There is now overwhelming evidence that the current organisation ofour economies and societies is seriously damaging biologicalecosystems and human living conditions in the very short term, withpotentially catastrophic effects in the long term. The enforcement ofnovel policies may be triggered by a grassroot approach, with a keycontribution from information and communication technologies (ICT).Nowadays low-cost sensing technologies allow the citizens to directlyassess the state of the environment; social networking tools alloweffective data and opinion collection and real-time informationspreading processes. In addition, theoretical and modeling toolsdeveloped by physicists, computer scientists and sociologists havereached the maturity to analyse, interpret and visualize complex datasets. The proposed project intends to integrate all crucial phases(environmental monitoring, awareness enhancement, behavioural change)in the management of the environment in a unified framework, bycreating a new technological platform combining sensing technologies,networking applications and data-processing tools; the Internet andthe existing mobile communication networks will provide theinfrastructure hosting such a platform, allowing its replication indifferent times and places. Case studies concerning different numbersof participants will test the scalability of the platform, aiming atinvolving as many citizens as possible leveraging on the low cost andhigh usability of the sensing devices. The integration ofparticipatory sensing with the monitoring of subjective opinions isnovel and crucial, as it exposes the mechanisms by which the localperception of an environmental issue, corroborated by quantitativedata, evolves into socially-shared opinions, eventually drivingbehavioural changes. Enabling this level of transparency criticallyallows an effective communication of desirable environmentalstrategies to the general public and to institutional agencies.