The Blob (Pacific Ocean) the surface waters of the mid-latitude Pacific Ocean flipping from a cold phase to a warm phase in a cycle known as the Pacific decadal oscillation (PDO). This poorly-understood change happens at irregular intervals of years or decades. During a warm phase, the west Pacific becomes cooler and part of the eastern ocean warms; during the cool phase, these changes reverse. Scientists believe a cold phase started in the late 1990s and the arrival of the Blob may be the start of the next warm phase. The PDO phases may also be related to the likelihood of El Nino events.
Climate change in the United States fundamental problem exists in that records for those such events are of worse quality with poorer details than temperature and rainfall records. A comprehensive article in "Geophysical Research Letters" in 2006 found "no significant change in global net tropical cyclone activity" during past decades, a period when considerable warming of ocean water temperatures occurred. Significant regional trends exist such as a general rise of activity in the North Atlantic area besides the U.S. eastern coast. Looking at the lack of certainty as to the causes of the 1995 to present increase in Atlantic extreme storm activity, a 2007 article in