Dr. Neil Frank, former Director National Hurricane Center
Over the past several weeks numerous articles suggest Harvey and Irma were the result of global warming. The concept is a warmer earth will generate stronger and wetter hurricanes. A number of people have said Irma was the most intense hurricane in the history of the Atlantic while Harvey was the wettest and both were good examples of what we can expect in the future because of global warming. What does a fact check reveal about these two hurricanes?
Irma was indeed a very powerful Cat 5 hurricane when it moved across the Leeward Islands and the 185 mph winds reported by a recon plane at 10,000 ft. were among the strongest recorded in Atlantic hurricanes. How does Irma compare to other intense Atlantic hurricanes? To answer that question, we must first look at the history of the methods used to determine the strength of a hurricane because it changed early this century.
There are two ways to determine the strength of a hurricane. One is to measure the winds with an airplane. The Air Force always flies at 10,000 ft. and empirical relationships are used to convert the 10,000 ft. winds to surface winds. The other is to drop a barometer into the eye and measure the pressure. Since there is a direct relation between the pressure and the wind, if you know one you can compute the other.
Historically, the central pressure was the predominate factor in determining the strength of a hurricane. When the Saffir/Simpson hurricane scale was developed in the early 1970s, all past hurricanes were ranked on the Saffir/Simpson hurricane scale according to their central pressure. Today that policy has changed and now hurricanes are ranked exclusively by the wind. That is why it was possible to declare Irma was the strongest hurricane ever observed in the Atlantic when the plane reported 185 mph winds. But, what does the central pressure tell us about Irma?
For those not familiar with pressure, one of the standard units of measure is millibars (mb). The normal pressure in the U.S. is usually between 1010 and 1030 mb. In the tropics if the pressure drops below 1000 mb, it generally means a Cat 1 hurricane has formed. The pressure in a major Cat 3 hurricane is usually around 950 mb and a Cat 5 occurs when the pressure is below 920 mb. When the pressure drops below 900 mb., you have a super hurricane comparable to the most intense Pacific typhoons.
How does Irma compare with other strong historical hurricanes if we use the central pressure to determine the strength rather than wind? The lowest central pressure recorded in Irma was 914 millibars. The lowest pressure ever recorded in an Atlantic hurricane was 882 mb while Wilma was in the northwest Caribbean Sea in 2005. The lowest pressure for a land falling hurricane was 892 mb when the 1935 hurricane crossed the Florida Keys. There have been 10 hurricanes with central pressures below 910 mb of which 5 were below 900 mb. Irma did not even make the top 10; therefore, it was not close to being the strongest hurricane ever observed In the Atlantic.
Now lets us turn our focus on hurricane Harvey. Harvey has been labeled the wettest hurricane in history; however, the 50 inches recorded in the hurricane is not related to global warming. The reason for the heavy rain is the hurricane stalled for 3 days and unfortunately southeast Texas is where that happened.
The amount of rain in a tropical system is not related to the strength of the wind, it depends on the forward speed of motion. Before we had sophisticated numerical models to forecast the amount of rain a system would produce, we used a simple empirical equation that gave good results. Determine the forward speed of motion and divide it into 100.
If a tropical system is moving 10 mph, expect 10 inches of rain, 20 inches for a system moving 5 mph and if the forward speed is only 2 mph be prepared for 50 inches. That is exactly what happened in Harvey. The hurricane was moving around 2 mph for 3 days and a broad band of 40 to 50 inches of rain covered a large portion of southeast Texas and southwest Louisiana.
There are numerous examples of stalled tropical systems producing excessive rains. For example, in 1979 tropical storm Claudette stalled for 2 days and generated over 40 inches in a broad area south of downtown Houston. The 42 inches that fell in 24 hours in Alvin is the record for a 24 hour rain in the U.S. A year earlier, stalled tropical Storm Amelia produced 48 inches in central Texas. In 1967 slow moving Hurricane Beulah moved into in south Texas and generated between 30 and 40 inches inland from Brownsville.
If there had been a rain gauge in the area east of the Bahamas where Hurricane Jose stalled for four days, I am sure it would have recorded over 60 inches.
The U.S. has a long history of bad hurricanes. Listed below are several noteworthy intense hurricanes that occurred in the late 1800s long before there was an increase of CO2.
The most active year for landfalling hurricanes in the lower 48 states was in 1886 when 7 hurricanes crossed the coast. Four were in Texas and two of these were major. The August Cat 4 destroyed what remained of Indianola. Indianola was a thriving sea port community on the south shore of Matagorda Bay in the mid-1850s before being nearly destroyed by a Cat 4 hurricane in 1875. They were in the process of rebuilding when the 1886 hurricane struck.
There were two Cat 4 hurricanes in 1893. The one in Louisiana killed 1800 people on a coastal island. In the second one, another 1800 died when a 16 ft. storm surge inundated Hilton Head Island, South Carolina.
The deadliest hurricane in U.S. history occurred in 1900 when a 17 ft. storm surge swept across Galveston Island killing over 10,000 people.
The 1900 hurricane was a Cat 4.
In conclusion, Harvey and Irma were typical intense Atlantic hurricanes. They both developed from African disturbances during the peak of the hurricane season. The strength of Irma as determined by central pressure was consistent with a number of other past intense hurricanes. The heavy rain in Harvey was the result of a stalled hurricane and was not caused by increased atmospheric moisture associated with global warming.
There was nothing identifiable with these two hurricanes that would justify an urgent request to support actions that would limit global warming. It is sad that those promoting these actions are so insensitive to the shredded emotions of hundreds of thousands of people in Texas, Louisiana and Florida who have just experienced nightmarish losses and now they are being blamed for causing the hurricanes because they did not support actions to reduce CO2.
Speaking of CO2, there is a very intense controversy over what is causing the earth to warm. The earth has been warming for over 150 years. That is not debatable. What is debatable is the cause. Is it CO2 as “warmest” proclaim or other natural cycles? Solar experts in Asia, the Middle East and parts of Europe believe it is the sun. Over the past 3 1/2 years they have published over 400 papers that discredit CO2 and support natural cycles of the sun. If this is true, why is there intense pressure to spend billions and billions of dollars on green energy?
So what do “warmest” want you to do? First and foremost they demand you endorse the Paris Climate Accord made in December 2015 and agreed to by 194 countries. President Trump withdrew from this agreement earlier this year and the “warmest“ are livid. The stated purpose of the plan is to reduce CO2 and develop Green Energy.
One of the objectives of the agreement is to establish a Green Climate Fund that will be distributed to developing nations to help them convert to green energy. The goal is to have $100 billion in this fund by 2020. Where is the money coming from? Approximately 45 nations have been designated donor countries which means there will be about 150 receiver nations including China.
At the original Paris meeting donor nations pledged about $10 billion of which over 80% would come from 6 nations; England, Germany, France, Sweden, Japan and the U.S.. The U.S. made the biggest pledge of $3.5 billion with the other 5 nations pledging between $1 and $1.5 billion each. To date the U.S. has sent $1 billion to the U.N. as a down payment on our pledge and the other 5 nations around $1/2 billion each. The U.N. has hired 156 employees to monitor the plan with an annual salary of $29 million.
This only the beginning. Christiana Figueres, the U.N. Chairperson of the Paris Conference said recently the Paris plan will cost $1.5 trillion over the next 3 years if every nation complied with the program.
If President Trump were to reverse his decision and once again have the U.S. participate in the Paris Accord, we would immediately owe the U.N. $2.5 billion against our pledge. Just maybe it would be better to take that money and help the 150,000 whose homes were flooded in SE Texas during Harvey.
One last comment, what is the real reason for the Paris Accord? One of the most revealing statements I have seen comes from a top official in the U.N. climate change program. Ottmar Odenhofer said ”We redistribute de facto the world’s wealth by climate policy. One has to free oneself from the illusion that international climate policy is environmental policy”. In other words, it an international program to redistribute wealth: Whose wealth? Our wealth!