The earth's climate is changing more rapidly than we had thought possible only a few years ago, and we had better both prepare for that change and do what we can to stem it.

That was one of the principal points last week at a journalists forum on climate change and cities sponsored by the Lincoln Institute of Land Policy, the Nieman Foundation for Journalism at Harvard, and the Harvard Graduate School of Design. The intensive two-day program in Cambridge, Massachusetts, brought together about three dozen journalists, plus elected officials and experts in land use, transportation, geology, conservation, water and public policy. I intend to post a number of blog entries based on research and ideas presented at the forum, but today I'll start with an overview of general impressions.

• First, the science. Daniel Schrag, a professor of earth and planetary science at Harvard, said that we still do not know what the effects increased carbon dioxide in the atmosphere will be. But, he emphasized, "The uncertainty is all in the wrong direction." Scientists, Schrag said, have been making conservative estimates about global climate change for decades and all of the estimates have proven wrong. In fact, the situation has grown more dire more quickly than anyone predicted.

This was the part of Schrag's presentation that stuck in the forefront of my mind: Carbon dioxide is present in the atmosphere at about 380 parts per million (ppm) today, a sudden rise from 310 ppm. The carbon dioxide level will hit 500 ppm within a few decades, and could reach 1,000 ppm this century. The last time atmospheric carbon dioxide was present at 500 ppm to 2,000 ppm was during the Eocene era, 55 million to 36 million years ago. At that time, sea level was 100 meters (330 feet) higher than it is now. Are atmospheric carbon dioxide and sea level related? Yes.

• A number of speakers emphasized the need to both mitigate the problem, and adapt to the likely conditions. It's not an either/or question. Mitigation means reducing energy usage, developing noncarbon sources of energy, and somehow capturing and sequestering carbon emissions. Adaptation means creating ways for people to live less energy-dependent lifestyles — in other words, transit instead of single-occupancy cars, decreased heating and cooling through better building design and construction, and drought-tolerant landscaping. Some adaptations are also mitigations.

• What many planners and advocates call "smart growth," or simply good planning, has positive consequences for climate change. Think density, mixed-uses, transit, walkability, stormwater control. In other words, everything that California's post-war suburban model lacks.

• What level of risk are we willing to tolerate? Mortgage lenders require homeowners to buy fire insurance, even though the risk of catastrophic fire is quite small, even in fire-prone areas. We spend billions of dollars to protect against a flood that has a 1-in-100 or even 1-in-500 chance of happening. Yet the risk of climate change influencing cataclysmic events — enormous floods, fires, hurricanes and droughts — appears to be more on the order of 1 in 20, or even 1 in 5. Shouldn't this drive public and private spending decisions?

• A surprising number of speakers at the forum knew exactly how many days remain in the Bush administration. There's a feeling that the U.S. could not possibly have had two oil men in charge of the White House at a worse time. No one believes the next president, Republican or Democratic, will ignore the issues.

• There's this place out there called "the rest of the world." Most Americans are pretty bad about considering this place, except maybe as a vacation destination or as the place where their job went. Yet three-fourths of greenhouse gases are generated in the rest of the world, and developing countries will soon produce more than half. Billions of people want the mobility, convenience and gadgetry that most Americans take for granted. This makes for an extremely sensitive situation, especially when, as one South African reporter pointed out, the rest of the world sees the U.S. as a climate change pariah that's unwilling to be accountable.

• Most journalists are missing the big picture. What came through during forum discussions was that many journalists are skeptical of the problem, unsure of the scientists, and doubtful about the solutions offered so far. As one television reporter said, the end of the world has been predicted before but we're all still here.

Frankly, I was amazed at level of skepticism, especially considering that these were elite journalists with expertise in the environment and land use. Maybe that's why I found Ronald Sims, the elected executive of King County, Washington, to be so compelling. Sims is a leading voice for climate change adaptation. He pointed out that daily journalists often underreport historic trends and events. Before the attack on Pearl Harbor, newspapers in the U.S. contained modest coverage of the war in Europe and virtually nothing about Japan while they devoted their news columns to trivial local matters. Lincoln's Gettysburg Address was a turning point in our country's history, yet it received almost no coverage at the time.

What people are doing — or not doing — to ensure the planet remains habitable 100 years from now is the biggest story ever.

— Paul Shigley