Extreme weather conditions, such as heat waves, excessive rainfall, hail and floods, which often occur in summer - including this year - remind us of the stark reality of climate change. Such wake-up calls have made us realise that global warming is not a problem for our future grandchildren, but rather a serious, immediate challenge.
At the same time, debate rages on about who is responsible for global warming and who should foot the bill. Some are asking, "Why us and not the 'other big polluters'?" One of many answers is that we, Europeans, have historically used - and continue to use - much more than our fair share of the Earth's resources. We should also be clear that the global answer comes from local action.
There is no easy recipe for creating climate-friendly and green cities, nor is there a one-size-fits-all solution. Yet, there are many good practices to be copied from cities across Europe.
We need to build on these, so that every city can create its own green mix of measures. Currently, there is a lively discussion going on about the future of the covenant of mayors, which I have been following closely as the Committee of the Regions' rapporteur on the issue.
Essentially, it is a movement of cities - now more than 6400 around the world - that are taking responsibility and action, and making a voluntary pledge to reduce their CO2 emissions beyond the EU's target of 20 per cent by 2020.
They are committed to cutting their emissions by 28 per cent on average. But reducing CO2 emissions alone is not enough, and a holistic approach is needed. Mitigation and adaptation are two sides of the same coin.
Cities can become climate friendly by promoting green buildings, through 'green building codes', which contain techniques such as solar access and shading, natural cross-ventilation, triple glazed windows, renewable energy sources and smart meters, better insulation, and heating and lighting system upgrades.
Buildings are responsible for more than half of total final energy use. Transport represents close to one third of overall energy use. Cities can help make active transportation choices - such as walking and cycling - safe, comfortable and enjoyable for all ages.
In addition, it is essential to maintain and expand good quality, low-carbon and affordable public transport. Where possible, authorities should consider closing streets to cars and using them as public spaces. Trees and urban ecosystems are carbon sinks, and therefore key to mitigating greenhouse gas emissions.
Creating space for community gardening, growing edible plants, and planting trees on public and private properties are some effective measures in this direction.
Cities can help and inspire local communities to move away from the idea of the 'perfect lawn', which has a huge carbon footprint because of its fertilisation and irrigation needs, and instead promote climate friendly backyards, natural parks and drought-resistant plants and trees.
Installing smart meters, reducing the sale of bottled water in public buildings and around the city, while expanding public access to drinking water are essential to reducing our water consumption. Using rainwater is also a key measure.
In big cities, rain is considered more of a problem since it is collected through drains and then discarded. With more parks, green roofs, green spaces or grass based permeable pavers, rain water can be absorbed, cleaned and used for other purposes.
Cities should encourage sharing economy models to reduce their overall carbon footprint - community bikes, car sharing, co-working spaces, community gardens or even tool libraries could all help.
Making local food available in city-run facilities, encouraging citizens to buy local food by supporting neighbourhood food hubs, community kitchens, farmers’ markets and community gardens can also make a real difference.
We need to make waste reduction and reuse a priority. No solid waste should go to landfills. We must collect waste separately and reuse, recycle, or make compost from yard waste and kitchen scraps. We must also aim to go plastic bag-free.
These are some practical examples of what European cities can do to address climate challenges. Many of these measures require considerable public and private funds, which are not automatically available, especially in crisis-struck countries.
Yet, beyond economic considerations, no measure can be successful if it is not accompanied by a real change of culture when it comes to people’s attitudes. In this respect, local and regional authorities can lead by example and raise citizens' awareness.