Which Scenario Best Describes How Climate Trends Might Affect Animal Migration?
Over the by few years, an international squad of climate scientists, economists and energy systems modellers have built a range of new "pathways" that examine how global society, demographics and economics might change over the next century. They are collectively known as the "Shared Socioeconomic Pathways" (SSPs).
These SSPs are at present beingness used as important inputs for the latest climate models, feeding into the Intergovernmental Panel on Climate Alter (IPCC) sixth cess report due to exist published in 2020-21. They are also being used to explore how societal choices will affect greenhouse gas emissions and, therefore, how the climate goals of the Paris Understanding could exist met.
The new SSPs offering five pathways that the world could take. Compared to previous scenarios, these offering a broader view of a "business as usual" globe without future climate policy, with global warming in 2100 ranging from a low of 3.1C to a high of v.1C above pre-industrial levels.
They show that it would be much easier to mitigate and adapt to climatic change in some versions of the future than in others. They suggest, for example, that a hereafter with "resurgent nationalism" and a fragmentation of the international order could make the "well beneath 2C" Paris target incommunicable.
What are the SSPs?
In the late 2000s, researchers from dissimilar modelling groups around the earth began the process of developing new scenarios to explore how the world might change over the rest of the 21st century.
Earlier efforts during the 1990s had developed the "SRES" scenarios, which looked at four unlike possible future trajectories of population, economic growth and greenhouse gas emissions. However, these were fast becoming dated and lacked some large changes to guild and the global economy that have occurred over the past 20 years.
Glossary
Radiative Forcings: Radiative forcing is the difference between incoming and approachable energy in the Earth's climate. When increased greenhouse gases result in incoming energy beingness greater than outgoing free energy, the planet will warm due to increased radiative forcing. Some forcings are positive while others, such as those from volcanoes or human-emitted aerosols, are negative.
Radiative Forcings: Radiative forcing is the departure between incoming and outgoing free energy in the Earth's climate. When increased greenhouse gases result in incoming energy beingness greater than outgoing energy, the planet will warm due… Read More than
I group of researchers then adult the "Representative Concentration Pathways" (RCPs), describing dissimilar levels of greenhouse gases and other radiative forcings that might occur in the future. They adult four pathways, spanning a broad range of forcing in 2100 (ii.6, 4.5, half-dozen.0, and eight.5 watts per meter squared), but purposefully did not include any socioeconomic "narratives" to go alongside them.
A second grouping worked on modelling how socioeconomic factors may change over the next century. These include things such every bit population, economical growth, pedagogy, urbanisation and the rate of technological evolution. These "Shared Socioeconomic Pathways" (SSPs) look at five unlike ways in which the earth might evolve in the absence of climate policy and how unlike levels of climatic change mitigation could exist achieved when the mitigation targets of RCPs are combined with the SSPs.
The two efforts were designed to be complementary. The RCPs set pathways for greenhouse gas concentrations and, finer, the amount of warming that could occur by the stop of the century. Whereas the SSPs fix the stage on which reductions in emissions volition – or volition not – be achieved.
The SSPs likewise define unlike baseline worlds that might occur in the absence of whatever concerted international attempt to address climatic change, beyond those already adopted by countries. These exclude whatsoever commitments to enact new policies, such as those within the Paris Understanding up to 2025 and 2030.
The SSPs feature multiple baseline worlds because underlying factors, such equally population, technological, and economic growth, could atomic number 82 to very different future emissions and warming outcomes, even without climate policy.
While the RCPs were finished in time to be used in the IPCC Fifth Assessment Study, developing the more complex SSPs has been a much longer and more than involved process. The SSPs were initially published in 2016, only are just now just starting to exist used in the next round of climate modelling – known as the Coupled Model Intercomparison Project version 6, or CMIP6 – in preparation for the IPCC's 6th cess report.
Narratives of the future
The SSPs are based on v narratives describing wide socioeconomic trends that could shape hereafter lodge. These are intended to span the range of plausible futures.
They include: a world of sustainability-focused growth and equality (SSP1); a "middle of the road" world where trends broadly follow their historical patterns (SSP2); a fragmented world of "resurgent nationalism" (SSP3); a earth of e'er-increasing inequality (SSP4); and a earth of rapid and unconstrained growth in economic output and energy use (SSP5).
The narrative for each is described in detail below:
SSP narratives
| SSP1 | Sustainability – Taking the Green Route (Low challenges to mitigation and accommodation) The globe shifts gradually, just pervasively, toward a more than sustainable path, emphasizing more inclusive development that respects perceived ecology boundaries. Direction of the global commons slowly improves, educational and health investments advance the demographic transition, and the emphasis on economical growth shifts toward a broader emphasis on human well-beingness. Driven past an increasing commitment to achieving development goals, inequality is reduced both across and within countries. Consumption is oriented toward low material growth and lower resource and energy intensity. |
| SSP2 | Eye of the Road (Medium challenges to mitigation and accommodation) The globe follows a path in which social, economic, and technological trends do not shift markedly from historical patterns. Evolution and income growth proceeds unevenly, with some countries making relatively good progress while others fall brusque of expectations. Global and national institutions work toward but make ho-hum progress in achieving sustainable evolution goals. Ecology systems experience deposition, although at that place are some improvements and overall the intensity of resource and energy utilisation declines. Global population growth is moderate and levels off in the second half of the century. Income inequality persists or improves only slowly and challenges to reducing vulnerability to societal and environmental changes remain. |
| SSP3 | Regional Rivalry – A Rocky Route (High challenges to mitigation and adaptation) A resurgent nationalism, concerns about competitiveness and security, and regional conflicts push countries to increasingly focus on domestic or, at most, regional issues. Policies shift over time to get increasingly oriented toward national and regional security bug. Countries focus on achieving energy and food security goals within their ain regions at the expense of broader-based development. Investments in educational activity and technological development decline. Economic evolution is irksome, consumption is material-intensive, and inequalities persist or worsen over fourth dimension. Population growth is low in industrialized and loftier in developing countries. A low international priority for addressing ecology concerns leads to strong ecology degradation in some regions. |
| SSP4 | Inequality – A Road Divided (Low challenges to mitigation, high challenges to adaptation) Highly diff investments in human capital letter, combined with increasing disparities in economic opportunity and political power, lead to increasing inequalities and stratification both across and within countries. Over fourth dimension, a gap widens between an internationally-connected lodge that contributes to knowledge- and capital-intensive sectors of the global economy, and a fragmented collection of lower-income, poorly educated societies that work in a labor intensive, low-tech economy. Social cohesion degrades and conflict and unrest get increasingly common. Engineering science development is high in the high-tech economic system and sectors. The globally continued energy sector diversifies, with investments in both carbon-intensive fuels like coal and unconventional oil, but besides low-carbon energy sources. Environmental policies focus on local issues around eye and high income areas. |
| SSP5 | Fossil-fueled Development – Taking the Highway (Loftier challenges to mitigation, low challenges to adaptation) This world places increasing faith in competitive markets, innovation and participatory societies to produce rapid technological progress and development of human capital every bit the path to sustainable development. Global markets are increasingly integrated. In that location are also potent investments in health, education, and institutions to enhance human and social capital. At the same time, the push for economic and social evolution is coupled with the exploitation of abundant fossil fuel resources and the adoption of resource and energy intensive lifestyles effectually the globe. All these factors atomic number 82 to rapid growth of the global economy, while global population peaks and declines in the 21st century. Local ecology bug similar air pollution are successfully managed. There is faith in the ability to finer manage social and ecological systems, including by geo-engineering if necessary. |
Narratives for each Shared Socioeconomic Pathway, from Riahi et al 2017.
These narratives describe alternative pathways for future club. They present baselines of how things would look in the absence of climate policy, and permit researchers to examine barriers and opportunities for climate mitigation and accommodation in each possible future earth when combined with mitigation targets.
SSP1 and SSP5 envision relatively optimistic trends for man development, with "substantial investments in pedagogy and health, rapid economic growth, and well-performance institutions". They differ in that SSP5 assumes this will be driven by an energy-intensive, fossil fuel-based economy, while in SSP1 there is an increasing shift toward sustainable practices.
SSP3 and SSP4 are more than pessimistic in their future economic and social evolution, with little investment in didactics or health in poorer countries coupled with a fast-growing population and increasing inequalities.
SSP2 represents a "middle of the road" scenario historical patterns of development are connected throughout the 21st century.
The SSPs were designed to reflect worlds in which mitigation and adaptation challenges vary from depression to very high. While the baseline SSP scenarios assume an absence of climate policy, researchers also wanted to look at how the underlying socioeconomic weather condition would affect the implementation of climate policy.
For example, SSP1 features low challenges to mitigation and adaptation due to its rapid technological development, relative global equality of income and focus on environmental sustainability. SSP4, on the other paw, features similarly depression challenges to mitigation due to its rapid technological development, merely high challenges to climate adaptation due to persistent inequality and poverty in many parts of the earth.
Many of the SSPs cease upward being broadly similar in the narratives to the old SRES scenarios, used in the IPCC's tertiary and fourth assessment reports. For example, the sustainability-focused SSP1 is rather like to SRES B1, while the more eye-of-the-route SSP2 is like to SRES B2. The globally fragmented SSP3 is quite similar to SRES A2 and the high fossil-fuel reliant, high-growth SSP5 shares many elements with SRES A1F1.
Different the SRES scenarios, even so, mitigation is considered separately from the underlying pathways. Each SSP has a baseline scenario that describes future developments in the absence of new climate policies, beyond those already in place today. SSPs can so be combined with diverse emission mitigation targets.
Specifically, each SSP looks at how each different RCPs could be accomplished inside the context of the underlying socioeconomic characteristics and shared policy assumptions of that world, though, as discussed below, not all SSPs are compatible with the RCPs limiting warming to 1.5C or 2C above pre-industrial levels.
Future scenarios for population and GDP
The main differences between SSPs come from their assumptions on global population growth, access to education, urbanisation, economic growth, resources availability, technology developments and drivers of demand, such equally lifestyle changes.
The effigy below shows different global population (left) and GDP projections (right) for each of the v SSPs over the 21st century. While multiple groups of researchers created population and GDP estimates, a single projection was chosen equally representative for each SSP to ensure consistency across modelling efforts.
Global population (left) in billions and global gross domestic production (right) in trillion US dollars on a purchasing power parity (PPP) ground. Data from the SSP database; chart by Carbon Brief using Highcharts.
To create different global population scenarios, researchers used a demographic model based on assumptions of future fertility, mortality, migration and instruction. Assumptions for futurity female person admission to teaching strongly influence fertility and population growth. These assumptions were varied to be consistent with each SSP narrative.
Population levels are lowest in SSP1 and SSP5, peaking at 8.5 billion between 2050 and 2060, and declining to today'southward level of effectually 7 billion by 2100. This is broadly consequent with the United Nation'southward depression fertility scenario.
SSP2 and SSP4 are more heart of the road, with population peaking between 2070 and 2080 around 9.5 billion, though this is still lower than the UN medium fertility scenario of around 11.five billion. Finally, SSP3 shows continued global population growth through to the finish of the century, reaching 12.half dozen billion by 2100. SSP3 is higher than the United nations medium fertility scenario, only even so below the Un'due south high fertility scenario.
The population projections in the SSPs are generally a scrap lower than in prior modelling efforts (for example, SRES), due to the decline of fertility rates in developing countries over the past two decades and the faster-than-expected expansion of education among young women in the least developed countries.
All SSPs project dramatic growth in the global economy, with global GDP in 2100 between four and 10 times larger than it was in 2010. This translates into an boilerplate annual global GDP growth charge per unit of betwixt 1.8% at the low end and iii.4% at the high end, though in all models the growth rate slows over the century.This growth is one of the master drivers of future CO2 emissions, though different scenarios foresee unlike levels of future "decoupling" of growth and emissions associated with a decarbonising of the economy.
The GDP numbers incorporate population projections from each SSP, as well equally assumptions of international trade flows, technological development and other factors consequent with the SSP narratives.
The highest Gdp growth is establish in SSP5, with rapid evolution and convergence amid countries and global average per-capita GDP of around $140,000 per year in 2100. The everyman Gross domestic product growth occurs in SSP3, where development is slow and fragmented. In SSP3 global average income is around $20,000 in 2100, only modestly above today'due south levels.
SSPs too differ markedly in the level of future inequality within and between countries. SSP4 has the highest inequality, followed by SSP3. Both SSP1 and SSP5 feature relatively equitable evolution and a rapid catch-up of the world's poorest countries over the coming century.
Finally, SSPs provide estimates of how the world will become more urban in the future. This ranges from a low of threescore% of the population living in cities in 2100 in SSP3 – similar to today's rate of 54% – to up to 92% in SSP1, SSP4, and SSP5. SSP2 is in the middle, reaching 80% urbanisation by 2100.
Baseline CO2 emissions and warming
Researchers employed 6 dissimilar integrated assessment models (IAMs) to translate the socioeconomic atmospheric condition of the SSPs into estimates of futurity energy utilisation characteristics and greenhouse gas emissions.
Glossary
Integrated Assessment Models: IAMs are computer models that analyse a broad range of data – e.g. physical, economic and social – to produce information that can be used to assistance controlling. For climate research, specifically, IAMs are typically used to project time to come greenhouse gas emissions and climate impacts, and the benefits and costs of policy options that could be implemented to tackle them.
Integrated Assessment Models: IAMs are computer models that analyse a broad range of information – e.thousand. physical, economic and social – to produce data that can exist used to help controlling. For climate inquiry, specifically,… Read More than
IAMs add aspects of gild to an energy systems model, simulating how population, economic growth and energy utilisation bear upon – and interact with – the concrete climate. They produce scenarios of how greenhouse gas emissions may vary in hereafter based on underlying socioeconomic factors – and how energy use, production and economic action may alter to meet climate mitigation targets.
Half-dozen IAMs were used to create free energy use and emissions characteristics for the SSPs – AIM-CGE, GCAM, Prototype, MESSAGE-GLOBIOM, REMIND-Magpie, and WITCH-GLOBIOM. A total of 24 baseline scenarios were created past the different models simulating dissimilar SSPs, though not all models ran all SSPs.
To make these results easier for the climate modelling community to work with, a single model was called as the "mark" scenario for each SSP, so that, for instance, climate researchers looking at SSP1 would expect at the IMAGE model outputs, while SSP2 would utilize the Message model.
The simple climate model MAGICC was used to convert greenhouse gas emissions from the IAMs into atmospheric concentrations and future warming.
(More detailed earth system and general circulation climate models are currently beingness run as part of the ongoing Coupled Model Intercomparison Projection half-dozen (CMIP6), in preparation for the IPCC's sixth assessment report, though the resulting global temperature increases should be broadly similar.)
The figure beneath shows the CO2 emissions (left) and global boilerplate temperature increases relative to pre-industrial levels (right) for each SSP'southward baseline scenario. Each line represents an individual model run, with the colours indicating the SSP and the "marker" scenarios for each SSP shown by thick lines.
CO2 emissions (left) in gigatonnes (GtCO2) and global mean surface temperature alter relative to pre-industrial levels (right) in degrees C beyond all models and SSPs for baseline no-climate-policy scenarios. The "marker" model for each SSP is shown by a thicker line, while all other model runs for that SSP accept sparse lines. Data from the SSP database; chart past Carbon Brief using Highcharts.
Global CO2 emissions vary considerably across the different SSP baselines. In full general, i of the strengths of the SSP framework is to highlight the importance of baseline assumptions on resulting emissions and temperatures.
In the relatively sustainability-focused SSP1, emissions peak between 2040 and 2060 – fifty-fifty in the absence of specific climate policies, declining to around 22 to 48 gigatonnes of CO2 (GtCO2) per year by 2100. This results in iii-iii.5C of warming past 2100.
In the "middle of the route" SSP2, emissions go along to increment through the end of the century, reaching between 65GtCO2 and 85GtCO2, with resulting warming of 3.eight-four.2C.
Models bear witness a wide range of possible baseline emissions for the "regional rivalry" SSP3, with virtually runs showing increases up to effectually 76-86GtCO2 by 2100, just ane model (Message) having emissions of 129GtCO2, the highest of whatsoever SSP. These differences relate to access to economically recoverable oil, as discussed in the next department. Warming in 2100 in SSP3 is estimated at three.9-4.6C.
Despite its high inequality, emissions are relatively low in SSP4 due to rapid technological progress on low-carbon free energy sources. SSP4 emissions range from 34GtCO2 to 45GtCO2 by 2100, with warming of 3.5-3.8C.
Finally, the high-growth free energy-intensive SSP5 shows the most overall emissions of any SSP, ranging from 104GtCO2 to 126GtCO2 in 2100, resulting in warming of 4.vii-5.1C.
Energy use in the SSP baselines
While the SSP baseline scenarios all represent worlds without new policies to address climate modify, they differ significantly in how they meet global energy use irresolute.
Some scenarios, such every bit SSP3, foresee lilliputian development of cost-constructive low-carbon alternatives, or technologies that can cheaply address non-climate negative impacts of fossil fuels, such every bit air pollution in SSP5. In these worlds, coal continues to exist i of the primary global energy sources through to the end of the century, leading to loftier CO2 emissions and warming.
Others, such equally SSP1 and SSP4, take a much larger share of energy coming from renewable sources, with some electrification of current fossil fuel cease-uses, such as transportation or heating, but driven by falling costs rather than climate concerns.
The effigy below shows how free energy is used in 2100 in each SSP and IAM. While they differ a flake in their mix of fuel sources, with a few exceptions – such as the MESSAGE model in SSP3 – the total master free energy use is similar for all models in a given SSP.
Global principal energy use by fuel type in 2100 in exajoules (EJ) for baseline scenarios in each IAM and SSP. Current energy use (as of 2010) is shown for reference in the far left bar. Data from the SSP database and Riahi et al 2017; nautical chart past Carbon Brief using Highcharts.
The SSP baselines span a wide range of futurity energy demand. At the upper stop of the range, the SSP5 scenario has energy demand of over 1,500 exajoules (EJ) per yr, more than than 3 times higher than today's 500EJ. SSP2 and SSP3 have more than twice current energy need, while in SSP1 energy need stays only around fifty% higher up today's levels, despite rapid economic growth.
Energy admission is besides quite dissimilar across SSPs. In the SSP3 and SSP4 baseline scenarios in that location is continued use of traditional biomass, such as wood or animal dung, in the households of developing countries, while the use of coal and biomass in households decreases dramatically in the other three scenarios.
In SSP3, the Bulletin model has unusually loftier coal use due, in office, to the exhaustion of economically viable oil reserves and the conversion of coal into hydrocarbons to meet transportation fuel needs. Other SSP3 models presume larger economically viable oil reserves and, thus, less dramatic coal use.
Overall, coal utilize is quite high in SSP3 and SSP5. In the SSP5 baseline marker scenario (REMIND), coal use between 2005 and 2100 is around 44,500 exajoules (EJ), considerably larger than current technologically and economically recoverable reserves of around 21,000EJ.
However, it is still well inside the range of all known coal resources, which are estimated at around 490,000EJ, a portion of which could get economically recoverable with boosted technological developments. That said, high coal-use scenarios, such as those plant in the SSP5 baseline (which corresponds to RCP8.5), accept been criticised in the by equally potentially unrealistic.
Even in the relatively sustainability-focused SSP1 coal use is shut to today's levels in 2100, reflecting the challenge of switching away from fossil fuels in the absence of climate policy.
The figure below shows how global free energy use changes over time in each of the SSP no-policy baseline marker scenarios.
Global primary energy use by fuel type betwixt 2005 and 2100 in exajoules (EJ) for each SSP baseline marker scenario (IMAGE for SSP1, Message for SSP2, AIM for SSP3, GCAM for SSP4, and REMIND for SSP5). Information from the SSP database and Riahi et al 2017; chart by Carbon Brief using Highcharts.
While renewable energy and biomass make upwards a larger portion of the free energy mix in the more sustainability-focused SSP1, effectually sixty% of energy demand in 2100 still comes from fossil fuel sources. In the absence of boosted climate policy, these scenarios exercise not foresee technological progress by itself leading to an energy system dominated by depression-carbon sources during this century.
(Information technology is worth noting that energy scenarios have been repeatedly criticised for overestimating the costs and underestimating the potential of low-carbon technologies.)
Combining SSPs and mitigation targets
While the baseline SSP scenarios portray a range of outcomes in the absence of additional climate policy, researchers also wanted to examine how unlike levels of climate mitigation and accommodation would fit into the hereafter described by each SSP.
To model this, they used shared policy assumptions around how apace international collaboration on climate policy could occur within each SSP, as well as respecting limitations imposed by the underlying assumptions around population growth, economic activity and technological evolution in each pathway.
The mitigation targets examined are defined by radiative forcing levels (in watts per meter squared) analogous to the RCPs, which set a target level of atmospheric greenhouse gas concentrations (and associated radiative forcing) in 2100.
The figure below shows the emissions over time under all the SSP baselines (grey lines) and under unlike mitigation targets, where radiative forcings in 2100 are limited to 6.0, iv.5, 3.4, 2.half-dozen and i.nine watts per meter squared (coloured lines). The average amount of warming associated with the range of baselines and each of the targets is also shown, on the right.
With the release of the SSPs, modellers have expanded the range of mitigation targets that they are because. The IPCC fifth cess report focused on RCP2.6, RCP4.v, RCP6.0 and a high-terminate no-mitigation RCP8.5 pathway. The SSPs have added RCP1.9, RCP3.four and are planning to add RCP7.0.
RCP1.9 is a new pathway that focuses on limiting warming to below 1.5C, the aspirational goal of the Paris Agreement. Pre-Paris, the research community was focussed on limiting warming to 2C as the most ambitious climate outcome. However, after the adoption of the Paris Agreement and the inclusion of 1.5C in its long-term temperature goal, there was a need to clearly understand the implications of this more than ambitious target.
RCP3.iv, on the other hand, represents an intermediate pathway between the "very stringent" RCP2.six and less stringent mitigation efforts associated with RCP4.v. It provides an alternative to explore given "recent discussions well-nigh…the attainability of the 2C objective". A variant of RCP3.4 is also being explored where where forcings "essentially overshoot" the target mid-century and are brought back downwards by 2100 through the employ of large amounts of negative emissions afterwards in the century.
Finally, RCP7.0 will stand for the medium-to-loftier stop of the range of future emissions and warming, and is a baseline effect rather than a mitigation target. It will fill an of import gap past providing a pathway similar to the SSP2 "center of the road" baseline, and may provide a compelling alternative or complement to the commonly used RCP8.5 for studies comparing mitigation and "business-as-usual" scenarios.
The combination of v SSPs and six RCPs is shown in the figure below. (RCP7.0 is not shown equally the runs are non yet complete.)
Each box in the figure shows the number of models that were able to successfully reach the RCP target, out of the total number of models available for a given SSP. For example, the "3/four" in the SSP5 / RCP2.half-dozen cell ways that iv IAMs tried to attain RCP2.6 in an SSP5 world, simply only iii of the models could find a solution. The other model could not either reduce emissions fast enough or generate sufficient negative emissions. Similarly, only SSP5 could generate scenarios that reached RCP8.v-levels of radiative forcings, while emissions were also depression in other SSP baselines.
To define whether the underlying socioeconomic factors in an SSP allow for the level of mitigation necessary to meet RCP targets, models used shared policy assumptions about limits to international cooperation in the short-to-medium term and the possible speed of emissions reductions.
For instance, SSP1 and SSP4 see it equally possible for there to be "global collaboration" on climate policies past the year 2020. The more than fossil fuel-driven SSP2 and SSP5 worlds have delays in establishing global activeness, with regions moving to global cooperation between 2020–2040. The regionally fragmented SSP3 has some higher-income regions joining a global effort to mitigate emissions betwixt 2020–2040, while lower income regions follow between 2030 and 2050.
For land use, which is an important and hard-to-regulate source of emissions, SSP1 and SSP5 allow constructive international cooperation to reduce emissions. SSP2 and SSP4 allow some more limited efforts to reduce emissions from deforestation and agriculture, while SSP3 mostly assumes it will not be possible to encourage individual countries to avert deforestation.
The differences between SSPs touch the ability of scenarios to have large near-term mitigation of greenhouse gas emissions. While SSP1 and SSP4 allow for quick global action in reducing emissions beyond those already agreed to in the nationally adamant contributions (NDCs) under the Paris Agreement, other scenarios, such equally SSP3 and SSP5, find that fifty-fifty these existing commitments are challenging to accomplish in full.
In SSP5, emissions rising too far and fall too slowly to meet the Paris targets without large amounts of negative emissions in the latter part of the century, to offset slower near-term emissions reductions. Three out of four SSP5 models were able to develop possible scenarios to reach RCP2.6 targets of limiting warming below 2C, while just two out of four were able to find a way to reach RCP1.9 and limit warming to below 1.5C.
In SSP3, models were simply not able to achieve either RCP2.six or RCP1.9 targets due to regional rivalry and resurgent nationalism limiting the ability of the world to cooperate on reducing emissions over the next few decades.
While the rapid technological development in SSP4 makes it easier to attain more than modest mitigation targets, the high inequality makes it more than difficult to accomplish very strong emission reductions, peculiarly for state-use emissions in poorer countries. This means that, while all three SSP4 models can achieve a RCP2.6 target, but 1 of iii can reach of RCP1.ix and limit warming to beneath 1.5C.
The figure beneath shows the different emissions trajectories broken out by SSP, as well every bit indicating the level of adaptation and mitigation challenges associated with each. In full general, SSP1 (lesser left box) has faster emission reductions and less negative emissions required later in the century nether deeper mitigation scenarios, compared to other SSPs.
The fact that IAMs could not find a feasible solution for some below-2C and below-1.5C scenarios does not necessarily mean that these scenarios are impossible. Models are necessarily imperfect and cannot foresee all of the technological or societal changes that will happen over the coming century. For example, models used to struggle to reach 2C targets before they started including large-scale negative emissions technologies – though these withal largely exist only in the models, rather than in real-world deployments at calibration.
Similarly, what modellers consider every bit plausible rates of emission reduction or negative emissions may turn out to be overly conservative (or optimistic). Pathways such as SSP3, where strong mitigation scenarios cannot be modelled, should exist seen equally an indication that such a globe of resurgent nationalism and regional divisions greatly increases the take a chance that the transformations required might not be doable.
Negative emissions in the SSPs
All scenarios in the SSP database that go on warming below 2C incorporate some bioenergy with carbon capture and storage (BECCS). Even so, the degree to which they rely on BECCS – or on negative emissions more broadly – to meet the goal varies both past model and SSP.
In full general, SSPs that allow more rapid near-term emissions reductions, such as SSP1, rely less on BECCS later in the century. The effigy below shows the total amount of energy generated from BECCS over the century for each SSP/RCP scenario, as well equally IAM. It shows the departure in the amount of BECCS used by each model and each SSP, with some models showing considerably larger amounts than others for the aforementioned RCP mitigation target.
Cumulative 2005-2100 bioenergy with carbon capture and storage (BECCS) utilize in exajoules past SSP, RCP target and integrated assessment model. RCP1.9 data not included as it is not even so available from the SSP database. Chart past Carbon Cursory using Highcharts.
In the below-2C RCP2.6, cumulative BECCS use ranges from a low of 1,660EJ to a high of 19,000EJ, or between 4% and 26% of all free energy generated betwixt present and 2100. SSP1 more often than not has the everyman BECCS employ, followed past SSP2 and SSP4. SSP5, which limits near-term emission reductions, requires betwixt two and viii times more BECCS than in SSP1.
A similar pattern holds in RCP3.four, but here 1 model (AIM) meets the target in SSP1 with next-to-no negative emissions. Across all the models, RCP3.4 requires 30-60% less BECCS than RCP2.6.
In RCP4.5, most models require little-to-no negative emissions in an SSP1 globe, though many still employ meaning amounts of BECCS in SSP3 and SSP5.
While BECCS is the primary negative emissions technology included in IAMs, it is largely a stand-in for any sort of future negative emissions. Its role could be replaced, at to the lowest degree in office, by other approaches and technologies, such as straight air capture or large-calibration reforestation, as they become price-constructive over the coming century.
No unmarried 'business as usual'
A key questions for scientists and policymakers is what will happen if the globe takes no activeness to accost climate alter.
One of the large changes brought by the release of the SSPs is a broadening of the baseline no-new-policy scenarios available to researchers. Over much of the past decade researchers have tended to use the high-emission loftier-warming RCP8.5 as their "business every bit usual" baseline – a worst-example scenario of unchecked warming to compare against futures where emissions are mitigated.
One important takeaway is a shift in the definition of "business as usual". Instead of a single worst-case scenario, the SSPs present a wide range of future emissions possible in the absence of climate policy, though all the new baseline scenarios result in at least 3.1C warming (and upwards to 5.1C) by 2100.
While RCP8.five lives on in the form of the SSP5 baseline, it is at present just one of many possible no-new-policy futures. The fact that only i of the SSPs, SSP5, tin can achieve the level of emissions found in RCP8.5 suggests that it may not now be all-time suited for use as the sole baseline scenario in hereafter research.
If any SSP can exist said to exist characteristic of electric current atmospheric condition information technology is SSP2, where social, economic and technological trends do not shift markedly from historical patterns. Greenhouse gas concentrations in the SSP2 baseline roughly correspond to the new RCP7.0, which shows lower emissions and most 1C less warming than RCP8.5 – though still three.8-4.2C of warming higher up pre-industrial levels.
It is also possible that the world will follow more of a SSP1 or SSP4 pathway of rapid technological development and falling costs of things such every bit solar energy, battery storage, transmission technologies and other changes. These would reduce barriers to mitigation and outcome in more pocket-sized emissions and warming, even in the absenteeism of climate policies.
However, the developers of the SSPs make no merits equally to the relative likelihood of any scenario coming to pass. It is certainly possible to imagine a SSP3 or SSP5 world of high emissions. With the multiple scenarios, researchers will now be able to compare mitigation outcomes to a more realistic range of baseline worlds.
Source: https://www.carbonbrief.org/explainer-how-shared-socioeconomic-pathways-explore-future-climate-change
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