If we want to solve the problem with CO2 emissions in practice, then we have to assess CO2 emissions, and nothing else, as I argued earlier. And we do not. As for much of our policies or our building and retrofit plans, there are a lot of nice intentions, but I never see graphs showing the accumulated CO2 curves, and the change in that by the proposed measures. That is because the cabbage and the goat are spared. Its best illustrated on the basis of for example, building assessments: in most tools the CO2 effects are hidden en drown in the countless other categories that are also considered important.  And that makes no sense, as colleagues abroad also note .
CO2 has been reduced to a marginal impact in the whole assessment. If we really want to tackle CO2, we will also have to measure and steer on CO2 emissions. Assessments like BREEAM and LEED , and all derivatives must be overruled, to fully steer on CO2. Currently it is still the case that every new building increases our CO2 problem. *
CO2 emissions related to building can have two causes ; operational and embodied in materials. The latter is often forgotten or marginalized, since it spoils the easy operational energy approaches, and makes things more complex. A comprehensive study by the Sturgis agency for the English RICS organization shows that it is almost the same for a modern office: the operational CO2 emissions and the material production emissions.  And please note that this is averaged over the lifetime. However, to average over lifetime is correct for the operational emissions, which are annual anyway. But to normalize the embodied emissions over the lifetime ( which is very common also in science) is making us look richer as we are: they are emitted at the moment of delivery: by normalizing them out over 50 or 60 years, the emissions do seem bearable , but they contribute today directly to our CO2 emissions, not in 50 years or so. So they greatly increase our problem. Right now. Which is another reason to count in direct CO2 emissions.
Since , even if we realize a 0-energy building, which rarely happens, the material emissions are still there. In other words, the frequently used term climate-neutral is often misused . This should imply that the emissions form materials are neutralized as well. There are only two ways to do this: by producing materials with renewable energy, (0-energy materials) , or by having a 0-energy buildings produce extra renewable energy, to compensate for those material emissions: This way a building can be 0-energy today (operational), but can only be climate-neutral in X years time, when investments have been compensated and from that moment on no net emissions are anymore added to the system .
These are the criteria that I would use for addressing CO2 reductions: 1) creating 0-energy buildings, buildings related production of renewable energy as much as required annually, (also called energy neutral) , and secondly: 2) climate neutrality in year X : the year in which the material impact have been leveled by a surplus RE production, building related. (both, incidentally, including the CO2 from extra materials for extra generating power like PV panels!)
For new buildings this is straight forward: we know how to realize 0-energy (energy-neutral) buildings, as there are by now many examples. Next the building has to generate surplus energy, which makes it easy to calculate in which year the building is (can be) climate neutral. ( divide the Embodied energy by the yearly surplus, which gives you years to add to the buildings completion date to become ‘ climate neutral’) . And the less embodied energy in the new building, the sooner that point can be reached.
When it comes to retrofitting buildings , it is slightly different: in that case it concerns existing emissions of CO2 for operational energy, which will be reduced by, for example, a deep retrofit for 0-energy performance. Extra materials are then invested for this retrofit, for reducting ( insulation) or production ( like PV panels) . In that case the operational savings (energy / CO2) will outweigh the investments (in embodied energy / CO2) in year X.
In a certain way retrofit is different compared to new construction, where the investments of the entire building are compensated by overproduction.That makes sense in a certain way, the building was not there before and contributes in its entirety to the climate problem. In existing buildings, however, there is already an accumulating stack of CO2 emissions from previous existing operational use, which are now stopped by an interim extra investment: the accumulated savings stabilize after year X emissions to zero. But there is also no profit (thereafter), the installed renewable energy generation covers only the operational use. In the case of new construction, an overproduction is still available after the climate neutral year X, which will contribute net to our (renewable) energy potential.
We could also argue in the same way for retrofits, so with an extra production installed (which would also imply that the climate-neutral year is reached more early (X2)). Which could , like for new construction, could eventually continue contributing to renewable or climate-neutral energy production. In this way actually takes an advance on the necessary investments in replacement and maintenance in the long term. (and after year X could also be counted partially or entirely for household use).
Mind you, CO2 has still actually been released in these interventions, and as such have contributed to the global warming. What is prevented with this investment is that they would still do that after year X. The cost goes for the benefit. **
Incidentally, as I described earlier, not all problems are solved: we have solved the energy-related problems (operational and embodied), but we still are depleting materials. There is third step to make, which is from Climate neutral to System Neutral. For the sake of clarity, I leave that out in this article, for the moment , if we already manage to steer operational and embodied emissions properly, we are already a long way off. ( it will be treated in my new book) ***
In fact, both in practice as well as in education a 0-energy operational performance requirement causes many problems: still other considerations are often found more important: functional design, construction, urban plan, comfort (growth), architecture, etc. But a 0-energy approach in Buildings Physics, is not different from what has been practiced for a long time in those other disciplines, but then implicitly: An architect will always make a ceiling high enough to be able to walk underneath. It is an almost unspoken – physiological – requirement that someone must be able to walk in a space, there must be a balance between space height and the length of people, between physiology and physical space. The same with the load bearing capacity of a column, which must be in balance with the force exerted on it. That is in fact no different than that emission free energy balance must be correct. Only that is not yet embedded in the consciousness, , where space and load capacity are self-evident The energy balance is not an extra requirement, it is a self evident condition, which we have neglected the past 150 years or so !
A remaining question could be, whether we should calculate in energy or in CO2. After all, the less energy needed, also less renewable energy, the less impact: since less (materials) have to be invested in generating power.
By being both zero-energy (zero-energy or just zero), and calculating the year of Climate Neutrality (with extra-produced renewable – more or less CO2-free – energy), we do not necessarily have to calculate in CO2 emissions. If we calculate in ( renewable) energy, and have to reduce that (the surplus to be produced to bring the climate neutral year closer) CO2 emissions are still reduced , in combination with a low energy requirement. We will have to target for climate neutrality within the shortest possible time.
In a recent first exercise with 14 groups of students, the approach worked very well. The outcomes of the project groups for their designs were between 5 years and 89 years of climate neutrality, (the lowest for a retrofitted building) and created the necessary discussions between the students in the groups, especially between the calculating students and the designing students.
In conclusion, the 0-energy plus Climate-neutral year-X calculation ***** seems to be an excellent combination to reduce CO2 emissions and building-related energy demand, a fair approach, which also has a large number of other adverse effects with a push in the right direction . [see also the kg / m2 article  It is not the egg of Columbus, but much more practical and effective than complex calculations with a large number of factors, whereby its invisible what exactly is achieved.
* negative emissions ?
I was reminded by a colleague of the fact that with wood construction negative emissions can be realized. Some tools and assessment methods work with this option. And it makes some sense, however, in our current situation this is questionable.
The CO2 that is supposedly stored in a wooden building, was already stored before that, as a tree. At most you could argue that no additional CO2 has been emitted, for the building material. Moreover, it must be guaranteed that the tree will re-grow. It has to grow in the garden of the building, as it were, to make sure it really happens. And that it is assured that additional CO2 is extracted from the atmosphere. But that effect only occurs after a period of decades, not during construction. You could normalize that in time, so that negative emissions arise if the building lasts longer, and the tree grows at the same time.
In time, when more wooden buildings are being built and trees are re-growing, there is indeed a continuous flow of CO2 extraction. But whether or not you could incorporate that future profit at the start of the construction of a building is debatable.
It is the same problem as the emissions that arise at any building normalized over the expected life of that building. Apart from the fact that nobody knows how long a building will last, what you do is spread the emissions over the future, which makes the impact look minor, while in fact they are acute, they have already taken place and are contributing to the problem today.
Normally you could say that resources are part of a continuous flow, and should calculate with resource flows over time. That makes sense and I also apply that in theoretical models, everything flows. However, we are now faced with an acute problem of trying to stay below 2 and preferably 1.5 degrees of global warming, and the emissions should drop to almost zero within a few years.
The time to let time do its work has long ago passed.
We have lived on creating debt, using nice calculations. We cant continue that. Every gram of emissions currently is 1 gram too much. Which, however, does not imply that we should not use wood, if we construct a building, wood is of course the best option, because apart from the potentially negative emissions (in the future), it has a low embodied energy, in other words low emissions ( in treatment and processing) , now, compared to other materials.
incidentally, that investment should also be as small as possible, because everything accumulated over the entire stock could be in total more than what we can afford to do within CO2 budgets. I wrote about that before: 
*** System neutral:
If we want to do it all right all the way, 0-impact, in closed cycles, then we have to make one more step, and go to System-neutral: taking into account material exhaustion: and add Circular energy to the calculation (CE), or apply the ‘ Trias eXergetica’   . But if we already would apply the above, already a huge step would be made in the right direction..
( in my new nook, as of September 2019 available, it will be described in more detail:: ‘PEOPLE vs RESOURCES’, check this website later)
In many countries we are faced with a kWh / m2 requirement, which hinders optimizing buildings from a materials point of view. Sometimes less insulation and a little more generation ( of renewable energy) could be more interesting with regard to OE and EE together. 
Except, of course, when it is possible to optimize only part of the house , and to average the heat load over the whole house m2’s. If that is allowed, you can realize less heated m2, perhaps with a slightly higher heat load for that part, but with a lower heat load for the building as a whole. And therefore with less insulated m2, and thus less material and embodied energy. (and less power to be generated). This is what I have named the “Summer-Winter House”: In ‘winter’, the so-called two weeks in the year that it is below 0 (in the Netherlands), you limit your living space to a core part of the house, kitchen-living area, Why would you retrofit the whole house for those two weeks? as if it is 365 days of winter?
***** The buttons
The ZEB and ZEEB (Zero embodied energy building) data together (the 0-energy requirement and the embodied energy calculation) as input for climate-neutral year, in fact provide the buttons you can turn to find a optimal design, read: with the lowest impact, and the earliest year of climate-neutrality . Namely produced energy, versus demanded energy (also for a possibly smaller surface area), and the embodied energy in the materials (including those for producing the – renewable – energy).
 current building evaluation tools wont help:
 risk of runaway global warming by ‘sustainable’ buildings…
 RICS/Sturgis redefining zero: /http://sturgiscarbonprofiling.com/redefining-zero/
 Trias eXergetica : http://www.ronaldrovers.com/from-tetra-materia-to-trias-exergetica/
 Ritzen, M. et all (2016) Environmental impact evaluation of energy saving and energy generation: Case study for two Dutch dwelling types, in: Building and Environment 108 ·July 2016