DURHAM, N.C. – Uncertainty is not a reason for inaction on U.S. climate policy.

That’s the message  William L. Chameides, dean of 91’s Nicholas School of the Environment, will share with federal policymakers when he testifies at a U.S. House of Representatives Subcommittee on Environment hearing Thursday, April 25 in Washington, D.C.

Chameides is one of three scientists invited to present expert testimony on policy-relevant climate issues before the House subcommittee at a 10 a.m. hearing in room 2318 of the Rayburn House Office Building.

In his testimony, he will brief the subcommittee on numerous scientifically documented changes that have occurred in Earth’s climate system over the past century, from substantial increases in surface temperatures and atmospheric carbon dioxide concentrations to rapid glacier melt and precipitation extremes.

These observed changes demonstrate that global warming is already occurring and is not merely conjecture based on future climate models or simulations.

Human-caused climate changes and impacts will continue for many decades and in some cases for many centuries, Chameides will explain.  The precise nature of these impacts cannot be predicted with great certainty, in part because scientists are not yet able to predict exactly how the climate will respond to increasing levels of greenhouse gases and in part because we are unable to predict how our energy and economy will evolve in coming decades.  However, we do know that the risks for human well-being from climate change are considerable.

In the face of uncertain but substantial risks from climate change, a prudent course of action is to develop and implement a risk-based and flexible response to the climate change challenge, Chameides will tell policymakers.

He will summarize the recommendations of a report entitled “America’s Climate Choices,” which was issued in 2011 by the National Research Council of the National Academy of Sciences (NAS) at the request of Congress.  More than 90 experts from the public and private sectors contributed to the report, which is considered one of the most comprehensive and objective analyses of climate change’s causes and consequences to date.  Chameides, an NAS member and atmospheric scientist by training, served as vice chair of the report.

The report’s recommendations include many “win-win” opportunities, where policy actions to curb climate change also will yield economic and social benefits, such as increasing U.S. energy independence, reducing communities’ vulnerability to natural weather extremes, and mitigating air pollution and its health impacts.

The Subcommittee on Environment is part of the House Committee on Science, Space and Technology.

Chameides’ testimony before the subcommittee will be posted online following Thursday’s  hearing and linked to this story.

The “America’s Climate Choices” final report is available free online at .