She held senior posts at the U.S. Department of State, National Security Council, and Environmental Protection Agency before founding the Pew Center on Global Climate Change in 1998.

She then joined the Environmental Protection Agency, where she served as the Director of the office of Solid Waste Characterization and Assessment Division and the Deputy Assistant Administrator for Air and Radiation.

Under Claussen's direction, the Pew Center has produced nearly 100 peer-reviewed reports and a broad collection of white papers and briefs by noted climate experts covering a range of critical topics including economics, environmental impacts, policy, science, business, technology and solutions.

Claussen regularly testifies before the United States Congress and meets with other key stakeholders to share ideas for addressing climate change.

According to a 2001 profile in Green@Work magazine, Her insistence on engaging and recognizing the influence of the private sector has earned Claussen a reputation of being somewhat of a maverick in the NGO community, but she says she is convinced that solutions that do not make economic sense will eventually follow the declining path of the oceans, ecosystems, species and natural resources the Pew Center is trying to protect.

In fact, the joint statement of the BELC states, "We believe that the response must be cost-effective, global and equitable, and also allow for economic growth based on free market principles.