Hurricanes Reading Handout
CLASS SET
Are Hurricanes Becoming Stronger and More Frequent?
Hurricanes can be the deadliest, strongest, and costliest storms in the world and they have been more severe
than usual in recent years, causing an amazing amount of damage to coastal towns and cities. In 2004, a
record number of hurricanes affected Florida and typhoons struck Japan. A hurricane even formed in the South
Atlantic Ocean, off the coast of Brazil, where no one had ever seen a hurricane before. The 2005 Atlantic
hurricane season was predicted to be above normal as well and one of those storms, Hurricane Katrina,
devastated the gulf coast of the United States as it passed through.
Why are these monster storms becoming even more monstrous? Some scientists have identified that the
number of hurricanes probably waxes and wanes with a regular and natural cycle. Other scientists have
identified that the strength and length of storms is probably affected by global warming. Both processes might
be at work, and researchers continue their studies so that we can better understand these monstrous storms.
Read on to learn more about these theories.
A natural cycle may control the number of storms
There is evidence that the number of storms each year is controlled, at least in part, by a natural 20 to 40-year
cycle. For example, the number of hurricanes each year was less than usual from the mid-1960’s to the mid1990’s. This was the part of the cycle when there were fewer hurricanes. But since 1995 there have been
typically more hurricanes than usual each year. This means we are currently in the phase of the cycle when
there are more hurricanes than usual. Scientists predict that the number of storms will be higher than normal
until about 2015.
Global warming causes stronger storms
As global warming causes oceans to become warmer, and more moisture is held in the atmosphere, the
intensity of hurricanes and the amount of rain they produce will likely increase, according to NCAR scientist
Kevin Trenberth and others. There is strong evidence that global warming has been increasing the intensity of
hurricanes for over the past few decades.
In the past 30 to 50 years the oceans have warmed about 0.1 degree Fahrenheit. This may not seem like
much of a temperature change, but it is quite significant. Think about a pot of water heating on a stove. A small
pot of water will heat quickly, while a large pot of water will heat very slowly. This is due to a difference in heat
capacity. The oceans have an enormous heat capacity because of their large size, thus, they are like an
enormous pot of water, and so it takes a great amount of heat to warm them. The fact that they have warmed
significantly in 30 to 50 years is remarkable. And this change appears to be causing a remarkable change in
the strength and length of hurricanes.
The warming oceans are very likely causing the strength of hurricanes to increase. According to MIT scientist
Kerry Emmanuel, hurricanes have become 70-80% more powerful over this time. Hurricanes take heat energy
from the oceans and convert it into the energy of the storm. The warmer oceans offer more heat energy to
hurricanes. This makes them become stronger storms.
How Hurricanes Form
A tropical thunderstorm can grow into a massive hurricane under certain conditions. Sometimes several
thunderstorms start rotating around a central area of low pressure. This is called a tropical depression. If the
depression strengthens so that winds reach at least 39 mph, it is called a tropical storm. And if wind speeds
increase to more than 74 mph, it is called a tropical cyclone or hurricane.
Once formed, hurricanes take energy from the warm ocean water to become stronger. A storm will strengthen
if there is a supply of warm, moist air to feed it. Warm, moist air is found above warm, tropical ocean waters.
While a hurricane is over warm water it will continue to grow. A hurricane dies when it moves away from the
tropics. When a hurricane moves into areas with cooler ocean water, it weakens. It will also weaken if it travels
over land.
From the Windows of the Universe Website: http://www.windows2universe.org/earth/climate/hurricane_climate.html
Hurricanes Reading Handout
CLASS SET
The rotation of the storm is due to the Coriolis Effect, a product of the Earth's rotation. This causes the air
being drawn into the central low pressure to curve. The air rises as it rotates. This rising air, which is saturated
with water, cools and condenses, forming clouds. Hurricanes do not occur within 300 miles (500 kilometers) of
the equator because there is no Coriolis Effect at the equator.
From the Windows of the Universe Website: http://www.windows2universe.org/earth/climate/hurricane_climate.html