It was warmer 9,000 years ago than it is today and the oceans were about 20 to 30 feet higher than today. Reason? That was when the temperature peaked at the beginning of the inter-glacial after coming out of the last ice age. It's been getting cooler ever since.
Take a look at this graph.
Temperatures were warmer than today for most of the past 10,000 years
http://iceagenow.info/2010/05/temperatures-were-warmer-than-today-for-most-of-the-past-10000-years/