The research shows the ancient Antarctic supported stunted trees and vegetation along its edges.
By examining the remnants of plant leaf wax found in sediment cores taken below the Ross Ice Shelf, scientists from the University of Southern California (USC), Louisiana State University and Nasa's Jet Propulsion Laboratory determined summer temperatures along the Antarctic coast 15-20 million years ago were 11degC warmer than today.
Temperatures reached up to about 7degC, with several times more rain.
This occurred during a period of global warming in the middle Miocene epoch that coincided with increased levels of atmospheric carbon dioxide.
Prof Wilson, who heads the University of Otago marine science department, said the outcomes showed the value of "the time and effort that it takes to get some of these answers".
Prof Wilson has been a member of the Andrill project's international scientific committee and has been closely involved in the project's work in the Antarctic.
"This is not about doing the easy work. It's about doing the important work," he said.
He was interested in studying previous global warming to better understand how the world's climate was likely to operate later this century.
At two sites in the Antarctic, in 2006 and 2007, Andrill, the Antarctic Drilling Project, gathered information about past periods of global warming and cooling.
International scientists, including from New Zealand and the United States, drilled through ice, sea water, sediment and rock to a depth exceeding 1200m, recovering a core record nearly 20 million years old.
Sarah Feakins, an assistant professor of earth sciences at USC, was the lead author of a paper on the research just published in Nature Geoscience.
Scientists began to suspect that high-latitude temperatures during the middle Miocene were warmer than previously believed when Sophie Warny, co-author of the Nature Geoscience paper, and an assistant professor at Louisiana State University, discovered large quantities of pollen and algae in sediment cores taken in the Antarctic.
Plant fossils in the Antarctic are hard to find because massive ice sheets covering the landmass grind away the evidence.
Deep sea cores were ideal to look for "clues of past vegetation" because the fossils deposited were protected from ice sheets but were difficult to acquire and required international collaboration, Prof Warny said.
Leaf wax found in the sediment cores acts as a record of climate change by documenting details about the hydrogen isotope ratios of water the plant drank while it was alive.