We can tackle climate change by cleaning up our cities | Nick Stern

Many cities will showcase their green credentials in Paris. But greenhouse gas targets, and the lives of citizens, rely on making them more efficient

With more than 190 countries gathering in Paris this week the world still has a chance to avoid dangerous global warming - but only just. Already more than 160 countries have submitted pledges to reduce or limit their emissions of greenhouse gases by 2025 or 2030. Collectively these represent a substantial improvement on "business as usual", but they are some way from a path that offers a reasonable probability of restricting the rise in global average temperature above its pre-industrial level to no more than 2C.

There is a serious emissions gap over the next 15 years: under the current pledges, emissions will go on rising until at least 2030. Warming of about 2C creates deeply worrying risks of triggering the kind of consequences - such as rapid sea level rise or the release of methane from gas hydrates in the ocean - that could prove catastrophic, potentially causing hundreds of millions of people to move from receding coastlines and more extreme weather. That will mean more migration, more refugees, more conflict and a world without peace and prosperity. That is why the world community, via the UNFCCC, regards warming above 2C as dangerous.