In exploring this field , a wide range of terminology has been identified to support claims. From above examples, but also from workshops in different cities targeting this approach, I drafted a list as follows:

sustainable society

Climate neutral city

Carbon neutral city

CO2 neutral city

Zero emissions

Energy neutral city

0-energy city

energy autarkic community

Fossil fuel free city/municipality/region

100 % Renewable energy community

Zero ecological footprint city

And with some imagination others could be:

green city, self sustainable city, agro city.

Systems-resources-targets

In general 3 elements can be recognised as being part of the definitions: the system addressed, the resource involved, and the target itself.

System can be:

building, community, city, regions

Resource can be:

Climate, Carbon, CO2, "emissions" , energy, fossil fuels, renewable energy,

Target can be:

"neutral" , 100%, 0, "free" , autarkic,

Time is not included in the claims, but usually a general accepted period.

There is a few more exotic or holistic terms, like "Sustainable" or "green". They can include a wide range of topics, and are not included in these analyses.

Regarding systems:

In general this is the least complicated of the three elements. Whether it's a building or a city or a region, all can be bordered more or less exactly, with physical limits. And in fact for the exact target calculation or strategy, the size of the system is unimportant, the principle applies for all the same.

The problem is in most cases that it's not clear whether every sector within the system is included or not. This can mystify the claim a lot: claiming an "energy neutral city" if only buildings are addressed, is completely different notion from when industry or transport is included. This is illustrated by the discussion that took place in developing the Dutch program, with the pilot cities: How to deal with transport kilometres: is it all transport within the city for instance, including that of cars passing through? In the end it was decided, also due to practicalities of measuring, to include all ( energy from) kilometres driven by cars registered in the city, as part of the cities burden. This implies that also kilometres driven by registered cars, outside the system (on holiday in Spain for instance) count for the systems CO2 emissions or energy consumption.

The discussion has continued since then To appoint the load to the system where a vehicle is registered, is a practical solution, though somewhat unsatisfying, since the load in some cases is elsewhere: at the holiday location for instance. Recent discussions in the Dutch Pilot program suggest to use the petrol stations 'production 'as the basis for the load, and their location in a system. This of course appeals much better to the principle that the load should be appointed to the location of action.

This relates similar to the transport of goods: the petrol station is the location determined in the system. Regarding production of goods this is of no influence: it's the system in which the production is established, that takes the load. Of course exchange of goods between systems can be taken into account by exchanging renewable energy or CO2 credits.

For other indirect use of energy by a system, solutions are more obvious, as we will see in the next paragraph.

In fact if spoken of a spatial system, all consumers/polluters should be included, otherwise a limited system has to be claimed: "0-energy built environment" for instance, if transport and industry are excluded.

Regarding resources

This is already a bit more complicated. Some are clear: CO2 for instance: it's about CO2. However, in general it's meant as the day to day emissions of CO2 by operating the system. Indirect CO2 emissions should however also be counted, but by the system for which the emissions are direct. For instance for building materials: would the load count for the system that uses the products, or in the system that produces the products? In fact the answer should be: the system that produces the load: its load by industry operations related CO2 emissions, within a certain system addressed. The transport is then again counting for the system in which the vans are registered, the same as with cars operational emissions in the previous example.

Carbon is even more difficult, since it includes much more then CO2. And in fact Carbon will be misleading, since it is part of many normal processes, for instance forest growth. So to use Carbon as a term should be avoided. However, in all found cases where Carbon is used, anyhow CO2 is meant. So preferred is CO2, but Carbon to be interpreted as CO2, could be a workable solution.

So far the above are all resource impact related references and claims for one of the effects of that use: For instance CO2 is directly affecting climate change, but a result from the use of fossil fuels. CO2 is not the only one affecting climate change, and therefore have limited effect on that ( at this moment for about 80 %, considering the volume as well), its also a side effect of fossil fuels use, but the strategy for CO2 reduction does not necessarily prevent fossil fuel use, which could be a target if the depletion-impact is considered as well. Therefore: a CO2 approach, will not lead to exclusion of use of a resource, nor neutralise the full effect of the use of a resource.

Which relates to border setting and offsets outside the system, which we will address later.

The second group of "resources" used in claims are more direct ones: energy, Fossil fuels, renewable energy.

If fossil fuels are excluded, automatically all CO2 and other emissions related are excluded, and as well the depletion impact is addressed. This will have a more wide range effect.

"Fossil Fuel", as a resource addressed will cause little discussion as what exactly is aimed at. However we should note that in some practical cases described before, the claim is fossil fuels, but in practice its oil that is targeted, and not gas or coal. "Oil free" in that case would be better. However, it should be "oil fuel free", to avoid misunderstanding about oil used for products. (And again, in most cases were fossil fuels-Oil is meant, measuring is in CO2…)

Renewable energy in general is an accepted term as well, however there is need for a more detailed definition of renewable energy, what exactly is included and what not, since some sources to be claimed renewable are not what they look like. Energy from Biomass for instance is more and more doubted as an effective alternative for fossil fuels. Similar discussion can be held for Nuclear energy, for which uranium is depleted as well. This is not in depth explored in this paper. (a second paper is under development targeting this subject) . A short analyses of definition of renewables will follow below.

The term "energy" is somewhat misleading. 0-energy for instance would exclude all activity, when taking literally. The point is that in most cases by energy is referred to fossil fuels. So it would be better to use the term fossil fuels or renewable energy. The definition at least needs a specification of what is referred to.

Regarding targets

"neutral" , 100%, 0, "free" , autarkic

The targets are all aiming at a balanced situation for demand/use and supply. One can imagine that there will also be targets defined that strive for a positive balance: as we can see regarding the building level: energy producing houses are already constructed and even commercially on the market. {x}

However here we focus firstly on clarifying what is meant by the way of target description.

The difference between the terms is twofold: its how they use the system (-borders) and if they accept offsetting. How exactly is not always clear from the definitions in use.

Autarkic is however clear: its independent from anything outside the defined system, it operates independent: however does not exclude fossil fuels, if the system includes an oil well… But in general that is not assumed.

Free is also clear: it means the resource referred to is not available nor used in the system. (anything else however can be used or is not excluded).

0 in energy ( 0-energy refers to fossil fuels), and in general the definition includes that a net balance over time of 0 consumption is established: ) is related to time. It should be specified in a definition how exactly.

100 % does not specify whether this is from within the system or also from outside, and neutral suggest it can be outside the system as well, and also with offsets. This implies that demand/use of energy, or emissions production is always related to within the system actions (in principle also for transport) and resources supply can be in or outside, depending the definition of the target. As we will specify and analyse hereafter.

"Emissions", is also little bit vague. But could be used if more specified: "Greenhouse-effect- accelerating-gas-emissions", for instance. It relates to the next term in use: "Climate". A climate neutral city could mean that 'none of it's activities will have an effect on our climate. But it could also refer to the fact that the city/system is not affected by climate change.

Even if the second term is meant, it's still a very wide claim, that hardly can be defined undisputedly, and should preferably be avoided. "Climate" suggests to address also changing land use, next to emissions from all green house gases. Considering that both terms are popular to use, they should, if used, be meant at least to address all gases that effect the greenhouse, as a separate and distinguished target field next to CO2 alone.