1. Is our climate warming? If so, are we the cause?
2. What exactly causes global climate change?
3. Isn’t CO2 a naturally occurring gas?
4. What are some of the ways we produce CO2 in our daily lives?
5. Isn’t water vapor a more important greenhouse gas than CO2?
6. Are we sure global climate change is happening?
7. Why should I be concerned about sea ice melting in the Arctic Ocean?
8. How else will I see effects of global climate change?
9. Didn’t satellite data show that the air is not warming?
10. What’s the recent talk about “global cooling”?
11. Ice ages and large climate variations occurred in the past. Why do we think this current situation isn’t natural?
Scientists and public policymakers have made these two of the most discussed questions of our time. And the overwhelming majority of scientists and policymakers have come to the conclusion that yes, the climate is warming, and yes, we are to blame for much of it.
This Q&A section provides a full discussion of the science behind global warming and addresses a third, all-important question about climate change: What will it mean for us?
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The earth’s atmosphere has a natural ‘greenhouse effect’. That is, heat from the sun radiates down to earth, and much of this heat is re-emitted from the earth’s surface back into the air, toward outer space. Certain molecules, or gases, in the air absorb and trap this heat. This is fundamentally a good thing, because it prevents all of the sun’s heat from escaping back into space, and keeps our air warm enough to promote all kinds of life. Without the greenhouse effect, our air would be extremely cold.
One of the gases that absorbs the sun’s heat and traps it in the air is CO2. Scientists agree that global climate change is, by most measures, caused by too much CO2 and other greenhouse gases in our atmosphere.
Image Source: Woods Hole Research
Yes. Carbon is a basic building block of life. CO2 comes from the natural decomposition of organic materials like plants and animal matter, ocean evaporation and volcanic eruptions. We even exhale CO2 when we breathe!
However, we are now emitting CO2 into the atmosphere at rates that are far from natural. According to the IPCC, the level of CO2 in our atmosphere is increasing faster than at any time in our known history and far exceeds the natural range in the past 650,000 years.
The CO2 is coming in large part from our modern way of life and from industrial processes. In fact, nearly any time we use energy, we produce CO2 and other greenhouse gas pollution because much of our energy comes from the burning of carbon-based fossil fuels like oil, gas and coal. Combustion of these fuels releases carbon into the air that has been naturally stored in these materials over millions of years. If left to nature, it would take millions more years for this carbon to be very slowly re-released back into the air, if ever, through the natural carbon cycle. We are, in effect, accelerating this process very drastically due to our high demand for energy.
Chart adapted from the IPCC. Year 2052 CO2 levels are estimated based on a 1.9 ppm annual increase (current rate). For more information on the IPCC: http://www.ipcc.ch/
We are so used to our way of life that we often use energy without thinking about it or even realizing it. Coal-fired electricity plants emit large amounts of CO2 into the air to generate the electricity that we use every day in our homes and offices. Nearly every time we turn on the light switch, the TV, the computer or any other electronic device, heat or air condition our homes, wash and dry our clothes or take a hot shower, we emit CO2 into our air. And when we drive or idle our cars or trucks and mow our lawns, we are burning fossil fuels and emitting CO2 pollution. In fact, the average American uses about six times more energy than the average person living on earth and produces about 40,000 pounds of CO2 emissions per year.
Just as importantly, even activities many of us don't consider to be "polluting" are, indeed, causing global climate change. For example, when we buy clothes, toys and other items that come from far away and we carry them home in petroleum-based plastic bags, we are creating demand for products that often take substantial amounts of energy to produce, package and transport. And when we throw things away, we create waste that can enter the landfill and emit methane, a powerful greenhouse gas. This is why it has become so important to Reduce, Reuse and Recycle.
Even our food is laden with hidden fossil fuel energy—from the fertilizers used by industrial farming operations to the plastic packaging, from the shipping to the refrigerated storage. Table grapes grown in Chile travel about 4,200 miles just to get to the grocery store in Iowa. All of these things require a lot of energy.
For more information on how we use energy in America, see these two links:
Water vapor is, by volume, the most prevalent greenhouse gas in our atmosphere. It plays an important role in climate, and scientists are working to learn more about it.
Basically, though, we know that evaporation, condensation and cloud formation is, in part, a process of removing heat from the earth’s surface and transferring/releasing this heat into the air. This is why, in moist tropical areas, we don’t notice a big difference between the earth’s surface temperature and the air temperature. In drier, desert areas, however, this difference is much greater because there is less moisture in the air to draw the heat up.
Yet, water vapor is not the driving cause of climate change. Our forcing of very large amounts of CO2 and other greenhouse gases (like methane) into the air is the driving cause of climate change. This is because CO2 and these other greenhouse gases absorb heat from the sun and trap it in the earth’s atmosphere. Simply put, the more CO2 we force into the air, the warmer the air becomes.
In fact, the amount of water vapor in the atmosphere is, in part, a response to the amount of CO2 in the air. The warmer the earth, the more water evaporates from the oceans and the earth’s surface, and the more water vapor in the air. This effect, known as “positive water vapor feedback,” further increases air temperature.
As such, reduction of CO2 and other greenhouse gases that we are forcing into the air must be the target of any solution to the problem of global climate change.
Note: CO2 lasts 100 years in the atmosphere. Water vapor lasts one to two days.
For more information on water vapor, visit NASA’s Goddard Space Flight Center:
The United Nations Intergovernmental Panel on Climate Change (IPCC)—a group of more than 2,500 expert reviewers, 800 contributing authors, and 450 lead authors from over 130 countries that has put more than six years of work into studying this problem—calls the evidence "unequivocal" and says there is little doubt that it is mostly due to human activities.
Global climate change is happening now, and we are seeing its early effects. Unfortunately, it is accelerating faster than scientists expected. Sea ice in the Arctic Ocean, for example, is melting much faster than anyone anticipated; the volume of arctic sea ice at the end of last summer was half of what it was just four years ago. A NASA climate scientist says the Arctic Ocean could be almost completely ice-free within 4 to 5 years. He says: “The Arctic is screaming.”
To learn more about how and why the IPCC convened: http://www.ipcc.ch/about/index.htm
For the IPCC’s full reports, go to: http://www.ipcc.ch/
For more information on the status of the arctic sea ice, see this ABC News story: http://abcnews.go.com/Technology/story?id=5941683&page=1
There are two reasons why we should all be concerned. First, the events that are happening in places like the Arctic Ocean and Alaska are a bellwether of things to come around the entire globe. Warming is simply occurring faster there because more than two-thirds of the heat from the sun reflects off of the white ice and back into the air. But as the atmosphere warms and the ice melts, the dark oceans absorb much more of the heat, and as little as 10% of the sun’s heat emits back into the air. As a result, these areas of the world are undergoing the earliest changes.
Second, melting of both sea ice and land-based ice sheets causes sea levels to rise.* Scientists believe that the complete melting of Greenland would raise sea levels by 23 feet. That’s higher than a typical two-story building. Even a 3-foot rise, they say, would submerge densely-populated areas of low-lying countries like Bangladesh, driving hundreds of millions of people from their land and creating widespread unrest. This would also wreak havoc on our own Gulf Coast and the entire eastern seaboard, including the New Jersey shore and New York City.
* How does this cause sea levels to rise? Melted sea ice increases sea levels because warmer water takes up more space than cooler water, due to a phenomenon known as thermal expansion. Melting of land-based ice sheets also causes large amounts of water to drain off of the land and into the oceans.
For more information on sea level rise, see this National Geographic story:
Image: Sea Ice Breaking Away in AntarcticaSource: http://visibleearth.nasa.gov/
There are many other effects of global climate change. One is reduced crop yields. Research suggests that a 2-degree increase in temperature can reduce corn and soybean yields by 17%, because these plants thrive in cooler nighttime temperatures. Global climate change also threatens entire fish and animal populations, and these serious disruptions in our ecosystem and food chain can affect our ability to live on earth.
Global climate change is causing drought; yet, rising populations demand more and more water to drink and grow food. In Alaska, for example, up to 40% of fresh water supplies in some areas are now gone because the permafrost that used to hold the ponds and lakes is melting—as if someone pulled the plug out of a bathtub.
Global climate change also causes disease. More "red alert" ozone days are projected for Pennsylvania, as are higher rates of insect-borne diseases in many parts of the world.
In addition, global climate change threatens our local, national and global economies—and our national security. Right now, fossil-fuel energy is the lynchpin of our economy.
For more information on global climate change in Alaska, see this USA Today story: http://www.usatoday.com/weather/climate/2006-05-29-alaska-globalwarming_x.htm
Lobell DB, Asner GP. Climate and management contributions to recent trends in US agricultural yields. Science. 2003;Feb 14:5609.
[insert photo from: http://photo.saroy.net/2006/10/dying_corn.html]
Yes and no. Climate models predict that as the earth’s surface warms, so should the layer of air nearest the earth (the troposphere). Yet, for some time, satellite measurements suggested that there was little to no warming of the troposphere.
Since 2003, however, important research has revealed that some of these satellite measurements were unreliable:
1. First, satellites were launched over several decades with different kinds of instruments and technologies. Initially, scientists didn’t correct for these differences when comparing temperatures from one year to the next, nor did they correct for variables that distort the readings, like the tendency of satellites to tip and drift toward and away from the sun’s rays. Now, they do.2. Second, the satellites were taking measurements from the troposphere and part of the stratosphere (the upper air). This skewed the measurements because the stratosphere is actually cooling about five times faster than the troposphere is heating.*
Just as importantly, satellites have recorded temperatures for only about 20 years. This is not enough time to establish a trend, because factors other than greenhouse gases also affect temperatures. Temperatures go up and down from day to day, month to month, and year to year.
To create a longer-term picture of temperature trends, scientists use a host of other measures (not just satellite data) that extend further back in time. These “paleoclimatic” data are generated from the study of things like tree rings, corals, fossils, sediment cores, pollens, ice cores and cave stalactites. This paleoclimatic record allows scientists to look at global temperature fluctuations over the last several centuries, and it permits scientists to examine climate even further back in time over the course of millennia and longer. This perspective is an important part of the global warming puzzle. So far, paleoclimatologists have been unable to find any natural climatic explanations for our present-day warming.
*Want to know why the stratosphere is cooling? There are two basic reasons. The first is ozone depletion in the stratosphere; ozone is a greenhouse gas in the upper atmosphere that absorbs UV radiation from the sun. As ozone depletes due to air pollution, the stratosphere’s ability to absorb this UV radiation diminishes. The second reason is that the large volumes of CO2 that we are forcing into the lower atmosphere are trapping the sun’s heat there, preventing it from emitting back out.
For more information on satellite measurements, visit these three websites:
For more information on paleoclimactic data, visit the National Climactic Data Center:
According to respected outlets that track temperatures, the global 2007-2008 winter season was the coolest since 2001. You may have heard some columnists, news reporters and internet bloggers refer to this as “global cooling.” Some even claimed that this erases the existence of global warming.
This is false. We contacted the source of the data (Met Office, Exeter, England), and they told us that the fact that 2007-2008 was the coolest winter since 2001 does not erase the reality of global warming, or even put it into question. In fact, these temperature variations are normal and were predicted, because they are largely caused by a well-known cyclical phenomenon known as the El Niño Southern Oscillation. This is a naturally occurring climate cycle that causes large-scale changes in sea-surface temperature across the eastern tropical Pacific. This, in turn, causes weather changes across the world.
It’s called an “oscillation” because the cycle occurs every few years and shifts between drops and spikes in sea surface temperatures—and, thus, corresponding drops and spikes in average worldwide temperatures. The drops are known specifically as La Niña and the elevations are called El Niño. In 2007-2008, we have been in the La Niña down phase.
The evidence still clearly points to global warming. Global warming is a trend that happens over time, with natural temperature variations occurring all the time. This graph shows this upward trend, and it also shows the El Niño up-and-down oscillations. Finally, the physical evidence is everywhere, from rapid melting of arctic ice to dead undersea coral in the tropics to increasingly severe weather patterns globally.
For more information and for a link to our source, go to:
While theories exist, no one knows for sure what caused ice ages or large climate fluctuations in the past. However, the fact that these vast climate changes did happen, and the fact that they drove entire species to extinction, is proof that they can happen again. These historic variations also suggest that our climate system is delicately balanced, and that it can be disrupted, with severe consequences. In fact, decades ago, climate experts predicted that our forcing of greenhouse gases into the air could cause the climate system to reach a “tipping point” — a point at which the climate system destabilizes, causing temperatures to fluctuate up and down and causing severe storms, droughts and floods. This is known as the “staggering drunk” theory.
We now understand that when we force so much heat-trapping gas into the air so quickly, as we are now doing, we are disrupting this delicate equilibrium. We do not fully understand how our complex climate system will respond, but it is apparent that it will be much more volatile than it is today.
The sea takes a coastal village in Alaska. (Image: Alaska Native Science Commission)