1. Does the study of climate-health linkages lead directly to the use of climate forecasts in public health?

The study of climate-health linkages by itself does not establish the utility of climate forecasts in public health.

The study of climate-health linkages seeks to determine the effects of climatic factors on human health. For example, "if rainfall is intense every day for a week", "then mudslides are very likely in parts of Rio de Janeiro". These "if - then" relationships are necessary for the scientific use of climate forecasts in public health. The degree of uncertainty of these impacts can vary.

Even if the possible impacts are well known, making decisions on the use of climate forecasts must take into account the uncertainty of future climate. The results are not certain even in the case of seasonal climate forecasts. Seasonal forecasts project only three months or six months ahead. The structure of climate forecasts also imposes certain limitations. See question 2.

2. What is the difference between a climate forecast and a weather forecast?

The main difference between a climate forecast and weather forecast is the time scale. Weather forecasts are made on a daily basis or more frequently. Climate forecasts are longer-term. For example, a weather forecast might address tomorrow's precipitation while a seasonal climate forecast might project that the next three months will be wetter than normal. In practice, climate forecasts often apply to broader geographic areas, too. For example, a weather forecast might apply to a city while a seasonal climate forecast might apply to a region of a continent.

This difference is very important for linking climate-health impacts to the use of seasonal climate forecasts. For example, although the El Niño phenomenon causes heavy rainfall in northern coastal Peru, the detailed pattern of rainfall can be different in different El Niño events. Changes in the detailed patterns alter the breeding of the mosquitoes that transmit malaria. Conditions are best for breeding mosquitoes as the rains come to an end. In 1982/83, the daily precipitation was heavy and the mosquito vector population increased only at the end of the rainy season. In 1997/98, there were wet spells and dry spells, the latter of which allowed the mosquito vector population to grow quickly. A seasonal climate forecast does not predict the daily patterns of precipitation and therefore cannot predict the detailed timing of malaria transmission.

3. What is the difference between climate variability and climate change?

Climatologists draw the distinction based on timescale. Climate change is change in the global climate system over periods of centuries and longer. Climate variability is change in the global climate system over seasons, years and decades. However, other groups may introduce their own terminology. Climate change often refers to the consequences of enhanced global warming caused by increased emissions of greenhouse gases from anthropogenic sources.

4. Was the dengue outbreak in Rio de Janeiro in the austral summer of 2002 caused by El Niño?

The two major factors in the dengue outbreak of the 2002 austral summer (Jan - Mar 2002) in Rio de Janeiro are:

1) a large number of people susceptible to the type 3 strain of the dengue virus, which was introduced only a year earlier, and

2) problems in vector control due to difficulties in the coordination of different units of government and the resistance of mosquitoes to insecticides.

Climate may also play a role, especially in considering why dengue was not such a big problem in the previous year (2001).

Dengue transmission has been occurring regularly in the austral summer. There is no evidence to suggest that the El Niño conditions developing in the Pacific Ocean early in 2002 were to blame for the outbreak.

5. Where can I find the latest forecasts for El Niño?

The International Research Institute for Climate Prediction (IRI) produces ENSO Quick Look. The National Oceanic and Atmospheric Administration (NOAA) produces ENSO Diagnostic Discussion.