These changes in precipitation in turn increase the frequency and intensity of extreme weather events like floods, droughts, heat waves, hurricanes and tornados. The effects of these severe weather disturbances range from lower agricultural yields, glacial retreat, less summer stream flows, extinction of species and increase in the number of disease vectors (Wikipedia).
The scientific community is now nearly unanimous in heaping the blame for global warming on human activities, with only a small minority of the scientists absolves man for the phenomenon. But the persistent debate centers somewhere else, such as on how much worse climate change will occur in the future, and what needs to be done to reverse or at least reduce it.
The relationship between global warming and hurricanes is another subject that is hotly debated. If the world's climatic scientists agree on one thing, it is on the superlative force of Hurricane Katrina, which swept across the Americas and Europe in 2004. The consensus is that no natural calamity in memory matched the scope and magnitude of the damage it wrought on lives, property and the economy. But the suspected link between weather events like Katrina and global warming is yet to be proven. Research by a group of German scientists argues that the devastating floods in central Europe in 2002, for example, were perfectly normal events based on historical record (Murray, I., 2006). Other hurricane scientists agree that there is no way to blame global warming for Hurricane Katrina. Allegations that extreme weather events had become more damaging lately do not take into account the fact that human beings now live and invest resources in more dangerous areas, such as mountainside and seacoasts. The increase in the recorded number of these weather disturbances may be due to better observation and reporting methods. Thus, when the Inter-government Panel on Climate Change (IPCC) claimed that global warming exacerbated the 2004 hurricane season that produced Katrina, a top IPCC expert resigned in January 2005 in complete disagreement. Philip Klotzbach of the Colorado State University says that based on his own studies, most increases in Category 4-5 hurricanes between the period 1986-95 and 1996-2005 are due to improved observation technology. This indicates that other factors dictate the intensity and frequency of tropical cyclones.
There is as yet no scientific consensus that global warming will cause damaging climate change, notwithstanding claims by UNEP, IPICC and the US National Academy of Sciences that there is such a growing agreement. But the scientists do agree that the global average temperature is rising. What the scientists don't know yet are: 1) whether past temperature changes should be attributed to carbon dioxide levels; 2) predicting future temperature levels confidently and accurately; and 3) what temperature change levels would be damaging to life on earth. The NAS itself says that the 20 years' worth of knowledge and data on this discipline is not long and sufficient enough to estimate long-term trends.