Sea Surface Temperatures in Tropical North Atlantic Rise to Record Levels in 2010, With Impacts from the Amazon to Canada

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Sea surface temperatures (SSTs) in the Tropical North Atlantic are rising over the long term (see figure below for the month of September, 1951-2010), driven in part by rising concentrations of greenhouse gases. Record SSTs in the region throughout 2010 are largely responsible for one of the worst coral bleaching episodes on record in the Caribbean, are a principal contributor to one of the most active hurricane seasons on record, and are likely a key factor behind the second extreme drought in the Amazon in 5 years.

In 2010, SSTs in the tropical North Atlantic have been at record levels every month through September; and at record or near record highs in the Caribbean.  See the map below showing the temperature anomalies in September.  A very similar situation occurred in 2005 -- but this year is even warmer.

Above: The North Tropical Atlantic SST Index for the Month of September, 1951-2010.  SST anomalies (relative to 1951-2000) averaged over the region of the tropical Atlantic between Africa and the Caribbean (the region is indicated by NTA on this map) for the month of September from 1951 through 2010.

Sea surface temperature anomalies, October 2010. Source: UK Met Office Hadley Centre.

Above:  Sea surface temperature anomalies, October 2010.  The areas with water temperatures that are the most elevated above 1961-1990 levels are in shades of red.  A plus sign in any grid box indicates that the temperature anomaly in that area in October was the highest since the dataset began in January 1850. Similarly a minus sign indicates the lowest SST anomaly since 1850. White areas represent land and areas where there no SST observations were made. Source: UK Met Office's Hadley Centre.

Three notable consequences are associated with the elevated tropical north Atlantic SSTs (and other factors) in both 2010 and in 2005: 

  • Record and near record coral bleaching in the Caribbean.
  • Record and near record hurricane seasons
  • Record droughts in the Amazon.

Each of these recent impacts partially attributed to elevated SSTs in the tropical north Atlantic are summarized in the sections below.

Tropical Atlantic SSTs are projected to increase over the course of the 21st century as a result of rising greenhouse gas concentrations in the atmosphere. In large part because of that, all three impacts (coral bleaching, more energetic Atlantic hurricane seasons, and Amazon droughts) are projected to pose greater threats.  Among the areas affected by these actual and projected impacts are two of WWF's priority areas:

  • Amazon: Severe droughts  (1) threaten ecosystems and people who depend on them in the Amazon, (2) undermine the capacity of region to sequester carbon, and (3) affect regional and global climate by altering large scale exchanges of energy, carbon and water between the Amazon and the atmosphere.
  • Mesoamerican Reef region (from the northern tip of Mexico’s Yucatan Peninsula to the Bay Islands in northern Honduras):  Coral reef ecosystems are adversely affected by coral bleaching.  More intense hurricanes affect coastal areas, including coral reefs and mangrove forests; and bring heavier rains to inland areas.  Longer term climate change impacts to the region will include ocean acidification and sea level rise.  Human communities throughout the region are being -- and will be -- affected by these increasingly disruptive changes.

Actions are urgently needed to slow climate change and ocean acidification by sharply reducing net greenhouse gas emissions.  Efforts also are required to prepare for the impacts of climate change and ocean acidification. WWF has been working with a wide range of partners and stakeholders both in Mesoamerican Reef and Amazon regions -- and elsewhere -- towards those ends.

Amazon: Two "Once-in-a-Century" Droughts in Five Years

Drought in the Amazon (1 month assesment period, through 16 October 2010).  Source: University College London,

Above: Drought in the Amazon (1 month assessment period, through 16 October 2010).  Source: University College London Global Drought Monitor. 

In 2005, the Amazon region of Brazil experienced one of the worst droughts on record, one scientists subsequently linked to both the 2002-2003 El Nino in the Tropical Pacific (which suppressed precipitation during the 2002-2003 wet season) and to high SSTs in the Tropical North Atlantic that in 2005 intensified the drought during the dry season.  The wet season typically extends from September-November through March-May 

In a very similar scenario in 2010, the 2009-2010 El Nino reduced rainfall during the wet season and record high SSTs in the Tropical North Atlantic appear to have intensified the drought during the Amazon's dry season. In a press release on 22 Oct (Seca pode bater recorde na Amazônia / Drought may hit record in the Amazon), Brazil's Amazon Environmental Research Institute (Instituto de Pesquisa Ambiental da Amazônia or IPAM) said the drought "still hasn’t ended in the Amazon and could surpass that of 2005 as the region’s worst during the past four decades."

"Scientists described the 2005 drought as a once-in-a-century phenomenon," says Jeff Tollefson in Drought strikes the Amazon rainforest again (Nature News, 29 October 2010).  "But clearly it wasn't."

Later this week we will have much more to say about the two Amazon droughts and climate change [see Another Extreme Drought Hits the Amazon and Raises Climate Change Concerns, 23 Nov 2010].  Meanwhile, see the excellent discussion of those topics in the video below from GlobalPost, Rumble in the Jungle: Is the Amazon Losing the Fight Against Climate Change? by Erik German and Solana Pyne.  See also their online article, Rivers run dry as drought hits Amazon (GlobalPost, 3 November 2010). 


Coral Bleaching: 2010 Event Rivals "Worst on Record" Event of 2005. 

In 2005, elevated SSTs in the Caribbean contributed to what scientists from 22 countries reported yesterday (15 November 2010)  was the worst coral bleaching event on record up to that time.  In Caribbean Corals in Crisis: Record Thermal Stress, Bleaching, and Mortality in 2005 (Eakin CM, Morgan JA, Heron SF, Smith TB, Liu G, et al.,  PLoS ONE, 5(11), Nov 2010), the authors found that "over 80% of corals bleached and over 40% died at many sites. The most severe bleaching coincided with waters nearest a western Atlantic warm pool that was centered off the northern end of the Lesser Antilles." 

They concluded that "[t]hermal stress during the 2005 event exceeded any observed from the Caribbean in the prior 20 years, and regionally-averaged temperatures were the warmest in over 150 years.

This severe, widespread bleaching and mortality will undoubtedly have long-term consequences for reef ecosystems, and events like this are likely to become more common as the climate warms” said C. Mark Eakin, Ph.D., coordinator of the National Oceanic and Atmospheric Administration (NOAA) Coral Reef Watch Program in a press release issued yesterday (Heat Stress to Caribbean Corals in 2005 Worst on Record, 15 November 2010).  

The researchers also noted that "[h]igh ocean temperature also contributed to the record 2005 hurricane season that damaged coral reefs in Jamaica, Cuba, the Yucatan, Flower Garden Banks, and the Florida Keys as well as causing major damage to communities and loss of human life."

Among the most severe prior bleaching events were those of 1995 and 1998.  Damage from the 1998 bleaching was compounded by the especially powerful and destructive Hurricane Mitch.  See Threshold Decline in Mesoamerican Coral Growth and Resiliency (Nature Precedings, 28 July 2008) for a discussion of the impacts that year on the Mesoamerican reefs.  The authors of that paper concluded:

"Our records reveal a unique reduction in growth rate associated with the 1998 coral bleaching event that has no parallel in the past 75 to 150 years...The 1998 event apparently surpassed a threshold in coral tolerance precipitating a catastrophic shutdown in growth that had lasting effects throughout the Mesoamerican reef system..."

In 2010, large areas of the Caribbean yet again have seen record or near record SSTs. The Caribbean SST Index, which represents SST anomalies relative to 1951-2000 in the Caribbean region (CAR on this map), indicates that for the region overall,  SSTs during the first 7 months of 2010 were warmer than in 2005.  Only in August and September was 2005 warmer (the October values have not yet been released). 

One measure of the potential severity of bleaching events are "degree heating weeks," which indicate how long water temperatures have exceeded the bleaching threshold (1°C above the highest summertime mean).  As the map below suggests, the accumulated heat stress in 2010 is more extensive than in 2005; both bleaching episodes were concentrated in the Eastern Caribbean and areas to the east.  See a six-month animation of showing the evolution of the bleaching event in the Caribbean.

Above: Degree Heating Weeks for Summer 2005 (upper image) and Summer 2010 (lower image).  Source: NOAA.

In its press release yesterday, NOAA said that "The Caribbean is suffering severe bleaching again this year, and in some locations, this bleaching event is worse than the event in 2005. Not only are temperatures causing further damage to reefs hit hard during the 2005 event, but new locations have also been impacted." 
In Analysis of October 2010 Coral Bleaching Thermal Stress and Seasonal Guidance Through February 2011 (issued on 26 October 2010), NOAA says:  "[T]hermal stress has continued to develop in the southeastern Caribbean since July... The highest thermal stress currently spans the southern Lesser Antilles, from Barbados to Tobago and westward across the southern Caribbean basin to the north of Venezuela. Many coral reef areas in this region have experienced accumulated bleaching thermal stress exceeding 10 Degree Heating Weeks [see figure above] that usually lead to mass coral bleaching. Observed bleaching throughout this region has ranged from mild to severe; we have received bleaching reports from Panama, Guadeloupe, St. Lucia, Curacao, and Bonaire, and there is concern that bleaching off Venezuela may be worse than 2005. Fortunately, there is now some sign of cooling in this area and around the northern Caribbean." 

Conditions since then have continued to improve and by 15 November, the extent of Alert Areas defined by NOAA had dramatically declined.

For additional references, see Caribbean Coral Reefs, Climate Variability and Change, and Ocean Acidification: Online Resources (WWF Climate Change blog, 19 Nov 2010).

Atlantic Hurricane Seasons: 2010 is Third Most Active on Record, while 2005 Tops the List


Hurricanes Igor, Julia and Karl at 1445Z, September 16 2010.  Source: NOAA.

Above: Hurricanes Igor, Julia and Karl, September 16 2010.  Source: NOAA.

The 2005 Atlantic hurricane season was the most active on record, partly because of elevated SSTs in the north tropical Atlantic.  In addition to the devastation seen in the U.S., portions of Mexico and Central America also were very hard hit.  In 2005, hurricanes Wilma  (the strongest Atlantic Hurricane on record) and Emily severely damaged portions of the Mesoamerican reef system.  Just 7 years earlier, in 1998, parts of the Mesoamerican reef were severely damaged by category 5 Hurricane Mitch -- the second deadliest Atlantic hurricane ever. In 2007, another category 5 Hurricane, Dean, swept over the Mesoamerican reef region, across the Yucatan and into Veracruz, Mexico.

From the outset, hurricane forecasters had expected the 2010 Atlantic hurricane season to be very active, with record high sea surface temperatures identified as one of the reasons.  See NOAA Sees Potential for "Hyperactive" Hurricane Season; Record High Sea Surface Temperatures Among Contributing Factors (WWF Climate Change Blog, 1 June 2010); and Rising Greenhouse Gas Concentrations Driving Up Sea Surface Temperatures that Fuel More Intense Hurricanes, (WWF Climate Change Blog, 12 July 2010).
Tropical Cyclone Heat Potential, tropical north Atlantic, 15 September 2010.  Source: NOAA.

Above: Tropical Cyclone Heat Potential -- the heat available in the upper levels of the ocean to energize tropical storms -- in the tropical north Atlantic, 15 September 2010.  According to NOAA:  "Yellow and orange show places where the amount of available heat is enough (at least 50 kilojoules per square centimeter) to have a significant impact on the intensity of hurricanes, provided that atmospheric conditions are also favorable." Source: NOAA.

With 19 tropical storms by mid-November, including five that were major hurricanes (category 3 and above), the 2010 hurricane season has lived up to expectations.  Septembers 2002, 2007 and 2010 and August 2004 -- all within the last decade -- each recorded 8 named storms, making them the busiest months on record in the Atlantic. So far, 2010, 1995 and 1887 together are the third most active hurricane seasons on record, behind 1933 in second place and 2005 in first place.   

Hurricane Alex, the first of the 2010 season with landfall in Mexico as a category 2 hurricane on 30 June, was tied with hurricane Audrey in 1957 as the most intense (946 mb [hPa]) June hurricane on record.  It brought devastating rains to parts of Central America and Mexico. See the image below; and Flooding in Northern Mexico (NASA's Earth Observatory, 16 July 2010) and Rainfall from Hurricane Alex (NASA's Earth Observatory, 8 July 2010) .  

Flooding around Anahuac, Mexico, on 12 July 2010, from Hurricane Alex.  NASA Earth Observatory.

Above: The cities of Anáhuac and Rodriguez, Mexico, on 12 July 2010.  As Hurricane Alex moved inland with heavy rains, it pushed the upstream Venustiano Carranza Dam to capacity, forcing authorities to release water. Seventy kilometers (43 miles) downriver, the Salado River flooded the area around Anáhuac and Rodriguez with muddy waters.  Source: NASA.

Later in the season, Hurricane Karl became the first major hurricane ever in the Bay of Campeche, with landfall along the coast of Mexico on 17 September as a major category 3 hurricane. Like Alex, Hurricane Karl dropped disastrous rains on Mexico. Each of the two storms reportedly inflicted billions of dollars of damage on parts of Mexico.

As Hurricane Karl struck Mexico, Hurricane Igor was churning across the Atlantic trailed by Hurricane Julia (see satellite photo showing all three storms).  At their peaks, both Igor and Julia were category 4 storms.  While Julia dissipated far from land in the Atlantic, Hurricane Igor eventually made its way past Newfoundland as a category 1 hurricane --  bringing damaging winds and flooding to the region on 20 and 21 September.  "Hurricane Igor and its severe impacts certainly represent a rare event in Newfoundland history which has been described as the worst in memory," said Environment Canada in a Special Weather Summary. "In statistical terms, this was effectively a 50 - 100 year event depending on how one chooses to define it."

It would not be the last of the extraordinary rains fed by the tropics for Canada -- and for parts of the U.S. East Coast -- as storms drew energy from the tropics and carried it north.  Tropical Storm Nicole formed over Caribbean on 29 September and dissipated the next day -- but produced flooding rains from the Caribbean to eastern North Carolina (see Nicole kills five in Jamaica; historic rains in North Carolina; tornadoes in the Mid-Atlantic in Jeff Master's Wunderblog, 30 Sep 2010).  A similar pattern developed with Hurricane Tomas which formed on 29 October several hundred miles southeast of Barbados, becoming only the third "T" storm in Atlantic hurricane history. 

"The formation of a tropical storm so far south and east this late in the season is unprecedented in the historical record; no named storm has ever been present east of the Lesser Antilles (60°W) and south of 12°N latitude so late in the year," said Dr Jeff Masters of the Weather Underground in his WunderBlog (Strengthening Tomas headed for the Lesser Antilles, 30 October 2010).  When Tomas continued beyond the end of October, Masters noted that 2010 is the fourth consecutive year with a November hurricane, an unbroken series without precedent in records that go back to 1851

In Is the North Atlantic Hurricane Season Getting Longer? [PDF] Geophysical Research Letters (9 Dec 2008), James Kossin (University of Wisconsin, Madison) said:  "I find an apparent tendency toward more common early- and late-season storms that correlates with warming SST, but the uncertainty in these relationships is high." (see Jeff Masters' discussion, Is the Atlantic Hurricane Season Getting Longer?, 11 Nov 2010).

Tomas, which ultimately became a category 2 hurricane, brought devastating rains to parts of the Caribbean -- including St Lucia, Jamaica (which already had been hit hard by Nicole) and to Hait where it aggravated a cholera epidemic.  In Deadly late-season Atlantic hurricanes growing more frequent (17 Nov 2010), Jeff Masters notes a recent increase in "powerful and deadly November hurricanes" and says it is "primarily a Caribbean phenomena."  He adds that Tomas, for example, ranks as the 6th deadliest late-season (on of after 1 November) Atlantic hurricane since 1851.

Though Tomas did not move beyond the latitude of Fort Lauderdale, Florida, as a tropical storm, it sent a plume of tropical moisture north -- right into the Canadian Maritimes (see map below).

Precipitable water anomaly, North America, 4-9 November 2010. Source: NOAA Earth System Research Laboratory.

Precipitable water anomaly, North America, 4-9 November 2010.  Areas ranging from orange to red have anomalously high precipitable water in the atmosphere.  The figure clearly shows a plume of water vapor extending from the Caribbean to the Canadian Maritimes (units above and below the 1968-1996 mean are expressed in kg of water per square meter).  Source: NOAA Earth System Research Laboratory.

From 4 through 9 November, many areas of New Brunswick and Nova Scotia, Canada, received more than 200 mm (7.9 inches) of rain, and some received over 300 mm (11.8 inches). Just two months earlier, on 4 September, Nova Scotia was hit by Tropical Storm Earl.  "To say that it's incomprehensible may actually be an understatement," Nova Scotia Premier Darrell Dexter said on 10 November at a news conference.  "The simple reality is that we haven't seen these kinds of severe and regular weather events for, well, forever."

Online Resources

Rising Ocean Temperatures:


Coral Bleaching:

Drought in the Amazon:


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