Hansen, featured prominently in Al Gore's global warming documentary, "An Inconvenient Truth," has been warning of the potential dangers of climate change since the 1980s.
In late 2005, he accused NASA of trying to improperly censor him after he warned that Earth's climate might be approaching a dangerous "tipping point."
A public affairs employee, a political appointee of the Bush administration, later resigned over the incident.
Members of Congress also weighed in, criticizing NASA for cutting the budgets of satellite programs that help monitor the effects of climate change.
"Setting aside NASA Administrator Griffin's personal views on the significance of global warming, I remain concerned that NASA is not doing as much as needs to be done on climate change data collection and research," said Rep. Bart Gordon, D.-Tenn., in a statement. Gordon is the chairman of the House Science and Technology Committee, which oversees the space agency.
Last year, many NASA scientists were upset when reports surfaced that the agency had quietly deleted the phrase "to understand and protect our home planet" from the NASA mission statement. The scientists believe research on issues like climate change will suffer as NASA shifts priorities toward exploration missions to the moon and Mars.
"Earth has always been central to NASA's science," Hansen said.