The global
warming potential is a measure of how much heat a greenhouse gas traps in
the atmosphere over a specific time period compared to CO2. Methane’s GWP is
estimated to be 28-34 times greater than that of CO2 over a 100-year period.
This means that methane has a much stronger impact on global warming per unit
of mass emitted than CO2 does over a century.
The increase in temperature and
substrate availability can potentially boost methane (CH4) production in soil microbes.
However, warming also enhances processes like aerobic and anaerobic CH4 oxidation,
while changes in inundation areas may counteract the increase in CH4 production.
In the Boreal-Artic region, both positive and negative trends in CH4 emissions
have been observed, leading to uncertainty in assessments due to factors such
as the representation of biogeochemical processes, atmospheric transport, wetland
emissions, and limited ground observations.
The amount of methane emitted from wetlands in the
Boreal-Arctic region is still not very well understood. Previous estimates have
varied widely, ranging from about 9 to 53 million tons of methane per year.
Different models used to estimate these emissions also provide conflicting results,
with some suggesting higher emissions than others. The uncertainty in these
estimates is actually larger than the emissions they’re trying to measure. In
fact, the uncertainty in Boreal-Arctic wetland methane emissions is twice as
big as the total changes in methane level in the Earth’s atmosphere each year,
which makes it hard to draw definite conclusions about how much methane is
coming from natural sources versus human activities, impacting our understanding
of the global methane budget.
To better understand and accurately estimate methane
emissions from wetlands in a specific region, researchers need to improve their
knowledge and models regarding how these emissions are influenced by various
environmental factors. Previous studies have shown that methane emissions from
wetlands are affected by temperature, as well as other factors like water levels,
types of vegetation, microbial communities, and the availability of certain substances.
These relationships between methane emissions and environmental conditions can
be quite complex and can involve delays or interactions between different
processes. These factors can significantly impact both the timing and amount of
methane released from wetlands, yet they haven’t been fully taken into account
when studying how wetlands in the Boreal-Arctic region might respond to climate
change.
Moreover, methane emissions from wetlands in the
Boreal-Arctic region vary greatly in space and time, emphasizing the importance
of collecting data from a wide range of locations to improve the models. Eddy
covariance (EC) measurements, shown as red circles in the figure below, have
been collected since 2006 but are mainly from non-hotspot wetlands. Chamber observations,
depicted as yellow circles in the same figure, extend beyond the years of EC observations and
cover hotspot regions like the Western Siberian lowlands (WSL) and Hudson Bay lowlands
(HBL). By combining data from EC and chamber measurements, researchers can
enhance their understanding of methane emissions across different areas and periods,
although integrating these data poses challenges due to their differing spatial
and temporal scales.
 |
| Figure: Spatial distribution of the long-term averaged wetland CH4 emissions in the Boreal–Arctic upscaled by combining chamber and EC datasets. (Sourced from: Yuan et al. (2024), CC BY 4.0 DEED) |
In the research titled "Boreal–Arctic wetland methane emissions modulated by warming and vegetation activity," scientists from the USA quantified the decadal responses of wetland methane (CH4) emissions to environmental changes in the Boreal-Arctic region. They analyzed the lagged dependence of CH4 emissions on various environmental factors, using the largest dataset of Boreal-Arctic CH4 compiled to date, which includes data from both EC towers and chamber measurements. This dataset consists of 139 site years of EC measurements and 168 site years of chamber measurements, sampled across both hotspot and non-hotspot regions.
The long-Term Changes in Wetland Methane Emissions Over Dacades
Using a machine learning model guided by causal
relationships inferred from observations, the researchers generated an upscaled
dataset of Boreal-Arctic wetland CH4 emissions covering 2002 to 2021. This
approach led to higher accuracy compared to commonly used machine learning
methods. With the upscaled dataset, they investigated the main drivers
influencing the long-term trend and variability of CH4 emissions. Additionally,
they assessed the performance of BU and TD models involved in the most recent Global
Carbon Project - CH4 budget.
The latest
research on methane emissions from Boreal-Arctic wetlands, published in Nature
Climate Change, a prestigious journal of Nature, reveals some key findings. Between
2002 and 2021, these wetlands emitted an average of 20.3 ± 0.9 teragrams of
methane per year. Notably, over half of this methane came from just two hotspots:
the Western Siberian Lowlands (WSL) and the Hudson Bay Lowlands (HBL). The WSL
emitted around 6.6 teragrams annually, significantly more than the HBL’s 4.2
teragrams.
Moreover, there’s been a significant increasing trend
in methane emissions over this period, with an approximately 8.9% rise since
2002. This increase is mainly seen in the WSL and non-hotspot regions,
particularly during the boreal summer months. This coincides with observations
of increasing methane levels in the atmosphere, indicating that wetlands likely
serve as the main contributors to these emissions, particularly in the summer
months.
What's
driving methane emission variability in the Boreal-Arctic?
Over the past two decades, while there hasn’t been a
significant increase in the total area of wetlands in the Boreal-Arctic region,
research suggests that the rise in methane emissions is mainly due to changes
in emission intensity rather than the expansion of wetland areas. Temperature appears
to be the primary factor influencing methane emissions from these wetlands.
Additionally, vegetation activity also plays a role, potentially promoting the
transport of methane through plants and providing more organic material for
methane-producing microbes.
High methane emissions tend to occur during years with
annually warm temperatures, such as during major El Niño events. For instance,
the exceptionally warm year of 2016 saw a significant spike in methane emissions,
particularly in hotspot regions like the Western Siberian Lowlands. This increase
in emissions was attributed to the abnormally high temperatures associated with
the El Niño event.
Method of measuring
methane emission from the Boreal-Arctic Wetland
Scientists used
a dataset called WAD2M, which comes from satellite technology, to map wetlands.
Unlike traditional methods using cameras, this dataset can see through
vegetation and is better at spotting water. It also prevents counting the same
wetland multiple times in certain regions. They also used another dataset
called BAWLD to understand different types of wetlands like bogs, marshes,
etc., and to avoid counting the same wetland twice.
To cover a
wider range of wetlands, they included data from other sources too. They
gathered various environmental data like temperature, plant growth, water
levels, etc., because these factors affect methane emissions from wetlands. For
instance, they got plant growth data from a satellite called Orbiting Carbon
Observatory-2 and other environmental data from European datasets. To
understand methane emissions from wetlands, they collected data from different
sites across the Boreal–Arctic region, combining information from various
sources.
They used a
special computer model to predict methane emissions from wetlands. This model
is good at understanding cause-and-effect relationships in data. By using this
model, they could better predict how different factors influence methane
emissions from different types of wetlands. They analyzed which environmental
factors have the most impact on methane emissions from wetlands over the years. This helps them
understand what mainly influences methane emissions in different areas. They used a
statistical method to figure out how much changes in temperature, plant growth,
and water levels contribute to the overall trend of increasing methane
emissions from wetlands.
Consequences
of Modelling Methane Emissions from Wetlands
Scientists have long grappled with accurately
estimating methane emissions from Arctic wetlands. It turns out, most models
miss the mark, either overestimating or underestimating these emissions
compared to real-world data. The lack of accurate predictions spells trouble
for the future. With climate change driving warmer temperatures and altering
precipitation patterns, methane emissions from wetlands could soar. This means
more methane in the atmosphere, contributing to global warming. Underestimating
emissions sets off a dangerous chain reaction. As wetlands expand due to
thawing permafrost and increased rainfall, the underestimated emissions could
multiply, further fueling climate change.
Wetland methane emissions are a big deal in the
climate system. Ignoring or underestimating them means we’re missing a crucial
piece of the puzzle in our fight against global warming. By collecting
comprehensive datasets and considering factors like temperature and plant
processes, scientists can refine their models and make more accurate
predictions. This new dataset offers hope for better predictions. By
fine-tuning models and addressing gaps in our knowledge, scientists can paint a
clearer picture of future methane emissions and their impact on the climate.
Crucial
Insights
The
investigation into methane emissions from Boreal-Arctic wetlands uncovers an
important piece of the climate change puzzle. Despite the difficulties in
measuring these emissions, recent studies have revealed their significant role
and complexities. Methane, a potent greenhouse gas, is a major contributor to
global warming, with wetlands being key sources of its release.
Furthermore,
advancements in how we measure and predict methane emissions offer hope for
better understanding and managing their impact. By using detailed data and
considering factors like temperature and plant growth, scientists can improve
their models and provide more accurate predictions about future methane
emissions and their effects on the climate.
The importance of accurately estimating methane emissions from wetlands cannot be overstated. Ignoring these emissions hampers our ability to understand and tackle climate change effectively. As we work towards a greener future, ongoing research efforts and improved models are vital for addressing the challenges posed by methane emissions from Boreal-Arctic wetlands and their impact on our planet's climate.
References
Yuan, K., Li, F., McNicol, G. et al. Boreal–Arctic wetland methane emissions modulated by warming and vegetation activity. Nat. Clim. Chang. 14, 282–288 (2024). https://doi.org/10.1038/s41558-024-01933-3