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What is "global warming"?

Global Warming Basics

Michael Oppenheimer (Professor, Princeton University) gives expert video advice on: How will climate in the future be different?; Is global warming happening right now?; What factors are making the current climate change so severe? and more...

What is "global warming"?

Certain gases that exist naturally in the atmosphere let sunlight through, which warms Earth's surface. But then they trap heat that would otherwise escape into space. That's called the greenhouse effect, and it keeps Earth about 6 degrees Fahrenheit warmer than it would otherwise be. In other words, without the natural greenhouse effect, Earth would be a frozen desert. The greenhouse problem and global warming arise because human beings are causing an increase in the natural levels of those gases, causing a thickening of this natural blanket around Earth, and that inevitably will cause global warming. In fact, global warming is already happening, Earth is already warmer due to this thickening greenhouse blanket – more than a degree warmer than it was a century ago.

How will climate in the future be different?

Climate change accompanies global warming. As there are temperature changes, circulation of the atmosphere will change, the temperature and volume of the oceans, patterns of storms will be altered and the frequency of drought and flooding will change -- the whole framework of the world we're used to will change.

Is the sun a major cause of global warming?

The sun is a very minor cause of global warming— at least over the period that human beings are interested in, say decades or centuries. Over very long periods of time, millions of years, hundreds of thousands of years, changes in the sun may be an important factor in influencing earth's climate. But during the past century and the future century, the one we're living in, changes in the sun are not going to matter very much. The key effect is not the sun but the build-up of green house gases

Is global warming happening right now?

Global warming is already happening, and it's only going to get worse until we stem the emissions of the gases that are causing the problems. The Earth is already about one degree of Fahrenheit warmer than it was a century ago, and though that may not sound like a lot, the earth has only warmed 5 to 9 degrees since deep ice-sheets covered New York, thousands of years ago. That's about as much warming as we may get in the coming century, and we are well on our way to very significant changes.

Why has climate change recently become such an issue of concern?

Scientists have been concerned about this issue for thirty or forty years, and the theory itself, goes back more than a hundred years. Recently, the average person has seen the possible effects of bad weather close-up. We had a couple of really bad hurricane seasons, alongside Katrina, and 140 people died in a heat wave in California this past summer. There have been unusual storms in many places in the world. While these may not be directly linked the global warming, they help to raise awareness about environmental fluctutations; people learn their lives are not insulated from the changes in the climate.

What factors are making the current climate change so severe?

Climate change is natural, and has occurred throughout Earth's history. Due to changes in Earth's orbit, for instance, we move in and out of ice ages, and Earth, in fact, is now in a relatively warm period naturally. The trouble is that those changes are very slow, they occur over the course of hundreds of thousands of years. Human beings, through the build-up of greenhouse gases, are going to telescope a climate change of the size that occurred as Earth came out of its last glacial period, all into a century. It's going to be an earthshaking climate change that will be the largest and fastest global change by far in the history of civilization, that's why climate change is a big risk.

Are there any credible scientists who disagree that global warming is a real danger?

There are always different views on how successful human beings will be in dealing with climate change, and there are legitimate differences in opinion. There is no doubt, however, that the earth has warmed over the last century, and that this warming will continue if we don't reduce the greenhouse gas emissions. It is important to consider whether or not human beings will be able the adjust to the changes that occur, as a result of irreversible global warming. Scientists are worried that, unless we slow down, we may find ourselves in a very uncomfortable position.

How much have average global temperatures risen over the 20th century?

The global average temperature has risen a little more than a degree Fahrenheit over the past century, and that change in global temperature has already been accompanied by significant changes in the climate. Heat waves are more frequent because of climate change, sea level is rising, rainstorms have become more intense, as have hurricanes. There's more drought in certain areas because of climate change. Basically, we're seeing an all-pervasive climate change, and that's only accompanying a one-degree warming. Projected warming over the coming century, if we don't limit the emissions of the gases, could be anywhere between two and ten times the size of the warming that's already occurred.

What could happen in the 21st century if temperatures continue to rise?

If temperatures continue to rise, this is the world we're looking at. Record heat, record drought in some places, record flooding in others, sea level rising flooding coastal areas, undermining infrastructure, removing and destroying and permanently drowning beaches and wetlands. We're likely to see ecosystems, like forests, trying to move to other places because they're no longer suited to live in the place that they originated. And some ecosystems like, for instance, the coral reefs that people like to snorkel and dive in, simply may not have any future at all because they can't tolerate even a small warming, and coral reefs don't have legs. They can't just pick up and move like we can, for instance. Maybe most troubling is that in many parts of the world where moisture is already in short supply we may see significant decreases in both precipitation and the runoff of rainfall that's necessary for drinking water and for agriculture, so it looks like food availability in many parts of the world that already have trouble getting enough food, like much of sub Sahara Africa, parts of India, maybe even parts of Mexico, we could see agricultural productivity decreasing, more malnutrition and even more starvation.

Why is it important for me to know about global warming and the environment?

It's important for you to know about global warming, because there's something you can do about it. We still have the ability to get this problem under control, to limit the emissions, to stabilize the atmosphere and the climate, and to pass on to our children and grandchildren a world that we would want to live in. That's why it's important for you to understand, for everyone to understand, that this is a problem that they have a stake in, and that they can do something about.