This global simulation invites you to use currently available technology to
Billions of humans living on our planet require energy for all aspects of life, and contribute to changes in global biogeochemical cycles. This simulation focuses on human-caused greenhouse gas emissions, and the expected impacts these will have on four parameters that regulate important aspects of our physical world: global greenhouse gas concentrations, ocean acidity, average global surface temperature, and sea level rise. At the top of the simulation is an interactive graph of projected greenhouse gas emissions, and effects of those emissions are shown on the impact circle below.
Select each emissions sector with buttons above the graph. Move the sliders in each sector, to design the changes in those activities you’d like to see humans achieve to chart our sustainable future. The starting position of the arrow at the top of the yellow triangle represents our current trajectory, 'business as usual', where no major technological or behavioral changes are made. Can you design a future in which we have brought the projected greenhouse gas emissions down close to net zero by 2050, helping to avoid some of the worst impacts of climate change? As you change the sliders, keep an eye on the Reality Check bar just below the graph, to see if your changes are realistic. The question mark icons on any part of the model show the assumptions at work.
This instructions page can be accessed from the menu bar, using Help → Instructions.
In this simulation, you'll be exploring ways of reducing greenhouse gas emissions.
We'll start with electricity-related emissions.
This simulation gives a semi-quantitative overview of anthropogenic greenhouse gas emissions, or human activities that release heat-absorbing (and, in the case of carbon dioxide, acidic) compounds into the atmosphere. This includes the compounds carbon dioxide, methane, nitrogen oxides, and hydrofluorocarbons. Of these, carbon dioxide is by far the most abundant (IPCC 2013). Note that this simulation excludes several other environmentally relevant compounds, such as ozone, and sulfur hexafluoride.
When predicting the impact of certain technologies on the future of global greenhouse gas emissions, unless stated otherwise, it is assumed that no technological improvements or societal changes will be made. This was done to simplify the design of the simulation. As a result, predictions made within the simulation tend to be conservative.
In this model, the greenhouse gas emissions from all slider settings are added together to give the total projected global emissions in 2100, and the most recently available data is connected to 2100 with a straight line. Note that emissions are not expected to change linearly between now and 2100. The scenarios with the lowest negative impacts on human life reach peak emissions very soon, and then rapidly decrease emissions by 2050. This is simplified as the bottom line on the graph, labeled "our goal".
The initial settings of the simulation are considered to be the outcome of continuing with 'business as usual' until 2100. The total global emissions are calibrated to match the RCP8.5 'worst case business as usual' scenario (IPCC2013) greenhouse gas emission projection in 2100. This is done so that the simulation, which is vastly simplified compared to scientific climate models, gives qualitatively meaningful predictions even though it ignores a number of important dependencies and interactions.
This graph shows global historical emissions data, and a range of projections for future scenarios for planet Earth. Toggle the arrows at the bottom left of the graph to see emission rates since the beginning of the industrial revolution, when atmospheric carbon dioxide concentrations were 280 ppm.
The future projections form a (truncated) triangle, which we refer to as a carbon reduction triangle. More accurately, here we have a greenhouse gas (GHG) reduction triangle, since greenhouse gases such as nitrous oxide, methane, and hydrofluorocarbons, are included as carbon dioxide equivalents. The upper edge of this triangle is generated from projections made by this applet, and is consistent with GHG emissions assumed under the RCP8.5 'worst case' or 'high emissions business as usual' scenario (Riahi 2011)(IPCC2013). This corresponds to the Shared Sociocenomic Pathway SSP5 (Riahi2017)
The lower edge (our goal) aims for net zero carbon emissions by 2050, in line with the 2015 Paris Agreement, and the United Nations Framework Convention on Climate Change (UNFCC) recommendation to keep global average temperature increase below 1.5 degrees Celsius, in order to increase our chances of avoiding the worst impacts of climate change as outlined by the Intergovernmental Panel on Climate Change (Paris2015)(IPCC2018).
To break down this wicked problem, the triangle formed by the two extremes is divided into autofill individual wedges, each corresponding to a decrease in total greenhouse gas emissions of about autofill Gt carbon dioxide equivalents by 2100.
The concept of 'carbon stabilization wedges' was initially developed by the Carbon mitigation Initiative (CMI) and has been expanded and updated in this simulation. Historical carbon emission data were taken from the U.S. Department of Energy (Boden).
The Reality Check indicator is not intended to be a quantitative measure of any sort. Rather, the Reality Check is meant to be a subjective, qualitative indicator to keep the user within the realm of possibility.
This display shows estimated impacts of the projected greenhouse gas emissions on Earth's climate. While we acknowledge that the local impact of particular changes will be very different in different places around the world, the green circle suggests reasonably safe global boundaries to stay within, to maintain a habitable planet. The red circle indicates extreme levels that should be avoided. These extreme levels pose high risks, such as causing irreversible tipping points to be passed in other Earth systems.
Even a reasonably safe boundary may be problematic, when the rate of change exceeds the capacity of an organism or ecosystem to adapt.
The dashed lines represent the present value for each impact.
Click on each sector in the climate impact circle for details on the underlying assumptions.
Current Value: 1.0 ° C
Reasonable Boundary: 1.5 ° C
Extreme Level: 2.0 ° C
Currently, global average surface temperature has increased by 1.0 degree Celsius since the industrial revolution (IPCC 2018). Global average surface temperature change is considered to be the average change in temperature at the surface of the earth since the pre-industrial reference time period 1850-1900. The United Nations Framework Convention on Climate Change (UNFCC), based on risk analysis by the intergovernmental panel on climate change (IPCC) recommends a reasonable boundary of 1.5 degrees Celsius, and that global temperature change not exceed 2 degrees Celsius, in order to avoid high risks of dangerous climate effects (IPCC 2018). Since this is an average, certain regions in the world experience more extreme temperatures than others. For example, the arctic is currently warming at a rate twice the global average (NOAA ARC 2018).
This model assumes that the global surface temperature will increase by 3 degrees relative to 1750 for a doubling of carbon dioxide concentration (UCAR). You can learn more about the range of temperature change anticipated for different emission scenarios in the IPCC Fifth Assessment report (IPCC 2014 SYR).
Current Value: 410 ppm
Reasonable Boundary: 350 ppm
Extreme Level: 450 ppm
Atmospheric carbon dioxide is a major greenhouse gas. Other GHGs included in the emissions graph are nitrous oxide, methane, and hydrofluorocarbons. Current carbon dioxide concentration in the atmosphere is 410 parts per million (ppm) (NOAA 2019). This means that out of every million molecules of air, 410 of them are CO2. In 1750, prior to the industrial revolution, this value was 280 ppm (NOAA 2019). The reasonable boundary for atmospheric CO2 is 350 ppm (which was surpassed before 1990), and it should not go above 450 ppm (OECD 2012).
Adapting to a changing climate is possible for some animals and humans, but becomes harder the faster change occurs. Both the current amount of greenhouse gases in the atmosphere, and the rate of change since the beginning of the industrial revolution, are unparalleled in human existence. (AR 2017)
To estimate atmospheric CO2 in 2100 from Carbon dioxide emissions, it is assumed that every 2.13 Gt of CO2 raises concentrations by 1 ppmv (Clark 1982). You can learn more about the range of atmospheric carbon dioxide concentrations anticipated for different emission scenarios in the IPCC Fifth Assessment report (IPCC 2014 SYR).
Current Value: 7.7 cm
Reasonable Boundary: 0.9 m
Extreme Level: 1.8 m
There are two main contributors to sea level rise: ocean expansion and melting ice. Water expands as it warms, and the melting of land-based ice (such as the glaciers of Greenland and Antarctica) adds more water to the oceans. The melting of floating ice does not contribute to sea level rise (try this with a glass of ice water!), but has other effects, including changing the ability of the Earth to absorb or reflect sunlight. Currently, global sea levels have risen on average by 7.7 cm (Lindsey 2018). Sea level rise affects coastal and island communities, as the ocean rise floods habitable areas, as well as low-lying agricultural lands. Indicated by the green circle, a "reasonably safe" boundary for sea level rise is 90 cm. Indicated by the red circle, a sea level rise above 1.8 m represents an extreme level (see Climate Impact Assumptions). (WEF 2019).
Sea level rise is modelled here using the following method: (NOAA SLR 2012):
E(t) = 0.0017t + bt2
in which E(t) is the sea level rise, t is the time since 1992, and b is a constant that scales linearly with net emissions between 0.0000271 (for net 0 in 2050) and 0.000156 (current starting point). You can learn more about the range of sea level rise anticipated for different emission scenarios in the IPCC Fifth Assessment report (IPCC 2014 SYR)
Current Value: 8.1
Reasonable Boundary: 7.7
Extreme Level: 7.4
When carbon dioxide reacts with water, some of it forms carbonic acid, increasing the acidity of oceans. pH is a measure of acidity: More acidic environments have a lower pH. Lower ocean pH makes it difficult for many shelled organisms to grow. Since the industrial revolution in 1750, the ocean pH has decreased by 0.1 units, from 8.2 to 8.1 (NOAA OA). Because pH is a logarithmic scale, this actually corresponds to approximately 30% increase in acidity. When ocean acidity rises, carbonate in the shells of sea creatures becomes more soluble, and their shells can begin to dissolve (NOAA OA). To prevent this, it is recommended that ocean pH remain above 7.7 and not go below 7.4 (Caldeira 2003).
The modelling of ocean acidification is fairly complicated, and depends on the salinity, and temperature of the water, as well as the concentration of carbon dioxide in the atmosphere. In this simplified estimation, carbon dioxide concentration is calculated from your emission choices in DOCs, and the remaining values come from (Bozlee 2008). To see how ocean acidification is actually modelled, go to the KCVS resource "Ocean pH Learning Tool " (Click for Link) tool
In combination with the changes in lifestyles since the Industrial Revolution, the increase in global population is a key pressure on our global support systems. Global population is an important driver of demand for food, transportation, electricity, buildings, goods, etc., each with associated emissions. The global population slider is based on three scenarios from the United Nations Department of Economic and Social Affairs (UNDESA). The UNDESA population estimates and projections form a comprehensive set of demographic data to look at population trends and possible outcomes at the global, regional, and national levels. The default value in the simulation is set at the medium variant projection, which is 10.9 billion people in 2100. The lower limit is set at 7.2 billion in 2100 based on the low fertility scenario, and the upper limit is set at 15.6 billion in 2100 based on the high fertility scenario (UNDESA 2019).
There is inherent uncertainty in population projections, and at the global level that uncertainty is dependant on the range of plausible future trends in fertility, mortality, and international migration, in addition to environmental factors like rises in the spread of disease and natural disasters. While the medium variant for the global population is considered the most likely outcome, UNDESA says that there is roughly a 27% chance that the world's population could stabilize or even decrease before 2100, depending on a number of factors (UNDESA 2019). For example, access to voluntary, high-quality family planning, as well as education can substantially reduce the amount of greenhouse gas emissions generated from increasing global population (Drawdown P 2019).
In 2017, the global total of electricity generated was 25,679 TWh, which is approximately 3,400 kWh per person (WEO 2018, BP Statistics 2019). The default values for electricity assume that global behavior continues in the direction it is headed as of today to the year 2100. Therefore, the global electricity production is predicted to be approximately 6,880 kWh per person. Reducing electricity production to no less than 4000 kWh per person is considered to be a reasonable lower limit (WEO 2018, BP Statistics 2019). Since cooling (included on the buildings page) is 98% electric (IEAb 2019), the emissions for cooling buildings are included here in total electricity used. The worldwide demand for cooling was almost 10% of total electricity used in 2018, and is projected to continue to increase (TCEP 2019).
The simulation will automatically decrease coal when other electricity sources are increased since coal currently has both the highest contribution to electricity generation and the highest carbon intensity. Each slider represents the share of a particular electricity source in the overall electricity mix - this means they all must add up to 100%. Once you have removed all coal shares, you will be prompted to choose to reduce another electricity source in order to be able to increase other contributions. It's important to note that the alternative energy sources for electricity are not considered carbon neutral. The carbon intensities, listed in gCO2 eq/kWh, can be found in the assumptions for each individual source. Note that the sources for electricity in this simulation are not the only technologies that may be available in 2100. Only currently available technology has been included in this model.
In 2017 coal accounted for 38% percent of the global electricity production and is one of the primary fossil fuels used for electrical power generation (WEO 2018). In this simulation, coal has a carbon intensity of 1001 gCO2 eq/kWh assuming an efficiency of 45% for the average coal-fired power plant (Whitaker 2012). However, they could reasonably increase to 55% efficiency (Whitaker 2012). The simulation sets the default value for coal electricity production in 2100 to 33%, and assumes that it can reasonably be substituted by alternative sources (WEO 2018).
Natural gas accounted for 23% of global electricity production in 2017 and second to coal, is one of the primary fossil fuels used in electrical power generation (WEO 2018). While still significant, natural gas has lower carbon intensity relative to coal at 461 gCO2 eq/kWh (Heath 2014). This simulation assumes that natural gas can replace coal with minimal modifications to current infrastructure. The default share in electricity production for natural gas in 2100 is 24% and can reasonably be substituted by other alternative sources (WEO 2018).
Carbon capture and storage (CCS) refers to a variety of technologies that prevent the release of CO2 emissions into the atmosphere, store them in appropriate geological sinks (sequestration) or use them for processes such as CO2-enhanced oil recovery (EOR). While carbon capture, utilisation and storage (CCUS) is undergoing development and research, in the context of reducing emissions it is considered unlikely for CCUS to ever be a realistic alternative to long-term sequestration (MacDowell 2017). CC(U)S is also among the most expensive measures to reduce emissions, in contrast, for example, to energy efficiency, and renewable energy measures.
The Internaional Energy Agency's predictions for the amount of emissions mitigated by CCS used here assume that carbon capture and storage (CCS) is widely deployed to both electricity generation and industrial applications including chemical, gas processing, refining, cement production and more (IEA 2013). The percent of global emissions avoided by CCS has been quite small to date, so the default value for the CCS slider is 1%. However, increased deployment could reasonably reduce total CO2 emissions by 14%, if cost is not a barrier, and coal still maintains a relatively high share in the electricity mix (MacDowell 2017, IEA 2013). Coal electricity generates a large portion of the CO2 emissions that can be mitigated by CCS. Therefore, the simulation will reduce the percentage of avoided CO 2 emissions to a maximum of 7% if coal has no share in the electricity mix (IPCC 2005, IEA 2013). The simulation does not consider technologies for the direct air capture of emissions. Direct air capture, which removes carbon dioxide from ambient air (containing just 0.04% carbon dioxide) is still under development and not readily deployable.
Solar power includes a variety of technologies that generate electricity from solar radiation – sunlight. For simplicity's sake, only solar photovoltaic (PV) systems are considered in this simulation. Keep in mind, however, that solar thermal, solar concentrator, and photocatalytic technologies are being developed. In 2017, global electricity generation from solar PV was over 460 TWh making up 2% of the electricity generation mix (WEO 2018). The default solar PV share in 2100 is set to 7%, and it is considered reasonable to have up to 70% of global electricity supplied by solar PV (Bogdanov 2019).
Solar PV can be either grid connected or function as a standalone system. The electricity generated depends on the amount of sunlight reaching the panels. Since sunlight varies over time, the simulation assumes that the electricity distribution system has sufficient storage capacity to compensate for the inherent variability, though this is currently still in the early stages of deployment. Another key assumption is that solar PV, with a carbon intensity of 46 g CO2 eq/kWh, can directly substitute fossil fuels to generate electricity (NREL 2018).
Most solar panels used today are made up of mono/polycrystalline silicon PV solar cells that have cell efficiencies ranging from 15-20%. While there are other solar PV cell technologies with varying efficiencies in development, they are not considered in this simulation because they are either not commercially available or do not make a significant contribution. Other environmental impacts to consider with respect to solar PV electricity generation include land-based resources and materials availability. Land requirements were estimated based on a required area of 1kW/m2, however, this land does not have to be solely devoted to solar power generation – PV panels can be installed on existing structures to minimize the area requirement, and dual use of land for beekeeping and sheep grazing is being explored.
Both onshore and offshore wind power systems accounted for approximately 16% of renewable capacity and 4% of the total global electricity production in 2016 (WEO 2018). The default wind power share in 2100 is set to 9% and an increase up to 36% is considered reasonable (WEO 2018). Wind levels are not constant over time, so the simulation assumes that the electricity distribution system has sufficient storage capacity to compensate for variability. The simulation assumes that wind power, with a carbon intensity of 11 gCO2 eq/kWh, can directly substitute electricity from fossil fuels (NREL 2018).
The simulation considers both onshore and offshore wind turbines and assumes that they are located in areas with sufficient wind to be viable. The land requirements are based off 2 MW Vattenfall’s Horns Rev 1 wind turbines, which occupy approximately 3100 m2. Keep in mind, however, that wind power installations can exist in shallow waters, and that the land beneath the turbines can be utilized for other purposes as well. In terms of implementing wind power, there are other things to remember, including: environmental impacts on animal habitats and movements, disruption of bird foraging areas and nesting, and in offshore developments, fish and marine animals (Morrison 2004).
In 2017, there were 29 countries with operative nuclear plants that produced 2637 TWh, which is about 11% of the world’s electricity (WEO 2018, Drawdown N 2019). Nuclear plants use fission of atoms. This splitting of atomic nuclei releases energy, which is used to heat water and power steam turbines to generate electricity. Current nuclear technology employs uranium fission reactors, so this simulation does not include alternative nuclear fuels such as thorium, which are still in development.
Using nuclear technology as an electricity source tends to be complicated. On the one hand it is a technology that can help supply the world with electricity while avoiding the emissions that drive climate change, easing the energy transition substantially (WEO 2018, Drawdown N 2019). On the other hand, public acceptance can be an issue due to concerns with tritium releases, abandoned uranium mines, mine-tailings pollution, and radiative waste, among others (Drawdown N 2019). As a result of these complications, many experts predict that nuclear growth will be limited in the future, so the default nuclear power share in 2100 is set to 9% (WEO 2018). However, an increase up to 17% is still considered reasonable (WEC 2016).
This simulation assumes that nuclear power can directly substitute coal power. Nuclear electricity has a carbon intensity of 16 gCO2 eq/kWh; however, unlike other alternative electricity sources most of the emissions are from fuel processing and decommissioning stages of operation rather than manufacturing and installation (Sathaye 2011, Warner 2012).
Geothermal electricity uses heat from the earth to generate power. Different types of geothermal electricity production include steam-driven or binary cycle plants. Less than 10 percent of the planet contains prime geothermal conditions (Drawdown G 2019). Geothermal is reliable, abundant and efficient, in part because it can take place at all hours and under almost all weather conditions (Drawdown G 2019). Upfront costs like drilling are expensive, but the heat source itself is free (Drawdown G 2019). Note that geothermal that provides only heat is not considered in this section of the simulation, but is considered in the buildings section.
In 2017 global electricity generation from geothermal electricity was approximately 85 TWh making up less than 1% of the electricity generation mix (WEO 2018). The default geothermal electricity share in 2100 is set to 1% and an increase up to 5% of electricity shares is considered reasonable (WEO 2018, Drawdown G 2019). The carbon intensity of geothermal is 37 gCO2 eq/kWh and accounts for implementation of the energy resource (NREL 2018).
Hydroelectricity (often shortened to hydro) uses flowing water to drive a turbine that can generate electricity. To keep things simple, this simulation only considers reservoir-based or run-of-river hydroelectric plants since Tidal and wave-based hydroelectric power technologies are still being developed. Large hydroelectric dams produce huge amounts of electricity and are reliable, but they must be installed on a suitable river and have significant impacts to keep in mind (Drawdown H 2019)(IRENA 2018). Hydroelectric dams occupy large amounts of natural and human habitat, affect water movement and quality, sediment patterns, and fish migration. (Drawdown H 2019) Smaller run-of-river technologies are placed within a free-flowing river or stream without creating a reservoir,however this introduces variability as the flow of rivers depends on seasons and weather patterns (Drawdown H 2019). While run-of-river technologies have the potential to impact the surrounding environment, careful design and installation can ensure that is ecologically sound (Drawdown H 2019).
In 2017 global electricity generation from hydroelectricity was approximately 4109 TWh, making up the highest share of renewable electricity options in the overall mix at 16% (WEO 2018). The default hydroelectricity share in 2100 is set to 14% due to experts expecting solar and wind to dominate shares in the near future. However, an increase up to 25% of electricity shares is considered reasonable (WEO 2018, Drawdown H 2019). Like the other renewable sources considered in this simulation, hydroelectricity is not carbon neutral, and has a carbon intensity of 4 gCO2 eq/kWh (IPCC Hydro 2011).
Biomass can be harvested to generate steam for electricity production, or can be processed into oil or gas. This is an alternative energy source because it employs carbon that is already in circulation – from the atmosphere to plants and back again. Electricity from biomass is most effective in reducing emissions if appropriate feedstocks are employed, such as waste from mills and agriculture or sustainably grown perennial crops (Drawdown B 2019). Annual grain crops like corn and sorghum deplete groundwater and require high inputs of energy (Drawdown B 2019). Biomass has a carbon intensity of 47 gCO2 eq/kWh for electricity generation, however, if use and replenishment remain in balance it can be considered to produce net zero emissions (Drawdown B 2019, O'Conner 2013).
In 2016 global electricity generation from biomass electricity was approximately 500 TWh making up 2% of the electricity generation mix (WEO 2018). The default biomass electricity share in 2100 is set to 3% and an increase up to 5% of electricity shares is considered reasonable (WEO 2018, Drawdown G 2019.
This page invites you to explore factors relating to the efficiency and use of cars and air travel. On this page, vehicle refers only to personal cars (or light-duty automobiles); heavy trucks, trains and boats are not considered. The emissions on this page relate only to use, they do not include the emissions associated with the rest of a vehicle or airplane's lifecycle (production and disposal).
Considering current vehicle ownership rates in the industrialized world and projected population growth (WEO 2018), it is predicted that there will be around 2.5 billion light duty vehicles in use in 2100. Reducing the number of vehicles projected for 2100 to 1.2 billion is assumed to be reasonable. The simulation represents these values as a percentage of people who own a vehicle.
This gasoline fuel consumption slider impacts all vehicle types on this page, except for electric and hydrogen fuel cell vehicles. Other technologies (such as LPG vehicles and diesel-powered vehicles) are assumed to follow the same developments, so their fuel consumption will change with gasoline fuel consumption. Thus, as you change the fuel consumption, all fossil fuel powered vehicles are assumed to change in efficiency.
The average fuel consumption of gasoline vehicles is currently around 10 L/100km (Natural Resources Canada 2010), and the average distance each car is driven per year is around 21 000 km (TEDB 2018). Decreasing fuel consumption to 5 L/100km and decreasing the distance driven to 8000 km/year by 2100 is assumed to be reasonable.
The average fuel consumption of gasoline vehicles is currently around 10 L/100km (Natural Resources Canada 2010), and the average distance driven per vehicle is around 21 000 km/year (TEDB 2018). Decreasing fuel consumption to 5 L/100km and decreasing the distance driven to 8000 km/year by 2100 is assumed to be reasonable.
In the Sources of Vehicle Fuel section below, the ratio of the different fuels is illustrated with a bar distribution. Gasoline-powered is assumed to be the default vehicle type; increasing other vehicle types will automatically decrease the amount of gasoline vehicles in use. If you're curious about the impact of increasing the number of gasoline vehicles, simply decrease the other options.
Ethanol produced from plant matter can be added to gasoline to reduce its carbon emissions. One of the most widely used biofuels is E85, a mixture of 85% ethanol and 15% gasoline. Ethanol production from plant matter and its use as a fuel reduces emissions by about 12% (Hill 2006). Note the production of substantial amounts of bioethanol reduces the availability of agricultural land for food production.
Based on current sales, it is projected that 10% of vehicles in 2100 can run on ethanol-based fuels (NPC 2012), increasing this to 40% by 2100 is assumed to be realistic.
Natural gas is a mixture of light hydrocarbons, mostly ethane, propane and butane. It can be burned in an internal combustion engine in a manner similar to gasoline or ethanol, and is stored either as a compressed gas or as a liquid. A typical autogas vehicle uses liquefied petroleum gas (LPG, which is propane), and is about 25% less fuel efficient per litre than gas-powered vehicles. LPG is assumed to be pure propane, which is converted to 1.5 kg of carbon dioxide per litre of fuel burned (USEIAStats 2019). Including production, the "well-to-wheels" carbon intensity is 2.5 kg of carbon dioxide per litre of fuel burned (USDOEc).
Based on current sales, it is projected that 10% of vehicles will use natural gas fuels in 2100(NPC 2012); increasing this to 40% is assumed to be realistic.
Hydrogen fuel cells react hydrogen gas with oxygen gas under controlled conditions to generate electricity, often to power a vehicle. Hydrogen can be produced from a number of sources, but it is assumed that hydrogen produced for vehicles will come from the electrolysis of water, due to this method's simplicity, purity, and low carbon emission (Wang 2014). In electrolysis, electricity is used to split water into hydrogen and oxygen. A typical electrolysis cell operates at a potential of around 2.0 V and produces hydrogen with an efficiency of 57 kWh per kg of hydrogen (Wang 2014). Note that hydrogen currently is commonly generated by steam-methane reforming, which produces carbon dioxide, or other carbon-byproducts.
Hydrogen fuel cell vehicles are the least studied of the alternative fuel vehicles presented here, so detailed information is unavailable. As a rough estimate, a hydrogen fuel cell vehicle is assumed to have a fuel consumption of about 0.9 kg of hydrogen per 100 km (USDEa 2019). Based on current sales, it is projected that 5% of all vehicles will be powered by hydrogen fuel cells in 2100, (NPC 2012); and increasing this to 30% is not considered unreasonable.
The carbon emissions from the use of hydrogen fuel cells come from the production of hydrogen itself, which here is assumed to be electricity (Rau 2018). Thus, increasing the number of hydrogen fuel cell vehicles will require more electricity production. As with electric vehicles, the impact on emissions reductions (compared to gasoline vehicles) will be larger as you decrease the emissions of the electricity supply mix you select on the electricity page of this simulation. You will see the carbon intensity of hydrogen fuel cell vehicles change as you make changes to the electricity supply mix.
In an electric vehicle, electricity stored in a battery is used to drive an electric motor.
Based on current sales, it is projected that 15% of all vehicles will be electric in 2100, (NPC 2012); and increasing this to 60% is not considered unreasonable. Electric vehicle technology is improving rapidly, so the consumption of an electric vehicle is very roughly approximated to be 19 kWh/100km (USDEb 2018). This does not include emissions from production of the vehicle. Look into embodied energy and lifecycle analyses for more information.
Note that increasing the number of electric vehicles will require more electricity production. You will see the carbon intensity of electric vehicles change as you make changes to the electricity supply mix you select on the electricity page of this simulation.
A hybrid vehicle is a combination of an electric vehicle and a gas-powered vehicle in one system. Depending on the driving conditions and distance, the vehicle can switch between a traditional gas engine, or an electric, battery-operated engine. In this section, only plug-in electric vehicles are considered, whose batteries can be charged by plugging the vehicle into a source of electricity. Other kinds of hybrid vehicles are not considered.
Based on current sales, it is projected that 15% of all vehicles will be hybrids in 2100, (NPC 2012); and increasing this to 50% is not considered unreasonable.
It is assumed that this type of vehicle typically operates 2/3 of the time on electricity, and uses its gas engine the remaining 1/3. The fuel consumptions of each of these modes are considered the same as the fully-electric or fully-gas counterparts (USDEb 2018)(USEIAStats 2019). This does not include the energy needed to produce the vehicle. Research embodied energy and lifecycle analyses for more information.
As with hydrogen fuel cells and electric vehicles, note that increasing the number of hybrid vehicles will require more electricity production. You will see the carbon intensity of hybrid vehicles change as you make changes to the electricity supply mix you select on the electricity page of this simulation.
Diesel engines differ from gasoline engines in that they use pressure, not sparks, to ignite the fuel. Like gasoline, this fuel typically comes from petroleum. Biodiesel is also available, but is not considered here.
A typical diesel vehicle is about 25% more efficient than one that is gas-powered, and one litre of diesel is converted to 2.7 kg of carbon dioxide when burned (USEIAStats 2019). Including emissions during mining and refining of petroleum, the carbon intensity of diesel ranges from 3.2 to 4.5 kg of carbon dioxide per litre of fuel, depending on the origin of the petroleum used in production (Woo 2017, Masnadi 2018). This simulation uses the lower value. Not considered is the energy needed to produce the vehicle. Look into embodied energy and lifecycle analyses for more information.
Based on current sales, it is projected that 10% of vehicles will use diesel fuels in 2100 (NPC 2012); increasing this to 70% is assumed to be realistic.
Gasoline is a product of petroleum refining. Used in a combustion engine, a litre of gasoline is converted to 2.3 kg of carbon dioxide (USEIAStats 2019). Well-to-wheel emissions, which include mining and refining of petroleum, range from 2.8 to 3.9 kg of carbon dioxide per litre of gasoline, depending on the origin of the petroleum (Woo 2017, Masnadi 2018). This simulation uses the lower value of 2.8 kgCO2/L. Not considered is the energy needed to produce the vehicle. Look into embodied energy and lifecycle analyses for more information.
Cars running on gasoline are currently the most common vehicle type, so that one consideration is to improve fuel efficiency. You can modify the fuel consumption of gasoline vehicles using the fuel consumption slider above. This model assumes that other technologies (such as LPG vehicles and diesel-powered vehicles) will follow the same developments, so their fuel consumption will change with gasoline fuel consumption.
Since gas-powered cars are currently the most common, increasing another vehicle type will replace gasoline vehicles in this model.
Aviation refers only to passenger air travel, and does not include shipping and transport. The current distance traveled by plane per person is 900 km a year, based on 2018 total passenger kilometers flown and global population. This is projected to be the same in 2100 (IATA 2019), and can likely be reduced to 600 km per year.
Why is aviation often targeted as a personal impact?This model assumes every human travels by aircraft once per year. For those of us who do actually fly, for business or pleasure, this emission source may constitute a large part of our personal carbon footprint, or our emission contributions. Because taxi/take-off are the most emission-intensive, short-haul flights come with a larger relative emission contribution. There are currently no renewable alternatives that could be implemented at the necessary scale.
Currently, the average fuel consumption per person on a typical transatlantic flight is 3 L/100km (Graver 2018). This makes assumptions about the occupancy of the aircraft, with consumption increasing as more seats are left empty; further, the fuel consumption is higher for short-haul flights. Lifecycle emissions for aviation fuel or aircraft are not included here. Note that some airlines do use biofuels in an effort to reduce carbon emissions, though there is not yet sufficient research to indicate this is a feasible method for emissions reduction.
A forest in this case is defined to include naturally grown forests as well as replanted forests and tree plantations (FAOstat 2018). Deforestation is defined as the loss of forest area, and includes both natural and human-caused forest loss. Currently, there are 4 billion hectares of forests in the world, 93% of which is natural (FAO 2019). The world's forests have an average carbon density of about 7.4 ktC/km2 (FAOstat 2018); it is assumed that all of this carbon is released upon deforestation. Carbon released from other sources such as soils is assumed to be negligible.
The current deforestation rate is approximately 96 thousand km2/year (IPCC 2019 Ch4). Because of increased reforestation efforts, it is assumed that the NET deforestation rate can be decreased to 0 in 2100. This means that deforestation and reforestation rates are equal; keep in mind that this still has impacts on biodiversity, carbon stored, and other ecosystem functions (FAO 0def).
Reforestation is the planting of forests in areas that historically had them, but presently do not, mainly due to deforestation. Research suggests that reforestation is a viable method for climate change mitigation because of its usefulness in carbon sequestration (Crowther 2017, Cunningham 2015).
The current reforestation rate is estimated to be 25 thousand km2/year (FAD 2011). Because of previous record high rates and research suggesting that reforestation will greatly increase in the coming years, it is assumed that the reforestation rate can be increased to 52 thousand km2/year.
Land Use, Forestry and Agriculture are estimated to have contributed 23% to global anthropogenic greenhouse gas emissions from 2007-2016 (IPCC2019) - in other words, this sector contributed a quarter of our emissions in that timespan. This model includes considerations about forest use, conservation tillage of fields, and an umbrella category of total emissions from agriculture.
To reduce emissions, agricultural practices are moving toward regenerative practices, which include soil-carbon sequestration through pasture and grasslands management, perennial cropping approaches with reduced fertilization, and addition of biochar to soils. With good grazing practices, such as multi-paddock adaptive grazing, grasslands have the potential to make meaningful contributions to soil carbon sequestration.
It is important to recognize the complexity of our food system. The details of our practices must be considered in evaluating the impacts of land use, forestry, and agriculture both on greenhouse gas emissions and ecology and biodiversity (IPBES2019).
Conservation tillage is defined as any method of soil tillage that leaves at least 30% of the soil surface covered in plant material (Busari 2015). Conservation tillage is often used to improve soil quality and minimize erosion, but another benefit is that conservation tillage allows soil to absorb carbon dioxide from the atmosphere at a rate of 1.85 metric tons per hectare per year (Tebrügge 2018). Soil undergoing conventional tillage practices, by comparison, cannot absorb carbon in this way (Busari 2015).
The total amount of agricultural cropland is currently around 49 million km2; of this, around 4 million km2 is used for rice paddies and other crops that do not require the soil to be tilled (FAOstat 2018). It is assumed that by 2100, all of the remaining 45 million km2 of cropland could be farmed with conservation tillage techniques.
The main agricultural greenhouse gas emissions are nitrous oxide (N2O), which is produced from crop fertilizers, and methane (CH4), from ruminant animals and manure. There are a variety of methods that can be used to reduce the amounts of these gases that are produced (EPA 2019). Nitrous oxide emissions can be reduced through more efficient fertilization methods, and methane emissions can be reduced through methods such as more efficient manure management, alternative livestock arrangements, and changes in feed (EPA 2019, Legesse 2015).
These techniques are difficult to quantify on a global scale, so the simulation allows the reduction of the overall percentage of emissions associated with agriculture. Current Agricultural emissions are considered to be 5.5 Gt CO2 equivalents/year for non-CO2 emissions (nitrous oxide and methane) and 0.5 Gt CO2/year for carbon dioxide emissions (FAOstat 2018). This is projected to stay the same in 2100 and it is assumed that reducing these emissions by 50% is reasonable.
The building sector accounts for about 40% of total CO2 emissions (IEAa 2019), making it an important target for mitigation. Mitigation strategies revolve around reducing emissions during building construction and operation, which include energy efficiency measures such as the transition from incandescent lightbulbs to LEDs, and improving insulation and air-tightness, as well as renewable energy measures such as using energy sources with low or no greenhouse gas emissions for heating and cooling in buildings.
In this simulation, buildings are defined as commercial and residential structures. Cooling is currently 98% electric (IEAb 2019), so that the emissions associated with cooling are already included in this simulation as total global electricity use, and electricity sources, as well as refrigerant management under the materials page. District heating is an important development in building efficiency improvements that will be integrated in this simulation in the future.
The construction and use of buildings represent a significant portion of global carbon emissions (GABC 2016). The total floor area of buildings worldwide can be projected to reach 665 billion m2 by 2100 (GABC 2017). We estimate this growth may reasonably be restricted to 300 billion m2.
Embodied emissions are the total carbon emitted during the retrieval, processing, and construction of building materials and are considered to be proportional to operational emissions (Ibn-Mohammed 2013). We estimate a global average of 645 kgC/m2 is emitted during a building's operation (Aye 2012)(Pons 2011), which is in turn used as basis to calculate construction emissions. Reducing this value to 350 kgC/m2 is assumed to be realistic.
The average lifetime of a building impacts the rate at which new buildings must be built. Assuming building renewal phases and architecture advancement, the average building lifetime is estimated to be about 50 years (Daigo 2017). Increasing this timespan to 70 years is assumed to be realistic.
One of the largest uses of energy within a building, one which is most easily reduced, is lighting (GABC 2016). Lighting in this case refers only to illumination produced from electricity; other sources of lighting, such as the burning of fuels for lights, are not considered. The total number of lights worldwide is projected to reach 50 billion by 2100--restricting this value to 30 billion is assumed to be realistic.
Since most of the carbon emitted from light sources is caused by electricity consumed during use (USEERE), carbon emitted during manufacturing and disposal is assumed to be negligible. Because of this, the main factor affecting carbon emissions is the energy usage of the lighting device. The default lighting device is assumed to be 100 W incandescent light bulbs--low energy light sources include 10 W light emitting diodes (LED) or compact fluorescent lights (CFL).
Low energy light sources, such as LEDs, currently make up around 40% of lighting in buildings, and this value is increasing rapidly. It is assumed that having nearly all light sources use low energy lighting devices by 2100 is realistic. Note that increasing the amount of low energy lightbulbs is less effective if the current electricity supply is generated from mostly low carbon sources.
Water waste accounts for the emissions that come out of heating water. Low-flow water taps and showerheads decrease water waste, making them a viable strategy in emissions mitigation. In this case, it is assumed that more low-flow water fixtures leads to less water waste, which in turn leads to less emissions in water heating. For each additional percentage share of low-flow water fixtures, it is estimated that 0.11 GtCO2 eq/year is saved (Drawdown WS 2019). Increasing low-flow water fixtures to 95% is considered to be reasonable.
Geothermal heating is a direct use of the geothermal energy stored in the earth. It entails the movement of heat using heat pumps, which are commonly powered by electricity. Geothermal heating is considered a renewable source of energy, and is estimated to emit 14 kgCO2 eq/MWh of heat (McCay 2019).
Biomass is a source of energy developed from organic materials such as wood, agricultural residue, and waste (WBDG 2016). Heat is released through the burning of biomass, which may be burned directly--mainly in the form of wood pellets or pine chips--or after the biomass has been converted to fuel (EIAa 2019). Biomass is renewable and sustainable when waste materials are used. Once biomass (such as trees) is grown specifically for heating, both land use emissions and time required for growth have to be taken into consideration. Thus, the 'realistic' limit for biomass heating is fairly low at 30% global contribution.
Biomass may be considered carbon-neutral since its source plants capture almost the same amounts of CO2 that the production and burning of biomass emit (EIAb 2019). Combustion of biomass for heating of buildings is estimated to emit 38 kgCO2 eq/MWh heat (FRUK 2019).
Natural gas is a fossil fuel trapped in and extracted from below the Earth's surface. In a natural gas burner, water is heated, pumped through a metal coil to heat air, and the air is blown through ducts to provide space heating (CAPP 2019). Combustion of natural gas is estimated to emit 227 kgCO2 eq/MWh heat in buildings (FRUK 2019).
Oil is a fossil fuel combusted in boilers and furnaces to heat and pump water. The carbon intensity of oil as a building heat fuel is 314 kgCO2 eq/MWh heat (FRUK 2019).
The "other" heating category is made up of electric heat, including heat recovery ventilators (HRVs), and solar thermal heating. The carbon intensity used here is the carbon intensity of the electricity grid you choose in the Electricity sector of this simulation.
Coal is a carbon-rich fossil fuel burned to heat residential and commercial buildings. Although using coal for heating buildings has decreased in favour of alternative fuels, coal consumption for heating use is still on the rise in some countries (Kerimray 2017). Heating through burning coal is estimated to contribute 414 kgCO2 eq/MWh heat to building emissions (FRUK 2019).
Natural gas is estimated to emit 0.8 GtCO2 eq/year in buildings, taking up about 2% of fuel shares for space cooling in buildings (IEAb 2019).
Space cooling, or air conditioning, has recently become a leading driver for electricity demand with an increase of about 5% in 2017 (IEAb 2019). Electricity for air conditioning is fuelled largely by fossil fuels, with an estimated 2.7 GtCO 2 eq/year in buildings emissions for coal, while natural gas has an estimated 0.8 GtCO2 eq/year in buildings emissions.
The cement sector holds the second largest share of industrial CO2 emissions at 27%. In 2100, it is projected to emit 9.4 GtCO2 eq (IEA TR 2018). Carbon emissions considered here arise from the chemical reaction in cement hardening, which releases carbon dioxide. Up to 43% of these emissions may be reabsorbed by the cement over its lifetime, which is not included here.Clinker is the binding ingredient in the production of concrete, which allows the cement to harden in reaction to water. Cement emissions may be decreased by 0.1 GtCO2 eq/year for each percent of substituting conventional clinker with materials such as volcanic ash, finely ground limestone, and fly ash. (Drawdown C 2019). Increasing the substitution of alternative materials in the composition of cement to 35% is considered to be reasonable (IEA TR 2018).
Refrigerants are substances that absorb and release heat in cooling systems, such as refrigerators and air conditioning, with the use of compressors and evaporators. CFCs and HCFCs used to be the main refrigerants, which have been effectively phased out by the Montreal Protocol restricting the release of these gases into our atmosphere (IPCC 2014). The ability of CFCs and HCFCs to break down ozone was a major contributor to the formation of the ozone hole. HFCs have replaced CFCs and HCFCs as most common refrigerant. While HFCs are not ozone-depleting, they are strong greenhouse gases that don't naturally occur on Earth, with an emissions growth rate of 10-15% each year (CCAC 2016).
Mitigation of HFC emissions includes proper lifetime management (leak management), refrigerant recovery and disposal, and substituting HFCs with alternative, naturally occurring refrigerants, such as ammonium and propane. (IPCC 2014, Drawdown RM 2019) HFC emissions are estimated to be 8.8 GtCO2 eq/year in 2050 (EPA 2009), and we assume this remains constant under business as usual. Because aims are at phasing HFCs out, decreasing HFC emissions by 100% is considered to be reasonable (Drawdown RM 2019).
Freight transport is another steadily growing sector (ITF 2017). We estimate the annual total goods shipped per-person from the ITF baseline scenario for 2050, which projects a global shipping service of 329,000 billion tonne-km of freight, and a population of 9.55 billion (ITF 2017). The simulation assumes this per-person service remains constant to 2100. Your population prediction on the common sliders is then used to calculate the total amount of goods shipped in 2100. Shipping is considered to be the international (maritime and aviation) and intranational (road and rail) transport of goods. Each type of transport is assumed to have the current share in 2100: 87% by sea; 8% by road; 4.9% by train; and 0.1% by air.
Global freight shipping by road is increasing, accounting for about 6% of GHG emissions (Drawdown T 2019). The main mitigation strategy for decreasing road shipping emissions is adopting more fuel efficient technologies for freight trucks. The carbon intensity of road shipping is estimated to be 63.8 gCO2 eq/tonne-km (CN 2019). Decreasing this to 40 gCO2 eq/tonne-km is considered to be reasonable (ECTA 2011).
Rail shipping accounts for the transport of 12 billion tons of freight per year (Drawdown R 2019). Mitigation strategies for rail shipping include improving train fuel and operational efficiency and the electrification of railways. The carbon intensity of rail shipping is estimated to be 15.2 gCO2 eq/tonne-km (CN 2019). Decreasing this to 0 gCO2 eq/tonne-km is considered to be reasonable as electric trains increase along with renewable energy (Drawdown R 2019).
Maritime shipping accounts for 87% of shipping and 3% of global GHG emissions. Through design and technology replacement, increasing ship efficiency and less fuel-intensive shipping are the main mitigation strategies for shipping by sea (Drawdown S 2019). The carbon intensity of maritime shipping is estimated to be 8.3 gCO2 eq/tonne-km (CN 2019). Decreasing this to 4 gCO 2 eq/(tonne*km) is considered to be reasonable (Walsh 2011).
Emissions from air transport are estimated to be 2-3 times higher impact in relation to ground transport because of close proximity to the atmosphere (TFC 2019). Fuel efficiency is the main mitigation strategy for reducing the GHG emissions of airplanes (Drawdown Air 2019). The carbon intensity of shipping by air is estimated to be 750 gCO2 eq/tonne-km (Howitt 2011). Decreasing this to 500 gCO2 eq/tonne-km is considered to be reasonable (TFC 2019).
The following approximate area sizes are used for this estimation:
|The United Kingdom||200,000|
|Prince Edward Island||5,000|