Greenhouse gasses (GHG), such as carbon dioxide, methane, and nitrous oxide, accumulate and become trapped in the atmosphere, where they absorb heat energy and prevent it from escaping to space. As the concentrations of GHG increase, the surface temperatures on Earth also increase. This condition is known as global warming.
Concentrations of carbon dioxide, methane, and nitrous oxide in the atmosphere are much higher today than in the last 800,000 years, which is primarily due to human activities. The main causes include the burning of fossil fuels, deforestation, cement production, land clearing, soil destruction, animal agriculture, and waste production.
Nature-based solutions (NBS) can reduce GHG emissions in several ways:
- sequestration of carbon in the air by vegetation
- reductions in heating and cooling energy consumption of buildings
- recycling and reuse of waste products
- harvesting and reuse of rainwater
- decreasing irrigation water and pesticides/herbicides use
- reducing fuel consumption in vehicles
The City of Barcelona has doubled the area of green space in the past 10 years to improve the local environment. The goal is to provide residents with green spaces and pocket gardens within a 5-minute walk, increase biodiversity and the number of street trees, and improve ecosystem services. The air quality in Barcelona has improved greatly during the last decade, and currently has particulate matter concentrate well below the levels for urban areas; as shown in the figure (different coloured lines represent different neighbourhoods of the annual mean concentration of particulate matter, or pollutants, in the air that are less than 10 micrometers, PM10, in diameter).
Nature-based solutions such as boulevard trees, green walls and roofs, rain barrels, local materials, and native species, urban parks, and multi-use pathways can sequester carbon and reduce the production of CO2 and other gasses, which helps to reduce GHG emissions.