rlacombe/ClimateX huggingface dataset:
Several studies using complementary methods indicate that agricultural N 2O emissions have increased by more than 45% since the 1980s (IPCC AR6_WGI, confidence: high)
Supported by multiple studies and extensive observational evidence (Sections 5.2.3.2–5.2.3.4 and Figure 5.17), anthropogenic emissions contributed about 40% (7.3; uncertainty range: 4.2 to 11.4 TgN yr–1) to the total N 2O source in 2007–2016 (IPCC AR6_WGI, confidence: high)
This estimate is larger than in AR5 (WGI, 6.4.3) due to a larger estimated effect of nitrogen deposition on soil N 2O emissions and the explicit consideration of the role of anthropogenic nitrogen in determining inland water and estuary emissions.Based on bottom-up estimates, anthropogenic emissions from agricultural nitrogen use, industry and other indirect effects have increased by 1.7 (1.0 to 2.7) TgN yr–1 between the decades 1980– 1989 and 2007–2016, and are the primary cause of the increase in the total N 2O source (IPCC AR6_WGI, confidence: high)
For North Asia, Europe, Temperate North America and West Asia, the most dominant GHG source is CO 2 (IPCC AR6_WGI, confidence: high)
Persistent emissions of CO 2 are observed for Tropical and South America, northern Africa, and South East Asia (IPCC AR6_WGI, confidence: medium)
Ocean warming decreases the solubility of dissolved oxygen in seawater, and it contributes to about 15% of the dissolved oxygen decrease in the oceans according to estimates based on solubility and the recent SROCC assessment (IPCC AR6_WGI, confidence: medium)
Western Pacific coral records show depleted δ13C trends since the late 19th century that are more prominent since the mid-20th century (IPCC AR6_WGI, confidence: high)
Overall, many of the records show a highly variable seawater pH underlaying strong imprints of internal climate variability (high confidence) and, in most instances, superimposed on a decreasing δ11B trend that is indicative of anthropogenic ocean acidification in recent decades (IPCC AR6_WGI, confidence: medium)
Observations over past decades of basin-wide and global syntheses of ocean interior carbon show that the extent of acidification due to anthropogenic CO 2 invasion tends to diminish with depth (IPCC AR6_WGI, confidence: very high)
The regions of deep convection such as subpolar North Atlantic and Southern Ocean present the deepest acidification detections below 2000 m (IPCC AR6_WGI, confidence: medium)
Its rates at depths are controlled by the ventilation of the ocean interior as well as anthropogenic CO 2 uptake at the surface, thereby diminishing with depth (IPCC AR6_WGI, confidence: very high)
It is concluded that the oxygen content of subsurface ocean is projected to transition to historically unprecedented condition with decline over the 21st century (IPCC AR6_WGI, confidence: medium)
Projected oxygen loss in the ocean is thought to result in an ocean-climate feedback through changes in the natural emissions of GHGs (IPCC AR6_WGI, confidence: low)
New syntheses since AR5 corroborate that the effect of elevated CO 2 on plant growth and ecosystem carbon storage is generally positive (IPCC AR6_WGI, confidence: high)
Recent studies (Katavouta et al., 2018; Jiang et al., 2019; Arora et al., 2020; Rodgers et al., 2020) suggest with medium confidence that the decrease in the ocean CO 2 uptake ratio to anthropogenic CO 2 emissions, under low to no mitigation scenarios over the 21st century, is predominantly attributable to the ocean carbon- concentration feedback through the reduction of the seawater CO 2 buffering capacity, but with contributions from physical drivers such as warming and wind stress (medium confidence) and biological drivers (IPCC AR6_WGI, confidence: low)
Overall, there is medium confidence on three outcomes in the ocean from projected CO 2 uptake under medium to high CO 2 concentration scenarios: (i) a weakening of the buffering capacity, which impacts the airborne fraction via the reduction of the ocean CO 2 buffering capacity due to cumulative ocean CO 2 uptake, which reduces the net ocean CO 2 uptake ratio to anthropogenic CO 2 emissions (Katavouta et al., 2018; Arora et al., 2020; Rodgers et al., 2020); (ii) an amplification of the seasonal cycle of CO 2 variables, which impacts both the ocean sink and ocean acidification (Hauck et al., 2015); (iii) a decrease in the aragonite and calcite saturation levels in the ocean, which negatively impacts the calcification rates of marine organisms (IPCC AR6_WGI, confidence: high)
Other disturbances such as tree mortality will increase across several ecosystems (medium agreement) with decreased vegetation carbon (IPCC AR6_WGI, confidence: medium)
The permafrost region was a historic carbon sink over centuries to millennia (IPCC AR6_WGI, confidence: high)
One study inferred a multi-year net CO2 source for the tundra in Alaska (Commane et al., 2017), which is equivalent to 0.3 PgC yr–1 when scaled up to the northern permafrost region (IPCC AR6_WGI, confidence: low)
There is robust evidence that some CH 4 emissions sources for some regions have increased over the past decades (IPCC AR6_WGI, confidence: medium)
This suggests that large emissions of CH 4 from old carbon sources will not occur in response to future warming (IPCC AR6_WGI, confidence: medium)
Near-surface permafrost is projected to decrease significantly under future global warming scenarios (IPCC AR6_WGI, confidence: high)
In conclusion, thawing terrestrial permafrost will lead to carbon release under a warmer world (IPCC AR6_WGI, confidence: high)
In summary, oceanic and terrestrial carbon sinks are projected to continue to grow with increasing atmospheric concentrations of CO 2, but the fraction of emissions taken up by land and ocean is expected to decline as the CO 2 concentration increases (IPCC AR6_WGI, confidence: high)
Despite the wide range of model responses, uncertainty in atmospheric CO 2 by 2100 is dominated by future anthropogenic emissions rather than carbon–climate feedbacks (IPCC AR6_WGI, confidence: high)
However, given the contemporary estimate for CH 4 from wildfires of no more than 16 TgCH 4 yr–1 (van der Werf et al., 2017; Saunois et al., 2020), this feedback is small, adding no more than 40 ppb to the atmospheric CH 4 by the end of the 21st century (IPCC AR6_WGI, confidence: medium)
Abrupt Change/ Tipping PointKey Region(s)Probability to Occur in the 21st CenturyMaximum CO 2 or CH 4 Release in the 21st CenturyPrincipal Development Time ScaleMaximum CO 2 or CH 4 Rate of Change Over the 21st Century(Ir)reversibility Tropical forests dieback (Section 5.4.9.1.1)Amazon watershed Low<200 PgC as CO 2 (Section 5.4.9.1.1; medium confidence)Multi-decadal CO 2: <0.5 ppm yr–1Irreversible at multi-decadal scale (medium confidence) Boreal forests dieback (Sections 5.4.9.1.1, 5.4.3.2)Boreal Eurasia and North AmericaLow<27 Pg (Section 5.4.9.1.2; medium confidence)Multi-decadal Small (low confidence)Irreversible at multi-decadal scale (medium confidence) Biogenic emissions from permafrost thaw (Section 5.4.9.1.2)Pan-Arctic Highup to 240 PgC of CO 2 and up to 5300 Tg of CH 4 (Section 5.4.8.1.2; low confidence)Multi-decadalCO 2: ≤1 ppm yr–1 CH 4: ≤10 ppb yr–1Irreversible at centennial time scales (IPCC AR6_WGI, confidence: high)
This implies an upper limit to the release of tropical land carbon of <200 PgC over the 21st century (assuming tropical warming of <4°C , and no CO 2-fertilization), which translates to dCO 2/dt <0.5 ppm yr–1.Boreal forest dieback is not expected to change the atmospheric CO 2 concentration substantially because forest loss at the south is partly compensated by: (i) temperate forest invasion into previously boreal areas; and (ii) boreal forest gain at the north (Friend et al., 2014; Kicklighter et al., 2014; Schaphoff et al., 2016) (IPCC AR6_WGI, confidence: medium)
However, these are very likely to be small compared to the uncertainty associated with future anthropogenic emissions (IPCC AR6_WGI, confidence: high)
Monteiro (South Africa), Jean-Baptiste Sallée (France), Piers Foster (United Kingdom), Baylor Fox-Kemper (United States of America), Helen T. Hewitt (United Kingdom), Masao Ishii (Japan), Joeri Rogelj (United Kingdom/Belgium), Kirsten Zickfeld (Canada/Germany) Context In the past 60 years, the ocean has taken up and stored 23 ± 5% of anthropogenic carbon emissions (IPCC AR6_WGI, confidence: medium)
These processes are typically simplified into widely verified expressions that link the flux to wind stress, the solubility and the gradient across the air–sea interface (IPCC AR6_WGI, confidence: medium)
The role of the biological carbon pump in influencing the ocean sink of anthropogenic carbon into the ocean interior is assessed to be minimal during the historical period, but this may change, particularly in regional contexts, by 2100 (IPCC AR6_WGI, confidence: medium)
Its role is important in the natural or pre- industrial carbon cycle (IPCC AR6_WGI, confidence: medium)
In contrast, in the Southern Ocean, the future 21st century projected increase in upper ocean overturning circulation (IPCC AR6_WGI, confidence: low)
In this way, the processes of the ocean carbon-heat nexus help understand the quasi-linear and path independence of properties of TCRE, which forms the basis for the zero emissions commitment (ZEC; Section 5.5) (IPCC AR6_WGI, confidence: medium)
Increasing ocean warming and stratification may decrease exchanges between the surface and subsurface ocean, which could reduce the path independence of TCRE, though this effect can be partially counterbalanced regionally by increasing circulation associated with increasing winds (IPCC AR6_WGI, confidence: low)
Whether the transition to source occurs at all, the timing of the transition and the magnitude of the CO 2 source are determined by the magnitude of the removal and the rate and amount of net CO 2 emissions prior to emissions becoming net negative (IPCC AR6_WGI, confidence: medium)
In response to increasing risks to permanence of carbon stocks of some types of afforestation practices and the competition for land, there has been an increasing recognition that secondary forest regrowth and restoration of degraded forests and non-forest ecosystems can play a large role in carbon sequestration (IPCC AR6_WGI, confidence: high)
Forest- based methods can either raise or lower N 2O emissions, depending on tree species, previous land use, soil type and climatic factors (IPCC AR6_WGI, confidence: low)
Afforestation will decrease biodiversity if native species are replaced by monocultures (IPCC AR6_WGI, confidence: high)
Some soil carbon sequestration methods, such as cover crops and crop diversity, can increase biodiversity (IPCC AR6_WGI, confidence: medium)
Biochar application improves many soil qualities and increases crop yield (medium confidence) (Ye et al., 2020; SRCCL, Chapter 4.9.5), particularly in already degraded or weathered soils (Woolf et al., 2010; Lorenz and Lal, 2014; Jeffery et al., 2016), increases soil water holding capacity (IPCC AR6_WGI, confidence: medium)
Fischer et al., 2019; Verheijen et al., 2019) and evapotranspiration (IPCC AR6_WGI, confidence: low)
The use of biochar reduces nutrient losses (IPCC AR6_WGI, confidence: low)
Biochar addition may decrease methane (CH 4) emissions in inundated and acid soils such as rice fields (IPCC AR6_WGI, confidence: low)
In non-inundated, neutral soils, CH 4 uptake from the atmosphere is suppressed after biochar application (low confidence) (Jeffery et al., 2016), and soil N2O emissions decline (IPCC AR6_WGI, confidence: medium)
High water level and anoxic conditions are prerequisites for restoring by returning drained and/or degraded peatlands back to their natural state as CO 2 sinks, but restoration also results in enhanced CH 4 emissions which are similar to or higher than the pre-drainage fluxes (IPCC AR6_WGI, confidence: high)
Rewetting drained peatlands will decrease N2O emissions (IPCC AR6_WGI, confidence: medium)
Peatland restoration can also recover much of the original biodiversity (IPCC AR6_WGI, confidence: medium)
BECCS has several trade- offs to deal with, including possible threats to water supply and soil nutrient deficiencies (IPCC AR6_WGI, confidence: medium)
Highest co-benefits are obtained with methods that seek to restore natural ecosystems and improve soil carbon sequestration (Figure 5.36) while highest trade- off possibilities (symmetry with the highest co-benefits) occur for reforestation or afforestation with monocultures and BECCS, again with strong dependence on scale and context (IPCC AR6_WGI, confidence: medium)
While coastal habitat restoration potentially provides significant mitigation of national emissions for some countries (Taillardat et al., 2018; Serrano et al., 2019), the global sequestration potential of blue carbon approaches is <0.02 PgC yr–1 (IPCC AR6_WGI, confidence: medium)
EW can also contribute to freshwater salinization as a result of increased salt inputs and cation exchange in watersheds, and so adversely affecting drinking water quality (IPCC AR6_WGI, confidence: low)
Ocean alkalinization ameliorates surface ocean acidification (IPCC AR6_WGI, confidence: high)
Despite the large uncertainty in modelled NPP response, existing modelling studies consistently show that SRM would increase the global land carbon sink relative to a high-CO 2 world without SRM (IPCC AR6_WGI, confidence: high)
Based on available evidence, SRM with elevated CO 2 would increase global mean NPP and carbon storage on land relative to an unperturbed climate, mainly because of CO 2 fertilization of photosynthesis (IPCC AR6_WGI, confidence: high)
As a result of enhanced global carbon uptake, SRM would reduce the burden of atmospheric CO 2 (IPCC AR6_WGI, confidence: high)
Compared to a high-CO 2 world without SRM, SRM would enhance the net uptake of CO 2 by the terrestrial biosphere and ocean, thus acting to reduce atmospheric CO 2 (IPCC AR6_WGI, confidence: high)
Recent Evolution in Short-lived Climate Forcer (SLCF) Emissions and Abundances Over the last decade (2010–2019), strong shifts in the geographical distribution of emissions have led to changes in atmospheric abundances of highly variable SLCFs (IPCC AR6_WGI, confidence: high)
Evidence from satellite and surface observations shows strong regional variations in trends of ozone (O 3), aerosols and their precursors (IPCC AR6_WGI, confidence: high)
In particular, tropospheric columns of nitrogen dioxide (NO 2) and sulphur dioxide (SO 2) continued to decline over North America and Europe (high confidence), and to increase over Southern Asia (medium confidence), but have declined over Eastern Asia (IPCC AR6_WGI, confidence: high)
Global carbon monoxide (CO) abundance has continued to decline (IPCC AR6_WGI, confidence: high)
The concentrations of hydrofluorocarbons (HFCs) are increasing (IPCC AR6_WGI, confidence: high)
Radiative forcings induced by aerosol changes lead to both local and remote temperature responses (IPCC AR6_WGI, confidence: high)
The temperature response preserves the south to north gradient of the aerosol ERF – hemispherical asymmetry – but is more uniform with latitude and is strongly amplified towards the Arctic (IPCC AR6_WGI, confidence: medium)
The spatial and temporal distribution of the net aerosol ERF from 1850 to 2014 is highly heterogeneous, with stronger magnitudes in the Northern Hemisphere (IPCC AR6_WGI, confidence: high)
Near its maximum, the response slows down but will then take centuries to reach equilibrium (IPCC AR6_WGI, confidence: high)
For SLCFs with longer lifetimes (e.g., a decade), a delay equivalent to their lifetimes is appended to the delay due to thermal inertia (IPCC AR6_WGI, confidence: high)
The net global emissions‑based ERF of NO x is negative and that of non‑methane volatile organic compounds (NMVOCs) is positive, in agreement with the AR5 Assessment (IPCC AR6_WGI, confidence: high)
For methane, the emissions‑based ERF is twice as high as the abundance‑based ERF (IPCC AR6_WGI, confidence: high)
Over the 1750–2019 period, the contributions from the emitted compounds to changes in global surface air temperature (GSAT) broadly match their contributions to the ERF (IPCC AR6_WGI, confidence: high)
As such, these effects are assessed to be of second order in comparison to the direct CO 2 forcing (high confidence), but effects of ozone on terrestrial vegetation could add a substantial (positive) forcing compared with the direct ozone forcing (IPCC AR6_WGI, confidence: low)
A warmer climate is expected to reduce surface ozone in regions remote from pollution sources (IPCC AR6_WGI, confidence: high)
Future climate change is expected to have mixed effects, positive or negative, with an overall low effect, on global surface PM and more generally on the aerosol global burden (medium confidence), but stronger effects are not excluded in regions prone to specific meteorological conditions (IPCC AR6_WGI, confidence: low)
Under the SSP3‑7.0 scenario, PM levels are projected to increase until 2050 over large parts of Asia, and surface ozone pollution is projected to worsen over all continental areas through 2100 (IPCC AR6_WGI, confidence: high)
Without climate change mitigation but with stringent air pollution control (SSP5‑8.5), PM levels decline through 2100, but high methane levels hamper the decline in global surface ozone at least until 2080 (IPCC AR6_WGI, confidence: high)
Sectors producing the largest SLCF-induced warming are those dominated by methane emissions: fossil fuel production and distribution, agriculture and waste management (IPCC AR6_WGI, confidence: high)
On these time scales, SLCFs with cooling effects can significantly mask the CO 2 warming in the case of fossil fuel combustion for energy and land transportation, or completely offset the CO 2 warming and lead to an overall net cooling in the case of industry and maritime shipping (prior to the implementation of the revised fuel‑sulphur limit policy for shipping in 2020) (IPCC AR6_WGI, confidence: medium)
Ten years after a one‑year pulse of present‑day aviation emissions, SLCFs induce strong but short‑lived warming contributions to the GSAT response (IPCC AR6_WGI, confidence: medium)
Consequently, on time scales longer than about 30 years, the net long-term global temperature effects of sectors and regions are dominated by CO 2 (IPCC AR6_WGI, confidence: high)
About 30 years or more after a one‑year emission pulse occurs, the sectors contributing the most to global warming are industry, fossil fuel combustion for energy and land transportation, essentially through CO2 (IPCC AR6_WGI, confidence: high)
Current emissions of SLCFs, CO 2 and N 2O from Eastern Asia and North America are the largest regional contributors to additional net future warming on both short (medium confidence) and long time scales (IPCC AR6_WGI, confidence: high)
Energy and industry are important PM 2.5 contributors in most regions, except Africa (IPCC AR6_WGI, confidence: high)
Further improvements in the efficiency of refrigeration and air ‑conditioning equipment during the transition to low‑global‑ warming‑potential refrigerants would bring additional greenhouse gas reductions (IPCC AR6_WGI, confidence: medium)
This warming is stable after 2040 in scenarios leading to lower global air pollution as long as methane emissions are also mitigated, but the overall warming induced by SLCF changes is higher in scenarios in which air quality continues to deteriorate (induced by growing fossil fuel use and limited air pollution control) (IPCC AR6_WGI, confidence: high)
Sustained methane mitigation, wherever it occurs, stands out as an option that combines near‑ and long‑term gains on surface temperature (high confidence) and leads to air ‑quality benefits by reducing surface ozone levels globally (IPCC AR6_WGI, confidence: high)
Additional methane and BC mitigation would contribute to offsetting the additional warming associated with SO 2 reductions that would accompany decarbonization (IPCC AR6_WGI, confidence: high)
Strong air pollution control as well as strong climate change mitigation, implemented separately, lead to large reductions in exposure to air pollution by the end of the century (IPCC AR6_WGI, confidence: high)
Implementation of air pollution controls, relying on the deployment of existing technologies, leads more rapidly to air quality benefits than climate change mitigation (IPCC AR6_WGI, confidence: high)
However, in both cases, significant parts of the population are projected to remain exposed to air pollution exceeding the WHO guidelines (IPCC AR6_WGI, confidence: high)
Global anthropogenic NO x emissions decreased by a maximum of about 35% in April 2020 (IPCC AR6_WGI, confidence: medium)
Global fossil CO 2 emissions decreased by 7% (with a range of 5.8–13.0%) in 2020 relative to 2019, largely due to reduced emissions from the transportation sector (IPCC AR6_WGI, confidence: medium)
Consistent with this small net radiative forcing, and against a large component of internal variability, Earth system model simulations show no detectable effect on global or regional surface temperature or precipitation (IPCC AR6_WGI, confidence: high)
The SRCCL concluded that: (i) there is no agreement about the direction of future changes in mineral dust emissions; (ii) fossil fuel and biomass burning, and secondary organic aerosols (SOA) from natural BVOC emissions are the main global sources of carbonaceous aerosols whose emissions are expected to increase in the near future due to possible increases in open biomass burning and increase in SOA from oxidation of BVOCs (IPCC AR6_WGI, confidence: medium)
However, Chinese emissions declined by nearly 70% between about 2006 and 2017 (IPCC AR6_WGI, confidence: high)
Since about 2011, global NO x emissions appear to have stabilized or slightly declined (IPCC AR6_WGI, confidence: medium)
Liu et al., 2016; Miyazaki et al., 2017; Silver et al., 2018): a strong decline of NO 2 column over eastern China (IPCC AR6_WGI, confidence: high)
Efforts to control transport emissions (i.e., increasing stringency of vehicle emissions limits) were largely offset by the fast growth of emissions from chemical industries and solvent use, as well as from fossil fuel production and distribution, resulting in continued growth of global anthropogenic NMVOC emissions since 1900 (IPCC AR6_WGI, confidence: high)
Increasing (since 2008) oil‑ and gas‑extraction activities in North America lead to a strong growth of NMVOC emissions (IPCC AR6_WGI, confidence: high)
Emissions of carbonaceous aerosols (BC, OC) have been steadily increasing and their emissions have almost doubled since 1950 (IPCC AR6_WGI, confidence: medium)
Before 1950, North America and Europe contributed about half of the global total but successful introduction of diesel particulate filters on road vehicles (Fiebig et al., 2014; Robinson et al., 2015; Klimont et al., 2017a) and declining reliance on solid fuels for heating brought in large reductions (IPCC AR6_WGI, confidence: high)
Currently, global carbonaceous aerosol emissions originate primarily from Asia and Africa (Bond et al., 2013; Hoesly et al., 2018; Elguindi et al., 2020; McDuffie et al., 2020), representing about 80% of the global total (IPCC AR6_WGI, confidence: high)
Overall, a factor two uncertainty in global estimates of BC and OC emissions remains, with post‑ 2005 emissions overestimated in Asia (high confidence) and Africa (IPCC AR6_WGI, confidence: medium)
Bottom‑up global emissions estimates of methane (Lamarque et al., 2010; Hoesly et al., 2018; Janssens‑Maenhout et al., 2019; Höglund‑Isaksson et al., 2020) for the last two decades are higher than top‑down assessments (e.g., Saunois et al., 2016, 2020) but trends from the two methods are similar and indicate continued growth (IPCC AR6_WGI, confidence: high)
NH 3 emissions are estimated to have grown strongly since 1850, especially since 1950, driven by continuously increasing livestock production, widespread application of mineral nitrogen fertilizers, and lack of action to control ammonia (IPCC AR6_WGI, confidence: high)
Overall, we assess that historical global isoprene emissions declined between the pre‑industrial period and the present day by 10–25% (IPCC AR6_WGI, confidence: low)
This increase is assessed to be 109 ± 25 Tg (IPCC AR6_WGI, confidence: medium)