GLOBAL WARMING FREQUENTLY ASKED QUESTIONS
How much has the global temperature risen in the last 100 years?
Averaged over all land and ocean surfaces, temperatures have warmed roughly 1.33°F (0.74ºC) over the last century, according to the Intergovernmental Panel on Climate Change (see page 2 of the Summary for Policymakers in the IPCC’s 2007 Synthesis Report). More than half of this warming—about 0.72°F (0.4°C)—has occurred since 1979. Because oceans tend to warm and cool more slowly than land areas, continents have warmed the most (about 1.26°F or 0.7ºC since 1979), especially over the Northern Hemisphere.
The year 1998 was the warmest on record for the contiguous United States, followed closely by 2006 and 1934, according to the National Climatic Data Center. In 2008, the U.S. saw its coolest year in more than a decade. It was the first time since 1997 that the nation has been close to its 100-year average temperature (though 2008 was still slightly above that norm). The United States was actually one of the least-warm spots on Earth in 2008 when compared to local averages. The globe as a whole had its coolest year since 2000, but the global average for 2008 was still warmer than any year from 1880 to 1996, according to NCDC.
There are slight differences in global records between groups at NCDC, NASA, and the University of East Anglia. Each group calculates global temperature year by year, using slightly different techniques. However, analyses from all three groups point to the decade between 1998 and 2008 as the hottest since 1850.
This graph from NOAA shows the annual trend in average global air temperature in degrees Celsius, through 2008. For each year, the range of uncertainty is indicated by the vertical bars. The blue line tracks the changes in the trend over time.
How much carbon dioxide (and other kinds of greenhouse gas) is already in the atmosphere?
One of the strongest pieces of evidence for human-induced climate change is the consistent rise in carbon dioxide (CO2) in modern times, as measured at the Mauna Loa Observatory in Hawaii, where CO2 has been observed since 1958. As of December 2008, the concentration of CO2 in Earth’s atmosphere was about 386 parts per million (ppm), with a steady recent growth rate of about 2 ppm per year.
Because CO2 stays in the air so long, it becomes very well mixed throughout the global atmosphere. This makes the Mauna Loa record an excellent indication of long-term trends.
This graph shows an annual seasonal cycle and a steady upward trend since CO2 measurements began at Mauna Loa in 1958.
The seasonal cycle is due to the vast land mass of the Northern Hemisphere, which contains the majority of land-based vegetation. The result is a decrease in atmospheric carbon dioxide during northern spring and summer, when plants are absorbing CO2 as part of photosynthesis. The pattern reverses, with an increase in atmospheric carbon dioxide during northern fall and winter. The yearly spikes during the cold months occur as annual vegetation dies and leaves fall and decompose, which releases their carbon back into the air.
This graphic portrayal of rising CO2 levels is known as the Keeling curve in honor of the originator or these measurements, Charles David Keeling of Scripps Institution of Oceanography.
Current atmospheric concentrations of CO2 are about 30% higher than they were about 150 years ago at the dawn of the industrial revolution. According to the Scripps Institution of Oceanography, ice core reconstructions going back over 400,000 years show concentrations of around 200 ppm during the ice ages and about 280 ppm during the warm interglacial periods. In other words, our current CO2 levels are higher than they've been in at least the last 400 millenia. See the Scripps Web site for a graphic illustrating this trend.
Almost a quarter of the carbon dioxide emitted by human activities is absorbed by land areas; another quarter is absorbed by the ocean. The remainder stays in the atmosphere for a century or longer.
Carbon dioxide accounts for more than half of the human-produced enhancement to Earth’s greenhouse effect. Among the other gases involved is methane, which has increased dramatically over the last century. Methane concentrations rose about 1% a year in the 1980s, but since about 2000 the concentration has leveled off, though a rise was observed in 2007. The reasons for this slow growth in recent years are not yet clear, although one possibility is a drop in the amount of methane leaked from natural gas pipelines and plants. Methane stays in the atmosphere for much less time than carbon dioxide (around a decade) and there is much less of it, but molecule for molecule, it is a far more powerful greenhouse gas. As of 2008, the concentration of methane in Earth’s atmosphere was about 1786 parts per billion.
Learn More
Keeling Curve Lessons (Scripps CO2 Program)
The Carbon Cycle (Windows to the Universe)
Earth's Greenhouse Gases (Windows to the Universe)
Other important greenhouse gases include nitrous oxide and near-surface ozone. Water vapor is actually the most prevalent greenhouse gas, but human activity has not directly increased its concentration in the atmosphere, unlike the other chemicals above. However, as global temperatures increase, more water vapor is released by oceans and lakes, and this in turn helps to increase temperatures further. This is one of many feedback loops that help to reinforce and intensify climate change.
Hasn't the amount of carbon dioxide in the atmosphere decreased recently?
People don’t always produce more CO2 from one year to the next. When the global economy weakens, emissions from human activities can actually drop slightly for a year or two. Yet the accumulation of CO2 in the atmosphere continues to rise, as shown in the graph above. It’s a bit like a savings account: even if your contributions get smaller in a tight budget year, the total in your account still goes up.
Vegetation also makes a difference, because growing plants absorb CO2. Large-scale atmospheric patterns such as El Niño and La Niña bring varying amounts of flooding, drought, and fires to different regions at different times, which affects global plant growth. Thus, the amount of human-produced CO2 emissions absorbed by plants varies from as little as 30% to as much as 80% from year to year. Over the long term, just over half of the CO2 we add to the atmosphere remains there for as long as a century or more. About 25% is absorbed by oceans, and the rest by plants. This "balance sheet" is known as the global carbon budget.
It’s not yet clear which forests absorb the most CO2. Because the answer will influence global planning and diplomatic agreements on climate, scientists are working hard to measure how CO2 varies by latitude, altitude, and season. One such study is HIPPO, a field project led by NCAR and colleagues from 2009 to 2011 to take pole-to-pole measurements aboard an airborne laboratory, the NSF/NCAR Gulfstream V jet. Satellites such as Japan's GOSAT and others on the drawing board at NASA will help fill in more carbon-budget details.
We've zoomed in for a closeup of temperatures over the last three decades, taken from a longer timeline discussed above. This closeup shows the annual trend in average global air temperature, in degrees Celsius, from 1975 to 2008. For each year, the range of uncertainty is indicated by the vertical bars. The blue line tracks the changes in the trend over time. Click here or on the image to see the full graph. (Image courtesy NOAA's National Climatic Data Center.)
Hasn't Earth been cooling since 1998?
Thanks in large part to the record-setting El Niño of 1997–98, the year 1998 was the warmest year globally in the 20th century. Since 2001 the global trend has been relatively flat, and 2008 was the coolest year so far this decade (see graph at left). However, a simple calculation shows that global temperatures continue to run much warmer now than in the past: the average from 1999–2008 exceeds the average from 1989–1998, even though the latter period includes the record-warm 1998.
Although scientists are confident that global temperatures will rise further in the coming decades, there could still be occasional "pauses" in warming that last a few years, like the one we're seeing now.
Some of the contributing factors to these breaks in warming could include erupting volcanoes that spew sunlight-blocking ash skyward, a lack of El Niño events, and/or the natural minimum in the 11-year solar cycle. Since we are now emerging from the most recent solar minimum, and an El Niño is developing in 2009, there's good reason to believe global temperatures will climb significantly as the 2010s approach.
Glaciers started melting long before human industrial activity. Aren't there other factors besides temperature determining whether a glacier advances or retreats?
Glacier dynamics are indeed complex, and melt rates can be influenced strongly by many factors. For example, dark particles of pollution that fall on ice and snow fields can increase melting because they absorb more sunlight than the lighter colored surface. But the vast majority of glaciers across the planet are melting, with the melt rate accelerating in many areas. This global phenomenon can be best explained by research that includes the rise in global temperatures as a main driver. The involvement of other factors does not negate the role of warming temperatures in ice and snow melt.
The National Snow and Ice Data Center tracks changes in glaciers, including where they end (terminus) and how large they are (mass balance) on its State of the Cryosphere site. Their Glacier Photograh Collection provides stark evidence of how rapid the decline is for many glaciers around the world.
What does the ozone hole have to do with climate change?
There are a few connections between the two, but they are largely separate issues. First, it's important to know that ozone plays two different roles in the atmosphere. At ground level, "bad ozone" is a pollutant caused by human activities; it's a major component of health-damaging smog. The same chemical occurs naturally in the stratosphere, and this "good ozone" acts as a shield, filtering out most of the ultraviolet light from the Sun that could otherwise prove deadly to people, animals, and plants.
The ozone hole refers to the seasonal depletion of the ozone shield in the lower stratosphere above Antarctica. It occurs as sunlight returns each spring, triggering reactions that involve chlorofluorocarbons (CFCs) and related molecules produced by industrial processes. These reactions consume huge amounts of ozone over a few weeks' time. Later in the season, the ozone-depleted air mixes with surrounding air and the ozone layer over Antarctica recovers until the next spring. Other parts of the globe have experienced much smaller losses in stratospheric ozone.
Learn More
Introduction to Ozone (UCAR Education & Outreach)
Repairing the Antarctic Ozone Hole (Windows to the Universe)
Ozone Depletion (U.S. EPA)
Because of international agreements to limit CFCs and related emissions instituted with the Montreal Protocol, it's expected that the ozone hole will be slowly healing over the next few decades.
The ozone hole does not directly affect air temperatures in the troposphere, the layer of the atmosphere closest to the surface, although changes in circulation over Antarctica related to the ozone hole appear to be changing surface temperature patterns over that continent. Ozone is actually a greenhouse gas, and so are CFCs, meaning that their presence in the troposphere contributes slightly to the heightened greenhouse effect. The main greenhouse gas responsible for present-day and anticipated global warming, however, is carbon dioxide produced by burning of fossil fuels for electricity, heating, and transportation.
Higher up, the loss of stratospheric ozone has led to some cooling in that layer of the atmosphere. An even larger effect comes from carbon dioxide, which acts as a cooling agent in the stratosphere even though it warms the atmosphere closer to ground level. This paradox occurs because the atmosphere thins with height, changing the way carbon dioxide molecules absorb and release heat. Together, the increase in carbon dioxide and the loss of ozone have led to record-low temperatures recently in the stratosphere and still higher up in the thermosphere. Far from being a good thing, this cooling is another sign that increasing levels of carbon dioxide are changing our planet's climate.
Isn't the natural El Niño cycle to blame for atmospheric global warming?
El Niño events can raise the average global temperature by a few tenths of a degree Fahrenheit for a year or two. Likewise, La Niña events can produce a comparable cooling effect. Neither of these short-lived cyclic phenomena explain the longer-term warming observed in the last century and especially in the last 30 to 40 years.
Isn't there still a lot of debate among scientists?
The scientific method is built on debate among scientists, who test a question, or hypothesis, and then submit their results to the scrutiny of other experts in their field. That scrutiny, known as "peer review," includes examining the scientists' data, experiment and/or analysis methods, and findings.
The spirited debate around remaining uncertainties in climate science is a healthy indicator that the scientific method is alive and well. But the fundamental elements of climate change are not in dispute. To take just a few examples, we understand
• how greenhouse gases such as carbon dioxide trap heat (see above: What is the Greenhouse Effect?)
• how much carbon dioxide we have added to the atmosphere since the Industrial Revolution (see above: How much carbon dioxide?)
• how observed warming has been affecting plants, animals, the ecosystems they live in, and us, the people who depend on them (see previous article: Impacts on Natural Systems)
The questions on this page represent many of those raised by debaters who are not actively engaged in climate research. Whether through lack of understanding, suspicion of science or scientists, economic motives, or other reasons, these questions have been answered again and again with evidence from research that has been tested by the scientific method. Science is a human activity, and no human is infallible, but the science reported by researchers at NCAR and our collaborating institutions around the world is built on decades of investigation and represents the current state of our knowledge on climate change.
The majority of climate scientists who specialize in understanding the complex interactions of our atmosphere, Earth, and Sun have examined the evidence, understood the remaining uncertainties, and concluded that:
Global warming is unequivocal and primarily human-induced (U.S. Global Change Research Program, citing its 2009 report on Global Climate Change Impacts in the United States).
Changes in the atmosphere, the oceans, and glaciers and ice caps now show unequivocally that the world is warming due to human activities (United Nations, citing the IPCC 2007 report).
Here's what the major scientific organizations say about global warming and climate change, including the uncertainties climate scientists continue to examine (each opens a new window):
• Human Impacts on Climate (American Geophysical Union, 2007)
• Statement on Climate Change (American Meteorological Society, 2007)
• Statement on Ocean Acidification (European Geosciences Union, 2008)
What can we do about global warming?
There are two basic types of response to climate change. Mitigation is reducing the emissions of greenhouse gases responsible for climate change, so that less change occurs. Adaptation is dealing with the consequences of warming and other aspects of climate change, such as changes in extreme weather events.
Because some amount of climate change has already occurred, and more change is inevitable based on the greenhouse gases already emitted, society will need to adapt. Yet in order to prevent even more-extreme climate change from happening, mitigation will be required.
Policymakers are now examining these two types of responses, including how much attention and what resources to devote to each one and how to find a balance between mitigation and adaptation.
"Business as usual" is also a choice. This option saves expenditures for mitigation in the near term, but risks higher adaptation costs to wildlife, human populations, infrastructure, and economies later on. It also increases the odds of unforeseen consequences from unchecked climate change.
The 2007 IPCC report helps policymakers weigh these options. To promote discussion of policy choices in our democracy, NCAR's parent organization, UCAR, has joined with professional societies and other members of the atmospheric sciences community to offer policy-relevant Advice to the Administration and Congress: Making Our Nation Resilient to Severe Weather and Climate Change.
As impacts on natural systems are being felt, human adaptation is already happening on some fronts. Many insurance companies are examining their practices and taking climate change into account in setting their rates and their policies. Air conditioning is becoming more widespread in North America and Europe. Some communities on small islands are already making plans to abandon their homes due to rising sea levels. The fate of plants and animals that cannot readily adapt is being discussed.
The United States joined with many other nations in signing a treaty in 1994 known as the United Nations Framework Convention on Climate Change. The UNFCCC, which has been ratified by 192 countries, recognizes that the climate system has no boundaries and that international cooperation is needed to seek solutions to the problems posed by rising greenhouse gases.
Considered a first step in a long diplomatic process, the Kyoto Protocol was an early and well-known agreement that emerged from the UNFCCC process. The protocol, which set modest targets for reducing greenhouse gas emissions, was adopted in 1997 and ratified by most countries in the world, though not the United States and Australia. Its targets have been in force for over 180 signatory nations since early 2005. NCAR scientist Tom Wigley's research has shown that adherence to the Kyoto Protocol alone, without subsequent action, would have a minimal impact on global warming. However, he notes, "This does not mean that the actions implied by the Protocol are unnecessary."
An important UNFCCC meeting takes place in 2009. The 15th Conference of the Parties to the UNFCC, or COP 15, will meet in Copenhagen, Denmark, December 7–18, to focus on mitigation and adaptation strategies beyond the Kyoto Protocol, which is set to expire in 2012.
Many U.S. cities and states have committed to reducing their output of greenhouse gases over the coming decades. Mitigation is also happening on the personal level (buying a fuel-thrifty or hybrid vehicle, for instance, or installing energy-saving light bulbs) and in private industry (a growing number of businesses and organizations have pledged to become carbon neutral).
Volunteer "citizen scientists" are recording their observations to provide information about our climate over time. Some researchers are tapping a rich historical record of bird migration and seeking new volunteers to report migration arrivals and departures. A collaboration between public and private agencies hosted by UCAR's Windows to the Universe encourages volunteers to report the timing of budburst in spring. Participants record when dormant plants produce leaves and their flower buds first open in response to climate signals.
CLIMATE KILLERS
Read how Big Oil and Big Coal mounted aggressive lobbying campaigns to block progress on global warming in Jeff Goodell's "As the World Burns."
The Pundit
George Will
Commentator, ABC
From his institutional perches at the Washington Post, Newsweek and ABC's This Week, Will preaches about the "indoctrination" of Americans by "environmental Cassandra’s" in the "media-entertainment-environmental complex" over a climate threat that is "hypothetical" and only "allegedly occurring.
Developing nations to "sacrifice their modernization on the altar of climate change
2
The Inquisitor
Rep. Joe Barton
Republican, Texas
In his view, the climate is changing for "natural variation reasons," and humans should just "get shade" and learn to adapt.
(Barton himself has received $1.4 million from oil and gas donors, plus $1.3 million from electric utilities.)
3
The Power Player
David Ratcliffe
CEO, Southern Company
Ratcliffe, the head of America's second-dirtiest electric utility its largest plant produces more carbon pollution than all of Brazil's power plants combined — and new limits on emissions being considered by the Senate could cost the utility some $400 million a year. He assembled an army of 63 lobbyists twice as many than any other company.
4
God's Denier
Sen. James Inhofe
Republican, Oklahoma
The senator from Oklahoma calls global warming "the greatest hoax ever perpetrated on the American people," insists that carbon dioxide is not "a real pollutant," and doesn't worry about rising sea levels, because, if all else fails, "God's still up there."
In December, the senator also vowed that a resurgent GOP would block the EPA from curbing carbon pollution: "After the 2010 election," he said, "I guarantee we'll have the votes to do it."
5
The Fake Protestor
Jack Gerard
President, American Petroleum
As head of the American Petroleum Institute, Gerard serves as the front man for the nation's oil and gas industry, including energy giants like Exxon, Shell, BP and Halliburton. According to an internal memo leaked in August, Gerard directed API's nearly 400 member companies to mobilize their employees to attend "Energy Citizen" rallies in 20 states to protest a cap on carbon pollution.
In the late 1990s, the institute conspired with Exxon and a cadre of right-wing think tanks to create the "Global Climate Science Communications Action Plan" — an $8 million effort to fund climate research that hypes the "weaknesses in scientific understanding" of global warming.
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The Flip Flopper
Sen. John McCain
Republican, Arizona
Although McCain frames his newfound stance as opposition to what he portrays as a $630 billion tax on corporate America, the measure as revised by the House actually provides the energy industry with more than $690 billion in pollution subsidies.
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The Dirty Democrat
Sen. Mary Landrieu
Democrat, Louisiana
In 2008, after providing the pivotal vote to preserve $12 billion in tax breaks for Big Oil, she received $272,000 from oil and gas interests Landrieu tried to kill climate legislation in the Senate by requiring that it be passed by a 60-vote supermajority.
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The Disinformer
Rupert Murdoch
CEO, News Corporation
In 2007, when the world's most powerful media baron announced his newfound conviction that global warming "poses clear, catastrophic threats," it seemed as though the truth about climate change might finally get the attention it deserves. Since then, however, Murdoch and his media operations have become the nation's leading source of disinformation about climate change. In October, Fox Business ran an extended segment on "The Carbon Myth," inviting a hack scientist to "make the case" that more carbon pollution is actually "good for the environment
9
The Arm Twister
Dick Gephardt
CEO, Gephardt Group
Gephardt has emerged as the most credible proponent of "clean coal" — an imaginary technology. ("Clean coal is like healthy cigarettes," says Al Gore. "It does not exist.") In July, Gephardt was the keynote speaker at the Clean Coal Technology Conference, an honor bestowed after he helped win $1 billion in stimulus funding for FutureGen, a "clean coal" boondoggle promoted by Peabody. That's a significant return on the $1.7 million that Peabody and the FutureGen Industrial Alliance have invested in Gephardt Group's services since 2007.
10
Burning Man
Rex Tillerson
CEO, ExxonMobil
Exxon is responsible for 397 million tons of CO2 emissions annually — more than twice those of the nation's dirtiest electric utility Exxon spent $29 million on lobbying in 2008 — second only to the U.S. Chamber of Commerce. And despite vowing to stop its funding of climate denial, it continues to foot the bill for bogus research by right-wing outfits like the Heritage Foundation, which asserts that "growing scientific evidence casts doubt on whether global warming constitutes such a threat."
In a disingenuous attempt to appear serious about the threat of climate change, Tillerson has recently begun to advocate a tax on carbon pollution — a measure he knows has absolutely no chance of passing. In 2007, spending $100 million on ads, Exxon boasted about its investments in renewable energy — even though such deals totaled only $10 million that year.
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The Know Nothing
Tom Donohue
President, U.S. Chamber of Commerce
In the first nine months of last year, the Chamber spent $65 million — three times more than ExxonMobil — mounting a campaign to block Congress from placing limits on carbon pollution. The extreme anti-climate position staked out by Donohue runs counter to the position of his own members.
Of the 23 companies on the Chamber's board that made their position on climate legislation public, only four are against it — and three of those are coal companies. Yet the Chamber claims, in scaremongering language, that climate legislation threatens to "completely shut the country down" and "virtually destroy the United States." For his part, Donohue is proudly ignorant of the risks that a changing climate poses to the business community: "Is the science right? Is science not right? I don't know."
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The Profiteer
Warren Buffett
CEO, Berkshire Hathaway
Despite being a key adviser to Obama during the financial crisis, America's best-known investor has been blasting the president's push to curb global warming.
The Oracle of Omaha has invested billions in carbon-polluting industries, seeking to cash in as the world burns. His conglomerate, Berkshire Hathaway, has added 1.28 million shares of America's biggest climate polluter, ExxonMobil, to its balance sheet. He also purchased the Burlington Northern Santa Fe railroad for $26 billion BNSF is the nation's top hauler of coal, shipping some 300 million tons a year. Although Berkshire is the largest U.S. firm not to disclose its carbon pollution — and second globally only to the Bank of China — its utilities have the worst emissions intensity in America, belching more than 65 million tons of CO2 into the atmosphere in 2008 alone.
As a savvy investor, Buffett would only buy a coal-shipping railroad if he felt certain that Congress will fail to crack down on climate pollution.
That's a strange position for the billionaire to take, given that he's promised to donate more than 80 percent of his fortune to the Bill & Melinda Gates Foundation. "
