environment

Are we soaking up more CO2 than we think?

Satellites watching over New Zealand might show our forests are soaking up more CO2 than estimated - and leave us better off under international climate change commitments.

The rise in humanity’s technological prowess has undoubtedly impacted the Earth’s environment. However, though technology has played a role in creating these problems, it is also helping scientists understand and tackle them.  

Researchers are developing and implementing a sophisticated array of modern instruments to measure climate change factors and assist in building greenhouse gas inventories for our government and the United Nations. 

Increasingly, earth observation satellites are being used around the world to measure greenhouse gases and to catalogue associated influencers of climate change, such as changes in forestry stocks. 

New Zealand is part of this movement, developing earth observation data to understand and manage the country’s carbon footprint and track progress in meeting its Kyoto Protocol obligations. 

All things being equal, New Zealand would be expected to exceed our emissions cap for this commitment period of the Kyoto protocol. However, by using removals from forestry and a portion of the surplus units from the first Kyoto commitment period, we are projected to come in under forecast.

Under the Kyoto Protocol framework, net removals from forestry activities can be used to counter-balance gross emissions. Forests absorb CO2 from the atmosphere as vegetation grows, acting as a carbon sink. The carbon budget is the balance of the sources of greenhouse gas emissions put against carbon sinks. In this commitment period from 2013 to 2020, emissions and removals from forestry are projected to amount to 102.9 million tonnes of CO2 uptake - going some way to meet our 2020 targets. New Zealand is currently projected to recognise 26 million of surplus CP1 units to meet its 2020 target.  

Understanding and evaluating a whole country's carbon emissions and uptake is a monumental job, only possible through the use of advancing technology. Earth observation satellites, for example, offer scientists ways to measure these carbon sinks and find ways to harness and calculate the effect of them. 

Reading the tree leaves 

One of the programmes using earth observation in this way is the Ministry for the Enviroment’s Land Use Carbon Analysis System (LUCAS) – monitoring land use change for greenhouse gas reporting..  

This is just one of the many in place to monitor emissions and removals of greenhouse gases. Information is compiled and submitted to the UN as part of the Government’s ongoing international commitments. 

The primary purpose of LUCAS is to monitor how much of the country is occupied by forestry. Forestry levels are a key component in understanding NZ’s footprint, because they indicate the amount of carbon being removed from the atmosphere. 

Deborah Burgess is the leader of the mapping workstream within the LUCAS programme. She and her team use earth observation satellites to monitor all land use changes, but Burgess said a key focus is keeping track of the new planting and deforestation of forest stocks. 

“Using satellite imagery, we can capture the extent of the forest. Really importantly, we can monitor how deforestation is occurring – because that is a big emission.”  

“When we lose forest, through it being chopped down and converted to another land use, then we have to pay for that - it becomes a negative on our emissions balance sheet.” 

Under the Kyoto rules, New Zealand is able to claim carbon removals in all forests established after 1989.  In the early 1990’s there was a big push for forestry plantations and as a result, forestry stocks were built quickly..  

However, these plantations were commercial stock intended to be harvested for timber. The trees planted in the 1990s are now reaching maturity and are starting to be harvested. This was one of the major factors in why the most recent greenhouse inventories report shows net emissions have risen 63.6% since 1990 – because as well as creating more emissions, NZ has also lost a portion of its carbon sink to harvesting.

 As well as losing the benefit from these trees when harvested, timber stock also emits C02 as it decays or is burnt - meaning timber harvesting not only limits carbon removal but creates more carbon in the atmosphere. 

Compounding this problem is the shift in land use over the past several decades - with tree planting slowing and a portion of forestry land being converted into other uses, such as agriculture.  

Forestry has gone from offsetting over 5 percent of NZ’s greenhouse emissions in 1990, to around 30 percent in 2015. 

Though the trend is not moving in the desired direction, this depth of understanding of NZ’s emissions allows the Government to counter the rise. 

The technology used to create this data is evolving all the time, allowing researchers to create a better picture of carbon emissions and uptake. 

For instance, at the time the baselines were set, all data to monitor forestry levels was from the Landsat 4 and 5 satellites - which offered only 30 metres resolution.

Now, LUCAS uses the European Space Agency’s Sentinel satellites, which every five days provide a multi-spectral snapshot over parts of the country at 10 metres resolution, a far better view of what is going on.

Better identification of the vegetation has the potential to make the carbon budget more accurate, as different trees have properties which Burgess says may make them better or worse at removing C02 from the air.  

“A Douglas Fir, for instance, is a lot slower growing - so there is a lot longer until it is harvested.” 

Balancing the budget 

Technology can sense directly how much carbon is being offset by forestry stocks.  

Forestry performance is traditionally calculated by sampling the forests to determine the growth rate and measuring the total area of these forests.  

A new technique developed by NIWA carbon cycle scientist, Dr Sara Mikaloff-Fletcher, uses satellite sensors to look at where greenhouse gases are being emitted. 

Her work is in back-trajectory analysis. This is a new process in which she identifies ‘clouds’ of greenhouse gases using earth observation satellites and tracks them back to their source, as well as following their dispersal course after identification.  Her colleague at NIWA, atmospheric scientist Dave Pollard, describes the process as “a weather forecast in reverse” -  instead of using data to predict where the cloud is going, it predicts where it has come from.   

Through this study Mikaloff-Fletcher discovered a larger than anticipated carbon sink in Fiordland National Park. These findings could have massive consequences for our carbon calculations, as it was thought at NIWA that NZ’s mature indigenous forests were carbon neutral - with the trees drawing carbon dioxide out of the atmosphere as they grow, and then when they die, decomposing and giving it back. 

“But, this latest research suggests that we don’t understand that properly,” Pollard said. “Perhaps there is a process which could allow us to take more carbon dioxide in, than is let out.” 

Pollard said that the increasing amount of coverage satellites are offering means Mikaloff-Fletcher’s trajectories are only going to become more accurate. It might not even be necessary to run them because with the higher resolution these satellites offer, it will be possible to identify plumes of these greenhouse gases in real-time.  

In the long term, there is potential to learn what it is about Fiordland that creates an effective carbon sink - and use this to create a more effective ongoing carbon strategy for the country.

This is the third in a series by Newsroom contributor Baz MacDonald looking at how satellites and their big deluges of data are helping New Zealand industries and the economy. The first two are here and here.

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