We are constantly hearing the word "sustainable" used in the context of the environment. People talk about sustainable development, sustainable retail, sustainable investments and sustainability in many other sectors as well. But how often do we stop and think about what it actually means?

The dictionary definition of sustainable is "able to continue over a period of time" (Cambridge dictionary) or "able to be maintained at a certain rate or level" (Google). So how do we apply that to environmental matters?

When I think about the sustainability of the environment, I consider it in terms of a product or action that can be produced/used/undertaken continuously without harming the planet or adversely affecting its future fitness for habitation. I also think of it as a product or action that improves the environment so that it will remain habitable for longer. But that in itself can be contradictory. Over-population is a problem for the environment. But if we think about sustainability of the human race, so too is the rapid decline in birth rates, creating problems associated with an ageing population - including insufficient workforce to put enough environmental measures into place.

I support the move towards renewable energy. However, I recognise that whilst it is a lot better for the environment than fossil fuels, it is not without its issues. I also recognise that any single piece of technology we have to date is not truly sustainable on its own. For example:

• there will be carbon emissions resulting from the manufacture of solar panels and other "green" technologies - and there is a question mark over how well we can recycle them when they become defunct or reach the end of their useful lives;
• the mining of lithium for the lithium-ion batteries that we use to store renewably generated electricity can create issues with the water supply around the mining fields and the lithium and other materials used can also cause contamination if leakages occur;
• the processing of materials to clean and recycle them results in carbon emissions and also involves the use of chemicals that may not be good for the environment;
• the creation of the materials and the construction processes for both new builds and retrofitting to create a more sustainable built environment results in carbon emissions.

What is sustainable depends on the end goal. Sustaining the current levels of carbon in the atmosphere is not the same as reducing them to sustain a habitable planet. 

Carbon offsetting has become a bit of a taboo subject. I do not know what level of carbon would be "safe" for the environment, but I cannot imagine humankind being willing to give up enough of its comforts to reduce emissions to that level. And so, whilst not a replacement for reducing emissions, offsetting will have a role to play. Even with the greatest of efforts from every person on the planet, there will be unavoidable emissions (such as in the food industry, or the production or transport industries and in nature). True sustainability will rely on a holistic approach.

Perhaps next time you write about or discuss sustainability, you might first think about what it means to you?