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Carbon sinks extract carbon dioxide from the atmosphere and absorb more carbon than they release. Carbon sources, conversely, release more carbon than they absorb. They cover about 30% of the Earth’s land surface and as much as 45% of the carbon stored on land is tied up in these sinks. Carbon sinks are therefore an essential means of helping fight climate change, but without major changes to current human practices, they are unable to mitigate the detrimental effects alone. 

The Carbon Cycle 

The carbon cycle refers to the natural flow of carbon between the ocean, rocks, fossil fuels and living organisms. Forests are examples of carbon sinks as trees and plants extract carbon dioxide from the atmosphere through photosynthesis – some is also stored. When plants die, the carbon dissolves into the soil where microbes are then able to release the carbon back into the atmosphere by process of decomposition, where it’s available to other plants for photosynthesis.

Oceans are considered to be the main natural carbon sinks, absorbing approximately 50% of the carbon emitted into the atmosphere. Plankton, corals, fish, algae and other photosynthetic bacteria contribute to this extraction of carbon

Any process that uses fossil fuels – such as burning coal to generate electricity – releases more carbon into the atmosphere than carbon sinks can absorb. Cattle farming also releases a lot of carbon into the atmosphere. It also contributes to deforestation, depleting the planet of its carbon sinks; according to the World Resources Institute, farms emitted 6.6 billions tons of greenhouse gases in 2011, equivalent to about 13% of total emissions. The agricultural sector is the world’s second largest emitter of GHGs, after the energy sector. 

Ideally, the carbon cycle would maintain Earth’s carbon concentration, helping to move carbon from one location to the next and keeping atmospheric carbon levels stable. However, due to human activity, the carbon cycle is changing: we are releasing more carbon into the atmosphere than Earth can handle by using fossil fuels and maintaining large livestock operations. Deforestation is further exacerbating this problem as it depletes the Earth’s  supply of carbon sinks. Since 2016, an average of 28 million hectares have been cut down every year, equivalent to one football field of forest lost every second. Consequently, the amount of carbon in the atmosphere is rising. 

Solutions to combat this problem include banning deforestation, planting more trees, utilising renewable energy sources and reducing the use of fossil fuels.

Carbons Sinks Examples

Aside from the aforementioned oceans being the main natural carbon sink in the world, forests are also significant carbon sinks examples as well. According to a report published in January 2021, forests absorb twice as much carbon as they release each year,  absorbing a net 7.6 billion metric tonnes of carbon dioxide annually.

As the world’s largest and best known tropical rainforest, the Amazon accounts for just over a third of tree cover across the tropics and is one of the most important natural carbon sinks in the world.  Their role is more important than ever especially as the world’s carbon emissions exponentially increase over the last few decades. However, recent studies have recorded the Amazon releasing higher carbon emissions than absorbing it due to deforestation and higher rates of wildfires.

Similarly, mangroves are highly regarded in their role of absorbing and capturing carbon in the atmosphere, and in fact, have been known to be a more effective carbon sink than forests. Mangroves have been recorded to absorb almost 10 times as much carbon dioxide from the atmosphere than terrestrial forests. Indonesia currently boasts the world’s largest mangrove ecosystem, accounting 23% of the world’s total.

Recent research in what has been dubbed as the world’s largest seagrass project, has also found seagrass to be a particularly effective carbon sink and hugely successful in restoring oceans and  purifying the water.

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carbon sinks

(Source: Earth.Org) 

Artificial Techniques 

In addition to natural carbon sinks, technological advances have helped produce artificial techniques that extract carbon from the atmosphere. 

Examples include: using geological carbon sequestration techniques that inject carbon dioxide into deep saline aquifers to produce large pockets of salt water; injecting carbon dioxide emissions from coal-fired power stations deep under the Earth’s surface and using light-sensitive algae that are capable of absorbing carbon dioxide and emitting oxygen.

Artificial technologies, however, are not efficient or advanced enough to cope with the effects of the climate crisis. Investing in research and companies who commit to finding alternate ways of extracting carbon dioxide from the atmosphere will prove worthwhile.

Greenhouse gases, particularly CO2, methane and nitrous oxide, have reached record levels despite COVID-19- induced lockdowns, according to the UN’s World Meteorological Organization (WMO)

The WMO Greenhouse Gas Bulletin shows that atmospheric CO2 is now 50% higher than in 1750 before the Industrial Revolution, hitting record levels not seen in up to 5 million years. CO2 traps two-thirds of the heat retained on the Earth’s surface by greenhouse gases and this warming effect has increased by 45% since 1990. Methane is responsible for 17% of this heating effect and its concentration is now 2.5 times pre-industrial levels. Additionally, nitrous oxide is now 23% higher than in 1750.

What is Happening?

The results show that not enough is being done to curb the increase in greenhouse gases. Emissions need to fall by half by 2030 to keep global heating to 1.5 degrees Celsius. 

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Petteri Taalas, the WMO secretary-general, says, “The lockdown-related fall in emissions is just a tiny blip on the long-term graph. We need a sustained flattening of the curve. We breached the global [annual] threshold of 400ppm in 2015 and, just four years later, we have crossed 410ppm. Such a rate of increase has never been seen in the history of our records.”

He continues, “CO2 remains in the atmosphere for centuries. The last time the Earth experienced a comparable concentration was 3m-5m years ago, when the temperature was 2-3C warmer and sea level was 10-20 metres higher than now. But there weren’t 7.7 billion [human] inhabitants.”

While many countries have pledged to either drastically reduce their emissions or have committed to carbon neutrality- a welcome move- so much more needs to be done to stave off the worst effects of climate change, such as extreme weather events and droughts or floods.

Featured image by: Flickr

According to a study published in the journal Nature Scientific Reports, the amount of atmospheric carbon dioxide (CO2) is approaching levels not seen in 15 million years and perhaps never experienced by hominoids. 

Atmospheric CO2 Levels Over Geologic Time

The study shows that within five years, atmospheric CO2 will pass 427 parts per million, which was the probable peak of the mid-Pliocene warming period 3.3 million years ago, when temperatures were 3C to 4C hotter and sea levels were 20 metres higher than today. 

Around 2025, the Earth is likely to have CO2 conditions not experienced since the Middle Miocene Climatic Optimum 15 million years ago, when our ancestors are thought to have diverged from orangutans.

Researchers from the University of Southampton were able to construct high-resolution records of atmospheric CO2 levels thought to be prevalent during the Pliocene epoch. This was achieved by deriving data from the boron levels in extremely small fossils collected from the Caribbean Sea. 

Their findings were able to confirm previous trends observed in ice cores, and enabled the researchers to build on this data in order to generate precise estimations of CO2 when solar radiation matched the levels observable today.

“A striking result we’ve found is that the warmest part of the Pliocene had between 380 and 420 parts per million CO2 in the atmosphere,” Thomas Chalk, one of the contributing researchers, said. “This is similar to today’s value of around 415 parts per million, showing that we are already at levels that in the past were associated with temperature and sea-level significantly higher than today.”

“Currently, our CO2 levels are rising at about 2.5 ppm per year, meaning that by 2025 we will have exceeded anything seen in the last 3.3 million years,” one of the researchers of the study said. 

The study outlines how data about what the climate was like in the past can assist in predicting what the climate is likely to be like in the future, which is especially important in formulating a response to the increase in atmospheric greenhouse gas emissions that have accumulated over the past two centuries as a result of industrialisation. 

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What Does this Mean for the Future of Earth’s Climate?

Gavin Foster, a professor of isotope geochemistry at the University of Southampton and contributor to the study, says, “Ice sheets today haven’t had a chance to catch up with CO2 forcing. We are burning through the Pliocene and heading towards a Miocene-like future.” 

During the Middle Miocene epoch, ice sheets shrank further and sea levels were significantly higher than the Pliocene- which Foster stated had occurred prior to any human habitation or evolution. This raises concerns about what the Earth’s future climate is going to be like given the burden of human-induced pollution. 

What is Being Done?

The rise in temperature trajectory for the current era is being addressed as part of a new international collaboration coordinated by the World Meteorological Organisation (WMO), led by the UK’s Met Office. In what will be an annually-updated five-year climate prediction, scientists and researchers alike stressed that there is a 20% chance the Earth will reach 1.5 degrees Celsius warming above pre-industrial levels before 2025.

The WMO secretary-general, Petteri Taalas, says, “this study shows – with a high level of scientific skill – the enormous challenge ahead in meeting the Paris Agreement on climate change target of keeping a global temperature rise this century well below 2C above pre-industrial levels and to pursue efforts to limit the temperature increase even further to 1.5C.” 

Carbon dioxide (CO₂) emissions have rebounded globally to average levels as lockdown conditions as a result of the pandemic have eased, raising fears that annual emissions of greenhouse gases could surge to higher levels than ever before once pandemic conditions abate.

Overall emissions fell by 25% when lockdowns were at their peak. The Integrated Carbon Observation System (ICOS) reported a peak decrease of 26% in daily global CO₂ emissions. However, emissions rebounded to within 5% of mean 2019 levels in early June as countries lifted or weakened their confinement policies. 

“Things have happened very fast,” said Corinne Le Quéré, a professor of climate change at the University of East Anglia and the lead author of the studies. “Very few countries still have stringent confinement. We expected emissions to come back, but that they have done so rapidly is the biggest surprise.” 

Emissions from January 1 to June 11 are currently 8.6% lower than in the same period for 2019 and the 2020 annual emissions are likely to be between 4% to 7% lower than for the whole of last year, which is not a enough to make a significant contribution to the cuts in emissions needed to fulfil the Paris Agreement. To do so will require structural changes to transport systems and how energy generation.

Emissions in the UK had fallen by 31% in early April when the lockdown was at its peak, however emissions during the week of June 11 were found to be 23% lower than those of last year’s. The reduction is set to shrink further as lockdown measures are further eased. 

Most of the fall and rebounds in emission have come from road transport. Le Quéré says, “Emissions from transport were always going to go back up, but government responses have not been as fast as I would have liked [to make changes to people’s driving habits.] It would be terrible if we carry on going back to normal. It would be a disaster.”  

Air pollution has not rebounded as fast as CO₂ emissions in Europe. Monitoring services have found that the expected increase in pollutants such as nitrogen oxides and particles was not yet apparent. However, concentrations of fine particles and nitrogen dioxide across China are now at the same levels as one year earlier, with indications that Europe will soon follow. 

While emissions overall are still down on last year, there are concerns that as lockdowns around the world ease further in the upcoming months, carbon dioxide emissions from cars could surge to levels higher than pre- pandemic levels as people avoid public transport.

Le Quéré added that the role of governments around the world would be key. She stated that the government should not be blinded by its goal to boost the economy, but instead should be aware of the possible climate change impacts that the surge in emissions could yield. Governments should use their economic rescue packages to encourage a switch to low carbon infrastructure, renovate buildings to make them more energy efficient and plant trees. “The window of opportunity will not be closed until the end of the year” she said. “But after that it will be closed.” 

Richard George of Greenpeace UK said focusing on a green recovery should be an urgent priority. “All efforts now need to be focused on supporting a green economic recovery, creating jobs and boosting clean technologies. We have a once-in-a-lifetime opportunity to create a permanent silver lining. Let’s not throw it away”. 

New research shows that tropical forests are taking up less carbon dioxide from the atmosphere, reducing their ability to act as ‘carbon sinks’ and instead becoming sources of carbon. What does this mean for the future of humanity?

The Amazon could turn into a source of carbon instead of one of the biggest absorbers of the gas as soon as the next decade, as a result of the damage caused by loggers and farming interests and the impacts of the climate crisis, according to new research in the journal, Nature

How much carbon is stored in tropical rainforests?

Intact tropical forests sequestered almost 50% of the global terrestrial carbon uptake over the 1990s and early 2000s, removing about 15% of carbon dioxide emissions. A new report shows that these carbon sinks are becoming saturated in both Amazonian and African rainforests, with different patterns of change. 

“We’ve found that one of the most worrying impacts of climate change has already begun,” said Simon Lewis, professor in the school of geography at Leeds University, one of the senior authors of the research. “This is decades ahead of even the most pessimistic climate models.”

These rainforests are now taking up a third less carbon than they did in the 1990s, owing to the impacts of higher temperatures (trees have only partially acclimated to recently rising temperatures), droughts and deforestation. This downward trend is likely to continue, as forests come under increasing threat from the climate crisis and exploitation. According to Lewis, the typical tropical forest may become a carbon source by the 2060s. 

Tropical rainforests act as net carbon sinks when the amount of carbon gained through the establishment of new trees and tree growth is larger than the amount lost through tree mortality. In these circumstances, the quantity of carbon stored in the biomass increases over time. 

The researchers of the study monitored tree establishment, growth and mortality in 244 undisturbed forest plots in Africa across 11 countries between 1968 and 2015. This data was then compared with similar measurements from 321 plots in the Amazonian region. The results showed that carbon uptake in the Amazonian region started to decline around 1990, whereas signs of a potential slowdown in Africa appeared in 2010. 

The uptake of carbon from the atmosphere by tropical forests peaked in the 1990s when about 46 billion tonnes were removed from the atmosphere, equivalent to about 17% of carbon emissions from human activities. By the last decade, that amount had sunk to about 25 billion tonnes, or 6% of global emissions, similar to a decade of fossil fuel emissions from the UK, Germany, France and Canada put together. 

According to the report, by 2030, the carbon sink in Africa will be 14% lower than in 2010-2015, while the Amazonian carbon sink will reach zero by 2035 (meaning that there will be no more net carbon uptake from the atmosphere). 

The researchers say that the reason for this difference between Amazonian and African tropical forests is because of increasing mean annual temperatures and droughts since 2000 that have reduced tree growth, offsetting the increase in carbon uptake. These reductions are smaller in Africa than in Amazonia.

Tropical Forests Losing Ability to Store Carbon
A figure showing estimated declines of carbon dioxide intake. By 2030, the carbon sink in Africa will be 14% lower than in 2010-2015, while the Amazonian carbon sink will reach zero by 2035 (Source: Nature).

Further, the higher carbon gains persisted for longer in Africa than in Amazonia because the warming rate was slower, there were fewer droughts and air temperatures were generally lower (because African forests are located at higher elevations). Generally, trees in Amazonia grow faster and have shorter residence times than those in African forests. 

According to the report, the carbon sink strength of the world’s two most extensive tropical forests ‘have now saturated’. Reaching emissions reduction targets counts largely on the continuation of a large tropical carbon sink, which are disappearing at a rapid rate and could soon turn into carbon sources by the end of the decade. The protection of these tropical forests as well as faster greenhouse gas emissions will be needed to prevent catastrophic climate changes. 

This year’s UN climate talks, Cop26, will most likely see many countries coming forward with plans to reach net zero emissions by mid-century. This will be crucial in the fight against anthropogenic global warming.

Featured image by: Jonathan Hull

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