The debate over climate change legislation is heating up. And as members of Congress grapple with which position to take, they'll be bombarded with opinions from many different sides of the debate.

But last week, as members of Congress arrived at work in the morning and left in the evening, they were greeted by the silent stares of one important (albeit non-voting) constituency: the plants and animals likely to be impacted by rising sea levels, changing weather patterns, and other impacts of climate change.

The round-the-clock sentinels were courtesy of a traveling photography exhibit (Irreplaceable: Wildlife in a Warming World) on prominent display in the rotunda of the Russell Senate Office building from May 18 through May 22, arguably the most critical week to date for climate change legislation. Starting this week, the images will be on display at another Capitol Hill landmark: the United Methodist building—just across the street from the Dirksen Senate Office Building.

From the polar bear the now-familiar face of climate change—to the monarch butterfly—whose annual pilgrimage to the fir forests of Central Mexico has been made more treacherous by freezing conditions—the species are among the 20 to 30 percent of animals and plants at increased risk of extinction because of climate change, according to the latest report by the United Nation's Intergovernmental Panel on Climate Change (IPCC).

The images, by award-winning photographers at the International League of Conservation Photographers, have traveled to cities and towns throughout the country, inspiring more than 42,000 people to add their name to a letter to members of Congress asking them to consider species impacted by global warming. The effort, led by Earthjustice, is a unified campaign by faith leaders, scientists, artists and environmental advocates.