While the other Washington — Washington, D.C. — finally is waking up to the threat of global climate change, Seattle continues to be a leader in the effort to reduce greenhouse gases right here at home.

In this city, people get how rising temperatures threaten our communities, our economy and our way of life: It's the snow.

The average snowpack in the Cascades has declined 50 percent since 1950 and will be cut in half again in 30 years if we don't start addressing the problems of climate change now. That snow not only provides our drinking water, it powers the hydroelectric dams that keep our lights on.

So, we can take great pride in the fact that Seattle City Light was the first major utility in the nation to produce zero net greenhouse-gas emissions. Think about it: We are showing the world how to power a city without toasting the planet! That is a powerful statement.

Yet, a recent state Supreme Court decision kills a key piece of City Light's climate-protection efforts. In its 5-4 decision, the court ruled that the utility can no longer use City Light funds to pay to offset its remaining carbon emissions. That's shortsighted.

We are fortunate that nearly all of City Light's power comes from clean, renewable sources. But the utility does produce some carbon emissions — mostly from trucks and other sources related to operations.

To compensate for some of those emissions, City Light has bought carbon offsets — essentially, credits that are used to reduce carbon emission from other sources, such as cruise ships. Put simply, it is paying others to pollute less. Unfortunately, some do not understand the benefit of this policy.

In fact, the utility's carbon-offset program directly and powerfully benefits City Light ratepayers. Consider this: Ninety percent of the power distributed by City Light comes from hydroelectric dams. When the snow goes away, so does our low-cost power. Offsets cost residential ratepayers less than 4 cents a month — a bargain when compared with the loss of snowpack from global warming.

The threat is widely recognized. Much already has been written about glaciers, including those on Mount Rainier, that are shrinking or on the cusp of disappearing. That would mean a loss of water for hydroelectric dams, irrigation systems, reservoirs and channels for spawning salmon.

At a 2002 climate-change conference in Seattle, University of Washington scientist Philip Mote offered a compelling presentation on how global warming could play out in the Northwest. With slides projecting mountain snow accumulations in the Columbia River Basin, from the early 20th century through the 2040s, Mote observed, "As warming progresses, the lower elevations are no longer snow-covered, and even the Cascades and Rockies lose snowpack."

Thanks to the support of ratepayers, City Light has avoided 630,000 tons of carbon-dioxide emissions by buying wind power and increasing conservation programs. The rest was offset with carbon credits. That's an achievement to be proud of and to protect, not one to restrict because the state Supreme Court misunderstood the carbon-offset program.

As the nation finally prepares to step up to the threat of global climate change, why in the world are we taking a step back?

I will be asking state lawmakers to make the legislative changes necessary to allow this important offset program to continue. The stakes are simply too high.

Greg Nickels is the mayor of Seattle.