The nation's top scientific organizations have an important reminder for members of Congress: human caused climate change is real, its impacts are already being felt in the U.S., and only a significant slashing of greenhouse gas emissions will stave off the worst risks.

The 31 groups including the American Meteorological Society, the American Society of Plant Biologists, and the American Association for the Advancement of Science (AAAS)—organizations representing "millions of scientists," according to the Associated Press—issued their statement in a letter (pdf ) to the lawmakers dated Tuesday.

Impacts in the U.S. include "extreme weather events, sea level rise, and increased risk of regional water scarcity, heat waves, wildfires, and the disturbance of biological systems," the letter states. "The severity of climate change impacts is increasing and is expected to increase substantially in the coming decades," it states.

The letter adds that "adaptation is necessary to address unavoidable consequences for human health and safety, food security, water availability, and national security, among others," and concludes by offering to collaborate with the lawmakers as they "seek to address the challenges of our changing climate."

The urgent statement, which comes in what may end up being the hottest year ever, reiterates the messages from a similar letter (pdf) sent back in 2009 by 18 leading scientific organizations to members of Congress—who continue to fail to take any substantive action on climate change.

"The reality of climate change is already upon us, and is affecting not only our lives but that of all life on earth," stated Dr. Robin L. Chazdon, executive director of the Association for Tropical Biology and Conservation, one of the signatory bodies. "We must do all that we can to mitigate these effects using scientific knowledge and mobilizing society for action. It is the responsibility of our politicians to move us forward in these actions."

Added Anne D. Yoder, president of the Society of Systematic Biologists: "We owe it to our children and to our children's children to take bold action now so that our descendants do not pay the price for our generation's greed."

According to a recent tally by the Center for American Progress Action Fund, the reminder from the scientists is needed: roughly a third of the lawmakers are climate change deniers.