"The administration should face down critics of the project, ensure that environmental standards are met and then approve it," Nature said in an editorial this week.
The editorial, entitled "Change For Good," argued that the pipeline won't determine whether the oilsands are developed.
"Nor is oil produced from the Canadian tarsands as dirty from a climate perspective as many believe (some of the oil produced in California, without attention from environmentalists, is worse)," the editorial reads.
"Tarsands development raises serious air- and water-quality issues in Canada, but these problems are well outside Obama’s jurisdiction."
Nature is among the few science journals that still publish original research articles, many of them highly technical, on a range of scientific topics. As such, it's one of the most respected publications of its kind.
The editorial argues that there are several benefits for U.S. President Barack Obama if he approves the pipeline.
"Obama can bolster his credibility within industry and among conservatives," Nature says.
"The president can also take advantage of rising domestic oil and gas production to defuse concerns over energy security. And the fact that U.S. emissions are apparently dropping, thanks to the economic crisis and the ongoing shift from coal to gas for electricity generation as well as state and federal policies, further plays into his hands."
Keystone XL has become a flashpoint for the U.S. environmentalists, who view it as a symbol of America's addiction to carbon-intensive fossil fuels. They have mounted a passionate campaign urging Obama to nix the US$7 billion project.
The U.S. State Department is expected to make a decision on Keystone in the months to come because it crosses an international border.
Environmentalists are hoping John Kerry, the new secretary of state, might put the boots to the pipeline given his longtime advocacy for climate issues as a five-term Massachusetts senator.
"We are excited that he will bring his strong credentials on climate to the critical decisions facing our planet, including increasing access to affordable clean energy options and stopping the expansion of dirty tarsands and coal worldwide," Sierra Club executive director Michael Brune said in a statement earlier this week.