As several contributions in this issue of International Journal of Public Health suggest (in particular that from Kjellstrom 2009), there is a wide range of potential—direct and indirect—health consequences of climate change. However, the science of such effects is still in its infancy and faces considerable challenges, as we try to suggest in our contribution (Xun et al. 2009). Possible events attributable to climate change range from rapid and catastrophic to slow and mild. For example, IPCC does not rule out (though it is very unlikely) a cascade of events leading to Bangladesh being swept away because of rapid Himalayan glacier melting. Apart from extreme and unlikely effects, some of the direct consequences of climate change are rather obvious and can be easily perceived, such as the deaths related to heat waves in Europe in 2003. The causal pathway in these cases is clear, and does not require any particularly sophisticated epidemiological technique. Confounding is irrelevant as far as we consider the causal association between the climate event (heat wave) and its direct health consequences. But still: were all heat waves in the recent past due to what we call climate change, i.e. a man-made trend in temperature and its related epiphenomena? Was the flood in Bangladesh in 1974 the first attributable to climate change, or the last not due to it? And what about the one in 1998? Clearly borders are fuzzy, and causal chains intricate. Uncertain inferences on the causal nature of events also concern the attribution to climate change of indirect health effects, such as infectious disease outbreaks, changes in food quality and availability, water salinization and the ensuing epidemic of hypertension (Xun et al. 2009). Even wars and conflicts (like in Darfur), mass migrations and effects on mental health have been attributed to climate change. In a survey conducted among children aged between 2 and 9 in Bangladesh, Durkin et al. (1993) found post-flood changes in behaviour and bedwetting. Children were reported to have ‘‘very aggressive behaviour’’ after floods, with a significant increase compared to the preflood situation. A qualitative study explored the experiences of female adolescents during the 1998 floods in Bangladesh, focusing on the implications of sociocultural norms related to notions of honour, shame, purity and pollution. A number of the girls were vulnerable to sexual and mental harassment through exposure to unfamiliar environment of flood shelters and relief camps. Common mental health disorders following climate-induced displacement include anxiety, depression, post-traumatic stress disorder, irritability, sleeplessness and suicide. Moreover, conflict situations that may arise among farmers in times of climate-induced natural disasters like droughts and floods need to be addressed. Is all of this attributable to what we call climate change? Where are the borders between the burden of events that would occur anyhow, particularly in low-income countries, even in the absence of climate change, and those attributable to the latter? How can we identify the chain of events that eventually explains the local outbreak? Again, fuzzy borders have to be acknowledged. It should be noted that the effects we have described are mainly occurring or Paolo Vineis is Chair of Environmental Epidemiology at Imperial College, London. His main interests are in the field of molecular epidemiology and gene–environment interactions. He also works on climate change with the Grantham Institute for Climate Change in London.