Methanotrophs are especially common in or near environments where methane is produced, although some methanotrophs can oxidize atmospheric methane.
Their habitats include wetlands, soils, marshes, rice paddies,
landfills, aquatic systems (lakes, oceans, streams) and more. They are
of special interest to researchers studying global warming, as they play a significant role in the global methane budget, by reducing the amount of methane emitted to the atmosphere.
Methanotrophy is a special case of methylotrophy,
using single-carbon compounds that are more reduced than carbon
dioxide. Some methylotrophs, however, can also make use of multi-carbon
compounds; this differentiates them from methanotrophs, which are
usually fastidious methane and methanol oxidizers. The only facultative methanotrophs isolated to date are members of the genus Methylocella silvestris, Methylocapsa aurea and several Methylocystis strains.
In functional terms, methanotrophs are referred to as
methane-oxidizing bacteria. However, methane-oxidizing bacteria
encompass other organisms that are not regarded as sole methanotrophs.
For this reason, methane-oxidizing bacteria have been separated into
subgroups: methane-assimilating bacteria (MAB) groups, the
methanotrophs, and autotrophic ammonia-oxidizing bacteria (AAOB), which cooxidize methane.
Classification
Methanotrophs can be either bacteria or archaea. Which methanotroph species is present is mainly determined by the availability of electron acceptors.
Many types of methane oxidizing bacteria (MOB) are known. Differences
in the method of formaldehyde fixation and membrane structure divide
these bacterial methanotrophs into several groups. There are several
subgroups among the methanotrophic archaea.
Aerobic
Under aerobic conditions, methanotrophs combine oxygen and methane to form formaldehyde,
which is then incorporated into organic compounds via the serine
pathway or the ribulose monophosphate (RuMP) pathway, and carbon
dioxide, which is released. Type I and type X methanotrophs are part of
the Gammaproteobacteria and they use the RuMP pathway to assimilate carbon. Type II methanotrophs are part of the Alphaproteobacteria
and use the serine pathway of carbon assimilation. They also
characteristically have a system of internal membranes within which
methane oxidation occurs. Methanotrophs in Gammaproteobacteria are known from the family Methylococcaceae. Methanotrophs from Alphaproteobacteria are found in families Methylocystaceae and Beijerinckiaceae.
In some cases, aerobic methane oxidation can take place in anoxic environments. "CandidatusMethylomirabilis oxyfera" belongs to the phylum NC10
bacteria, and can catalyze nitrite reduction through an "intra-aerobic"
pathway, in which internally produced oxygen is used to oxidise
methane. In clear water lakes, methanotrophs can live in the anoxic water column, but receive oxygen from photosynthetic organisms, which they then directly consume to oxidize methane.
Under anoxic conditions, methanotrophs use different electron acceptors for methane oxidation. This can happen in anoxic habitats such as marine or lake sediments, oxygen minimum zones, anoxic water columns, rice paddies and soils. Some specific methanotrophs can reduce nitrate, nitrite, iron, sulfate,
or manganese ions and couple that to methane oxidation without
syntrophic partner. Investigations in marine environments revealed that
methane can be oxidized anaerobically by consortia of methane oxidizing archaea and sulfate-reducing bacteria. This type of anaerobic oxidation of methane
(AOM) mainly occurs in anoxic marine sediments. The exact mechanism is
still a topic of debate but the most widely accepted theory is that the archaea use the reversed methanogenesis
pathway to produce carbon dioxide and another, unknown intermediate,
which is then used by the sulfate-reducing bacteria to gain energy from
the reduction of sulfate to hydrogen sulfide and water.
The anaerobic methanotrophs are not related to the known aerobic
methanotrophs; the closest cultured relatives to the anaerobic
methanotrophs are the methanogens in the orderMethanosarcinales.
In 2010 a new bacterium Candidatus Methylomirabilis oxyfera from the phylum NC10 was identified that can couple the anaerobic oxidation of methane to nitrite reduction without the need for a syntrophic partner. Based on studies of Ettwig et al., it is believed that M. oxyfera oxidizes methane anaerobically by utilizing oxygen produced internally from the dismutation of nitric oxide into nitrogen and oxygen gas.
Taxonomy
Many
methanotrophic cultures have been isolated and formally characterized
over the past 5 decades, starting with the classical study of
Whittenbury (Whittenbury et al., 1970). Currently, 18 genera of
cultivated aerobic methanotrophic Gammaproteobacteria and 5 genera of Alphaproteobacteria are known, represented by approx. 60 different species.
Methane oxidation
RuMP pathway in type I methanotrophs
Serine pathway in type II methanotrophs
Methanotrophs oxidize methane by first initiating reduction of an oxygen atom to H2O2 and transformation of methane to CH3OH using methane monooxygenases (MMOs). Furthermore, two types of MMO have been isolated from methanotrophs: soluble methane monooxygenase (sMMO) and particulate methane monooxygenase (pMMO).
Cells containing pMMO have demonstrated higher growth capabilities and higher affinity for methane than sMMO containing cells.
It is suspected that copper ions may play a key role in both pMMO
regulation and the enzyme catalysis, thus limiting pMMO cells to more
copper-rich environments than sMMO producing cells.
The Arctic region is one of the many natural sources of the greenhouse gas methane. Global warming could potentially accelerate its release, due to both release of methane from existing stores, and from methanogenesis in rotting biomass. Large quantities of methane are stored in the Arctic in natural gas deposits and as undersea clathrates.
When permafrost thaws as a consequence of warming, large amounts of
organic material can become available for methanogenesis and may
ultimately be released as methane. Clathrates also degrade on warming
and release methane directly.
Atmospheric methane concentrations are 8–10% higher in the Arctic than in the Antarctic atmosphere. During cold glacier epochs, this gradient decreases to practically insignificant levels.
Land ecosystems are considered the main sources of this asymmetry,
although it has been suggested in 2007 that "the role of the Arctic Ocean is significantly underestimated." Soil temperature and moisture levels have been found to be significant variables in soil methane fluxes in tundra environments.
Main sources of global methane emissions (2008-2017) according to the Global Carbon Project
Main sources of global methane emissions (2008-2017) according to the Global Carbon Project
Due to the relatively short lifetime of atmospheric methane, its global trends are more complex than those of carbon dioxide. NOAA
annual records have been updated since 1984, and they show substantial
growth during the 1980s, a slowdown in annual growth during the 1990s, a
plateau (including some years of declining atmospheric concentrations)
in the early 2000s and another consistent increase beginning in 2007.
Since around 2018, there has been a consistent acceleration in annual
methane increases, with the 2020 increase of 15.06 parts per billion breaking the previous record increase of 14.05 ppb set in 1991, and 2021 setting an even larger increase of 18.34 ppb.
These trends alarm climate scientists, with some suggesting that they represent a climate change feedback increasing natural methane emissions well beyond their preindustrial levels. However, there is currently no evidence connecting the Arctic to this recent acceleration.
In fact, a 2021 study indicated that the role of the Arctic was
typically overerestimated in global methane accounting, while the role
of tropical regions was consistently underestimated. The study suggested that tropical wetland methane emissions
were the culprit behind the recent growth trend, and this hypothesis
was reinforced by a 2022 paper connecting tropical terrestrial emissions
to 80% of the global atmospheric methane trends between 2010 and 2019.
Nevertheless, the Arctic's role in global methane trends is
considered very likely to increase in the future. There is evidence for
increasing methane emissions since 2004 from a Siberian permafrost site
into the atmosphere linked to warming.
Carbon cycle accelerates in the wake of abrupt thaw (orange) relative to the previous state of the area (blue, black).
Global warming in the Arctic accelerates methane release from both existing stores and methanogenesis in rotting biomass. Methanogenesis requires thoroughly anaerobic environments, which slows down the mobilization of old carbon. A 2015 Nature
review estimated that the cumulative emissions from thawed anaerobic
permafrost sites were 75–85% lower than the cumulative emissions from
aerobic sites, and that even there, methane emissions amounted to only
3% to 7% of CO2 emitted in situ. While they represented between 25% and 45% of the CO2's
potential impact on climate over a 100-year timescale, the review
concluded that aerobic permafrost thaw still had a greater warming
impact overall. In 2018, however, another study in Nature Climate Change performed seven-year incubation experiments and found that methane production became equivalent to CO2
production once a methanogenic microbial community became established
at the anaerobic site. This finding had substantially raised the overall
warming impact represented by anaerobic thaw sites.
Since methanogenesis requires anaerobic environments, it is
frequently associated with Arctic lakes, where the emergence of bubbles
of methane can be observed. Lakes produced by the thaw of particularly ice-rich permafrost are known as thermokarst
lakes. Not all of the methane produced in the sediment of a lake
reaches the atmosphere, as it can get oxidized in the water column or
even within the sediment itself. However, 2022 observations indicate that at least half of the methane produced within thermokarst lakes reaches the atmosphere. Another process which frequently results in substantial methane emissions is the erosion of permafrost-stabilized hillsides and their ultimate collapse.
Altogether, these two processes - hillside collapse (also known as
retrogressive thaw slump, or RTS) and thermokarst lake formation - are
collectively described as abrupt thaw, as they can rapidly expose
substantial volumes of soil to microbial respiration in a matter of
days, as opposed to the gradual, cm by cm, thaw of formerly frozen soil
which dominates across most permafrost environments. This rapidity was
illustrated in 2019, when three permafrost sites which would have been
safe from thawing under the "intermediate" Representative Concentration Pathway 4.5 for 70 more years had undergone abrupt thaw.
Another example occurred in the wake of a 2020 Siberian heatwave, which
was found to have increased RTS numbers 17-fold across the northern Taymyr Peninsula
– from 82 to 1404, while the resultant soil carbon mobilization
increased 28-fold, to an average of 11 grams of carbon per square meter
per year across the peninsula (with a range between 5 and 38 grams).
Until recently, Permafrost carbon feedback (PCF) modeling had
mainly focused on gradual permafrost thaw, due to the difficulty of
modelling abrupt thaw, and because of the flawed assumptions about the
rates of methane production. Nevertheless, a study from 2018, by using field observations, radiocarbon dating, and remote sensing to account for thermokarst lakes, determined that abrupt thaw will more than double permafrost carbon emissions by 2100.
And a second study from 2020, showed that under the scenario of
continually accelerating emissions (RCP 8.5), abrupt thaw carbon
emissions across 2.5 million km2 are projected to provide the same feedback as gradual thaw of near-surface permafrost across the whole 18 million km2 it occupies. Thus, abrupt thaw adds between 60 and 100 gigatonnes of carbon by 2300, increasing carbon emissions by ~125–190% when compared to gradual thaw alone.[30]
Methane emissions from thawed permafrost appear to decrease as bog matures over time.
However, there is still scientific debate about the rate and the
trajectory of methane production in the thawed permafrost environments.
For instance, a 2017 paper suggested that even in the thawing peatlands
with frequent thermokarst lakes, less than 10% of methane emissions can
be attributed to the old, thawed carbon, and the rest is anaerobic
decomposition of modern carbon.
A follow-up study in 2018 had even suggested that increased uptake of
carbon due to rapid peat formation in the thermokarst wetlands would
compensate for the increased methane release.
Another 2018 paper suggested that permafrost emissions are limited
following thermokarst thaw, but are substantially greater in the
aftermath of wildfires.
In 2022, a paper demonstrated that peatland methane emissions from
permafrost thaw are initially quite high (82 milligrams of methane
per square meter per day), but decline by nearly three times as the
permafrost bog matures, suggesting a reduction in methane emissions in
several decades to a century following abrupt thaw.
In 2011, preliminary computer analyses suggested that permafrost
emissions could be equivalent to around 15% of anthropogenic emissions.
A 2018 perspectives article discussing tipping points in the climate system
activated around 2 °C (3.6 °F) of global warming suggested that at this
threshold, permafrost thaw would add a further 0.09 °C (0.16 °F) to
global temperatures by 2100, with a range of 0.04–0.16 °C
(0.072–0.288 °F) In 2021, another study estimated that in a future where zero emissions
were reached following an emission of a further 1000 Pg C into the
atmosphere (a scenario where temperatures ordinarily stay stable after
the last emission, or start to decline slowly) permafrost carbon would
add 0.06 °C (0.11 °F) (with a range of 0.02–0.14 °C (0.036–0.252 °F)) 50
years after the last anthropogenic emission, 0.09 °C (0.16 °F)
(0.04–0.21 °C (0.072–0.378 °F)) 100 years later and 0.27 °C (0.49 °F)
(0.12–0.49 °C (0.22–0.88 °F)) 500 years later. However, neither study was able to take abrupt thaw into account.
In 2020, a study of the northern permafrost peatlands (a smaller subset of the entire permafrost area, covering 3.7 million km2 out of the estimated 18 million km2) would amount to ~1% of anthropogenic radiative forcing
by 2100, and that this proportion remains the same in all warming
scenarios considered, from 1.5 °C (2.7 °F) to 6 °C (11 °F). It had
further suggested that after 200 more years, those peatlands would have
absorbed more carbon than what they had emitted into the atmosphere.
The IPCC Sixth Assessment Report
estimates that carbon dioxide and methane released from permafrost
could amount to the equivalent of 14–175 billion tonnes of carbon
dioxide per 1 °C (1.8 °F) of warming. For comparison, by 2019, annual anthropogenic emission of carbon dioxide alone stood around 40 billion tonnes.
Nine probable scenarios of greenhouse gas emissions from permafrost thaw during the 21st century, which show a limited, moderate and intense CO2 and CH4 emission response to low, medium and high-emission Representative Concentration Pathways.
The vertical bar uses emissions of selected large countries as a
comparison: the right-hand side of the scale shows their cumulative
emissions since the start of the Industrial Revolution,
while the left-hand side shows each country's cumulative emissions for
the rest of the 21st century if they remained unchanged from their 2019
levels.
A 2021 assessment of the economic impact of climate tipping points
estimated that permafrost carbon emissions would increase the social cost of carbon by about 8.4%. However, the methods of that assessment have attracted controversy: when researchers like Steve Keen and Timothy Lenton had accused it of underestimating the overall impact of tipping points and of higher levels of warming in general, the authors have conceded some of their points.
In 2021, a group of prominent permafrost researchers like Merritt Turetsky
had presented their collective estimate of permafrost emissions,
including the abrupt thaw processes, as part of an effort to advocate
for a 50% reduction in anthropogenic emissions by 2030 as a necessary
milestone to help reach net zero by 2050. Their figures for combined
permafrost emissions by 2100 amounted to 150–200 billion tonnes of
carbon dioxide equivalent under 1.5 °C (2.7 °F) of warming, 220–300
billion tonnes under 2 °C (3.6 °F) and 400–500 billion tonnes if the
warming was allowed to exceed 4 °C (7.2 °F). They compared those figures
to the extrapolated present-day emissions of Canada, the European Union and the United States or China,
respectively. The 400–500 billion tonnes figure would also be
equivalent to the today's remaining budget for staying within a 1.5 °C
(2.7 °F) target. One of the scientists involved in that effort, Susan M. Natali of Woods Hole Research Centre, had also led the publication of a complementary estimate in a PNAS
paper that year, which suggested that when the amplification of
permafrost emissions by abrupt thaw and wildfires is combined with the
foreseeable range of near-future anthropogenic emissions, avoiding the
exceedance (or "overshoot") of 1.5 °C (2.7 °F) warming is already
implausible, and the efforts to attain it may have to rely on negative emissions to force the temperature back down.
An updated 2022 assessment of climate tipping points concluded
that abrupt permafrost thaw would add 50% to gradual thaw rates, and
would add 14 billion tons of carbon dioxide equivalent emissions by 2100
and 35 billion tons by 2300 per every degree of warming. This would
have a warming impact of 0.04 °C (0.072 °F) per every full degree of
warming by 2100, and 0.11 °C (0.20 °F) per every full degree of warming
by 2300. It also suggested that at between 3 °C (5.4 °F) and 6 °C
(11 °F) degrees of warming (with the most likely figure around 4 °C
(7.2 °F) degrees) a large-scale collapse of permafrost areas could
become irreversible, adding between 175 and 350 billion tons of CO2 equivalent emissions, or 0.2–0.4 °C (0.36–0.72 °F) degrees, over about 50 years (with a range between 10 and 300 years).
A major review published in the year 2022 concluded that if the goal of
preventing 2 °C (3.6 °F) of warming was realized, then the average
annual permafrost emissions throughout the 21st century would be
equivalent to the year 2019 annual emissions of Russia.
Under RCP4.5, a scenario considered close to the current trajectory and
where the warming stays slightly below 3 °C (5.4 °F), annual permafrost
emissions would be comparable to year 2019 emissions of Western Europe or the United States,
while under the scenario of high global warming and worst-case
permafrost feedback response, they would nearly match year 2019
emissions of China.
A 2015 study concluded that Arctic sea ice decline accelerates methane emissions from the Arctic tundra,
with the emissions for 2005-2010 being around 1.7 million tonnes higher
than they would have been with the sea ice at 1981–1990 levels.
One of the researchers noted, "The expectation is that with further
sea ice decline, temperatures in the Arctic will continue to rise, and
so will methane emissions from northern wetlands."
Clathrate breakdown
Methane clathrate is released as gas into the surrounding water column or soils when ambient temperature increases
The clathrate gun hypothesis is a proposed explanation for the periods of rapid warming during the Quaternary.
The hypothesis is that changes in fluxes in upper intermediate waters
in the ocean caused temperature fluctuations that alternately
accumulated and occasionally released methane clathrate on upper continental slopes. This would have had an immediate impact on the global temperature, as methane is a much more powerful greenhouse gas than carbon dioxide. Despite its atmospheric lifetime of around 12 years, methane's global warming potential is 72 times greater than that of carbon dioxide over 20 years, and 25 times over 100 years (33 when accounting for aerosol interactions). It is further proposed that these warming events caused the Bond Cycles and individual interstadial events, such as the Dansgaard–Oeschger interstadials.
Most deposits of methane clathrate are in sediments too deep to respond rapidly, and 2007 modelling by Archer suggests that the methane forcing derived from them should remain a minor component of the overall greenhouse effect. Clathrate deposits destabilize from the deepest part of their stability zone,
which is typically hundreds of metres below the seabed. A sustained
increase in sea temperature will warm its way through the sediment
eventually, and cause the shallowest, most marginal clathrate to start
to break down; but it will typically take on the order of a thousand
years or more for the temperature change to get that far into the
seabed. Further, subsequent research on midlatitude deposits in the Atlantic and Pacific Ocean
found that any methane released from the seafloor, no matter the
source, fails to reach the atmosphere once the depth exceeds 430 m
(1,411 ft), while geological characteristics of the area make it
impossible for hydrates to exist at depths shallower than 550 m
(1,804 ft).
Potential Methane release in the Eastern Siberian Arctic Shelf
However, some methane clathrates deposits in the Arctic are much
shallower than the rest, which could make them far more vulnerable to
warming. A trapped gas deposit on the continental slope off Canada in
the Beaufort Sea,
located in an area of small conical hills on the ocean floor is just
290 m (951 ft) below sea level and considered the shallowest known
deposit of methane hydrate.
However, the East Siberian Arctic Shelf averages 45 meters in depth,
and it is assumed that below the seafloor, sealed by sub-sea permafrost
layers, hydrates deposits are located. This would mean that when the warming potentially talik or pingo-like
features within the shelf, they would also serve as gas migration
pathways for the formerly frozen methane, and a lot of attention has
been paid to that possibility.Shakhova et al. (2008) estimate that not less than 1,400 gigatonnes of
carbon is presently locked up as methane and methane hydrates under the
Arctic submarine permafrost, and 5–10% of that area is subject to
puncturing by open talik. Their paper initially included the line that
the "release of up to 50 gigatonnes of predicted amount of hydrate
storage [is] highly possible for abrupt release at any time". A release
on this scale would increase the methane content of the planet's
atmosphere by a factor of twelve, equivalent in greenhouse effect to a doubling in the 2008 level of CO2.
This is what led to the original Clathrate gun hypothesis, and in
2008 the United States Department of Energy National Laboratory system
and the United States Geological Survey's Climate Change Science
Program both identified potential clathrate destabilization in the
Arctic as one of four most serious scenarios for abrupt climate change,
which have been singled out for priority research. The USCCSP released a
report in late December 2008 estimating the gravity of this risk. A 2012 study of the effects for the original hypothesis, based on a coupled climate–carbon cycle model (GCM)
assessed a 1000-fold (from <1 to 1000 ppmv) methane increase—within a
single pulse, from methane hydrates (based on carbon amount estimates
for the PETM, with ~2000 GtC), and concluded it would increase
atmospheric temperatures by more than 6 °C within 80 years. Further,
carbon stored in the land biosphere would decrease by less than 25%,
suggesting a critical situation for ecosystems and farming, especially
in the tropics. Another 2012 assessment of the literature identifies methane hydrates on the Shelf of East Arctic Seas as a potential trigger.
A risk of seismic activity being potentially responsible for mass methane releases has been considered as well. In 2012, seismic
observations destabilizing methane hydrate along the continental slope
of the eastern United States, following the intrusion of warmer ocean
currents, suggests that underwater landslides could release methane. The
estimated amount of methane hydrate in this slope is 2.5 gigatonnes
(about 0.2% of the amount required to cause the PETM),
and it is unclear if the methane could reach the atmosphere. However,
the authors of the study caution: "It is unlikely that the western North
Atlantic margin is the only area experiencing changing ocean currents;
our estimate of 2.5 gigatonnes of destabilizing methane hydrate may
therefore represent only a fraction of the methane hydrate currently
destabilizing globally." Bill McGuire notes, "There may be a threat of submarine landslides around the margins of Greenland,
which are less well explored. Greenland is already uplifting, reducing
the pressure on the crust beneath and also on submarine methane hydrates
in the sediment around its margins, and increased seismic activity may
be apparent within decades as active faults beneath the ice sheet are
unloaded. This could provide the potential for the earthquake or methane
hydrate destabilisation of submarine sediment, leading to the formation
of submarine slides and, perhaps, tsunamis in the North Atlantic."
Methane releases in Laptev Sea are typically consumed within the sediment by methanotrophs. Areas with high sedimentation
(top) subject their microbial communities to continual disturbance, and
so they are the most likely to see active fluxes, whether with (right)
or without active upward flow (left). Even so, the annual release may
be limited to 1000 tonnes or less.
Research carried out in 2008 in the Siberian Arctic showed methane
releases on the annual scale of millions of tonnes, which was a
substantial increase on the previous estimate of 0.5 millions of tonnes
per year. apparently through perforations in the seabed permafrost, with concentrations in some regions reaching up to 100 times normal levels. The excess methane has been detected in localized hotspots in the outfall of the Lena River and the border between the Laptev Sea and the East Siberian Sea.
At the time, some of the melting was thought to be the result of
geological heating, but more thawing was believed to be due to the
greatly increased volumes of meltwater being discharged from the
Siberian rivers flowing north.
By 2013, the same team of researchers used multiple sonar
observations to quantify the density of bubbles emanating from subsea
permafrost into the ocean (a process called ebullition), and found that
100–630 mg methane per square meter is emitted daily along the East
Siberian Arctic Shelf (ESAS), into the water column. They also found
that during storms, when wind accelerates air-sea gas exchange, methane
levels in the water column drop dramatically. Observations suggest that
methane release from seabed permafrost will progress slowly, rather than
abruptly. However, Arctic cyclones, fueled by global warming,
and further accumulation of greenhouse gases in the atmosphere could
contribute to more rapid methane release from this source. Altogether,
their updated estimate had now amounted to 17 millions of tonnes per
year.
However, these findings were soon questioned, as this rate of annual
release would mean that the ESAS alone would account for between 28% and
75% of the observed Arctic methane emissions, which contradicts many
other studies. In January 2020, it was found that the rate at which
methane enters the atmosphere after it had been released from the shelf
deposits into the water column had been greatly overestimated, and
observations of atmospheric methane fluxes taken from multiple ship
cruises in the Arctic instead indicate that only around 3.02 million
tonnes of methane are emitted annually from the ESAS.
A modelling study published in 2020 suggested that under the
present-day conditions, annual methane release from the ESAS may be as
low as 1000 tonnes, with 2.6 – 4.5 million tonnes representing the peak
potential of turbulent emissions from the shelf.
Hong et al. 2017 studied methane seepage in the shallow arctic seas at the Barents Sea close to Svalbard.
Temperature at the seabed has fluctuated seasonally over the last
century, between −1.8 °C (28.8 °F) and 4.8 °C (40.6 °F), it has only
affected release of methane to a depth of about 1.6 meters at the
sediment-water interface. Hydrates can be stable through the top 60
meters of the sediments and the current observed releases originate from
deeper below the sea floor. They conclude that the increased methane
flux started hundreds to thousands of years ago, noted about it,
"..episodic ventilation of deep reservoirs rather than warming-induced
gas hydrate dissociation." Summarizing his research, Hong stated:
The results of our study indicate
that the immense seeping found in this area is a result of natural state
of the system. Understanding how methane interacts with other important
geological, chemical and biological processes in the Earth system is
essential and should be the emphasis of our scientific community.
Methane
releases specifically attributed to hydrate dissociation in the
Svalbard appear to be much lower than the leaks from other methane
sources.
Research by Klaus Wallmann et al. 2018 concluded that hydrate dissociation at Svalbard 8,000 years ago was due to isostatic rebound (continental uplift following deglaciation).
As a result, the water depth got shallower with less hydrostatic
pressure, without further warming. The study, also found that today's
deposits at the site become unstable at a depth of ~ 400 meters, due to
seasonal bottom water warming, and it remains unclear if this is due to
natural variability or anthropogenic warming.
Moreover, another paper published in 2017 found that only 0.07% of the
methane released from the gas hydrate dissociation at Svalbard appears
to reach the atmosphere, and usually only when the wind speeds were low.
In 2020, a subsequent study confirmed that only a small fraction of
methane from the Svalbard seeps reaches the atmosphere, and that the
wind speed holds a greater influence on the rate of release than
dissolved methane concentration on site.
Finally, a paper published in 2017 indicated that the methane emissions
from at least one seep field at Svalbard were more than compensated for
by the enhanced carbon dioxide uptake due to the greatly increased phytoplankton
activity in this nutrient-rich water. The daily amount of carbon
dioxide absorbed by the phytoplankton was 1,900 greater than the amount
of methane emitted, and the negative (i.e. indirectly cooling) radiative forcing from the CO2 uptake was up to 251 times greater than the warming from the methane release.
In 2018, a perspective piece devoted to tipping points in the climate system
suggested that the climate change contribution from methane hydrates
would be "negligible" by the end of the century, but could amount to
0.4–0.5 °C (0.72–0.90 °F) on the millennial timescales. In 2021, the IPCC Sixth Assessment Report
no longer included methane hydrates in the list of potential tipping
points, and says that "it is very unlikely that CH4 emissions from
clathrates will substantially warm the climate system over the next few
centuries." The report had also linked terrestrial hydrate deposites to gas emission craters discovered in the Yamal Peninsula in Siberia, Russia beginning in July 2014,
but noted that since terrestrial gas hydrates predominantly form at a
depth below 200 metres, a substantial response within the next few
centuries can be ruled out.
Likewise, a 2022 assessment of tipping points described methane
hydrates as a "threshold-free feedback" rather than a tipping point.
Ice sheets
A 2014 study found evidence for methane cycling below the ice sheet of the Russell Glacier, based on subglacial drainage samples which were dominated by Pseudomonadota.
During the study, the most widespread surface melt on record for the
past 120 years was observed in Greenland; on 12 July 2012, unfrozen
water was present on almost the entire ice sheet surface (98.6%). The
findings indicate that methanotrophs
could serve as a biological methane sink in the subglacial ecosystem,
and the region was, at least during the sample time, a source of atmospheric methane. Scaled dissolved methane flux during the 4 months of the summer melt season was estimated at 990 Mg CH4.
Because the Russell-Leverett Glacier is representative of similar
Greenland outlet glaciers, the researchers concluded that the Greenland
Ice Sheet may represent a significant global methane source. A study in 2016 concluded that methane clathrates may exist below Greenland's and Antarctica's ice sheets, based on past evidence.
Mitigation of methane emissions has greatest potential to preserve Arctic sea ice if it is implemented within the 2020s.
Use of flares
ARPA-E
has funded a research project from 2021-2023 to develop a "smart
micro-flare fleet" to burn off methane emissions at remote locations.
A 2012 review article stated that most existing technologies
"operate on confined gas streams of 0.1% methane", and were most
suitable for areas where methane is emitted in pockets.
If Arctic oil and gas operations use Best Available Technology (BAT) and Best Environmental Practices (BEP) in petroleum gas flaring, this can result in significant methane emissions reductions, according to the Arctic Council.
Current efforts in fossil fuel phase-out involve replacing fossil fuels with sustainable energy sources in sectors such as transport and heating. Alternatives to fossil fuels include electrification, green hydrogen and biofuel. Phase-out policies include both demand-side and supply-side measures.
Whereas demand-side approaches seek to reduce fossil-fuel consumption,
supply-side initiatives seek to constrain production to accelerate the
pace of energy transition and reduction in emissions. It has been
suggested that laws should be passed to make fossil fuel companies bury
the same amount of carbon as they emit. The International Energy Agency
estimates that in order to achieve carbon neutrality by the middle of
the century, global investments in renewable energy must treble by 2030,
reaching over $4 trillion annually.
Scope
While crude oil and natural gas are also being phased out in chemical
processes (e.g. production of new building blocks for plastics) as the circular economy and biobased economy (e.g. bioplastics) are being developed to reduce plastic pollution,
the fossil fuel phase out specifically aims to end the burning of
fossil fuels and the consequent production of greenhouse gases.
Therefore, attempts to reduce the use of oil and gas in the plastic
industry do not form part of fossil fuel phase-out or reduction plans.
The annual amount of coal plant capacity being retired increased into the mid-2010s. However, the rate of retirement has since stalled, and global coal phase-out is not yet compatible with the goals of the Paris Climate Agreement.
In
parallel with retirement of some coal plant capacity, other coal plants
are still being added, though the annual amount of added capacity has
been declining since the 2010s.
To meet the Paris Agreement target of keeping global warming to well below 2 °C (3.6 °F), coal use needs to halve from 2020 to 2030.
However as of 2017, coal supplied over a quarter of the world's primary energy and about 40% of the greenhouse gas emissions from fossil fuels. Phasing out coal has short-term health and environmental benefits which exceed the costs, and without it the 2 °C target in the Paris Agreement cannot be met; but some countries still favour coal, and there is much disagreement about how quickly it should be phased out.
As of 2018, 30 countries and many sub-national governments and businesses had become members of the Powering Past Coal Alliance,
each making a declaration to advance the transition away from unabated
(abated means with carbon capture and storage (CCS), but almost all
power plants are unabated as CCS is so expensive) coal power generation. As of 2019, however, the countries which use the most coal have not joined, and some countries continue to build and finance new coal-fired power stations. A just transition from coal is supported by the European Bank for Reconstruction and Development.
In 2019 the UN Secretary General said that countries should stop building new coal power plants from 2020 or face 'total disaster'.
In 2020, although China built some plants, globally more coal power was retired than built: the UN Secretary General has said that OECD countries should stop generating electricity from coal by 2030 and the rest of the world by 2040.
In some countries natural gas is being used as a temporary
"bridge fuel" to replace coal, in turn to be replaced by renewable
sources or a hydrogen economy. However this "bridge fuel" may significantly extend the use of fossil fuel or strand assets, such as gas-fired power plants built in the 2020s, as the average plant life is 35 years.
Although natural gas assets are likely to be stranded later than oil
and coal assets, perhaps not until 2050, some investors are concerned by
reputational risk.
As of 2019, natural gas phase-out progressed in some regions, for example with increasing use of hydrogen by the European Network of Transmission System Operators for Gas (ENTSOG) and changes to building regulations to reduce the use of gas heating.
Reasons
Commonly cited reasons for phasing out fossil fuels are to:
Most of the millions of premature deaths from air pollution are due to fossil fuels. Pollution may be indoors e.g. from heating and cooking, or outdoors from vehicle exhaust. One estimate is that the proportion is 65% and the number 3.5 million each year. According to Professor Sir Andy Haines at the London School of Hygiene & Tropical Medicine the health benefits of phasing out fossil fuels measured in money (estimated by economists using the value of life for each country) are substantially more than the cost of achieving the 2-degree C goal of the Paris Agreement.
Climate change mitigation
Fossil-fuel phase-out is the largest part of limiting global warming as fossil fuels account for over 70% of greenhouse gas emissions. In 2020, the International Energy Agency said that to meet the goals of the Paris Agreement, the phase-out of fossil fuels would need to "move four times faster". To achieve the goal of limiting global warming to 1.5 °C above pre-industrial levels, the vast majority of fossil fuel reserves owned by countries and companies as of 2021 would have to remain in the ground.
Employment
The renewable energy transition
can create jobs through the construction of new power plants and the
manufacturing of the equipment that they need, as was seen in the case
of Germany and the wind power industry.
This can also be seen in the case of France and the nuclear power industry. France receives about 75% of its electricity from nuclear energy
and hundreds of jobs have been created for developing nuclear
technology, construction workers, engineers, and radiation protection
specialists.
Energy independence
Countries
which lack fossil fuel deposits, particularly coal but also petroleum
and natural gas, often cite energy independence in their shift away from
fossil fuels.
In Switzerland the decision to electrify virtually the entire railway network
was taken in light of the two world wars (during which Switzerland was
neutral) when coal imports became increasingly difficult. As Switzerland
has ample hydropower resources, electric trains (as opposed to those
driven by steam locomotives or diesel) could be run on domestic energy resources, reducing the need for coal imports.
The 1973 oil crisis
also led to a shift in energy policy in many places to become (more)
independent of fossil fuel imports. In France the government announced an ambitious plan to expand nuclear power
which by the end of the 1980s had shifted France's electricity sector
almost entirely away from coal gas and oil and towards nuclear power.
The trend towards encouraging cycling in the Netherlands and Denmark also coincided with the 1973 oil crisis and aimed in part at reducing the need for oil imports in the transportation sector.
Significant fossil fuel subsidies are present in many countries. Fossil fuel subsidies in 2019 for consumption totalled USD 320 billion spread over many countries. As of 2019 governments subsidise fossil fuels
by about $500 billion per year: however using an unconventional
definition of subsidy which includes failing to price greenhouse gas
emissions, the International Monetary Fund estimated that fossil fuel subsidies were $5.2 trillion in 2017, which was 6.4% of global GDP. Some fossil fuel companies lobby governments.
Phasing out fossil fuel subsidies is very important. It must however be done carefully to avoid protests and making poor people poorer.
In most cases, however, low fossil fuel prices benefit wealthier
households more than poorer households. So to help poor and vulnerable
people, other measures than fossil fuel subsidies would be more
targeted. This could in turn increase public support for subsidy reform.
Economic theory indicates that the optimal policy would be to
remove coal mining and burning subsidies and replace them with optimal
taxes. Global studies indicate that even without introducing taxes,
subsidy and trade barrier removal at a sectoral level would improve
efficiency and reduce environmental damage. Removal of these subsidies would substantially reduce GHG emissions and create jobs in renewable energy.
The IMF estimated in 2023 that removal of fossil fuel subsidies would
limit global heating to the Paris goal of substantially less than 2
degrees.
The actual effects of removing fossil fuel subsidies would depend
heavily on the type of subsidy removed and the availability and
economics of other energy sources. There is also the issue of carbon leakage,
where removal of a subsidy to an energy-intensive industry could lead
to a shift in production to another country with less regulation, and
thus to a net increase in global emissions.
In developed countries, energy costs are low and heavily subsidised, whereas in developing countries, the poor pay high costs for low-quality services.
A plan has been put forward to power 100% of the world's energy with wind, hydroelectric, and solar power by the year 2030. It recommends transfer of energy subsidies from fossil fuel to renewable, and a price on carbon reflecting its cost for flood, cyclone, hurricane, drought, and related extreme weather expenses.
Excluding subsidies the levelised cost of electricity from new large-scale solar power in India and China has been below existing coal-fired power stations since 2021.
A study by Rice University Center for Energy Studies suggested the following steps for countries:
Countries should commit to a specific time frame for a full phaseout of implicit and explicit fossil fuel subsidies.
Clarify the language on subsidy reform to remove ambiguous terminology.
Seek formal legislation in affected countries that codifies reform pathways and reduces opportunities for backsliding.
Publish transparent formulas for market-linked pricing, and adhere to a regular schedule for price adjustments.
Phase-in full reforms in a sequence of gradual steps. Increasing
prices gradually but on a defined schedule signals intent to consumers
while allowing time to invest in energy efficiency to partially offset
the increases.
Aspire to account for externalities over time by imposing a fee or
tax on fossil energy products and services, and eliminating preferences
for fossil fuels that remain embedded in the tax code.
Use direct cash transfers to maintain benefits for poor segments of
society rather than preserving subsidised prices for vulnerable
socioeconomic groups.
Launch a comprehensive public communications campaign.
Any remaining fossil fuel subsidies should be clearly budgeted at
full international prices and paid for by the national treasury.
Document price and emissions changes with reporting requirements.
Studies about fossil fuel phase-out
Reduction in fossil fuel capacity compared to renewables
Renewable energy sources, especially solar photovoltaic and wind power, are providing an increasing share of power capacity.
In
2023, electricity generation from wind and solar sources was projected
to exceed 30% by 2030, as fossil fuels' use continues to decline.
The
countries most reliant on fossil fuels for electricity vary widely on
how great a percentage of that electricity is generated from renewables,
leaving wide variation in renewables' growth potential.
In 2015, Greenpeace and Climate Action Network Europe
released a report highlighting the need for an active phase-out of
coal-fired generation across Europe. Their analysis derived from a
database of 280 coal plants and included emissions data from official EU
registries.
A 2016 report by Oil Change International, concludes that the
carbon emissions embedded in the coal, oil, and gas in currently working
mines and fields, assuming that these run to the end of their working
lifetimes, will take the world to just beyond the 2 °C limit contained
in the 2015 Paris Agreement and even further from the 1.5 °C goal.
The report observes that "one of the most powerful climate policy
levers is also the simplest: stop digging for more fossil fuels".
In 2016, the Overseas Development Institute
(ODI) and 11 other NGOs released a report on the impact of building new
coal-fired power plants in countries where a significant proportion of
the population lacks access to electricity. The report concludes that,
on the whole, building coal-fired power plants does little to help the
poor and may make them poorer. Moreover, wind and solar generation are
beginning to challenge coal on cost.
A 2018 study in Nature Energy, suggests that 10 countries
in Europe could completely phase out coal-fired electricity generation
with their current infrastructure, whilst the United States and Russia
could phase out at least 30%.
In 2020, the Fossil Fuel Cuts Database provided the first global account of supply-side initiatives to constrain fossil fuel production.
The latest update of the database recorded 1967 initiatives implemented
between 1988 and October 2021 in 110 countries across seven major types
of supply-side approaches (Divestment, n=1201; Blockades, n= 374;
Litigation, n= 192; Moratoria and Bans, n= 146; Production subsidies
removal, n=31; Carbon tax on fossil fuel production, n=16; Emissions
Trading Schemes, n= 7).
The GeGaLo index of geopolitical gains and losses assesses how
the geopolitical position of 156 countries may change if the world fully
transitions to renewable energy resources. Former fossil fuel exporters
are expected to lose power, while the positions of former fossil fuel
importers and countries rich in renewable energy resources is expected
to strengthen.
A Guardian
investigation showed in 2022, that big fossil fuel firms continue to
plan huge investments in new fossil fuel production projects that would
drive the climate past internationally agreed temperature limits.
Renewable energy potentials
In June 2021 Dr Sven Teske and Dr Sarah Niklas from the Institute for Sustainable Futures, University of Technology Sydney
found that "existing coal, oil and gas production puts the world on
course to overshoot Paris climate targets." In co-operation with the Fossil Fuel Non-Proliferation Treaty Initiative they published a report entitled, Fossil Fuel Exit Strategy: An orderly wind down of coal, oil, and gas to meet the Paris Agreement.
It analyses global renewable energy potential, and finds that "every
region on Earth can replace fossil fuels with renewable energy to keep
warming below 1.5°C and provide reliable energy access to all."
Assessment of extraction prevention responsibilities
In September 2021, the first scientific assessment of the minimum amount of fossil fuels that would need to be secured from extraction per region as well as globally, to allow for a 50% probability of limiting global warming by 2050 to 1.5 °C was provided.
Challenges of fossil fuel phase-out
Net income of the global oil and gas industry reached a record US$4 trillion in 2022.After recovering from the COVID-19 pandemic, energy company profits increased with greater revenues from higher fuel prices resulting from the Russian invasion of Ukraine, falling debt levels, tax write-downs of projects shut down in Russia, and backing off from earlier plans to reduce greenhouse gas emissions. Record profits sparked public calls for windfall taxes.
The phase-out of fossil fuels involves many challenges, and one of
them is the reliance that the world currently has on them. In 2014,
fossil fuels provided over 80% of the primary energy consumption of the world.
Fossil fuel phase-out may lead to an increment in electricity
prices, because of the new investments needed to replace their share in
the electricity mix with alternative energy sources.
Another impact of a phase-out of fossil fuels is in employment.
In the case of employment in the fossil fuel industry, a phase-out is
logically undesired, therefore, people employed in the industry will
usually oppose any measures that put their industries under scrutiny.
Endre Tvinnereim and Elisabeth Ivarsflaten studied the relationship
between employment in the fossil fuel industry with the support to
climate change policies. They proposed that one opportunity for
displaced drilling employments in the fossil fuel industry could be in
the geothermal energy industry. This was suggested as a result of their
conclusion: people and companies in the fossil fuel industry will likely
oppose measures that endanger their employment, unless they have other
stronger alternatives. This can be extrapolated to political interests, that can push against the phase-out of fossil fuels initiative. One example is how the vote of United States Congress members is related to the preeminence of fossil fuel industries in their respective states.
According to the people present at COP27 in Egypt, Saudi Arabian representatives pushed to block a call for the world to burn less oil. After objections from Saudi Arabia
and a few other oil producers, summit's final statement failed to
include a call for nations to phase out fossil fuels. In March 2022, at a
United Nations meeting with climate scientists, Saudi Arabia, together
with Russia, pushed to delete a reference to "human-induced climate
change" from an official document, disputing the scientifically
established fact that the burning of fossil fuels by humans is the main
driver of the climate crisis.
Major initiatives and legislation to phase out fossil fuels
China
China has pledged to become carbon neutral by 2060, which would need a just transition for over 3 million workers in the coal-mining and power industry.
It is not yet clear whether China aims to phase-out all fossil fuel use
by that date or whether a small proportion will still be in use with the carbon captured and stored. In 2021, coal mining was ordered to run at maximum capacity.
EU
At the end of 2019, the European Union launched its European Green Deal.
It included:
a review and possible revision (where needed) of the all relevant climate-related policy instruments, including the Emissions Trading System
a sustainable and smart mobility strategy
potential carbon tariffs for countries that don't curtail their greenhouse gas pollution at the same rate. The mechanism to achieve this is called the Carbon Border Adjustment Mechanism (CBAM).
It also leans on Horizon Europe, to play a pivotal role in leveraging national public and private investments.
Through partnerships with industry and member States, it will support
research and innovation on transport technologies, including batteries,
clean hydrogen, low-carbon steel making, circular bio-based sectors and the built environment.
The European Investment Bank contributed over €81 billion to help the energy industry between 2017 and 2022, in line with EU energy policy. This comprised nearly €76 billion for initiatives related to power grids, energy efficiency, and renewable energy throughout Europe and other parts of the world.
India
India is confident of exceeding Paris COP commitments. In the Paris Agreement, India has committed to an Intended Nationally Determined Contributions target of achieving 40% of its total electricity generation from non-fossil fuel sources by 2030.
Japan
Japan has pledged to become carbon neutral by 2050.
The UK is legally committed to be carbon neutral by 2050, and moving
away from the heating of homes by natural gas is likely to be the most
difficult part of the country's fossil fuel phase out. Alternative green recovery legislative plans have been proposed by multiple groups to phase out fossil fuels as fast as technology allows.
Bloomberg NEF reported that in 2022, global energy transition investment equaled fossil fuels investment for the first time.In 2020, renewables overtook fossil fuels as the European Union's main source of electricity for the first time.
Renewable energy is often deployed together with further electrification, which has several benefits: electricity can move heat or objects efficiently, and is clean at the point of consumption. From 2011 to 2021, renewable energy grew from 20% to 28% of global electricity supply. Use of fossil energy
shrank from 68% to 62%, and nuclear from 12% to 10%. The share of
hydropower decreased from 16% to 15% while power from sun and wind
increased from 2% to 10%. Biomass
and geothermal energy grew from 2% to 3%. There are 3,146 gigawatts
installed in 135 countries, while 156 countries have laws regulating the
renewable energy sector. In 2021, China accounted for almost half of the global increase in renewable electricity.
Globally there are over 10 million jobs associated with the renewable energy industries, with solar photovoltaics being the largest renewable employer.
Renewable energy systems are rapidly becoming more efficient and
cheaper and their share of total energy consumption is increasing, with a large majority of worldwide newly installed electricity capacity being renewable. In most countries, photovoltaic solar or onshore wind are the cheapest new-build electricity.
Many nations around the world already have renewable energy contributing more than 20% of their total energy supply, with some generating over half their electricity from renewables. A few countries generate all their electricity using renewable energy. National renewable energy markets are projected to continue to grow strongly in the 2020s and beyond.
According to the IEA, to achieve net zero emissions by 2050, 90% of
global electricity generation will need to be produced from renewable
sources. Some studies have shown that a global transition to 100% renewable energy across all sectors – power, heat, transport and industry – is feasible and economically viable.
Renewable energy resources exist over wide geographical areas, in contrast to fossil fuels, which are concentrated in a limited number of countries. Deployment of renewable energy and energy efficiency technologies is resulting in significant energy security, climate change mitigation, and economic benefits. However renewables are being hindered by hundreds of billions of dollars of fossil fuel subsidies. In international public opinion surveys there is strong support for renewables such as solar power and wind power. In 2022 the International Energy Agency
asked countries to solve policy, regulatory, permitting and financing
obstacles to adding more renewables, to have a better chance of reaching
net zero carbon emissions by 2050.
In 2015, hydroelectric energy generated 16.6% of the world's total electricity and 70% of all renewable electricity.
In Europe and North America environmental concerns around land flooded
by large reservoirs ended 30 years of dam construction in the 1990s.
Since then large dams and reservoirs continue to be built in countries
like China, Brazil and India. Run-of-the-river hydroelectricity and small hydro have become popular alternatives to conventional dams that may create reservoirs in environmentally sensitive areas.
Wind power
Wind power is the use of wind energy to generate useful work. Historically, wind power was used by sails, windmills and windpumps, but today it is mostly used to generate electricity. This article deals only with wind power for electricity generation.
Today, wind power is generated almost completely with wind turbines, generally grouped into wind farms and connected to the electrical grid.
In 2022, wind supplied over 2000 TWh of electricity, which was over 7% of world electricity and about 2% of world energy.With about 100 GW added during 2021, mostly in China and the United States, global installed wind power capacity exceeded 800 GW. To help meet the Paris Agreement goals to limit climate change, analysts say it should expand much faster - by over 1% of electricity generation per year.
Wind power is considered a sustainable, renewable energy source, and has a much smaller impact on the environment compared to burning fossil fuels.
Wind power is variable, so it needs energy storage or other dispatchable generation
energy sources to attain a reliable supply of electricity.
Land-based (onshore) wind farms have a greater visual impact on the
landscape than most other power stations per energy produced. Wind farms sited offshore have less visual impact and have higher capacity factors, although they are generally more expensive. Offshore wind power currently has a share of about 10% of new installations.
Wind power is one of the lowest-cost electricity sources per unit of energy produced.
In many locations, new onshore wind farms are cheaper than new coal or gas plants.
Regions in the higher northern and southern latitudes have the highest potential for wind power. In most regions, wind power generation is higher in nighttime, and in winter when solar power output is low. For this reason, combinations of wind and solar power are suitable in many countries.
In 2017, solar power provided 1.7% of total worldwide electricity production, growing at 35% per annum.
By 2020 the solar contribution to global final energy consumption is expected to exceed 1%.
Solar photovoltaic cells convert sunlight into electricity and many solar photovoltaic power stations have been built. The size of these stations has increased progressively over the last decade with frequent new capacity records.
Many of these plants are integrated with agriculture and some use
innovative tracking systems that follow the sun's daily path across the
sky to generate more electricity than conventional fixed-mounted
systems. Solar power plants have no fuel costs or emissions during
operation.
Concentrated solar power
The 150 MW Andasol solar power station is a commercial parabolic trough solar thermal power plant, located in Spain.
The Andasol plant uses tanks of molten salt to store solar energy so
that it can continue generating electricity even when the sun isn't
shining.
Concentrating Solar Power (CSP) systems use lenses or mirrors and
tracking systems to focus a large area of sunlight into a small beam.
The concentrated heat is then used as a heat source for a conventional
power plant. A wide range of concentrating technologies exists; the most
developed are the parabolic trough, the Compact linear Fresnel reflector, the Stirling dish and the solar power tower. Various techniques are used to track the Sun and focus light. In all of these systems a working fluid is heated by the concentrated sunlight, and is then used for power generation or energy storage.
The 2014 Intergovernmental Panel on Climate Change
(IPCC) report identifies nuclear energy as one of the technologies that
can provide electricity with less than 5% of the lifecycle greenhouse
gas emissions of coal power. There are more than 60 nuclear reactors shown as under construction in the list of Nuclear power by country
with China leading at 23. Globally, more nuclear power reactors have
closed than opened in recent years but overall capacity has increased.
China has stated its plans to double nuclear generation by 2030. India
also plans to greatly increase its nuclear power. The Manhattan 2
Project has presented a report that describes how to significantly
increase nuclear power via factory automation.
Several countries have enacted laws to cease construction on new
nuclear power stations. Several European countries have debated nuclear phase-outs and others have completely shut down some reactors. Three nuclear accidents have influenced the slowdown of nuclear power: the 1979 Three Mile Island accident in the United States, the 1986 Chernobyl disaster in the USSR, and the 2011 Fukushima nuclear disaster
in Japan. Following the March 2011 Fukushima nuclear disaster, Germany
has permanently shut down eight of its 17 reactors and pledged to close
the rest by the end of 2022. Italy voted overwhelmingly to keep their country non-nuclear. Switzerland and Spain have banned the construction of new reactors. Japan's prime minister has called for a dramatic reduction in Japan's reliance on nuclear power. Taiwan's president did the same. Shinzō Abe,
prime minister of Japan since December 2012, announced a plan to
restart some of the 54 Japanese nuclear power plants and to continue
some nuclear reactors under construction.
As of 2016, countries such as Australia, Austria, Denmark, Greece, Malaysia, New Zealand and Norway have no nuclear power stations and remain opposed to nuclear power. Germany, Italy, Spain and Switzerland are phasing-out their nuclear power. Despite this, most pathways for spurring a fossil fuel phase-out that keeps pace with global electricity demands include the expansion of nuclear power, according to the IPCC. Likewise, the United Nations Economic Commission for Europe has stated that global climate objectives would likely not be met without nuclear expansion.
Cost overruns, construction delays, the threat of catastrophic
accidents, and regulatory hurdles often make nuclear power plant
expansion practically infeasible. Some companies and organisations have
proposed plans aimed at mitigating the cost, duration, and risk of
nuclear power plant construction. NuScale Power, for example, has received regulatory approval from the Nuclear Regulatory Commission for a light-water reactor that would theoretically limit the risk of accidents and could be manufactured for less than traditional nuclear plants. The Energy Impact Center's OPEN100, a platform that provides open-source blueprints for the construction of a nuclear plant with a 100-megawatt pressurised water reactor,
claims that its model could be built in as little as two years for
$300 million. In both plans, the ability to mass manufacture small modular reactors would theoretically cut down on construction time.
Biomass is biological material from living, or recently living organisms, most often referring to plants or plant-derived materials. As a renewable energy source, biomass can either be used directly, or indirectly – once or converted into another type of energy product such as biofuel. Biomass can be converted to energy in three ways: thermal conversion, chemical conversion, and biochemical conversion.
Using biomass as a fuel produces air pollution in the form of carbon monoxide, carbon dioxide, NOx (nitrogen oxides), VOCs (volatile organic compounds),
particulates and other pollutants at levels above those from
traditional fuel sources such as coal or natural gas in some cases (such
as with indoor heating and cooking).
Use of wood biomass as a fuel can also produce fewer particulate and
other pollutants than open burning as seen in wildfires or direct heat
applications. Black carbon –
a pollutant created by combustion of fossil fuels, biofuels, and
biomass – is possibly the second largest contributor to global warming.
In 2009 a Swedish study of the giant brown haze that periodically
covers large areas in South Asia determined that it had been principally
produced by biomass burning, and to a lesser extent by fossil fuel
burning. Denmark has increased the use of biomass and garbage, and decreased the use of coal.
Sales of electric vehicles (EVs) indicate a trend away from gas-powered vehicles that generate greenhouse gases.
Many countries and cities have introduced bans on the sales of new internal combustion engine vehicles, requiring all new cars to be electric vehicles or otherwise powered by clean, non-emitting sources. Such bans include the United Kingdom by 2035 and Norway by 2025. Many transit authorities are working to purchase only electric buses while also restricting use of ICE vehicles in the city center to limit air pollution. Many US states have a zero-emissions vehicle mandate, incrementally requiring a certain per cent of cars sold to be electric. The German term de: Verkehrswende
("traffic transition" analogous to "Energiewende", energetic
transition) calls for a shift from combustion powered road transport to
bicycles, walking and rail transport and the replacement of remaining
road vehicles with electric traction.
Biofuels, in the form of liquid fuels
derived from plant materials, are entering the market. However, many of
the biofuels that are currently being supplied have been criticised for
their adverse impacts on the natural environment, food security, and land use.
Opinion
Those
corporations that continue to invest in new fossil fuel exploration,
new fossil fuel exploitation, are really in flagrant breach of their
fiduciary duty because the science is abundantly clear that this is
something we can no longer do.
Protest at the Legislative Building in Olympia, Washington. Ted Nation, a long-time environmental activist beside protest sign.
Polls
In 2023,
Pew commissioned a poll that estimated 31% of Americans were ready to
phase out the use of oil, coal and natural gas completely, 32% wanted to
phase out fossil fuel eventually and 35% said they never want fossil
fuel to be phased out.
Prominent individuals supporting a coal moratorium
If you're a young person looking at
the future of this planet and looking at what is being done right now,
and not done, I believe we have reached the stage where it is time for civil disobedience to prevent the construction of new coal plants that do not have carbon capture and sequestration.
Prominent individuals supporting a coal phase-out
Eric Schmidt, then CEO of Google, called for replacing all fossil fuels with renewable sources of energy in twenty years.
Mitigation of peak oil
The standard Hubbert curve, plotting crude oil production of a region over time.World energy consumption, 1970–2025. Source: International Energy Outlook 2004.
The mitigation of peak oil is the attempt to delay the date and minimize the social and economic effects of peak oil by reducing the consumption of and reliance on petroleum. By reducing petroleum consumption, mitigation efforts seek to favorably change the shape of the Hubbert curve, which is the graph of real oil production over time predicted by Hubbert peak theory.
The peak of this curve is known as peak oil, and by changing the shape
of the curve, the timing of the peak in oil production is affected. An
analysis by the author of the Hirsch report
showed that while the shape of the oil production curve can be affected
by mitigation efforts, mitigation efforts are also affected by the
shape of Hubbert curve.
Historically, world oil consumption data show that mitigation efforts during the 1973 and 1979 oil shocks lowered oil consumption, while general recessions since the 1970s have had no effect on curbing the oil consumption until 2007. In the United States, oil consumption declines in reaction to high prices.
Key questions for mitigation are the viability of methods, the
roles of government and private sector and how early these solutions are
implemented. The responses to such questions and steps taken towards mitigation may determine whether or not the lifestyle of a society can be maintained, and may affect the population capacity of the planet.
Alternative energy
The most effective method of mitigating peak oil is to use renewable or alternative energy sources in place of petroleum.
Transportation fuel use
Because most oil is consumed for transportation most mitigation discussions revolve around transportation issues.
While there is some interchangeability, the alternative energy
sources available tend to depend on whether the fuel is being used in
static or mobile applications.
Biofuel is a fuel that is produced over a short time span from biomass, rather than by the very slow natural processes involved in the formation of fossil fuels,
such as oil. Biofuel can be produced from plants or from agricultural,
domestic or industrial biowaste. Biofuels are mostly used for
transportation, but can also be used for heating and electricity. Biofuels (and bioenergy in general) are regarded as a renewable energy source.
However, the use of biofuel has been controversial because of the
several disadvantages associated with the use of it. These include for
example (and this varies on a case by case basis): the "food vs fuel" debate, biofuel production methods being sustainable or not, leading to deforestation and loss of biodiversity or not.
In general, biofuels emit fewer greenhouse gas emissions when burned in an engine and are generally considered carbon-neutral fuels as the carbon emitted has been captured from the atmosphere by the crops used in production. However, life-cycle assessments of biofuels have shown large emissions associated with the potential land-use change required to produce additional biofuel feedstocks. Estimates about the climate impact from biofuels vary widely based on the methodology and exact situation examined. Therefore, the climate change mitigation
potential of biofuel varies considerably: in some scenarios emission
levels are comparable to fossil fuels, and in other scenarios the
biofuel emissions result in negative emissions.
The two most common types of biofuel are bioethanol and biodiesel.
Brazil is the largest producer of bioethanol, while the EU is the
largest producer of biodiesel. The energy content in the global
production of bioethanol and biodiesel is 2.2 and 1.8 EJ per year,
respectively. Demand for aviation biofuel is forecast to increase.
Bioethanol is an alcohol made by fermentation, mostly from carbohydrates produced in sugar or starch crops such as maize, sugarcane, or sweet sorghum. Cellulosic biomass, derived from non-food sources, such as trees and grasses, is also being developed as a feedstock for ethanol production. Ethanol can be used as a fuel for vehicles in its pure form (E100), but it is usually used as a gasolineadditive to increase octane ratings and improve vehicle emissions.
Biodiesel is produced from oils or fats using transesterification. It can be used as a fuel for vehicles in its pure form (B100), but it is usually used as a diesel additive to reduce levels of particulates, carbon monoxide, and hydrocarbons from diesel-powered vehicles.
Static installations
Although
oil and diesel still generates a small share of global electricity,
some Middle East oil producing countries are replacing that with solar
power, as it is more profitable to export the oil.
The use of hydrogen fuel is another alternative under development in various countries, alongside, hydrogen vehicles though hydrogen is actually an energy storage medium, not a primary energy
source, and consequently the use of a non-petroleum source would be
required to extract the hydrogen for use. Though hydrogen is currently
outperformed in terms of cost and efficiency by battery powered vehicles,
there are applications where it would come in useful. Short haul
ferries and very cold climates are two examples. Hydrogen fuel cells are
about a third as efficient as batteries and double the efficiency of
petrol vehicles.
Electric vehicles powered by batteries are another alternative,
and these have the advantage of having the highest well-to-wheels
efficiency rate of any energy pathway and thus would allow much greater
numbers of vehicles than any other methods. In addition, even if the
electricity was sourced from coal-fired power plants, two advantages
would remain: first it is cheaper to sequester carbon
from a few thousand smokestacks than it is to retrofit hundreds of
millions of vehicles, and second encouraging the use of electric
vehicles allows a further pathway for scaling up of renewable energy sources.
Alternative aviation fuel
The Airbus A380 flew on alternative fuel for the first time on 1 February 2008. Boeing also plans to use alternative fuel on the 747. Because some biofuels such as ethanol contains less energy, more "tankstops" might be necessary for such planes.
The US Air Force is currently in the process of certifying its
entire fleet to run on a 50/50 blend of synthetic fuel derived from the Fischer–Tropsch process and JP-8 jet fuel.
More comprehensive mitigations include better land use planning through smart growth to reduce the need for private transportation, increased capacity and use of mass transit, vanpooling and carpooling, bus rapid transit, remote work, and human-powered transport from current levels. Rationing and driving bans are also forms of reducing private transportation. The higher oil prices of 2007 and 2008 caused United States drivers to begin driving less in 2007 and to a much greater extent in the first three months of 2008.
In order to deal with potential problems from peak oil, Colin Campbell has proposed the Rimini protocol, a plan which among other things would require countries to balance oil consumption with their current production.
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