WunderBlog Archive » Category 6™
Category 6 has moved! See the latest from Dr. Jeff Masters and Bob Henson here.The global hurricane season of 2006: was it unusual?
The year 2006 is in the books, and its time to review the notable tropical cyclones of the year. For the first time since 1997, there was little to talk about in the Atlantic. The only Atlantic storm of significance was Hurricane Ernesto, which killed five people in Haiti and did $500 million in damage to the U.S. East Coast. The action was much more intense in the Eastern Pacific, which saw 20 named storms (16 is average) and six major hurricanes (4.5 is average.) The Pacific coast of Mexico was pounded by three tropical cyclones in 2006: Hurricane John hit Baja as a Category 2 hurricane, killing 5; Hurricane Lane hit north of Mazatlan as a Category 3 hurricane, killing 4; and Tropical Storm Paul hit the same region, killing four. Also notable, although it did not affect land, was Hurricane Sergio. It formed in mid-November and grew to Category 2 strength, becoming the strongest Northeast Pacific hurricane so late in the season and the longest-lived November tropical cyclone on record in that ocean basin.
Figure 1. Tropical Storm Ernesto just before landfall in North Carolina, August 31, 2006.
Figure 2. Statistics for the global tropical cyclone season of 2006. The three numbers in each box represent the actual number observed in 2006, followed by the average for the period 1970-2005 (in parentheses), followed by the record from the same period (in red).
Looking at the statistics for the season (Figure 2), 2006 appears to be a fairly normal year. No records were set for tropical cyclone activity in any ocean basin. Was it was a good year for the proponents of the theory that global warming is causing an increase in strong hurricanes? Twenty-nine major hurricane formed in 2006, just one shy of the record of 30, and 21 Category 4 and 5 storms formed, half way between the average of 17 and the record high of 25. These numbers are similar to those of 2005, which had 27 major storms and 22 Category 4 and 5 storms. However, as reported in a Science article by Landsea et. al in July, the number of Category 4 and 5 storms between 1978-1990 globally may have been undercounted by 70 storms. If true, this would bring the statistics for 2005 and 2006 closer to average for these most powerful of tropical cyclones. A new policy statement regarding the unproven link between stronger hurricanes and climate change was adopted by the World Meteorological Organization in December, in response to the recommendations of a meeting of 125 hurricane researchers that attended a meeting in Costa Rica. The summary statement (which I agree with) is posted at the World Meteorological Organization web site, and the ten main points are presented below. There is also a detailed statement with references to the scientific literature available at the WMO web site.
Consensus Statements by International Workshop on Tropical Cyclones-VI (IWTC-VI) Participants:
The surfaces of most tropical oceans have warmed by 0.25 - 0.5°C during the past several decades. The Intergovernmental Panel on Climate Change (IPCC) considers that the likely primary cause of the rise in global mean surface temperature in the past 50 years is the increase in greenhouse gas concentrations. The global community of tropical cyclone researchers and forecasters as represented at the 6th International Workshop on Tropical Cyclones of the World Meteorological Organization has released a statement on the links between anthropogenic (human-induced) climate change and tropical cyclones, including hurricanes and typhoons. This statement is in response to increased attention on tropical cyclones due to the following events:
a) There have been a number of recent high-impact tropical cyclone events around the globe. These include 10 landfalling tropical cyclones in Japan in 2004, five tropical cyclones affecting the Cook Islands in a five-week period in 2005, Cyclone Gafilo in Madagascar in 2004, Cyclone Larry in Australia in 2006, Typhoon Saomai in China in 2006, and the extremely active 2004 and 2005 Atlantic tropical cyclone seasons - including the catastrophic socio-economic impact of Hurricane Katrina.
b) Some recent scientific articles have reported a large increase in tropical cyclone energy, numbers, and wind-speeds in some regions during the last few decades in association with warmer sea surface temperatures. Other studies report that changes in observational techniques and instrumentation are responsible for these increases.
1. Though there is evidence both for and against the existence of a detectable anthropogenic signal in the tropical cyclone climate record to date, no firm conclusion can be made on this point.
2. No individual tropical cyclone can be directly attributed to climate change.
3. The recent increase in societal impact from tropical cyclones has largely been caused by rising concentrations of population and infrastructure in coastal regions.
4. Tropical cyclone wind-speed monitoring has changed dramatically over the last few decades, leading to difficulties in determining accurate trends.
5. There is an observed multi-decadal variability of tropical cyclones in some regions whose causes, whether natural, anthropogenic or a combination, are currently being debated. This variability makes detecting any long-term trends in tropical cyclone activity difficult.
6. It is likely that some increase in tropical cyclone peak wind-speed and rainfall will occur if the climate continues to warm. Model studies and theory project a 3-5% increase in wind-speed per degree Celsius increase of tropical sea surface temperatures.
7. There is an inconsistency between the small changes in wind-speed projected by theory and modeling versus large changes reported by some observational studies.
8. Although recent climate model simulations project a decrease or no change in global tropical cyclone numbers in a warmer climate, there is low confidence in this projection. In addition, it is unknown how tropical cyclone tracks or areas of impact will change in the future.
9. Large regional variations exist in methods used to monitor tropical cyclones. Also, most regions have no measurements by instrumented aircraft. These significant limitations will continue to make detection of trends difficult.
10. If the projected rise in sea level due to global warming occurs, then the vulnerability to tropical cyclone storm surge flooding would increase.
Jeff Masters
Figure 1. Tropical Storm Ernesto just before landfall in North Carolina, August 31, 2006.
Figure 2. Statistics for the global tropical cyclone season of 2006. The three numbers in each box represent the actual number observed in 2006, followed by the average for the period 1970-2005 (in parentheses), followed by the record from the same period (in red).
Looking at the statistics for the season (Figure 2), 2006 appears to be a fairly normal year. No records were set for tropical cyclone activity in any ocean basin. Was it was a good year for the proponents of the theory that global warming is causing an increase in strong hurricanes? Twenty-nine major hurricane formed in 2006, just one shy of the record of 30, and 21 Category 4 and 5 storms formed, half way between the average of 17 and the record high of 25. These numbers are similar to those of 2005, which had 27 major storms and 22 Category 4 and 5 storms. However, as reported in a Science article by Landsea et. al in July, the number of Category 4 and 5 storms between 1978-1990 globally may have been undercounted by 70 storms. If true, this would bring the statistics for 2005 and 2006 closer to average for these most powerful of tropical cyclones. A new policy statement regarding the unproven link between stronger hurricanes and climate change was adopted by the World Meteorological Organization in December, in response to the recommendations of a meeting of 125 hurricane researchers that attended a meeting in Costa Rica. The summary statement (which I agree with) is posted at the World Meteorological Organization web site, and the ten main points are presented below. There is also a detailed statement with references to the scientific literature available at the WMO web site.
Consensus Statements by International Workshop on Tropical Cyclones-VI (IWTC-VI) Participants:
The surfaces of most tropical oceans have warmed by 0.25 - 0.5°C during the past several decades. The Intergovernmental Panel on Climate Change (IPCC) considers that the likely primary cause of the rise in global mean surface temperature in the past 50 years is the increase in greenhouse gas concentrations. The global community of tropical cyclone researchers and forecasters as represented at the 6th International Workshop on Tropical Cyclones of the World Meteorological Organization has released a statement on the links between anthropogenic (human-induced) climate change and tropical cyclones, including hurricanes and typhoons. This statement is in response to increased attention on tropical cyclones due to the following events:
a) There have been a number of recent high-impact tropical cyclone events around the globe. These include 10 landfalling tropical cyclones in Japan in 2004, five tropical cyclones affecting the Cook Islands in a five-week period in 2005, Cyclone Gafilo in Madagascar in 2004, Cyclone Larry in Australia in 2006, Typhoon Saomai in China in 2006, and the extremely active 2004 and 2005 Atlantic tropical cyclone seasons - including the catastrophic socio-economic impact of Hurricane Katrina.
b) Some recent scientific articles have reported a large increase in tropical cyclone energy, numbers, and wind-speeds in some regions during the last few decades in association with warmer sea surface temperatures. Other studies report that changes in observational techniques and instrumentation are responsible for these increases.
1. Though there is evidence both for and against the existence of a detectable anthropogenic signal in the tropical cyclone climate record to date, no firm conclusion can be made on this point.
2. No individual tropical cyclone can be directly attributed to climate change.
3. The recent increase in societal impact from tropical cyclones has largely been caused by rising concentrations of population and infrastructure in coastal regions.
4. Tropical cyclone wind-speed monitoring has changed dramatically over the last few decades, leading to difficulties in determining accurate trends.
5. There is an observed multi-decadal variability of tropical cyclones in some regions whose causes, whether natural, anthropogenic or a combination, are currently being debated. This variability makes detecting any long-term trends in tropical cyclone activity difficult.
6. It is likely that some increase in tropical cyclone peak wind-speed and rainfall will occur if the climate continues to warm. Model studies and theory project a 3-5% increase in wind-speed per degree Celsius increase of tropical sea surface temperatures.
7. There is an inconsistency between the small changes in wind-speed projected by theory and modeling versus large changes reported by some observational studies.
8. Although recent climate model simulations project a decrease or no change in global tropical cyclone numbers in a warmer climate, there is low confidence in this projection. In addition, it is unknown how tropical cyclone tracks or areas of impact will change in the future.
9. Large regional variations exist in methods used to monitor tropical cyclones. Also, most regions have no measurements by instrumented aircraft. These significant limitations will continue to make detection of trends difficult.
10. If the projected rise in sea level due to global warming occurs, then the vulnerability to tropical cyclone storm surge flooding would increase.
Jeff Masters
The views of the author are his/her own and do not necessarily represent the position of The Weather Company or its parent, IBM.