Researchers Dennis Avery and Fred Singer said climate change is more likely to be part of a cycle of warming and cooling that has happened regularly every 1500 years for the last million years.
"And the doom and gloom merchants, who point to the threat to the polar bear from the melting North Pole, are wrong," the Daily Mail quoted the authors as saying.
They said, even if the Earth's climate was changing, it was not all bad, because past cold periods had killed as many people as warm periods.
"Not all of these researchers who doubt man-made climate change would describe themselves as global warming sceptics but the evidence in their studies is there for all to see," said Avery.
"Two thousand years of published human histories say that the warm periods were good for people. It was the harsh, unstable Dark Ages and the Little Ice Age that brought bigger storms, untimely frost, widespread famine, plagues and disease," he said.
As part of the study, the researchers looked at the work of more than 500 scientists, and found that experts were really doubtful whether global warming was really caused by man-made greenhouse gases.
"We have a greenhouse theory with no evidence to support it, except a moderate warming turned into a scare by computer models whose results have never been verified with real-world events. The models only reflect the warming, not its cause," said Singer.
The duo said the most recent global warming was between 1850 and 1940, and was therefore probably not caused by man-made greenhouse gases.
They said historical evidence of the natural cycle included a record of floods on the Nile going back 5,000 years; Roman wine production in Britain in the first century AD; and thousands of museum paintings that portrayed sunnier skies during what is now called the Medieval Warming, and more clouds during the Little Ice Age.
In the current warming cycle, there was evidence that storm and drought had been fewer and milder; corals, trees, birds, mammals and butterflies had adapted well; and sea levels were not rising significantly, the study said.