Modern humans have been on Earth for 200 centuries. True sustainability means providing every person now alive, as well as generations yet to come, with a reasonable standard of living that can be maintained into the foreseeable future.
Today humanity uses the resources of the equivalent of 1.5 Earths. This means it now takes the Earth one year and six months to regenerate what we use in a year.
Present lifestyles in the richer countries have a disproportionate impact. For example, the ecological footprint per capita of the USA is more than 10 times that of Malawi or Mozambique.
Some expenditure, such as that on arms or promotional activity, could arguably be reduced if society's focus was more on human happiness and less on GDP growth and state and commercial competition.
As an individual, there are several things that you can do to help ensure the world is worth living in for future generations.
You can decide to have two or fewer children. This will be one of the most environmentally important decisions you ever make and should be part of an environmentally responsible lifestyle.
You can support Population Matters and help to raise awareness of the effects of overpopulation on the environment. The more widely they are discussed, the more widely population will be recognised as one of the key drivers of the looming environmental crisis, and the sooner any remaining notion that it is a 'taboo' subject will disappear.
As a media customer, you can complain about articles and programmes that discuss sustainability or the environment yet ignore population even though it is relevant.
As a voter, you can ask your local and national political leaders to recognise national and global population growth as a serious environmental problem.
Finally, as a citizen, you can contribute by consciously living more sustainably in your use of technology and personal priorities. This depends on both big decisions such as whether or not to go on a long-haul flight, and the large number of smaller choices you make on a day-to-day basis: waste less, reuse and recycle more, consume less meat and fewer dairy products, resist the blandishments of our consumer culture and decide which 'benefits' of modern society really matter to you.
Read more about things individuals can do to reduce their consumption of resources.