A report released by researchers at Tufts University, commissioned by the Natural Resources Defense Council (NRDC), presents two ways of estimating the costs of inaction on climate change, both leading to staggering bottom lines. A comprehensive estimate, based on state-of-the-art computer modeling, finds that doing nothing on global warming will cost the United States economy more than 3.6 percent of GDP - or $3.8 trillion annually (in today's dollars) - by 2100.

On the other hand, a detailed, bottom-up analysis finds that just four categories of global warming impacts - hurricane damage, real estate losses, increased energy costs and water costs - will add up to a price tag of 1.8 percent of U.S. GDP, or almost $1.9 trillion annually (in today's dollars) by 2100.

"The longer we wait, the more painful and expensive the consequences will be. This report's findings are undeniable - we must act now," said Dan Lashof, director of NRDC's Climate Center. "The Climate Security Act currently in the U.S. Senate is our best opportunity to set a concrete limit on global warming pollution and provide an accompanying market that rewards companies for making real reductions."

In the future, global warming will cause drastic changes to the planet's climate, with average temperature increases of 13 degrees Fahrenheit in most of the United States and 18 degrees Fahrenheit in Alaska over the next 100 years.

Costs and damages for the four detailed categories cited in the report if global warming continues:
- Hurricane damages: $422 billion
- Real estate losses: $360 billion
- Increased energy costs: $141 billion
- Water costs: $950 billion

"Some important impacts are priceless, so the real situation is worse than the numbers can convey," said the report's lead author, Frank Ackerman. "But the numbers, for those impacts we can put prices on, are bad enough. Climate change is on a collision course with the U.S. economy, long before the end of the century, unless we act now."

Global warming is already melting sea ice and glaciers that will contribute significantly to sea level rise. Sea level is expected to rise 23 inches in 2050 and 45 inches by 2100, with grave impacts expected for the Southeastern U.S. By 2100, an estimated $360 billion per year will be spent on damaged or destroyed residential real estate in the United States as a result of the rising sea levels inundating low-lying coastal properties. The effects of climate change will also be felt in the form of more severe heat waves, hurricanes, droughts, and other erratic weather events - and in their impact on our economy's bottom line.

Global warming will change the nature of where Americans live. For example, this analysis found that if global warming continues unchecked, by 2100, New York City will feel like Las Vegas does today and San Francisco will have a climate comparable to that in New Orleans. In 2100, Boston will have average temperatures similar to those in Memphis, Tennessee today.