Climate change and environmental issues have taken on an unprecedented role in the 2020 presidential election.
Many of the candidates have had significant help from staff and outside advisers navigating environmental policy, crafting their plans, dealing with interest groups and preparing for the election.
These people come from a variety of backgrounds, including serving in the Obama administration, environmental organizations or think tanks focused on climate issues. Some are policy generalists, while others have more specific training and expertise.
Here are some of the main people working with presidential candidates on climate and issues concerning the environment.
Aaron Burgess, Harold Mitchell, Vien Truong and David Weiskopf with former hedge fund manager Tom Steyer (D)
Burgess is the head of the climate team for Steyer's campaign. He worked for six years at NextGen America, Steyer's main political venture before he ran for president, most recently leading the climate and energy operations.
He has also done communications and consulting work for clients including former Michigan Gov. Jennifer Granholm (D) and the Center for the New Energy Economy.
Mitchell, another senior adviser, was Steyer's first major endorsement of his 2020 race. Mitchell was a Democratic state lawmaker in South Carolina, an early primary state, and founded ReGenesis, a community development corporation in Spartanburg, S.C.
Truong is the lead adviser for Steyer's climate justice policies. She has done justice- and environment-related work for numerous organizations, companies and others, and previously led the groups Green for All and Dream Corps.
Weiskopf is another NextGen alum, having come from the organization's California office, where he did climate and energy work. He previously worked in the Chicago-based Midwest office of the Natural Resources Defense Council.
Tammy Dickinson and Greg Gershuny with former South Bend, Ind., Mayor Pete Buttigieg (D)
Dickinson previously led the energy and environment office at the White House Office of Science and Technology Policy during the Obama administration and has been consulting since then.
She has a doctorate in geology and has worked at federal agencies including the U.S. Geological Survey and NASA.
Gershuny is the head of the energy and environment program at the Aspen Institute, a nonpartisan think tank perhaps best known for its annual Aspen Ideas Festival.
Gershuny was a senior aide in the Energy Department's policy office under President Obama and also held roles in the White House personnel office and the Office of Science and Technology Policy.
Robert Durand with former Massachusetts Gov. Bill Weld (R)
Durand is a former Democratic state senator in Massachusetts. Durand and Weld have been friends since at least 1996, when the two jumped into the Charles River together after Weld signed an environmental bill that Durand helped shepherd to passage.
Weld is one of two Republicans making long-shot campaigns against President Trump in the GOP primary. He has made climate issues a priority.
Stef Feldman with former Vice President Joe Biden (D)
Feldman is the policy director for Biden's campaign, overseeing development of all of the candidate's policy statements, including his extensive climate change plan.
Feldman has worked for Biden in policy roles since 2011, first in the White House and then at the University of Delaware's Biden Institute, before joining his presidential campaign.
Katie Thomas with Sen. Bernie Sanders (I-Vt.)
Thomas comes from Sanders' Senate office, where she is an energy and environment adviser, including for his work on the Energy and Natural Resources and Environment and Public Works committees.
She is an attorney by training, having previously worked at the Justice Department and at the firm Duncan, Weinberg, Genzer & Pembroke.
Maggie Thomas with Sen. Elizabeth Warren (D-Mass.)
Thomas went to Warren's campaign after serving in a senior climate role for Washington Democratic Gov. Jay Inslee's climate-focused presidential run, which he ended in August. She previously held various senior roles at NextGen America.
Antha Williams with former New York City Mayor Michael Bloomberg
Williams has long been the chief adviser to Bloomberg for climate change and environmental issues.
Before joining Bloomberg's campaign upon its launch in November, she was for six years the head of environmental matters at Bloomberg Philanthropies, the organization the media executive uses to oversee the charitable efforts he funds.