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Climate in Context: August 24, 2010

By Andrew Freedman and Michael D. Lemonick

Get Used to La Nina


Sea surface temperature anomalies for the first week of August,
2010. Blue areas indicate cooler-than-average temperatures.
Red areas are warmer-than-average. The area of cool
temperatures in the equatorial Pacific are characteristic
of La Nina conditions. 

Credit: NOAA Environmental Visualization Lab.

Following on the heels of the 2009/10 El Nino event, a moderate La Nina is underway in the Pacific Ocean, and is likely to continue through early 2011, according to an outlook released by the International Research Institute for Climate and Society (IRI) on August 19. La Nina is characterized by unusually cool water temperatures in the central and eastern equatorial Pacific Ocean, and warmer-than-average water temperatures in the western Pacific, with associated changes in air and water circulation. (This is in contrast to El Nino, which features warmer-than-average water in the central and eastern tropical Pacific).

La Nina conditions first emerged in mid-June and have strengthened since that time. Such conditions are evident in the map of sea surface temperature anomalies, or departures from average, below.

Sea surface temperature departures from average during the week of August 18. Credit: NOAA/NCDC.

The unusually warm water near Indonesia is harming coral reefs, according to a report detailed in the New York Times last week. "A striking rise in sea temperatures in waters off Indonesia may be responsible for one of the most rapid and destructive coral bleaching events on record, a marine conservation group reported this week. Large swaths of coral reef in the Andaman Sea off the north coast of Sumatra are now up to 80 percent bleached, with more colonies expected to die off in the coming months, according to marine biologists who conducted extensive surveys of the area," the Times reported.

You can find more information from the National Oceanic and Atmospheric Administration (NOAA), which monitors coral bleaching episodes worldwide via their "Coral Reef Watch" website.

According to IRI, computer models project that La Nina conditions will continue through the remainder of 2010 and into the first few months of 2011, although there is some disagreement about its maximum strength. Most computer models project the La Nina to continue at a moderate intensity, while a few models strengthen it further. In order to determine the strength of a La Nina event, scientists measure by how much water temperatures in a portion of the equatorial Pacific Ocean deviate from average conditions. 

Both El Nino and La Nina events tend to reach their maximum intensity during winter, and can significantly influence temperature and precipitation patterns across North America and worldwide. As the map below shows, La Nina events are associated with stronger than average South Asian Monsoons, and the ongoing La Nina may be contributing to the deadly flooding in Pakistan.

Sea surface temperature departures from average during the week of August 18. Credit: IRI.

El Nino events can also warm global average temperatures, and so far 2010 is the warmest year on record, partly related to the El Nino that ended in June. La Nina could knock 2010 out of the top spot in the record books, especially if it intensifies further.

It may also help foster an active Atlantic hurricane season, since cooler waters in the eastern Pacific and warmer than average waters in the tropical Atlantic are favorable conditions for hurricanes to form. Partly for this reason, NOAA is projecting an above average hurricane season this year.

Study Finds No Clear Links Between Disaster Losses, Climate Change

Have disaster losses increased due to man made climate change? That’s the title of a forthcoming paper in the Bulletin of the American Meteorological Society (BAMS). The answer, according to author Laurens M. Bouwer of Vrije University, in Amsterdam, is: not that you can reliably measure. It’s true that disaster losses have increased over recent decades, and the author does not deny that human-caused climate change is happening. But once you correct for inflation and population growth, he claims, the increase goes away. 

On his DotEarth blog, Andy Revkin cites the new study, acknowledging the temptation to make the link between climate change and increasing disaster-related losses, then says…

"But finding a statistically robust link between such disasters and the building human climate influence remains a daunting task."

On his own blog, Roger Pielke, Jr. of the University of Colorado at Boulder trumpets the study, which meshes with his own views, as well.

So could it be true? After a summer of withering heat and wildfires in Russia, and deadly floods in Pakistan and China, which are at the very least consistent with man made climate change, the study’s results sound somewhat hard to believe. 

But it’s not crazy: as the fifth anniversary of Hurricane Katrina approaches this week, it’s important to remember that the devastation wreaked by that iconic hurricane was magnified dramatically by the city’s abysmal infrastructure, including levees that were in disrepair long before the storm hit. 

Beyond that, the population and infrastructure in areas threatened by pretty much any weather-related disaster is much bigger than it was 50 years ago – cities like Phoenix and Las Vegas, which are booming in the drought-prone U.S. Southwest, coastal Florida where hurricanes are common, and greater Los Angeles where wildfires strike every year. The more valuable stuff you put in harm’s way, the more damage you’re going to sustain, climate change or not.

But this study only looks backward; it doesn’t include this summer’s events. If you look forward, population is still going to increase – but some of these events are likely to happen more often, too, and with greater severity. Take hurricanes: most models now show fewer North Atlantic storms overall during the next century, but an increase in the number of Category 4’s and 5’s, the most powerful storms – and even if there were no increase, higher sea levels would make storm surges more damaging

Back in 1988, James Hansen made headlines by telling Congress that the temperature signal of man made global warming could now be detected against the noise of natural fluctuations. Many climate scientists thought he was premature – but whether or not it was true in 1988, it had become very clear just a few years later.

So even if this new study is correct about the recent past, the author also suggests that the human influence is likely to increase in the future. "Studies that project future losses," Bouwer writes, "may give a better indication of the potential impact of climate change on disaster losses and needs for adaptation, than the analysis of historical losses." 

Past performance, in short, is no guarantee of future results.

Hurricane Season Heats Up

As Hurricane Danielle churns in the open Atlantic, destined to curve out to sea without making landfall in the United States (or anywhere else, for that matter), forecasters are turning their attention to another developing tropical cyclone off the African coast. For updates, background info on the hurricane season and more, go to our hurricane feature page. To mark the fifth anniversary of Hurricane Katrina, which sparked high profile discussions about the potential consequences of climate change, we will be adding print and video content throughout this week.

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