An emeritus physics professor writes me cautioning against the use of the word ‘anomaly’ since, “In many people’s mind, the word ‘anomaly’ means something unusual that is a temporary phenomenon.” He suggests “change,” which is probably better.
Certainly for those who are communicating to the general public, like NOAA and NASA, ‘anomaly’ is a confusing word as used in these charts. And that is especially true because the recent temperature trend is anything but an anomaly — it is in fact a prediction of basic climate science.
Indeed, besides the record April and record Jan-April, NOAA itself explain:
This was also the 34th consecutive April with global land and ocean temperatures above the 20th century average.
So, yes, that isn’t really an anomaly any more — unless of course you are in the anti-science crowd, in which case the whole thing is one big mysterious deviation from the norm.
As for the oceans, NOAA points out:
The worldwide ocean surface temperature was 0.57°C (1.03°F) above the 20th century average of 16.0°C (60.9°F) and the warmest April on record. The warmth was most pronounced in the equatorial portions of the major oceans, especially the Atlantic.
Meteorologist Jeff Masters discusses the implications in his WunderBlog:
Sea Surface Temperatures (SSTs) in the Atlantic’s Main Development Region for hurricanes had their warmest April on record…. The area between 10°N and 20°N, between the coast of Africa and Central America (20°W — 80°W), is called the Main Development Region (MDR) because virtually all African waves originate in this region. These African waves account for 85% of all Atlantic major hurricanes and 60% of all named storms.When SSTs in the MDR are much above average during hurricane season, a very active season typically results (if there is no El Ni±o event present.) SSTs in the Main Development Region (10°N to 20°N and 20°W to 85°W) were an eye-opening 1.46°C above average during April. This is the third straight record warm month, and the warmest anomaly measured for any month — by a remarkable 0.2°C. The previous record warmest anomalies for the Atlantic MDR were set in June 2005 and March 2010, at 1.26°C.
As of now, the El Ni±o has in fact faded and that trend is projected to continue.
Figure. The departure of sea surface temperature (SST) from average for May 13, 2010. Image credit: NOAA/NESDIS.
What is the cause of the high SSTs in the MDR?
During December — February, we had the most negative AO/NAO since records began in 1950, and this caused trade winds between Africa and the Lesser Antilles Islands in the hurricane Main Development Region to slow to 1–2 m/s (2.2–4.5 mph) below average. Slower trade winds mean less mixing of the surface waters with cooler waters down deep, plus less evaporational cooling of the surface water. As a result, the ocean heated up significantly, relative to normal, over the winter. Negative AO/NAO conditions have been dominant much of this spring as well, resulting in further anomalous heating of the MDR waters.This heating is superimposed on the very warm global SSTs we’ve been seeing over the past few decades due to global warming. Global and Northern Hemisphere SSTs were the 2nd warmest on record this past December, January, and February, the warmest on record in March, and will likely be classified as the warmest or second warmest on record for April, since NASA just classified April as the warmest April on record for the globe. We are also in the warm phase of a decades-long natural oscillation in Atlantic ocean temperatures called the Atlantic Multi-decadal Oscillation (AMO). This warm phase began in 1995, and has been partially responsible for the high levels of hurricane activity we’ve seen since 1995.
What does this mean for the 2010 hurricane season?
The high April SST anomaly does not bode well for the coming hurricane season. The three past seasons with record warm April SST anomalies all had abnormally high numbers of intense hurricanes. Past hurricane seasons that had high March SST anomalies include 1969 (0.90°C anomaly), 2005 (1.19°C anomaly), and 1958 (0.97°C anomaly). These three years had 5, 7, and 5 intense hurricanes, respectively. Just two intense hurricanes occur in an average year. The total averaged activity for the three seasons was 15 named storms, 11 hurricanes, and 6 intense hurricanes (an average hurricane season has 10, 6, and 2.) Both 1958 and 2005 saw neutral El Ni±o conditions, while 1969 had a weak El Ni±o.
The SSTs are already as warm as we normally see in July between Africa and the Caribbean, and we have a very July-like tropical wave approaching the Lesser Antilles Islands this weekend. However, wind shear is still seasonably high, and the tropical waves coming off of Africa are still too far south to have much of a chance of developing. The GFS model is indicating that shear will start to drop over the Caribbean the last week of May, so we may have to be on the watch for tropical storms forming in the Caribbean then.
The anti-science crowd have been cheering the death of El Ni±o, but in fact it it quite bad news for those in hurricane alley, including the long-suffering Gulf Coast.