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Ecosystems on land absorb everything from rainforests to savannas. Nearly 30%of the carbon dioxide that human activities have released into the atmosphere. These ecosystems are critical to stop the planet warming beyond 1.5℃ this century – but climate change may be weakening their capacity to offset global emissions.
This is a critical issue. OzFluxThe, an Australian and Aotearoa new Zealand-based research network, has been studying the topic for 20 years. Over this time, we’ve identified which ecosystems absorb the most carbon, and have been learning how they respond to extreme weather and climate events such as drought, floods and bushfires.
Savannas and temperate forest are Australia’s largest absorbers of atmospheric carbon dioxide. However, as climate change worsens, ecosystems like these are at high risk of tipping points. collapse.
In our latest Research paper, we look back at the two decades of OzFlux’s findings. The resilience of the ecosystems that we studied has been demonstrated by their ability to quickly return to being carbon sinks after a disturbance. This can be observed in the growth of leaves on trees shortly after bushfire.
But how long can this resilience last? Evidence suggests that carbon sinks may be less able to recover from climate-related disasters as climate change pressures grow. This highlights vital gaps in our knowledge.
150 million tonnes of carbon are absorbed each year by Australian ecosystems
Between 2011 and 2020, land-based ecosystems were sequestered 11.2 Billion tonnes (29%) of global CO₂ emissions. To put this into perspective, that’s Similar in many waysTo the amount China emitted by 2021.
OzFlux has made it possible to conduct the first comprehensive assessment on Australia’s carbon budgetFrom 1990 to 2011. This found Australia’s land-based ecosystems accumulate some 150 million tonnes of CO₂ each year on average – helping to offset national fossil fuel emissions by around one third.
For example, every hectare of Australia’s temperate forests absorbs 3.9 tonnes of carbon in a year, OzFlux data. Likewise, every hectare of Australia’s savanna absorbs 3.4 tonnes of carbon. This is 100 times more than a hectare Mediterranean woodland or shrubland.
But it’s important to note that the amount of carbon Australian ecosystems can sequester fluctuates widely from one year to the next. This is due to, for instance, the natural climate variability (such as in La Niña or El Niño years), and disturbances (such as fire and land use changes).
In any case, it’s clear these ecosystems will play an important role in Australia reaching its target of net-zero emissions by 2050. But how effective will these ecosystems continue to be in the face of climate change?
These carbon sinks are being affected by climate change
Extreme climate variability – Flooding rains, Drought Heatwaves – along with bushfires and land clearing, can weaken these carbon sinks.
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While many Australian ecosystems are resilient to these stressors, we found that they may be less resilient to more frequent and severe events. This could lead to a decrease in their long-term contribution to offset emissions.
Consider bushfire as an example. The carbon stored in plants is released into the atmosphere as smoke when it burns a forest. This makes the ecosystem a carbon source. Likewise, under drought or heatwave conditions, water available to the roots becomes depleted and limits photosynthesis, which can tip a forest’s carbon budget from being a sink to a carbon source.
If the drought or heatwave continues for a long period of time or a bushfire occurs before the forest has recovered, it is at risk of losing its status as a carbon sink.
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Globally, it can be beneficial to learn how carbon sinks might shift in Australia or New Zealand. Both countries are home to a broad range of climates – from the wet tropics, to the Mediterranean climate of southwest Australia, to the temperate climate in the southeast.
These unique ecosystems were created to adapt to these diverse climates that are often underrepresented in the global network.
This means long-term ecosystem observatories – OzFluxAlong with the Terrestrial Ecosystem Research Network – provide a vital natural laboratory for understanding ecosystems in this era of accelerating climate change.
OzFlux’s 20-year history has been a major contributor to the international understanding on climate change. Some of its most important findings include:
Bryn Pinzgauer/Wikimedia, CC BY – SA
Critical questions remain
Australia and New Zealand plans to achieve net zero emissions in 2050 heavily depend on the ability of ecosystems and other sectors to sequester emissions from industry and transport.
This is despite the fact that some management and technological innovations have been made to address it, such as in agricultural sectorLong-term measurements of carbon cycle are necessary to fully understand it. Limits to ecosystemsTheir Risk of collapse.
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Indeed, we’re already in uncharted territory under climate change. Extreme weather events HeatwavesHeavy rainfall is becoming more frequent and more intense. And CO₂ levels are more than 50% higherThey are much more than they were 200-years ago.
AAP Image/Dan Himbrechts
Our ecosystems have remained a net drain over the years. Last 20 years, it’s worth asking:
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Will they continue to do the heavy lifting required to keep both countries on course to meet their climate targets.
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how do we protect, restore and sustain the most vital, yet vulnerable, ecosystems, such as “coastal blue carbon” (including seagrasses and mangroves)? These are vital for nature-based climate solutions
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how do we monitor and verify national carbon accounting schemes, such as Australia’s Emissions Reduction Fund?
Critical questions remain about how well Australia’s and New Zealand’s ecosystems can continue storing CO₂.
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“Existential threat to our survival”: See the 19 Australian ecosystems that are already in decline
