One of the most apparent expressions of the urban micro-climate is the urban heat island, resulting from the land-surface properties and anthropogenic heating from traffic, buildings, and human metabolism. Approximately 50% of the global population reside within urban areas, and by the 2030s it may be 60% (UN Department of Economic and Social Affairs, 2007). The number of mega-cities with populations in excess of 10 million is also expected to rise in this time, and 30 such cities may contain up to 10% of the global population.

Projections of large-scale or regional climate change rarely account for local drivers of change such as those from urbanisation that will influence the potential climate change that human populations will feel directly. Here we present results from global and regional climate model simulations that incorporate a simple urban surface exchange scheme including additional anthropogenic heating, to show:

• Climate change modelled for urban areas as driven by both local (urbanisation) and global factors.

• Interactions between the urban heat island and climate change make empirical or off-line urban models potentially unreliable in the assessment of future climate change in cities.

• Changes in anthropogenic heating in cities impacting both the mean and extreme heat islands.