WASHINGTON, D.C. -- It's funny how history repeats itself.

For decades, tobacco companies denied the definitive link between smoking and cancer. They spent millions of dollars scripting a handful of skeptical scientists to assure us that smoking was safe and to create doubt among the public. Sure they bought themselves time with this tactic, but waiting for definitive proof of cigarette smoking's health impacts cost millions their lives.

Even though we're are in the midst of the worst drought since the Great Depression, fossil fuel companies have adopted the same strategy to stall action on global warming.

Just like the tobacco companies, they are spending millions of dollars on advertising and have hired a few skeptical scientists to convince us that we don't need to act on global warming because there is no scientific proof or concern. Nothing could be farther from the truth.

The key to the scientific debate on global warming is agreeing on when there is enough proof to sound the alarm. If the weatherman tells you there is an 80 percent chance of rain, you pack an umbrella.

When the Intergovernmental Panel on Climate Change (IPCC), the world's leading scientific body on global warming, tells you that "the balance of evidence suggests a discernible human influence on global climate," you begin to look for ways to reduce the threat.

It would be one thing if the IPCC were the only group of scientists expressing concern. However, other statements by scientists confirm the seriousness of the warming and call for leadership on global warming.

Two years ago, 3,000 U.S. scientists released the Scientists' Statement on Global Climatic Disruption, an unprecedented statement urging the United States to lead in the efforts to stop global warming.

Scientists in such fields as climatology, meteorology and atmospheric science signed the statement. In addition, ecologists, foresters, botanists, and biologists signed on because they are witnessing the wide-ranging, day-to-day impacts of global warming in their fieldwork.

Shortly after that, more than 1,500 scientists released the "World Scientists' Call for Action," urging government leaders to act immediately to prevent global warming. This statement included 110 Nobel laureates and 60 U.S. National Medal of Science winners.

Then, early this year, the 35,000 members of the American Geophysical Union released a position paper on Climate Change and Greenhouse Gases asserting that the increased concentrations of greenhouse gases are cause for legitimate public concern.

These different statements demonstrate consensus among scientists from a broad range of disciplines and make clear that global warming will affect untold aspects of our lives.

Scientists are not just speaking out in public. Every day new peer reviewed research is published revealing how global warming will impact everything from coastal communities and farming to the skiing and fisheries industries.

While there is no definitive proof of global warming, the "balance" of evidence suggests that global warming is real enough to merit action. The same was the case in the long struggle over tobacco.

The tobacco scientists who held out for 100 percent proof that cigarettes cause cancer are now responsible for the thousands of Americans with coughs that sound like a raccoon in a garbage can.

If history holds true, the scientific community will continue to provide a relentless onslaught of evidence on global warming and the fossil fuel interests will argue that we should wait for even more definitive proof.

With record droughts, tornadoes in the middle of Utah and a hurricane season that's predicted to break records, do we really need full scientific consensus to realize the weather has changed?