Latest Myths and Facts on Global Warming

Setting the Record Straight on Climate Change
4/15/2005

A vast majority of climate scientists agree that global warming is happening and that it poses a serious threat to society. They also agree that it is being caused largely by human activities that release greenhouse gases, such as burning fossil fuels in power plants and cars and deforesting the land. These highlights -- and the full full report -- lay out some common myths and misunderstandings regarding climate change.

MYTH: Global warming can't be happening, since winters have been getting colder.
FACT: Winters have been getting warmer. Measurements show that Earth's climate has warmed overall over the past century, in all seasons, and in most regions. The skeptics mislead the public when they bill the winter of 2003-2004 as record cold in the northeastern United States. That winter was only the 33rd coldest in the region since records began in 1896. Furthermore, a single spell of cold weather in one small region is no indication of cooling of the global climate, which refers to a long-term average over the entire planet.

MYTH: Satellite measurements of temperature over the past two decades show a much smaller warming in the atmosphere than is measured by thermometers at the surface. This contradicts global warming predictions based on climate models.
FACT: Recent research has corrected problems that led to underestimates of the warming trend in earlier analyses of satellite data. The new results show an atmospheric warming trend slightly larger than at the surface, exactly as models predict.

MYTH: The global warming over the past century is nothing unusual. For example, the Medieval Warm Period (MWP), roughly from A.D. 1000 to 1400, was warmer than the 20th century. This indicates the global warming we are experiencing now is part of a natural cycle.
FACT: Ten independent scientific studies all have found a large 20th-century warming trend compared to temperature changes over the past millennium or two. Uncertainty exists as to exactly how warm the present is compared to the MWP. Some studies have received valid criticism for possibly underestimating the magnitude of longer-lasting, century-scale temperature changes, such as the warming during the MWP. However, other studies, using different methods, still find no evidence of any period during the last 2,000 years that was warmer than the 1990s. Most importantly, any uncertainty about whether the present is warmer than the MWP has little effect on the finding that humans likely have caused most of the warming over the past 50 years. A separate body of studies has provided the main evidence for this finding. (See the Myth on causes of warming.)

MYTH: Human activities contribute only a small fraction of carbon dioxide (CO2) emissions, far too small to have a significant effect on the concentration of the greenhouse gas in the atmosphere.
FACT: Before the Industrial Revolution, the amount of CO2 emitted from large natural sources closely matched the amount that was removed through natural processes. That balance has now been upset by human activities, which since the Industrial Revolution have put twice as much CO2 into the atmosphere as can be readily removed by the oceans and forests. This has resulted in the accumulation of CO2 to the highest levels in 420,000 years.

MYTH: The Earth's warming is caused by natural factors like increased sunlight and sunspots or decreased cosmic rays, not by greenhouse gases (GHGs).
FACT: Modeling studies indicate that most of the warming over the past several decades was probably caused by the increase in human-produced GHGs. Climate models have difficulty reproducing the observed temperature changes over the past 150 years unless they account for the increase in GHGs as well as natural factors, such as sunlight and volcanic eruptions, and changes in the amount of human-produced sulfate particles, which cool the planet. Satellite measurements of the intensity of sunlight exhibit little or no trend over the past 25 years, when there was rapid warming on Earth. The purported correlations between the amount of cosmic rays and Earth's temperature are the result of flawed analysis methods.

MYTH: The warming observed during the past century was caused by urbanization (urban heat island effect).
FACT: Urbanization does increase temperatures locally, affecting thermometer readings in certain areas. But the temperature data used in trend analyses are adjusted to remove any bias from urbanization. In any case, urbanization has an insignificant effect on global temperature trends.

Read the full report, The Latest Myths and Facts on Global Warming. Adobe Acrobat required

MYTH: Models have trouble predicting the weather a few days in advance. How can we have any confidence in model projections of the climate many years from now?
FACT: Climate prediction is different from weather prediction, just as climate is different from weather. Models are now sophisticated enough to be able to reproduce the observed global average climates over the past century as well as over other periods in the past. Thus, scientists are confident in the models' ability to produce reliable projections of future climate for large regions. Furthermore, climate assessments typically consider the results from a range of models and scenarios for future GHG emissions, in order to identify the most likely range for future climatic change.

MYTH: The science behind the theory of global warming is too uncertain to draw conclusions useful to policy makers.
FACT: The primary scientific debate is about how much and how fast, rather than whether, additional warming will occur as a result of human-produced GHG emissions. While skeptics like to emphasize the lower end of warming projections, uncertainty actually applies to both ends of the spectrum--the climate could change even more dramatically than most models predict. Finally, in matters other than climate change, policy decisions based on uncertain information are made routinely by governments to ensure against undesirable outcomes. In the case of global warming, scientists have given society an early warning on its possibly dangerous, irreversible and widespread impacts.

MYTH: Global warming and increased CO2 would be beneficial, reducing cold-related deaths and increasing plant growth ("greening the Earth").
FACT: If society does not limit further warming, the beneficial effects probably will be heavily outweighed by negative effects. Regarding cold-related deaths, studies have indicated that they might not decrease enough to compensate for a significant increase in heat-related deaths. Even though higher levels of CO2 can act as a plant fertilizer under some conditions, they do not necessarily benefit the planet, since the fertilization effect can diminish after a few years in natural ecosystems as plants acclimate. Furthermore, increased CO2 may benefit undesirable, weedy species more than others.

MYTH: Society can easily adapt to climate change; after all, human civilization has survived through climatic changes in the past.
FACT: While humans as a species have survived through past climatic changes, individual civilizations have collapsed. Unless we limit GHGs in the atmosphere, we will face a warming trend unseen since the beginning of human civilization. Many densely populated areas, such as low-lying coastal zones, are highly vulnerable to climate shifts. A middle-of-the-range projection indicates the homes of 13 to 88 million people would be flooded by the sea each year in the 2080s. Many ecosystems and species already threatened by other human activities may be pushed to the point of extinction.

MYTH: CO2 is removed from the atmosphere fairly quickly, so we can wait to take action until after we start to see dangerous impacts from global warming.
FACT: Global warming cannot be halted quickly. CO2 and other GHGs can remain in the atmosphere for many centuries. Even if emissions were eliminated today, it would take centuries for the heat-trapping GHGs now in the atmosphere to fall to pre-industrial levels. Only by starting to cut emissions now can humanity avoid the increasingly dangerous and irreversible consequences of climate change.

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