The big argument over climate change used to be whether we really needed to worry about it – whether the climate was heating up, whether global warming was real. There are some doubters left, but nearly everyone else – scientists, elected officials, even the companies that produce oil, coal and gas – accepts the reality of global warming. Most governments and leaders around the world have accepted this as well, including the United Nations, the European Union and, after some initial doubts, President Bush.

So what’s the debate now? Well, what to do about it. How can we make sure that climate change is as moderate and gradual as possible, and how do we adapt to the changes that are already taking place. Here’s what you need to know:

“Greenhouse gases” like carbon dioxide come from the kinds of fuel we use most – namely, oil (which is mostly used for gasoline, diesel and jet fuel) and coal (almost all of which is used to produce electricity). Since people in the U.S. and around the world are burning more of these so-called fossil fuels, greenhouse emissions have also increased – they’re already 35 percent above what they were before the Industrial Revolution.

The Earth is getting warmer – global temperatures have risen a full degree Fahrenheit in the last century. And the warming trend is speeding up, with seven of the eight hottest years recorded occurring since 2001. An overwhelming majority of scientists have come to believe these two facts are connected, that human activities, especially the use of fossil fuels that give off carbon dioxide, are the major cause of this warming trend.

The potential impact is of global warming is nothing to sneeze at. A degree or two of global warming might seem minor, but it’s definitely not. Melting polar ice and glaciers cause coastal flooding in places thousands of miles away. This can devastate communities, especially in poorer countries. Crops that once thrived can fail causing economic upheaval. Miserable insects and diseases flourish in places that didn’t have them before. Many scientists also predict an increase in extreme weather -- fiercer hurricanes, tornados, and flooding, -- not to mention many more really bad summer heat waves.

We can slow down this warming trend by cutting back on greenhouse gas emissions, but the impact probably can’t be stopped or reversed. In other words, it’s a question of how much temperatures rise, not whether they rise. But the less they rise the easier it’ll be to cope.

To reduce greenhouse gas emissions, we’ll need to look for alternative fuels and ways to use fossil fuels as efficiently as possible. If you get 50 miles per gallon when you drive, you’ll do less environmental damage than if you only get 20 miles per gallon. Less fuel used, fewer emissions.

It helps to focus on which fuels produce greenhouse gases and which don’t. Oil and coal, yes. Nuclear, solar and wind power, no. Natural gas, which is also a fossil fuel, does produce some greenhouse gas emissions, but it’s not nearly as damaging as the big two.

As a country, we’re also going to have to adapt to the likely impacts of climate change, including extreme weather, crop changes and new diseases. We’re also going to have to adapt to reduce greenhouse gases and get our energy from cleaner sources. The question is how, exactly, that happens.

Key sources for this data: Intergovernmental Panel on Climate Change, Climate Change 2007 Synthesis Report, Summary for Policymakers; U.S. Climate Change Science Program, Analyses of the Effects of Global Change on Human Health and Welfare and The Effects of Climate Change on Agriculture, Land Resources, Water Resources, and Biodiversity in the United States; U.S. Environmental Protection Agency, Climate Change Site