other parts of the world endured crippling drought last year.
In the Amazon Basin, one of the Earth’s most vital ecosystems, record low river levels cut off transport routes and disrupted hydropower generation. Wildfires driven by the hot and dry weather burned through more than 52,000 square kilometres in September alone, releasing vast amounts of greenhouse gases.
In southern Africa, drought reduced maize production by more than 50%, leaving 30 million people facing food shortages. Farmers were forced to cull livestock as pastures dried up. The drought also reduced hydropower output, leading to widespread blackouts.
A rapidly changing climate
Over recent years, we have become used to being told the year just gone was the warmest on record. We will be told the same thing many times more in years to come.
Air temperatures over land in 2024 were 1.2°C warmer than the average between 1995 and 2005, when the temperature was already 1°C higher than at the start of the industrial revolution. About four billion people in 111 countries – half of the global population ? experienced their warmest year yet.
The clear and accelerating trend of rising temperatures is speeding up an increasingly intense water cycle.
Further change is already locked in. Even if we stopped releasing greenhouse gases today, the planet would continue warming for decades. But by acting now we still have time to avoid the worst impacts.
First, we need to cut greenhouse gas emissions as quickly as possible. Every tonne of greenhouse gas we do not release now will help reduce future heatwaves, floods and droughts.
Second, we need to prepare and adapt to inevitably more severe extreme events. That can mean stronger flood defences, developing more drought-resilient food production and water supplies, and better early warning systems.
Climate change is not a problem for the future. It’s happening right now. It’s changing our landscapes, damaging infrastructure, homes and businesses, and disrupting lives all over the world.
The real question isn’t if we should do something about it — it’s how quickly we still can.
The following people collaborated on the 2024 report: Jiawei Hou and Edison Guo (Australian National University), Hylke Beck (King Abdullah University of Science and Technology, Saudi-Arabia), Richard de Jeu (Netherlands), Wouter Dorigo and Wolfgang Preimesberger (TU Wien, Austria), Andreas Güntner and Julian Haas (Research Centre For Geosciences, Germany), Ehsan Forootan and Nooshin Mehrnegar (Aalborg University, Denmark), Shaoxing Mo (Nanjing University, China), Pablo Rozas Larraondo and Chamith Edirisinghe (Haizea Analytics, Australia) and Joel Rahman (Flowmatters, Australia).
Albert Van Dijk does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.
Christina Druery-Chiconi opened the farm north of Brisbane to families in her neighbourhood, including children with autism, trauma and speech impediments.
Monarch butterflies (Danaus plexippus) appear to be declining not just in North America but also in Australiasia. Could this be a consequence of global change, including climate change, the intensification of agriculture, and urbanisation?
We need more citizen scientists to monitor what is really going on.
Insect populations, even species that seemed impervious, are in decline globally. Monarch butterflies exemplify the problem. Once a very common species, numbers have declined dramatically in North America, engendering keen public interest in restoring populations.
The monarch butterfly is an iconic species. It is usually the species people recall when drawing a butterfly and observations are shared frequently on the online social network iNaturalist.
This is partly because monarch images are used in advertising, but the butterflies are also a species of choice for school biology classes and television documentaries on animal migration.
Monarchs in the southern hemisphere
Monarchs expanded their range to reach Australia and New Zealand during the mid-1800s.Kathy Reid, CC BY-SA
The monarch butterfly’s ancestral home in North America is noted for an annual mass migration and spectacular overwintering of adults in fir forests in a few locations in Mexico, at densities of 50 million per hectare, and at multiple sites in Southern California. These sites are monitored to track the decline.
What is not as well known is that this butterfly greatly extended its range, spreading across the Pacific in the mid-1800s to reach Australia and New Zealand by riding on storms that blew in from New Caledonia.
The species is now part of the roadside scene in these countries and was once known as “the wanderer” – reflecting its propensity to fly across the landscape in search of milkweed plants (known as swan plants in New Zealand). In both countries, monarchs lay eggs on introduced milkweed species for their caterpillars to feed and develop. They take up the plant’s toxins as part of their own defence.
Interestingly, in their expanded range in the southern hemisphere, monarchs have adapted their migration patterns to suit local conditions. They have established overwinter sites – places where large numbers of adults congregate on trees throughout winter.
Need for citizen science
In Australia, the late entomologist Courtenay Smithers organised people to report these sites and participate in a mark-recapture programme. Essentially, this involves attaching a small unique identifying tag to the wing, noting the age and condition of the butterfly and the date and location of capture.
If the same individual is then recaptured sometime later and the information shared, it provides valuable data on survival and the distance and direction it moved, and even population size. This volunteer tagging programme enabled many aspects of the monarch’s ecology in Australia to be documented, but it was discontinued a few years ago.
Moths and Butterflies Australasia now hosts the butterfly database and has become an umbrella group for encouraging everyone with a mobile phone to get involved and report and record sightings.
Monarchs have established wintering sites in New Zealand and Australia.Kathy Reid, CC BY-SA
A similar programme is run in New Zealand by the Moths and Butterflies of New Zealand Trust. Monarch overwintering sites and local breeding populations have been documented over the years. Alas, these data sets have been short term and haphazard.
What is intriguing is that populations appear to have declined in Australia and New Zealand, perhaps reflecting climate variability, expanding cities gobbling up local breeding habitats, and the intensification of agriculture.
What we need is reliable long-term data on adult numbers. Hence the call to reinvigorate interest in mark-recapture and reporting. We need the help of people who love the outdoors and love the monarch butterfly to become citizen scientists.
Citizen scientists are needed to help with tagging monarch butterflies.Anna Barnett, CC BY-SA
The Moths and Butterflies of New Zealand Trust is asking individuals, groups and schools to tag monarch butterflies late in the autumn when the butterflies head for their overwintering habitat. This is a great project for schools, involving students in real science and addressing an environmental issue.
Each tag has a unique code. A computer system calculates the distance the monarch has flown and the time it took to get there. This information can then be collated with weather data to get a clearer picture of what is happening.
We hope people will spot tagged monarchs in their gardens and record where the butterfly was sighted, together with its tag number.
The author wishes to thank Washington State University entomologist David James and Moths and Butterflies of New Zealand trustee Jacqui Knight for their input, and Australian National University ecologist Michael Braby for comments.
Myron Zalucki does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.
