They think that is what made Venus into its current nightmare - there is some thin evidence that Venus probably had oceans 3 billion years ago but increasing solar flux from the sun (which has increased 20% since the sun was born and will continue to increase) boiled them off. Water vapour being a greenhouse gas probably caused the runaway effect although Venus also shows evidence of catastrophic volcanism which has resurfaced a lot of the planet within the last 500 million years as well.

The trend for the last 30 million years has seen earth be significantly colder than has been the norm over the last 500 million years.