This simulation illustrates the effects many different technologies may have on the rate of carbon emissions. Your challenge is to determine how global anthropogenic climate change can be mitigated with technologies that exist today.
Select a technology category with buttons above the graph. Sliders are used to predict the extent of certain technologies in 2100. The arrow on the Projected Carbon Emissions graph will change in response to your predictions.
The starting position of the arrow on the top of the yellow triangle represents the current trajectory if no technological advances or behavioral changes are made. Try to bring the projected carbon emissions down until the arrow reaches the bottom of the yellow triangle.
As you change the sliders, keep an eye on the Reality Check bar just below the graph. This bar will indicate whether your predicted changes are realistic.
To find out more about any part of the model, look for the "Show Assumptions" buttons and the question-mark icons.
This instructions page can be accessed from the menu bar, using Help → Instructions.
In this applet, you'll be exploring ways of reducing carbon emissions.
We'll start with electricity-related emissions.
To begin, find the electricity button!
Carbon emission is defined as the anthropogenic release of carbon containing compounds into the atmosphere. This includes a wide variety of compounds including carbon dioxide, methane and chlorofluorocarbons. Of these, carbon dioxide is by far the most abundant (IPCC 2013). Note that only considering carbon emissions excludes several other environmentally relevant compounds, like ozone, nitrogen oxides and sulfur hexafluoride among many others.
All the data in this applet considers emissions in terms of a mass of carbon; to convert the mass of a carbon-containing compound to a mass of carbon, multiply by the molar mass of carbon (12.01 g/mol) and divide by the molar mass of the compound. For example, 10 kg of carbon dioxide equals 2.73 kg of carbon.
When predicting the impact of certain technologies on the future of global carbon emissions, unless stated otherwise, it is assumed that no technological improvements or societal changes will be made. This was done to simpilify the design of the applet, but as a result, predictions made within the applet tend to be conservative.
The initial projection of the simulation is calibrated to match the RCP8.5 'worst case' scenario (IPCC2013) carbon 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.
The upper bound of the triangle is generated from projections made by this applet, and is consistent with carbon emissions assumed under the RCP8.5 'worst case' scenario (IPCC2013). The lower bound aims to reduce carbon emissions to 5 Gt per year by 2100, and roughly follows the RCP4.5 scenario (IPCC2013). The triangle between these two bounds is divided into individual wedges, each corresponding to a decrease in the annual emission rate of 2 Gt per year 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 applet. Historical carbon emission data was taken from the U.S. Department of Energy (Boden).
This display demonstrates the estimated impacts that the projected carbon dioxide emissions will have on the climate. The green circle on the display represents values for each impact that are considered a reasonable boundary to stay within. The red circle on the display indicates a high boundary for each impact that should be avoided, as it may cause other problems in other earth systems.
The dashed line for each impact represents the present value for each impact.
Current Value: 1 ° C
Reasonable Boundary: 1.5 ° C
Extreme boundary: 2.0 ° C
Currently, global surface temperature has increased by 1 degree since the industrial revolution (IPCC 2018). Global surface temperature change is considered to be the average change in temperature at the surface of the earth since the year 1750, or the beginning of the Industrial Revolution. 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(IPCC 2018). Because this is an average, certain regions in the world may experience more extreme temperatures than others, as 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 for a doubling of carbon dioxide concentration. (IPCC 2018)
Current Value: 410 ppmv
Reasonable Boundary: 350 ppmv
Extreme boundary: 450 ppmv
Atmospheric carbon dioxide is a major greenhouse gas. Current atmospheric carbon dioxide concentration in the atmosphere is 410 parts per million (ppm) (NOAA 2019). This means that for every million molecules of air, 410 of them are CO2. In 1750, prior to the industrial revolution, this value was 280ppmv(NOAA 2019). The reasonable boundary for atmospheric CO2 is 350 ppm (which we have already surpassed), and it should not go above 450 ppm (qk citation).
To calculate atmospheric CO2 from Carbon dioxide emissions, it is assumed that every 2.3 Gt of CO2 raises concentrations by 1 ppmv. (Biello 2010)
Current Value: 7.7 cm
Reasonable Boundary: 0.9 m
Extreme boundary: 1.8 m
There are two main contributors to sea level rise: ocean expansion and melting ice. Currently, global sea levels have risen on average by 7.7 cm (Lindsey 2018). Sea level rise affects costal communities, as the ocean rise can flood habitable areas. The reasonable boundary for sea level rise is 0.9 m , and the seas should not rise above 1.8 m. (WEF 2019).
Sea level rise is modelled 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 2.71E-05 (net 0 in 2050) and 1.56E-4 (starting point).
Current Value: 8.1
Reasonable Boundary: 7.7
Extreme boundary: 7.4
When carbon dioxide reacts with water, some of it forms carbonic acid, increasing the acidity of oceans. This 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. Carbon dioxide concentration is calculated in this applet, and the remaining values come from (Bozlee 2008). To see how ocean acidification is actually modelled, go to the KCVS resource called "Ocean pH Learning Tool " (Click for Link) tool
This simulation considers global population because it is an important driver of demand for food, transportation, electricity, buildings, goods, etc., each with associated emissions. The global population slider is based off of 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 things (UNDESA 2019). Factors like voluntary, high-quality family planning and increased education can reduce the amount of greenhouse gas emissions generated from high numbers of people (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 electricity shares for cooling buildings are at 98% (IEAb 2019), this energy mix also accounts for those emissions.
The simulation is set to automatically decrease coal when alternative energies sources are increased because coal has both the highest contribution to electricity generation and the highest carbon intensity. The sliders represent the share of that in the electricity mix - this means they all must add up to 100%. If you remove all of the coal shares then you will have to reduce other alternatives before increasing another. 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 available. Among other reasons, some were excluded for the sake of simplicity and because the maturity of the technology on the market.
In 2017 coal accounted for 38% percent of the global electricity production and is one of the primary fossil fuels used for 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 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 and stores it in appropriate geological sinks or uses it for things like 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 realitic alternative to long-term sequestration (MacDowell 2017).
The IEA predictions for the amount of emissions mitigated by CCS used in the simulation assume that carbon capture and storage (CCS) is widely deployed to both power generation and industrial applications including chemical, gas processing, refining, cement production and more (IEA 2013). The percent of global emissions avoided by CCS in recent years has been quite small, and so the default value for the CCS slider is 1%, however, increased deployment could reasonably reduce total CO2 emissions by 14% if finances are not a barrier and coal power still maintains a relatively high share in the electricity mix (MacDowell 2017, IEA 2013). Coal power generates a large portion of the CO2 emissions that can be mitigated by CCS. Therefore, the simulation will reduce the percentage of avoided CO2 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, for the time being. While it is an important technology, it is still under development and not readily deployable.
Solar power covers a large group of varying technologies that generate electricity from solar radiation – sunlight. For simplicities 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 power generation mix (WEO 2018). The default solar PV share in 2100 is set to 7% and since a number of experts consider it reasonable to have up to 70% of global electricity supplied by solar PV, the simulation allows an increase up to this (Bogdanov 2019).
Solar PV can be either grid connected or function as a standalone system and depends on the amount of sunlight hitting the panels. Since sunlight varies over time, the simulation assumes that the electricity distribution system has sufficient storage capacity to compensate for the resulting intermittency. Another key assumption is that solar PV, with a carbon intensity of 40 gCO2 eq/kWh, can directly substitute fossil fuels to generate electricity (NREL 2018).
Most solar panels used today are made up of microcrystalline silicon PV solar cells that have efficiencies that range from 10-15% (Bogdanov 2019). 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 off a required area of 1kW/m2, however, this land does not have to be solely devoted to solar power – PV panels can be installed on existing structures to minimize the area requirement.
Both onshore and offshore wind power energy 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 intermittency. 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 to split atomic nuclei and release the energy that 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 12 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 power 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 36.7 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 in the energy 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 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 depletes groundwater and requires 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 power 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 defines factors relating to vehicle efficiency and use. A vehicle here refers only to personal light-duty automobiles; heavy trucks, rail and marine transportation are not considered.
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.
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.
For every litre of gasoline used, is is assumed that 5.18 kg of carbon dioxide is emitted.
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.
On the subsequent alternative fuels pages, the ratio of different fuels is illustrated with a bar visualization. Gasoline is assumed to be the default vehicle fuel; adding alternative fuel vehicles will decrease the amount of gasoline vehicles in use.
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. The gasoline in this mixture is assumed to be the major source of carbon dioxide emissions for this fuel type. Ethanol production is assumed to be almost carbon neutral, with a 25% overhead is to account for emissions during refining (Hill 2006).
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 natural gas vehicle used liquified natural gas (LNG), and is about 25% less fuel efficient per litre than gas-powered vehicles. Natural gas is assumed to be pure propane, and emits 3.35 kg of carbon dioxide per litre of fuel used (USEIAStats 2019).
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 oxygen, the other gas required by a hydrogen fuel cell, is not considered here.
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.
It is interesting to note that the carbon emissions from hydrogen fuel cells come primarily from the electricity used to produce the hydrogen (Rau 2018); if the current electricity supply mix is predominantly fossil fuel based, adding hydrogen fuel cell vehicles could result in an increase in carbon emissions.
In an electric vehicle, electricity stored in a battery is used to drive an electric motor to power the vehicle.
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. Because electric vehicle technology is improving so rapidly, the efficiency of an electric vehicle is very roughly approximated to be 19 kWh/100km (USDEb 2018).
As with hydrogen fuel cells, increasing the number of electric vehicles will increase the amount of electricity needed. If most of the electricity is being generated from carbon- intensive sources, increasing the number electric vehicles will result in increased carbon emissions.
A hybrid vehicle is a combination of an electric vehicle and a gas-powered vehicle. 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 power source. 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 it's gas engine the remaining 1/3. The fuel efficiencies of both of these modes are considered the same as the fully-electric or fully-gas counterparts (USDEb 2018).
As with hydrogen fuel cells and electric vehicles, increasing the number of hybrid vehicles will increase the amount of electricity needed. If most of the electricity is being generated from carbon- intensive sources, increasing the number hybrid vehicles will result in increased carbon emissions.
Diesel engines differ from gasoline engines in that they do not use sparks to ignite the fuel. Like gasoline, this fuel typically comes from petroleum, but biodiesels are also available. Biodiesel is not considered here.
A typical diesel vehicle is about 25% more efficient than one that is gas-powered, and one litre of diesel emits about the equivalent of 5.92 kg of carbon dioxide when used(USDEb 2018).
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 powered vehicles are assumed to be the default kind of vehicle, so when another vehicle type is increased, these vehicles will replace the gasoline vehicles. The fuel efficiency of gasoline vehicles is set using a slider, and it is assumed that other technologies (such as LNG vehicles and diesel – powered vehicles) will follow the same developments, and their fuel efficiencies will change with gasoline fuel efficiency.
In this category, aviation only refers to passenger travel. The current annual distance traveled by plane per person is 900 km a year, and this is projected to be the same in 2100 (IATA 2019). This can likely be reduced to 600 km/year.
Currently, the average fuel efficiency per person on a typical transatlantic flight is 3 L/100 km (Graver 2018).
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 (FAO 2019). Because of increased reforestation efforts, it is assumed that the deforestation rate can be decreased to 0 in 2100.
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.
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 gasses that are produced (EPA 2019). Reducing N2O concentrations in the atmosphere can be done through more efficient fertilization methods and CH4 can be reduced through methods like more efficient manure management, alternative livestock arrangements, and better feed (EPA 2019, Legesse 2015).
These techniques are difficult to quantify on a global scale, so the simulation reduces the overall percentage of emissions associated with agriculture instead. Current Agricultural emissions are considered to be 5.5GT CO2 eq/year for non-CO2 emissions and 0.5GT CO2/year for CO2 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 a very viable target for mitigation. mitigation strategies revolve around reducing emissions during building construction and operation, which includes the transition from incandescent lightbulbs to LEDs, and using more alternative, low-carbon fuels for heating and cooling in buildings.
In this case, buildings are defined to be commercial and residential structures. The heating and cooling of buildings refer to space heating and space cooling.
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)--restricting this growth to 400 billion m2 is assumed to be reasonable.
Embodied emissions are the total carbon emitted during the retrieval, processing, and construction of building materials and is said to be proportional to operational emissions (Ibn-Mohammed 2013). The carbon emitted during the construction of a building depends on a number of factors including location, building material, and intended building use. An estimated 645 kgC/m2 is assumed to be emitted during a building's construction. 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.
Another significant source of carbon emissions from buildings comes from the heating, ventilation, and air conditioning systems--referred to collectively as HVAC (GABC 2016). The amount of HVAC a building requires depends on a number of factors, including climate, building design, and building use. Because of this, assigning a global emissions rate for HVAC systems is difficult. An estimated 649 kgC/m2 over the lifetime of the building is taken as the current projection (Aye 2012)(Pons 2011). Recent advances in renewable energy heating a cooling have led to the development of zero-emission buildings (GABC 2016)--leading to the assumption that the average emissions from building HVAC systems will be nearly zero by 2100.
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.
While other heating sources go through a process in order to create heat, geothermal heating entails the movement of heat from one place to another by using heat pumps. Geothermal heating is a direct use of the geothermal energy stored in the earth from the sun and is a renewable source of energy estimated to emit 0.1 GtCO2 eq/year in buildings.
Biomass is a source of energy developed from organic materials such as wood, agricultural residue, and wase (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). Unlike a fossil fuel, biomass is renewable and sustainable.
Biomass may be considered carbon-neutral since its source plants capture almost equivalent amounts of CO2 that burning biomass emits (EIAb 2019). Combustion of biomass for heating is estimated to emit 0.2 GtCO2 eq/year in buildings.
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, and blown through ducts to provide space heating (CAPP 2019). Combustion of natural gas is estimated to emit 1.8 GtCO2 eq/year in buildings.
Oil is a fossil fuel combusted in boilers and furnaces to heat and pump water. Oil is considered a clean fuel with low emissions--an estimated 0.2 GtCO2 eq/year in buildings.
Other heating is assumed to include purchased and solar heating with an estimated 0.1 GtCO2 eq/year in building emissions.
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 emit 2.7 GtCO2 eq/year in building emissions.
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 has recently emerged as a leading driver in demand for electricity with energy raised by about 5% in 2017 (IEAb 2019). Electricity in cooling energy is fuelled by oil and coal 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.
At 27%, the cement sector holds the second largest share of industrial CO2 emissions--projected to emit 8.7 GtCO2 eq in 2100 (IEA TR 2018). Not assuming the property of cement which reabsorbs carbon, cement emissions may be decreased by 0.57 GtCO2 eq with each additional percent of substituting cement with materials such as volcanic ash, limestone, and fly ash (Drawdown C 2019). Increasing the substitution of alternative materials in the composition of cement to 45% is considered to be reasonable.
Refrigerants are chemical compounds that absorb and release heat in cooling systems, such as refrigerators and air conditioning, with the use of compressors and evaporators. CFCs and HCFCs were the main refrigerants used in these systems, but because of their ozone-depleting property, the Montreal Protocol has placed restrictions on the emissions of these gases, effectively phasing them out (IPCC 2014). CFCs and HCFCs have since then been replaced with HFCs--which are not ozone-depleting--but are strong greenhouse gases with an emissions growth rate of 10-15% each year (CCAC 2016).
Mitigation of HFC emissions include proper lifetime management (leaking), refrigerant recovery and disposal, and substituting HFCs with alternative, natural refrigerants, such as ammonium and propane. (IPCC 2014, Drawdown RM 2019) The carbon intensity of HFCs is estimated to be 8987 tCO2 eq/Mt in 2100 (UNEP 2017, EPA 2009). Because aims are at phasing HFCs out, decreasing its carbon intensity to 0 tCO2 eq/Mt is considered to be reasonable (Drawdown RM 2019).
Freight transport is a steady growing sector, with its CO2 emissions rate growing faster than the energy sector (ITF 2017). The per capita rate of shipping is estimated from the total amount of global shipping and population--with global shipping at an estimated 81, 000 billion tonne*km (ITF 2017). In this case, shipping is considered to be the international (maritime and aviation) and intranational (road and rail) transport of goods. The overall carbon intensity of shipping is estimated to be 837.3 gCO2 eq/(tonne*km).
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. The carbon intensity of rail 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 billions 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 what the main mitigation strategies for shipping by sea aim for (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 gCO2 eq/(tonne*km) is considered to be reasonable (Walsh 2011).
Emissions from air transport are estimated to be 2-3 times higher 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|