TODAY’S STUDY: WHAT THE PUBLIC DOESN’T KNOW ABOUT CLIMATE CHANGE WILL BE COSTLY

Americans’ Knowledge of Climate Change
Anthony Leiserowitz, Nicholas Smith, Jennifer R. Marlon, October 2010 (Yale Project on Climate Change Communication)

Executive Summary

Americans’ Knowledge of Climate Change reports results from a national study of what Americans understand about how the climate system works, and the causes, impacts, and potential solutions to global warming.

The study found that 63 percent of Americans believe that global warming is happening, but many do not understand why. In this assessment, only 8 percent of Americans have knowledge equivalent to an A or B, 40 percent would receive a C or D, and 52 percent would get an F. The study also found important gaps in knowledge and common misconceptions about climate change and the earth system. These misconceptions lead some people to doubt that global warming is happening or that human activities are a major contributor, to misunderstand the causes and therefore the solutions, and to be unaware of the risks. Thus many Americans lack some of the knowledge needed for informed decision-making in a democratic society. For example, only:

• 57% know that the greenhouse effect refers to gases in the atmosphere that trap heat;

• 50% of Americans understand that global warming is caused mostly by human activities;

• 45% understand that carbon dioxide traps heat from the Earth’s surface;

• 25% have ever heard of coral bleaching or ocean acidification.

Meanwhile, large majorities incorrectly think that the hole in the ozone layer and aerosol spray cans contribute to global warming, leading many to incorrectly conclude that banning aerosol spray cans or stopping rockets from punching holes in the ozone layer are viable solutions.

However, many Americans do understand that emissions from cars and trucks and the burning of fossil fuels contribute to global warming, and that a transition to renewable energy sources is an important solution.

In addition, despite the recent controversies over “climategate” and the 2007 IPCC report, this study finds that Americans trust scientists and scientific organizations far more than any other source of information about global warming. Americans also recognize their own limited understanding of the issue. Only 1 in 10 say that they are “very well informed” about climate change, and 75 percent say they would like to know more. Likewise, 75 percent say that schools should teach our children about climate change and 68 percent would welcome a national program to teach Americans about the issue.

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Introduction

Knowledge about climate change can be divided into several general and overlapping categories: knowledge about how the climate system works; specific knowledge about the causes, consequences, and potential solutions to global warming; contextual knowledge placing human-caused global warming in historical and geographic perspective; and practical knowledge that enables individual and collective action.

This study included measures related to each of these key dimensions, along with other measures such as public desire for more information, trust in different information sources, and climate change risk perceptions, policy preferences, and behaviors.

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Methodology

These results come from a nationally representative survey of American adults, aged 18 and older. The sample was weighted to correspond with US Census Bureau demographic and Gallup political party identification parameters for the United States. The surveys were conducted by Knowledge Networks, using an online research panel of American adults. The survey was conducted June 24 through July 22, 2010 with 2,030 American adults. The margin of sampling error is plus or minus 2 percent, with 95 percent confidence. Question order and wording can also introduce error into the results of surveys.

For analysis, some items were re-coded as a 1 (a correct answer) or 0 (an incorrect answer, including don’t know & refused). For example, several questions asked respondents whether a statement was “definitely true”, “probably true”, “probably false”, or “definitely false”. These responses were converted into a simple true vs. false dichotomous measure. Likewise, questions that provided the response options “a lot”, “some”, “a little”, “not at all” or “don’t know” were also converted into simple dichotomous variables for analysis.

In some cases, there is a clear “correct” or “incorrect” answer, strongly supported or strongly rejected by well-established scientific evidence. In other cases, there is a “best” answer reflecting broadly held scientific agreement, but somewhat more subjective. We provide references to peerreviewed, scientific sources for each answer (see the Appendix: Answer Key). Best or correct answers are indicated with a (√). Unknown or uncertain answers are indicated with a (*). All results show percentages among all respondents, unless otherwise labeled. Totals may occasionally sum to more than 100 percent due to rounding. The term “order of items randomized” refers to a standard survey technique in which questions and/or response categories are presented to respondents in a random order. This technique helps to prevent “order bias” in respondent answers.

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Grading the Public

As a first-brush estimate of overall public knowledge about climate change, a straight grading scale was constructed, using only those items for which there was a correct or best answer. To adjust for the difficulty of some items, only questions that were answered correctly by at least 25 percent of the respondents were included in the grade calculation (although all results are reported below in the results section). Thus this “grade” is based on a total of 81 individual questions. Each respondent was given a percentage score based on their total number of correct answers. Graded on a straight scale (scores 90% and above = A, 80-89% = B, 70-79% = C, 60-69 = D, and scores 59% and below = F), 1 percent of the public received an A, 7percent a B, 15 percent a C, 25 percent a D, and 52 percent an F, indicating that relatively few Americans have an in-depth understanding of climate change.

This “grade”, however, should be interpreted with caution. Some questions clearly were harder to answer than others. Likewise, other researchers might have chosen to assess different types of climate-related knowledge, which perhaps the public better understands. It is also important to recognize that very few Americans have ever taken a formal course on climate change, so it is perhaps unsurprising that they lack detailed knowledge about the issue. Instead, these results likely reflect the unorganized and sometimes contradictory fragments of information Americans have absorbed from the mass media and other sources. Further, many of these questions are outside the everyday practical needs of most people. Most people don’t need to know about climate change in their daily life, thus it is not surprising that they have devoted little effort to learning these details.

Nonetheless, many of these questions reveal important gaps in knowledge and common misconceptions about climate change and the earth system. These misconceptions lead some people to doubt that climate change is happening or that human activities are a major contributor, to misunderstand the causes and therefore the solutions, and to be unaware of the risks. Thus many Americans lack some of the knowledge needed for informed decision-making about this issue in a democratic society.

To further adjust for the difficulty of some questions, we constructed a curved grading scale as an alternative scoring system. First, the mean percentage score was calculated (54%). Scores +/- 0.5 standard deviations from the mean (44% to 65%) were assigned the letter grade C. Scores ranging from +/- 0.5 to 1.5 standard deviations from the mean were assigned the letter grades B (66% to 86%) and D (23% to 43%) respectively. Finally, scores ranging from +/- 1.5 to 2.5 standard deviations from the mean were assigned the letter grades A (87% or higher) and F (22% or less) respectively.

This grading system thus enables us to see that although overall public knowledge of climate change is low, there is significant variation within these scores, with a third of Americans scoring an A or B on this curved scale, over a third scoring a C, and over a quarter scoring a D or F. This grading system will be particularly useful for subsequent analyses comparing the relative levels of knowledge across different groups within American society.

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Summary Results

Self-reported Knowledge

• Relatively few Americans (11 to 14%) say they are “very well informed” about how the climate system works or the different causes, consequences, or potential solutions to global warming, while 51 to 52 percent say they are “fairly well informed.”

Climate Change Beliefs and Worry

• A majority (63%) of Americans understand that global warming is happening, while 19percent say it is not happening, and 19 percent say they don’t know.

• Half of Americans (50%) say that if global warming is happening, it is caused mostly by human activities. Over a third (35%) say that if it is happening, it is caused by natural changes, while 7 percent reject the question and say global warming is not happening.

• Thirty-nine percent (39%) say that most scientists think global warming is happening, while 38 percent say there is a lot of disagreement among scientists whether or not global warming is happening.

• Just over half of Americans say they are very (16%) or somewhat worried (39%) about global warming, while 45 percent say they are not very (26%), or not at all worried (19%).

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Understanding of the “Greenhouse Effect”

• A large majority of Americans (87%) have heard of the “greenhouse effect”, but 13 percent have not.

• Of those that have heard of the greenhouse effect, however, 66 percent correctly understand that it refers to “gases in the atmosphere that trap heat.” Twenty-one percent incorrectly believe it refers to the Earth’s protective ozone layer, while another 10 percent say they don’t know. Thus nationally, 57 percent of American adults have both heard of and correctly understand what the greenhouse effect is.

• Majorities of Americans correctly understand that greenhouse gases, changes in the Earth’s orbit around the sun, volcanic eruptions, the amount of dust in the atmosphere, sunspots, clouds, and whether the Earth’s surface is light or dark colored (albedo) can affect the average temperature of the Earth. Many incorrectly believe, however, that earthquakes and the phases of the moon also affect the Earth’s temperature. Finally, 16 to 33 percent of Americans say they don’t know whether any of the above can affect the average global temperature of the Earth.

• A plurality (45%) of Americans understand that carbon dioxide is good at trapping heat from the Earth’s surface. Relatively few, however, understand that methane (25%) or water vapor (12%) are important heat-trapping gases as well.

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Weather vs. Climate

• Majorities of American adults correctly understand that weather often changes from year to year (83%) and that “climate” means the average weather conditions in a region (74%). Majorities, however, incorrectly believe that the climate often changes from year to year or that “weather” means the average climate conditions in a region, suggesting that many people continue to confuse weather and climate.

The Flow of Heat Across the Planet

• A slight majority (54%) understands that ocean currents carry heat from the equator toward the poles, but 34 percent say they don’t know whether this is true or false. Fewer Americans (33%) correctly understand that the atmosphere does not carry heat from the poles (which are cold) towards the equator (which is warm), while 40 percent say they don’t know.

Climate Change: Past and Present

• A majority of Americans (73%) correctly understands that current conditions are not colder than ever before in Earth’s history, but a majority (55%) incorrectly believes the opposite – that the Earth’s climate is now warmer than it has ever been before (this is false – global temperatures have been warmer than current conditions many times in the past).

• A majority of Americans (67%) correctly understands that the Earth’s climate has not been the same for millions of years, but a large majority (67%) incorrectly believes that the Earth’s climate has always shifted gradually between warm and cold periods.

• Fewer than half of Americans (41%) understand that the last 10,000 years have been unusually warm and stable, compared to the climate of the past million years.

• While a majority (57%) understands that rising levels of carbon dioxide in the atmosphere have caused global temperatures to increase in the past, relatively few (24%) understand that the converse is also true – that rising temperatures have caused levels of carbon dioxide in the atmosphere to increase as well. (Global temperatures and carbon dioxide levels can influence each other through positive or negative feedbacks.)

• A majority (63%) believes that climate changes have played an important role in the advance or collapse of some past human civilizations.

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Temperature Estimates

• Respondents were given the current temperature of the Earth’s surface (approximately 58º Fahrenheit) as a reference point. They were then asked what they thought the average temperature was during the last ice age. The correct answer is between 46º and 51º. The median public response, however, was 32º – the freezing point of water – while many other people responded 0º.

• Americans, however, did much better estimating the Earth’s surface temperature 150 years ago (before the Industrial Revolution). The correct answer is approximately 56 to 57º Fahrenheit. The median public response was 54º.

• When asked what temperature they thought it would be by the year 2020 if no additional actions are taken to reduce global warming, the median response was 60º, slightly higher than the scientific estimate of 58.4º Fahrenheit.

• Likewise, when asked what temperature they thought it would be by the year 2050, the median response was 62º, slightly higher than the scientific estimate of 60 to 61º Fahrenheit.

Conceptual Models of Climate Change

• Americans have very different mental models of the stability of the climate system. Respondents were shown a series of simple pictures and text describing 5 different models of climate stability and asked which one best represented their understanding of how the climate system works. A third (34%) selected a “threshold” or “tipping point” model describing a stable climate, but stable only within certain limits. In this model, a small amount of global warming will have little to no effect, but a large amount of warming will cross critical thresholds and have dangerous effects. By contrast, nearly a quarter (24%) selected a “gradual” model describing a climate slow to change, in which global warming will gradually lead to dangerous effects. Next, 21 percent of Americans selected a “random” model describing a completely unpredictable climate system, in which we do not know what will happen. Finally, relatively few chose a “fragile” model describing a delicately balanced climate, in which a small amount of global warming will have abrupt and catastrophic effects (11%) or a “stable” model, describing a very stable climate system that will be unaffected by global warming (10%). At different time or spatial scales the climate system can exhibit each of these behaviors, but the best overall answer is the threshold model.

Fossil Fuels

• Most Americans correctly understand that coal (80%) and oil (76%) are fossil fuels. They are a little more confused, however, about natural gas – 60 percent correctly identify it as a fossil fuel, but 17 percent say it is not, while an additional 23 percent say they don’t know. Most Americans also correctly understand that solar energy and hydrogen are not fossil fuels, but 28 percent incorrectly believe that wood is a fossil fuel.

• Americans have a limited understanding of where the energy in fossil fuels originally came from. Just over half (52%) correctly understand that the energy in fossil fuels comes from photosynthesis by plants over millions of years, while 29 percent correctly understand that the sun was the ultimate source of energy in these fuels. Nearly half (47%) incorrectly say that fossil fuels are the fossilized remains of dinosaurs. Twenty percent of Americans say fossil fuels come from uranium in the Earth. Finally, substantial numbers (25-36%) say theydo not know whether each of these answers are true or false.

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Carbon Dioxide

• A large majority of Americans (67%) correctly identifies carbon dioxide as a gas produced by the burning of fossil fuels.

• Over three-quarters of Americans (76-78%) say they simply don’t know how much carbon dioxide was in the atmosphere in 1850 or today. Very few (6-7%) correctly understand that there were roughly 290 parts per million of carbon dioxide in the atmosphere in 1850, compared to 390 parts per million today.

• When presented with five simple graphs describing different trajectories of the amount of carbon dioxide in the atmosphere over the past 500 years, 40 percent of the public correctly selects the graph depicting exponential growth. Another 41 percent select the graph depicting a linear rise, while fewer than 10 percent choose each of the other three graphs depicting no change in the amount of carbon dioxide, a linear decrease, or an exponential decrease.

• A majority of Americans (62%) correctly understands that even if human beings were to stop burning fossil fuels today, global warming would not immediately stop, however, 57 percent incorrectly believe that the amount of carbon dioxide in the atmosphere would decrease almost immediately or don’t know.

• Likewise, few Americans (19%) correctly understand that on average carbon dioxide stays in the atmosphere hundreds to thousands of years once it has been emitted.

• Americans are equally likely to believe that either China (36%) or the United States (34%) is the world’s largest emitter of carbon dioxide. China recently supplanted the United States as the world’s largest emitter.

• A plurality (42%) of Americans correctly understands that the United States emits the most carbon dioxide per person. However, nearly a third (31%) say they don’t know, while 18 percent incorrectly say China.

Causes of Global Warming

• Majorities of Americans correctly understand that cars and trucks, burning fossil fuels for heat and electricity, deforestation, and cows contribute to global warming.

• Majorities of Americans, however, incorrectly believe that the hole in the ozone layer, toxic wastes, aerosol spray cans, volcanic eruptions, the sun, and acid rain contribute to global warming.

• A majority believes that nuclear power plants also contribute to global warming. Nuclear power plants do not emit greenhouse gases when they generate energy, although there are emissions associated with plant construction, operation, decommissioning, and the mining and milling of uranium.

• Almost half of Americans (49%) incorrectly believe that the space program contributes to global warming.

Climate Skeptic Arguments

• Many Americans incorrectly believe that since scientists can’t predict the weather more than a few days in advance, they can’t possibly predict the climate of the future (42%) or that computer models are too unreliable to predict the climate of the future (37%).

• A third of Americans (35%) incorrectly believe that in the 1970s, most scientists were predicting an ice age.

• A third of Americans (33%) also incorrectly believe that since the Earth’s climate has changed naturally in the past, humans are not the cause of global warming today.

• Relatively few (19%) incorrectly believe that any recent global warming is caused by the sun, that the record snowstorms last winter in the eastern U.S. prove that global warming is not happening (18%), or that the Earth is actually cooling, not warming (15%).

• Only 12 percent of Americans say that global warming is happening, but will be more
beneficial than harmful.

• All of these items, however, include from 19 to 47 percent of Americans who say they don’t know whether these statements are true or false.

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Impacts

• A large majority (68%) of Americans correctly understands that global warming will cause some places to get wetter, while others will get drier.

• Likewise 58 percent correctly understands that global warming will increase crop yields in some places, and decrease it in others.

• Half of the public (51%) correctly understands that the decade from 2000 to 2009 was warmer than any other decade since 1850.

• More than half (59%) of Americans incorrectly believe that global warming will cause temperatures to increase by roughly the same amount in all countries, or say they don’t know (some regions of the Earth will warm much more than others).

• Twenty-one percent of Americans correctly understand that most of the glaciers on Earth are melting. By contrast, 11 percent say all of them are melting, 48 percent say only some of them are, and 4 percent say none of them are melting.

• Of those who said that all, most, or some of the Earth’s glaciers are melting, the large majority (84%) correctly understands that the speed of melting has increased over the past 100 years.

• Large majorities correctly understand that the melting of land ice in Antarctica (76%), mountain glaciers (73%), and warmer ocean temperatures (60%) are causes of global sea level rise.

• A large majority (76%) also says that the melting of sea ice on the Arctic Ocean is a cause of sea level rise. For many years, it was assumed that sea ice melting would not contribute to sea level rise, as the ice already displaced an equal amount of water (which is why your glass of ice water does not overflow when the ice cubes melt). This assumption, however, has been challenged by recent research that finds a small, but significant contribution to global sea levels from Arctic sea ice as well, due to the difference in density and temperature between sea ice (fresh water) and the ocean below (salt water) (see Appendix).

• Most Americans, however, probably do not understand the above nuance, as evident in their response to the next question, which asked which of the listed causes has contributed the most to sea level rise so far. Arctic sea ice is the most commonly selected answer (34%), with Antarctic land ice second at 24 percent. The correct answer, however, is thermal expansion by the warming oceans (22%).

• Majorities of Americans say they simply do not know how much global sea levels rose from 1900 to 2000 (57%) or how much they may rise by 2100 (48%), if no additional actions are taken to reduce global warming.

• Large majorities of Americans have read or heard nothing about either coral bleaching (75%) or ocean acidification (77%).

• Of those Americans who have heard of these two climate-change related issues, 54 percent correctly understand that warmer ocean temperatures cause coral bleaching, while 32 percent correctly understand that absorption of carbon dioxide by the ocean causes ocean acidification.

Solutions

• Large majorities of Americans correctly understand that the following actions would reduce global warming if they were done worldwide: switching from fossil fuels to renewable energy sources (75%), planting trees (81%), reducing tropical deforestation (73%); switching from gasoline to electric cars (75%), driving less (76%), increasing public transportation (67%), switching from regular incandescent to compact fluorescent bulbs (69%), insulating buildings, (65%), and switching from fossil fuels to nuclear power (59%).

• Large majorities of Americans, however, incorrectly believe that reducing toxic waste (67%) or banning aerosol spray cans (69%) would reduce global warming. An additional 43 percent incorrectly believe that if we stopped punching holes in the ozone layer with rockets, it would reduce global warming.

• Majorities do not believe or don’t know if placing a large tax on all fossil fuels (53%), having at most 2 children per family (60%), or stopping the eating of beef (69%) would reduce global warming.

• Finally, large majorities of Americans do not believe that proposed geo-engineering solutions – like fertilizing the ocean to make algae grow faster (64%) or using airplanes to scatter dust high in the atmosphere (81%) – will reduce global warming, including more than 4 out 10 who say they simply don’t know.

• When asked which one action would do the most to reduce global warming, switching from fossil fuels to renewable energy sources was the action most selected (36%).

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Information Sources

• Americans’ most trusted sources of information about global warming are the National Oceanic and Atmospheric Administration (NOAA) (78%), the National Science Foundation (74%), scientists (72%), science programs on television (72%), natural history museums (73%), and science museums (72%).

• Roughly a quarter of Americans have visited a science, technology, or natural history museum in the past 12 months, while more have visited a nature center (37%) or zoo or aquarium (43%).

• Relatively few Americans (8%) have ever attended a global warming lecture or event with hands-on activities, while 14 percent have seen an exhibit on global warming at a science center or museum.

• Americans say they have learned the most about global warming from television (88%), newspapers (71%), family and friends (69%), books or magazines (68%), and the internet (65%).

• Nearly 4 out of 10 Americans (39%) say they follow news about the environment very (7%) or somewhat closely (32%), while 71 percent say they follow the local weather forecast very (32%) or somewhat closely (39%).

• Americans say they have thought about global warming a lot (17%), some (35%), a little (33%), or not at all (15%).

• Just over a quarter (27%) say that the issue of global warming is either extremely (7%) or very important to them personally (20%).

• A large majority, however, says that they need a lot more (25%), some more (26%), or a little more information (25%) about global warming before making up their mind about the issue.

• Americans say that the internet (38%) is the first place they would go to get more information about global warming, followed by television (16%), and government websites (12%).

• Finally, large majorities of Americans say that schools should teach our children about the causes, consequences, and potential solutions to global warming (75%) and that the government should establish programs to teach Americans about the issue (8%).