By Simon Ross, chief executive, Population Matters

Environmentalists agree on the issues facing us, including collapsing diversity, climate change and resource insecurity.

We also agree on the causal factors, including pollution, invasive species, resource over-exploitation, waste, population growth, global industrialisation, unsustainable consumption and poor business practices.

Solutions are harder. None will solve all our problems and all face obstacles and opposition.

Technological solutions, such as biofuels, fracking, shale oil, GM foods and nuclear have side effects, while renewables have limited scope. Environmentally conscious lifestyles, including less waste, travel and consumption, are increasingly adopted, but the impact may by limited given the billions seeking to improve their low living standards.

Changes to corporate and governmental practices have occurred, but are far from universal, particularly in the developing world.

In my lifetime, human numbers have grown from 3 billion in 1960 to 7 billion today. By 2085, they are projected to grow to 10 billion. One can argue about the impact this makes, but it clearly does not help.

We believe that a smaller population would help us to preserve the environment and live within the limit of renewable resources, as part of a comprehensive approach to the environment and sustainability.

Most would agree that improving living standards for the poor, women’s rights and access to health, including family planning, are desirable and they all tend to lead to women choosing to have smaller families.

We would argue that aid for family planning to developing countries should be prioritised, both for environmental reasons and because it contributes to poverty alleviation, women’s empowerment and better health. While individual consumption in those countries is low, growing populations do affect the environment and they will not always be poor as the world industrializes.

In developed countries, too, many pregnancies are unplanned, and we believe that funding better sex and relationships education and family planning services would be a worthwhile investment in our future, particularly in countries such as the US and UK. For individuals, we would argue that having one or two children rather than three or four is an important part of an environmental lifestyle.

By seeking to lower our numbers over time to a more sustainable level, we will be contributing to a future where we can live in harmony with nature, instead of the unachievable goal of seeking to exploit it ever more intensively.