"How we as a society use what we have learned from climate science could define our generation.
Right now, our nation and the world are at a crossroads. Yet we seem stalled despite an increasingly clear picture of what human-induced global warming is doing to our planet.
The scientific community often working closely with governments has produced numerous, carefully reviewed, international and national assessments of the scientific understanding behind climate change. The latest, Americas Climate Choices, recently released by the U.S. National Academy of Sciences, states that scientific evidence that the Earth is warming is now overwhelming.
So it is imperative that the public and policymakers question and debate the range of options for addressing climate change including the level of certainty about that evidence. But a fair debate requires understanding of the scientific process.
The essence of the scientific method is the cyclical process of observing nature, developing theories consistent with the observations and challenging the theories with new observations to build a robust body of understanding.
The path from theory to understanding is often far from simple. Sometimes, new insights lead to dramatic shifts in prevailing scientific views.
Consider the identification of the ozone hole in the 1980s. A consensus emerged among experts within a few years of finding key evidence though a small number of experts remained unconvinced.
Such is the case with climate science. Theories and observations have been tested, retested and reviewed. Today, a large body of evidence has been collected to support the broad scientific understanding that global climate warming, as evident these last few decades, is unprecedented for the past 1000 years and this change is due to human activities.
This conclusion is based on decades of rigorous research by thousands of scientists and endorsed by all of the worlds major national science academies.
The urgent need to act cannot be overstated. Climate change caused by humans is already affecting our lives and livelihoods with extreme storms, unusual floods and droughts, intense heat waves, rising seas and many changes in biological systems as climate scientists have projected.
Although uncertainties remain, they concern issues like the rate of melting of major ice sheets rather than the broader topic of whether the climate is changing.
The biggest question is what choices we and our children should make about energy use. The more dependent we are on carbon-emitting energy sources, the more our climate will change.
If policymakers, businesses and the public are to make smart decisions about climate change, there must be a clear picture of the elements of science that represent robust understanding, elements that remain uncertain and those that depend on future decisions about energy use.
This is the reason for a thorough discussion of scientific findings.
But regardless of how the debate proceeds, it should be clear that opinions or misinformation cannot change the extensive scientific evidence. The atmosphere, the oceans and the land are warming. Humans are contributing significantly to this, and as it continues, it will have a major impact on our society, economy, environment, energy, national security and health throughout, and well beyond, this century.
As climate scientists, we have a responsibility to share our understanding with the public and with policymakers.
But, the future depends not on what scientists have learned and conveyed. Rather, it depends on what society chooses to do with that knowledge."