With a large part of the world's population living close to the oceans, rising sea levels bring the potential for destructive  results. But scientists are still unable to make predictions exact enough for people to plan to handle the loss of land and the threat to coastal communities expected over this century. "We know sea level is going to rise, but how much, and how fast, and where, we really still don't know," said Josh Willis, a climate scientist.  _ It doesn't rise all the same as more water pours in. As global warming raises sea levels, some places are expected to see higher-than-average increases, and a few places, may even see decreases. It's reported that over the course of this century, sea levels will rise between 8 inches and 6.6 feet around the planet. Scientists know this increase will be driven by the expansion of water as it warms--warmer water takes up more space--and the melting of ice. But the effects of warming water and melting ice on sea-level rise are expected to vary from area to area. And the melting of ice of the Antarctic and Greenland presents the largest uncertainty for the future, but air, land and water also play roles in changes to sea level. For example, sea level near the ice getting melt actually decreases, because the ground under the melting ice rises as the heavy ice disappears. Climate change is expected to change ocean currents and the winds that help drive ocean currents. These changes will affect the distribution of heat within the oceans, and, as a result, affect changes in sea level. Nowadays, scientists use two types of models to make predictions about the future of sea levels, but the two don't agree. If scientists can't accurately predict sea-level increase for the coming years, the least we can do is measure what happening today with the help of the satellite, Jason-2, but it's reaching the end of its operational life. What problems will scientists meet with in predicting future climate changes?
It's too difficult to measure what's happening. Types of models for prediction are difficult to set up. There will probably be no satellites to help the scientists. There aren't enough scientists studying the changes of sea levels.