With so much money at stake for oil and coal producing nations, can the conference make a real difference?

Dan answers: Oil and coal exporting countries can create a variety of procedural road blocks that slow down action to combat global warming. But I'm convinced that if the rest of the world is united, sound science will prevail and significant pollution reductions are achievable. Of course, the conference itself doesn't reduce pollution -- only concrete action in each country can do that -- but a solid agreement in Kyoto can set in motion a process that does make a real difference.

Melting ice in a cup of water doesn't raise the water level, so why would melting polar ice caps raise sea levels?

Dan answers: Sea levels are predicted to rise by one to three feet during the next century if no action is taken to reduce global warming pollution. You are right, however, that melting the arctic ice cap does not contribute to sea level rise because this ice is already floating, just like ice cubes in a cup of water. Rather, global warming causes sea level rise for two main reasons: First, water expands slightly as it warms and because the oceans are so deep this becomes an appreciable amount, accounting for about half of the projected rise. Second, mountain snow packs and glaciers will melt, as well as some of the ice covering Greenland and maybe Antarctica. This contributes to sea level rise because melting these land-based reservoirs represents a net addition to the volume of sea water. The notion that the melting of polar ice caps causes sea level rise is a result of sloppy journalism.

How can my city, in order to set reduction goals, measure CO2 emissions?

Can you say beyond a shadow of a doubt that the threat of global warming is real?

Dan answers: "Beyond a shadow of a doubt" is not a standard used in science. The real question is: Do we know enough to take action? I believe the answer to that question is definitely yes. Leading scientists from around the world agree.

Dan answers: I was very disappointed, but not surprised, by the weak target that the President announced. On the other hand, I was somewhat encouraged that the President does really seem to get it -- both the seriousness of the threat and the opportunity to address it through innovation. Its just too bad that he didn't follow through with a bolder plan in response. But I haven't given up. I still think we have a chance to get an agreement in Kyoto that at least begins the process of making real reductions in global warming pollution.

I've heard cars are the biggest CO2 emitters -- true? What can be done?

Dan answers: Cars are one of the biggest sources of global warming pollution in the U.S., ranking just behind coal-fired powerplants. In the short run you may have no choice but to drive because good alternatives just aren't available in many places. Over time we can improve alternatives to individual cars with mechanisms ranging from light rail to vanpool services. And we can insist that new cars be designed to emit less pollution per mile driven by making them go farther on each gallon of gasoline (reducing dependence on imported oil as a co-benefit).

In the meantime, make sure your car is properly tuned and that your tires are properly inflated. Carpool whenever you can and chain your trips together minimize cold starts. If you are in the market for a new car, chose the most efficient model that meets your needs.

What's so bad about a warmer earth?

Dan answers: I know, especially to Northerners, it sounds like it might not be such a bad thing. But scientists predict that if global warming pollution is not cut substantially, the Earth's average temperature will increase by 2 to 6 degrees over the next century and that the rise will be accompanied by a rise in sea level of 1 to 3 feet, which would have devastating consequences for low-lying countries and coastal areas. This is a huge change for the Earth as a whole -- faster than anything during the last 10,000 years. Other potential consequences include extreme heat waves, floods, and the spread of disease. And any of these direct impacts would, of course, cause immense economic harm as well.

Don't satellites record a drop in temperature over the last 17 years?

Dan answers: Coal and oil lobbyists frequently refer to the temperature record measured by satellites since 1979, which shows virtually no trend, thus backing their claims that global warming is just hot air from environmentalists. What they fail to point out, however, is that the satellite measurements are only available for the last 20 years -- too short a period to reach any conclusions on long term trends. By contrast, the surface record is available for more than a century, and is corroborated by other records, such as the retreat of mountain glaciers throughout the world.

Furthermore, satellites measure the upper atmosphere, where temperature trends are not expected to be identical to surface measurements. For example, ozone depletion, which has occurred largely since 1979, has had a cooling effect in the upper atmosphere which influences the satellite measurements. Recently, additional questions have been raised about the calibration of instruments during transitions from one satellite to the next.