Continuation of historical trends of greenhouse gas emissions will result in additional warming over the 21 century, with current projections of a global increase of 2.5F to 10.4F by 2100, with warming in the U.S. expected to be even higher.
Hurricanes, tropical cyclones or typhoons, which can be defined as closed-circulation, warm-cored, low-pressure systems with maximum sustained surface wind speeds (1-minute mean) of at least 39 mph, are intense tropical storms with sustained winds above 74 miles/hour (Ahrens, C. Donald. Meteorology Today1) and are conventionally divided into two intensity classes: tropical storms (with maximum winds of 39-73 mph) and hurricanes (with maximum winds of at least 74 mph). Hurricanes have been subdivided into five potential damage classes depending on their maximum wind speed, minimum central pressure and storm surge magnitude.
Sea level is rising and will continue to rise as oceans warm and glaciers melt. Rising sea levels means higher storm surges, even from relatively minor storms, causing coastal flooding and erosion and damaging coastal properties. In a distressing new development, scientific evidence now suggests a link between hurricane strength and duration and global warming. Understanding the relationship between hurricanes and global warming is essential if we are to preserve healthy and prosperous coastal communities.
Storm intensity and duration increases as global warming emissions increase in our atmosphere. Rising sea levels, also caused in part by rising global temperatures, intensify storm damage along coasts. For hurricanes to occur, surface ocean temperatures must exceed or retain 80 degrees Fahrenheit. To understand how global warming can affect ocean storms, it's important to understand how these storms develop in the first place. Seasonal shifts in global wind patterns cause atmospheric disturbances in the tropics, leading to a local drop in pressure at sea level and forcing air to rise over warm ocean waters. As warm, moist air rises, it further lowers air pressure at sea level and draws surrounding air inward and upward in a rotating pattern called a vortex. When the water vapor-laden air rises to higher altitudes, it cools and releases heat as it condenses to rain. This cycle of evaporation and condensation brings the ocean's thermal energy into the vortex, powering the storm. Depending on the severity, meteorologists call these tropical storms or hurricanes in the Atlantic Ocean. Natural cycles alone cannot explain recent ocean warming. Because of human activities such as burning fossil fuels and clearing forests, today's carbon dioxide (CO2) levels in the atmosphere are significantly higher than at any time during the past 400,000 years. CO2 and other heat-trapping emissions act like insulation in the lower atmosphere, warming land and ocean surface temperatures. Oceans have absorbed most of this excess heat, raising sea temperatures by almost one degree Fahrenheit since 1970. September sea surface temperatures in the Atlantic over the past decade have risen far above levels documented since 1930. (Global Warming, Hurricanes and climate change)
By examining the number of tropical cyclones and cyclone days as well as