Climate change can contribute to a global increase in the burden of infectious diseases. Both the number of geographical areas as well as the number of yearly days that are suitable for transmission of certain infectious diseases can increase due to global warming. At the same time, increased 'suitability' does not always lead to a factual increase in disease burden and economic development and public health measures have resulted in marked reductions in the burden of several important infectious diseases in recent years. The net effect of global environmental change on infectious disease burden will be determined by a multitude of factors, including unpredictable outbreaks of pathogens and the extent to which public health programs can effectively function and adjust to changing health risks.