The second lecture addressed the 'dire' risks of unprecedented global environmental change, posing "perils to the planet that we simply cannot afford to take". We are at a decision point for the future of the planet; the optimistic economist explains how we might balance future economic growth and sustainable development.

Focusing on climate change as one of a grim list of interconnected global challenges (destruction of habitats, over-fishing, hunting and so on.), he presents us with a framework to crack the conundrum of sustainable development in a world bursting at the seams.

Sachs believes our only way forward is "science-based global policy-making based on world wide public awareness". The framework is the cascade of pressures and events, starting with rigorous science, feeding into public awareness and then to the development of technological alternatives; finally translating into brave new international political agreements.

The wellspring of his optimism is faith in the power of technology and human ingenuity to find solutions to reduce environmental impacts, leading to peace and prosperity. The closer we look, the less daunting the problems become, he soothes.

The Anthropocene is about the pressures one species – human – is exerting on the biological, physical and chemical systems that regulate life. Business as usual is not an option in a global economy that depends critically upon a healthy planet: "Nature has spoken more loudly than vested interests – this is not a matter of vested interests, this is a matter of common interests".

These interests are prosperity, founded on environmental sustainability, peace and poverty alleviation. Sachs advocates a political philosophy of 'activist problem solving'.

As China rises once again, Sachs points out that something wonderful is happening – "an age of convergence" - in which the convergence of methods, institutions, processes and the adaptation of technologies is becoming a global phenomenon (except in the very poorest countries). For Sachs, globalisation is wonderful news; an exciting global dynamism.

He argues that we can stabilise the climate, learning the costs of action are tiny compared to the risks of inaction. The economist's view is that climate change can be solved for an annual investment of less than 1% of world income, whereas the potential costs are a "devastating multiple of world income".

Welcome indeed. But hang on...

If the cost of avoiding global environmental and economic meltdown is really so small - a reduction in global economic growth from 5% to 4% - then why are we waiting?

If energy efficiency, nuclear power and renewable energy will solve climate change, then will these work better than policies implemented since the early 1970s in the name of energy security?

If political leadership through international agreements are the centrepiece, then how do we modernise our complex system of multilateral environmental agreements? How exactly is this engine of science-based public awareness-driven global policy-making going to work when international environmental agreements so often in practice descend into a paralysis of political rhetoric?

Professor, as you say, scientists and the engineers may well be scurrying but for your theory to hold true we really do need them sometime soon to whisper in the ears of politicians – "it's ok you can reach an international agreement - we can handle this".

Can we use technology as a way out of our climate fix? Are the solutions so simple we might hardly notice them? Have your say in the Reith Lectures forum.