The intensity of Bangkok’s urban heat island during the dry season can be as high as 6–7C and in the densest areas the urban heat island’s intensity is approximately 4C. The urban heat island thus is causing a city already oppressively hot to become even hotter. The urban heat island also contributes to health problems, such as heat stroke and fatigue, particularly to those with lower incomes. We historically examine the numerous causes of Bangkok’s urban heat island, such as the lack of green space, high levels of air conditioning, and high rates of vehicle exhaust fumes. For example, Bangkok has only three square metres of green space per person which is one of the lowest in all of Asia. Local governmental weaknesses, administrative fragmentation, prioritisation of economic growth and limited buy-in from the private sector have intensified Bangkok’s urban heat island, and imposed numerous barriers to actions that would reduce heat, such as establishing green space, restructuring urban transport or creating and following an effective urban plan. Ideas mooted to remedy these problems have yet to come to fruition, largely because of bureaucratic inertia, fragmentation and divisions within the relevant lead organisations. The political ecology lens also reveals how political–economic processes largely determine the vulnerability of urban inhabitants to heat, but also that thermal governance is highly unequal and unjust. Those who contribute to and profit the most from Bangkok’s urban heat island, such as real estate developers, shopping mall owners, and automobile corporations, suffer the least from its effects, whereas low income communities hardly contribute to this problem, yet are the most vulnerable.