The number of category 4 and 5 hurricanes have almost doubled in the past 30 years

http://news.mongabay.com/2005/0916-ucar.html
The author is the UCAR.
They are the National Center for Atmospheric Research, so they are a group of scientists.
The source is very credible.
They agree in saying that hurricanes have pretty much doubled.
I believe this source, because they are a group of scientists who spend everyday studying these type of things.

http://www.wunderground.com/education/webster.asp
The author is Dr. Jeff Masters.
He has a doctorate degree and is a credible source.
They agree in saying that hurricanes have pretty much doubled.
I believe this source, because he has a doctorate degree in this and also he did a lot of research to produce this as shown by his sources.

http://ezinearticles.com/?The-Number-of-Category-4-and-5-Hurricanes-Occurring-Has-Nearly-Doubled-During-the-Last-Three-Decades&id=1604589
The author is Lily Wilson.
She is a normal person who just loves to study and learn about the evironment.
This could be a credible source.
They agree in sayin that hurricanes have pretty much doubled.
I believe this source, because she spends her time learning and studying about the environment solely based on interest and also because she would have no reason to lie.

I agree with the fact that the number of category 4 and 5 hurricanes have almost doubled in the past 30 years. The reason why is because we have already seen an increase in the number of hurricanes and especially, in the more powerful ones. So, it would only makes sense that they would continue to increase and get more powerful.