417.88 ppm: tracking weekly climate news

Welcome to our regular segment on climate news stories you might have missed. The title refers to the daily average global concentration of carbon dioxide within the Earth’s atmosphere in parts per million (ppm) – meaning that for every million air particles, currently about 417.88 of them are CO₂.

The Amazon rainforest is approaching a tipping point

The Amazon rainforest is becoming less resilient – raising the risk of widespread dieback which would have profound implications for biodiversity, carbon storage, and climate change, new research has found.

Its resilience – the ability to recover from events such as droughts or fires – has declined consistently in more than three-quarters of the rainforest since the early 2000s and now shows characteristic signs of approaching a tipping point.

Scientists analysed 30 years of vegetation satellite data, finding more pronounced losses in drier areas and in regions within approximately 200km from human land use, such as large farms and settlements.

Their analysis indicates that this loss of resilience has brought the Amazon closer to a tipping point, where it risks undergoing an abrupt transition to a much drier habitat. The findings, published in Nature Climate Change, highlight the need to minimise human land use in the Amazon and limit greenhouse gas emissions globally.

El Niño events will only increase in frequency

The effects of La Niña have been particularly gnarly this year, with wild storms along the east coast of Australia and severe flooding in Queensland and New South Wales ongoing.

La Niña is part of a broader natural weather cycle known as the El Niño–Southern Oscillation (ENSO), but a new study has found that by 2040 we could see increased variability in the rain patterns associated with La Niña and El Niño, regardless of which climate emissions scenarios we follow.

The researchers used climate models to determine the “time of emergence” – the time when the signal of climate change is detectable from the normal background of natural climate variability – for changes in rainfall in the eastern equatorial Pacific.

They did this for four different emissions scenarios and found that, regardless of the emissions scenario, the best estimate of the time of emergence of changes converges on 2040. The research was published in Nature Climate Change.

This means El Niño events and associated climate extremes are now more likely “regardless of any significant mitigation actions” to reduce emissions, which might seem dire but is critical to know for future mitigation strategies and adaptation planning.

Caribbean coral reefs have been warming for at least 100 years

Climate change, as well as heating the atmosphere, heats the Earth’s oceans and results in the disruption of marine ecosystems. In particular, warming-induced changes to coral reefs – like coral bleaching events – have been documented worldwide.

Caribbean coral reefs have been warming since 1915 regionwide – and some sub-regions began warming even earlier during the second half of the 19th century – according to a new study.

Researchers built a database of over 5,000 Caribbean coral reefs, used three open-access datasets of satellite, and on-location sea-surface temperature observations to assess the history of warming from 1871 through 2020.

They found that Caribbean reefs have warmed by a total of 0.5 to 1°C in the past century, which suggests that if warming continues similarly these ecosystems will warm further by an average of about 1.5°C by the year 2100.

The study was published in PLOS Climate.

Climate change affects bird traits and behaviour

Climate change has impacted more than 60 different bird species, and half of all changes to key physical and behavioural characteristics since the 1960s can be linked to climate change – according to a new Australian study.

Focusing on birds in the United Kingdom and the Netherlands, the research found that the other 50% of changes are due to unknown environmental factors that have also changed at the same time as our climate. The findings were published in the Proceedings of the National Academy of Sciences.

Scientists used long-term datasets and statistical modelling to figure out to what extent the changes over time to three conditions – laying date, offspring number, and body condition – could be assumed to be due to increasing average temperatures.

“This study shows that the impact of climate change does not act in isolation and its effects are occurring in a world where the resilience of wildlife is already pushed to the limits due to the many other challenges they are experiencing in a human-dominated landscape,” says lead author Dr Nina McLean, from the Australian National University’s Research School of Biology.

High fire risk areas expected to increase by 2100

Driven by rising temperatures, by the end of the century we can expect a 29% increase in the area of the globe with frequent fire-prone conditions. For Australia in particular, the east coast and areas around Perth are likely to see some of the biggest increases in potential fire season.

Fire-prone areas in temperate regions and Northern Hemisphere boreal climates are expected to have the most significant expansion and lengthening of the fire season, according to a new climate modelling study, published in Nature Communications.