As for carbon dioxide, I would like to share some of my views here. While it's obvious that we are producing too much carbon dioxide, how some people are dealing with the problem makes me worried. Many innovative ideas have emerged in recent years. For example, to reduce the carbon footprint of concrete production, all kinds of stuff are being added to replace Portland cement in the concrete mix. Those materials include toxic industrial wastes such as EAF slag and EAF dust, sharp, edgy glass powder, aluminium dross, rice hull ash, waste incineration slag, silica fume, fly ash, etc. When classified as "encapsulated use" (contained in concrete), it is assumed by most governments that there's almost no or little leaching of toxic substances (e.g. heavy metals, VOCs, etc.) from the concrete and regulations (or execution of them) are not needed. But the truth is, with the modern mechinaries and power tools, concrete, the second most used material after water in the world, is being turned into huge amount of fine dust everyday, posing immediate and serious health threats to the public. From large-scale projects like bridges and tunnels, to home/shop/office renovation or DIY projects, not to mention demolitions, roadworks, housing estate construction or the many concrete batching plants around. Everyone is affected with no exception. What is more, the variation in concrete composition may make source apportionment of pollution difficult or even erroneous (e.g., if you found heavy metals in an air sample you may attribute them to steel-making but not construction, while the heavy metals may actually originated from the dust of slag cement). Do the construction industry or power tool industry know about that? Well I can't speak for them, but it's quite likely that they know it, just like the energy industry since the 1960s.

Besides substituting cement with hazardous materials, some also suggested using steel or plastic in place of concrete to build bridges. I had watched a documentary long long time ago, saying that the toxic metallic wastes produced during the production of a metal coin (mining, smelting, etc.) is a few times the weight of it. The metallic dust produced during bridge construction is a problem too. Using metal to build bridges isn't environmental friendly at all IMHO. Other innovative ways to reduce CO2 don't sound very attractive to me either. Storing CO2 underground would risk future leakage, sooner or later, and when that happens it can really kill. It seems that currently most efforts in reducing carbon dioxide emissions focus in power plants, and not much attention is paid to the many huge construction projects (fewer projects, less cement needed and less carbon dioxide released of course).

I'm not against construction. Without buildings we can't hide away from dust (dust and fumes may still be able to come out through the ventilation system though). Without roads and bridges we can't escape from polluted place. (Oh yes everything is inter-related..) Just that they should be built responsiblely and only when they are truly needed.

To solve a problem, one needs to find the root cause. If part of the problem is caused by the fast population growth in developing countries, then maybe more efforts in birth control are needed there (well, after all, we are all producing carbon dioxide every second just by breathing). As to other methods, I'd prefer more traditional, well-proved and direct ways like forestation (or simply less deforestation).

Adopting new ideas globally with drastic changes without thorough and in depth consideration (esp. from experience) can be dangerous. Everything in our environment is inter-related, just like what happened in the food chain. For example, even conservative methods like forestation may risk contaminating the environment with the overuse of cheap fertilizers containing toxic substances. And the choice of species is important so that the ecological balance is not altered. Using less plastics may mean we need to use more metal, wood, etc. (which is likely to cause even more problems to our health and the environment) , using hydropower may mean we have to build more dams (which takes years and use tons of concrete), use of electric cars may mean the use of a lot more toxic batteries...etc. It is just about choosing the lesser evil. The problem with human is that sometimes we are too arrogant. We believe we know everything. We believe that we can change or revert anything, in a short time, and in our own way, without respecting the development of history and the self-healing ability of the earth, which may then doing even more harm to it. What we believe to be the most advance knowledge/technologies are mostly wrong in the eyes of someone who lives 500 years later in the future. With a pandemic outbreak like Covid-19, I believe something must have gone wrong.

My opinion is, keep the "dirty projects" as few as possible and keep them far away from where people live and commuting (e.g., we really don't need a concrete plant a few blocks from homes, I know it can't be too far for immediate use, but we are really having too many in the cities), avoid "large-scale" things, no matter it is the world's the longest railway, the world's largest bridge, dam, building, artificial island or carbon storage facility. Those "record-breaking" projects are usually dangerous. Reduce unnecessary renovation, remodeling or building rehabilitation projects and regulate the inevitable ones. Putting human lives at first priority when implementing any policies, remedies or projects, and avoid bringing bad results with good intentions (sorry for the long post:).