The world's climate, about as global a topic as one can imagine, was the hot issue of 2007, primarily because most signs pointed to the climate itself heating up. But the controversial phenomenon known as global warming also played a big role in local politics and policy debates, and local scientists' voices were clearly heard.

Scientists, including many from the Scripps Institution of Oceanography, reported a host of data that seemed to support the controversial and increasingly influential theory, which predicts massive and disruptive changes to the planet's climate triggered by a thickening blanket of heat-trapping greenhouse gases.

The theory affected discussions about everything from transportation planning to a local utility's plan to string a huge power line through the North County backcountry.

But while there's no question global warming had a bigger real-world impact in policy debates in 2007, many people, including some scientists, continued to debate the scientific theory's veracity. They questioned how much of climate changes are being fueled by human activities.

Still, the Intergovernmental Panel on Climate Change, a United Nations body of scientists, produced a ground-breaking report in February that boldly asserted humans are to blame for a warming planet. And San Diego County scientists played a key role in crafting that report.

Scripps leads the way

The international panel relied on the work of 2,500 scientists from 130 nations in drawing its conclusions. Fourteen scientists at UC San Diego's Scripps Institution of Oceanography helped the panel write it.

So when former Vice President Al Gore was awarded the Nobel Peace Prize on Dec. 10 in Oslo, Norway, for his work in bringing the issue to public attention, he shared it with a scientific body that had a San Diego County presence. Gore focused cameras on the issue with the film, "An Inconvenient Truth."

Scripps has long been one of the world's leading sources of data and research into the global warming phenomenon.

After all, it was the late Scripps pioneer Charles David Keeling who first reported, from observations taken on Hawaii's Mauna Loa Observatory in the late 1950s, that carbon dioxide levels in the atmosphere were increasing.

His Keeling Curve charts the buildup of carbon dioxide, a greenhouse gas, in the years since. It shows that the concentration has increased from 315 parts of the gas per million parts of air around 1960 to about 380 million parts per million today.

The international panel produces reports updating the science on climate change every five years. One of this year's report's coordinating lead authors lives in North County: Climate researcher Richard Somerville lives in La Costa and supervised a chapter tracing the history of global warming science. He said the series of reports produced in 2007 made it clear the globe is warming, and that human activities are very likely responsible for most of it.

"My personal opinion is that there is no credible other side anymore," Somerville said. "Can you find people who dispute the IPCC? Yes. But every year they are fewer."

Still, skeptics, while in the minority, did not exit stage left.

That point was underscored when 100 scientists and professors from around the globe -- many of them climate researchers -- sent a letter to the United Nations secretary general in advance of the December climate conference in Bali saying the international panel has not proven its case.

The debate over the impact human activities are having on the climate "is not even close to being over," said Gary Sharp, scientific director for the Center for Climate/Ocean Resources Study in Salinas and one of the signatories. Sharp is a former Scripps student.

What's not debatable, Somerville said, is the changes taking place: Air temperatures are increasing, the oceans are warming, sea levels are rising and ice sheets are melting.

However, the letter signers said glacial retreats, rising seas and warming temperatures aren't proof of abnormal climate change because changes are within the range of fluctuations that have occurred for hundreds and thousands of years.

Debating the Sunrise

Global warming played a big role in a policy debate that raged across North County's backcountry in 2007.

Since 2005, San Diego Gas & Electric Co. has argued that it needs to build a massive new electric transmission line to meet San Diego County's future electricity needs. And the company said the line was needed to meet an impending state mandate for utilities to tap renewable sources of energy, including what is believed to be a deep well of clean sun, wind and underground-geyser power in the Imperial Valley.

As climate change began to make headlines regularly this year, the company started selling the global-warming benefits of the $1.3 billion, 150-mile Sunrise Powerlink.

Utility officials reasoned that the opportunity to plug into developing nonfossil-fuel sources in the desert would significantly slash the region's contribution to greenhouse gases from local natural gas-fired power plants.

Just as strongly, opponents insisted the project would aggravate the problem because there is no guarantee significant amounts of clean power will become available in the desert, so the line would just import natural-gas power produced elsewhere.

The California Public Utilities Commission has scheduled hearings to sort out those and other issues early in the year; a decision could come in late summer.

The policy debates

The Sunrise Powerlink debate was one of many public policy fronts in California in which global warming played a role in 2007.

The state Air Resources Board pressed ahead to write rules curbing greenhouse gas emissions from power plants, factories and oil refineries following passage of a landmark law the previous year. Strict new carbon dioxide limits take effect early next decade.

At the same time, the air board was preparing to enforce rules expected to deliver a batch of new low-carbon-emitting cars a few months from now when 2009 models come out. Those regulations were crafted in response to a 2002 state law.

However, California's automobile plan ran into a federal roadblock. On Dec. 19, the head of the U.S. Environmental Protection Agency refused to grant the state a waiver needed to allow the nation's first greenhouse-gas restrictions on automakers to take effect.

The state is in a unique position when it comes to tailpipe emissions. While the rest of the nation follows federal rules, California has been allowed to establish its own and often stricter limits because its air-pollution control program predates the federal government's. And the Environmental Protection Agency had granted the state more than 50 waivers without a denial until now.

Federal officials maintained the nation needs a uniform strategy for curbing greenhouse gases and not a hodgepodge of rules that differ state to state. And they suggested new fuel economy rules expected to boost gas mileage 40 percent by 2020 would accomplish the same goals.

California's rules aimed to curb carbon emissions from cars 30 percent by 2016.

Even plans heat up

Global warming was also a reason California took special interest in San Diego's regional planning in 2007.

In late November, as the San Diego Association of Governments was putting final touches on a transportation blueprint that will guide highway and rail projects over the next 23 years, Attorney General Jerry Brown fired off a critical letter saying the plan would only heat up the planet more.

Brown did not sue the agency, as he did San Bernardino County in April over a general plan, or something that serves as a guide for new development. But San Diego-area officials remained wary and said they would watch closely to see if the second shoe might drop in the form of a lawsuit.

While 2007 was the year in which global warming made its biggest splash yet in policy debates, the coming year may prove to be even more eventful, as governments big and small confront the dynamic science and hard choices awaiting anyone trying to address it.

Somerville summed it up this way: "In the same way that your doctor tells you how much you must reduce your cholesterol, science tells us how much we are going to have to lower our amounts of carbon dioxide. And it is not a little, trivial amount. Changing one light bulb is not going to do it. Changing the way the world gets energy is what it is going to take."

Contact staff writer Dave Downey at (760) 745-6611, Ext. 2623, or ddowney@nctimes.com.