IRI: what you always wanted to know about El Niño/La Niña

The International Research Institute for Climate and Society (IRI) has cleared up some misconceptions about El Niño and La Niña, and their impact on climate and natural disasters. But what are they exactly?

El Niño refers to the occasional warming of the eastern and central Pacific Ocean around the equator. The warmer water tends to get only 1 to 3 degrees Celsius above average sea-surface temperatures for that area, although in the very strong El Niño of 1997-98, it reached 5 degrees or more above average in some locations. La Niña is the climatological counterpart to El Niño-- a yin to its yang, so to speak. A La Niña is defined by cooler-than-normal sea-surface temperatures across much of the equatorial eastern and central Pacific. El Niño and La Niña episodes each tend to last roughly a year, although occasionally they may last 18 months or longer.

This warming/cooling of the Pacific can have serious impacts on changes in local climate, potentially leading to severe natural disasters, resulting in loss of life and property during floods, failed harvests, increased risk of certain vector-borne diseases such as malaria, ...
But here are some misconceptions - what El Niño and La Niña do not do:

• El Niño periods cause more disasters than normal periods.
• El Niño and La Niña significantly affect the climate in most regions of the globe.
• Regions that are affected by El Niño and La Niña see impacts during the entire 8 to 12 months that the climate conditions last.
• El Niño episodes lead to adverse impacts only.
• We should worry more during El Niño episodes than La Niña episodes.
• The stronger the El Niño/La Niña, the stronger the impacts, and vice versa.
• El Niño and La Niña events are directly responsible for specific storms or other weather events.
• El Niño and La Niña are closely related to global warming.

To find out what the actual effects are, read the extended blog post and check out the article on AlertNet.

• El Niño periods cause more disasters than normal periods. On a worldwide scale that is not the case. However, regionally more disasters may occur. These are fairly consistent, though, and quite predictable. Early warnings can reduce the negative impacts.
  
• El Niño and La Niña significantly affect the climate in most regions of the globe. Actually, they significantly affect only about 25% of the world's land surface during any particular season, and less than 50% of land surface during the entire time that ENSO conditions persist.
• Regions that are affected by El Niño and La Niña see impacts during the entire 8 to 12 months that the climate conditions last. No, impacts are only felt during one season, yet these seasons may differ across the world.
  
• El Niño episodes lead to adverse impacts only. El Niño events are also associated with reduced frequency of Atlantic hurricanes, warmer winter temperatures in northern half of U.S., which reduce heating costs, and plentiful spring/summer rainfall in southeastern Brazil, central Argentina and Uruguay, which leads to above-average summer crop yields.
• We should worry more during El Niño episodes than La Niña episodes. This is not necessarily the case - they each have their own specific effects. The El Niño effects tend to be more mediatised, however.
  
• The stronger the El Niño/La Niña, the stronger the impacts, and vice versa. The impacts on climate-related disasters are only predictions, they do not always occur.
  
• El Niño and La Niña events are directly responsible for specific storms or other weather events. Usually you can't pin a single event on an El Niño or La Niña, just like you can't blame global climate changes for any single hurricane.
• El Niño and La Niña are closely related to global warming. El Niño and La Niña are a normal part of the earth's climate and have likely been occurring for millions of years. Global climate change may affect ENSO cycles, but the research is still ongoing.