PORTSMOUTH, N.H. -- Driving past an undulating sea wall on New Hampshire's coast, Steve Miller pointed at the blue ocean and said the placid waters were deceptively calm. During winter storms now, the ocean gets busier than it has gotten in the past. Just across the road are miles of mansions with their manicured lawns and gazebos. Because of its high property values and the tourism dollars it attracts, the stretch is known as the Gold Coast. As the climate warms and the sea level rises, though, the Gold Coast could quickly become an expensive problem.