Currently, 55% of the world's population lives in urban areas, a percentage that is expected to increase to 68% by 2050. The abandonment of rural areas in favor of cities, combined with global population growth, could add 2.5 billion people to urban areas in just 30 years.

Although climate change is a global phenomenon, its impact is evident in urban areas, especially in resource-poor countries, which are home to three-quarters of the world's urban population. As a result of the increase in global temperature (1oC above pre-industrial levels), many cities are already suffering the consequences: extreme weather events (floods, droughts, fires and storms), loss of land area due to rising sea levels, spread of tropical diseases, worsening air quality, etc., problems that will worsen in the future according to climate change model projections.

Precisely because of the concentration of population, cities play a crucial role in climate change, being responsible for 70% of global CO2 emissions (about 25 gigatons). They are therefore the main threat to the climate, but they can also be an important part of the solution to the problem.

The public is expectantly awaiting the conclusions of the upcoming Climate Summit (COP25), where the participating countries are expected to reach a political agreement to reduce greenhouse gas emissions and thus keep the increase in global temperature below 2oC. However, beyond the results of the Summit, in which unfortunately there will be countries that do not ratify the reduction of emissions due to economic interests, we citizens have the commitment to act in the knowledge that our actions can have a decisive influence on the future of our planet. The well-known phrase "think globally, act locally" is more powerful than ever in an environmental problem such as climate change.

The challenge is transcendental, as there are significant barriers that need to be overcome to raise awareness in society; to this end, environmental education and the communication of clear, forceful, science-based messages are key to bringing about a change in behavior. Among the actions that citizens can take to mitigate climate change are energy saving, the use of sustainable means of transport, the implementation of the three Rs of sustainability (reduce, reuse and recycle), the consumption of local food (low-carbon diet), etc.

These practices can save each citizen from emitting several tons of CO2 per year, which demonstrates the importance of acting globally in cities to contribute to the decarbonization of the planet. For example, if we consider that 54% of the world's population is concentrated in cities, a simple reduction in the emission of 1 ton of CO2 per citizen would mean an overall reduction in emissions of 4.2 gigatons.

But citizens cannot undertake this task alone; municipalities must take the lead in urban climate change mitigation and adaptation actions, promoting sustainable policies and investing in innovative ideas aimed at reducing the carbon footprint. A successful example of the importance of municipal policies in the fight against climate change is the C40 coalition of climate-committed cities, which brings together a total of 90 cities. These cities, despite being home to 650 million citizens, contribute only 7% of the world's urban carbon emissions, demonstrating that it is possible to combat climate change at the local city level.

It is clear that the fight against climate change is everyone's business and that we cannot entrust the future of our planet to decisions taken at the political level (COP25), because unfortunately they will be insufficient to mitigate its effects. In this context, cities must play a key role, but this requires a change in the urban model, which must inevitably be accompanied by a change in the behavior and lifestyle of citizens. Are we willing to do so? Our future and that of future generations depends on it.