Common Denier Arguments

Deniers continue to repeat several arguments long after they have been debunked by experts. In the past, deniers have contended (and some continue to argue) that the world is not warming. Overwhelming amounts of data from throughout the world have made that argument so fallacious that the deniers have now shifted their contention; claiming that humans are not responsible for the warming. Because the basic physics of greenhouse gases has been well-established, along with the fact that human activity has generated billions of tons of greenhouse gases, make this argument untenable, the denier argument has shifted further. Some deniers now concede that warming will occur, but that impacts will be minimal, and some argue that even if climate change will have impacts, it will cost too much for us to do anything about it. Of course, the cost of failing to act will be much higher.

What follows are some common denier arguments and responses from leading scientific organizations, including the Intergovernmental Panel on Climate Change (IPCC), the US National Academy of Sciences, and the United Kingdom’s science academy, the Royal Society.

The Arguments and Responses


“Temperatures are not actually increasing they’re even dropping in some places.”

Climate is an overall average over a period of time (usually 30 years). Climate change refers to a shift in this average across the whole planet or a significant portion of the planet. A common denier tactic is to point to a narrow geographic area that may have seen relatively constant or even cooler temperatures in recent years. In fact, the earth as a whole has been warming for most of the last century. According to the IPCC, “surface temperatures have increased by about 0.74C (1.33F) over the past hundred years,” with especially rapid warming over the second half of the 20th century. Each decade since the 1970s has been warmer than the decade before it, and 9 of the 10 warmest years on record have been recorded since 2000. Global average temperature comes from many sources, including thousands of land and sea measurements taken every day, weather balloons, and satellites.

(IPCC 4th Assessment Working Group I, FAQ 3.1. The Royal Society’s Climate change: a summary of the science. NASA Goddard Institute for Space Studies, Global Temperature in 2011, Trends, and Prospects.)

global land temp index
Global Annual Mean Surface Air Temperature Change.
Source: NASA.

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“There was a drop in global temperatures around the middle of the last century. Therefore, climate change is not happening.”

According to the IPCC, the global average temperature increase of 0.74C (1.33F) over the last century occurred in two phases. First there was an increase of 0.35C (0.63F) in the global average temperature from the 1910s to the 1940s, followed by a slight cooling of 0.1C (0.18F), and then a rapid warming of 0.55C (0.99F) up to the end of 2006. Warming has continued since the IPCC’s last assessment came out, with 2010 tying 2005 for the warmest year on record. The mid-century dip in global average temperatures was caused by industrialization after World War II, which led to increased pollution from aerosol sulfates. Some aerosols tend to have a cooling effect. The slight drop in global average temperature observed mid-century, therefore, has been accounted for and does nothing to disprove climate change.

In addition, scientists have modeled historical conditions with the best estimates of natural (e.g., volcanic eruptions) and human-made (e.g., increased concentration of greenhouse gases in the atmosphere, aerosol sulfates from industrial activities) factors that affect climate. The figure shows that the models capture very well the observed “cooling” from 1940 to 1970, which as explained above, was due to sulfate aerosols from industrial activity. The volcanic eruption in 1963 (vertical line showing the eruption from volcano Agung in Indonesia) also played a role. Particles from large volcanic eruptions enter the stratosphere and remain there for long periods of time cooling surface temperatures for a few years. The models cannot replicate the observed overall warming in the last 100 years if only natural factors affecting our climate are considered. Model simulations that take into account both natural factors that affect climate and the observed increased concentration of greenhouse gases in the atmosphere explain very well the observed overall warming of our planet.

(IPCC 4th Assessment Working Group I, FAQs 2.1, 3.1 and 9.2. NASA Goddard Institute for Space Studies, Global Temperature in 2011, Trends, and Prospects.)

physical science chart
Global Mean Temperatures from Observations & Simulations.
Source: IPCC.

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“There isn’t a correlation between rising temperatures and CO2 emissions therefore, humans can’t be causing climate change.”

This is false as humans have put more greenhouse gases into the atmosphere, the global average temperature has indeed gone up. The amount of CO2 in the atmosphere began steadily rising since the mid 1800s, and increased more rapidly over the past 50 years. Ice cores and other evidence show that the current level of CO2 in the atmosphere is higher than any time in the last half-million years. Temperature increases followed this trend, with the second half of the 20th century being the warmest 50 year period in the past 1,300 years.
(IPCC 4th Assessment Working Group I, FAQs 6.2, 7.1, and 9.2.)

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ghg impacts
Concentrations of Greenhouse Gases from 0 to 2005. Source: IPCC.

“Greenhouse gases aren’t causing climate change it’s actually the sun, volcanoes, or some other source.”

Natural changes do have an impact on the climate. Output from the sun has increased gradually over the past 150 years, which has warmed the planet to a small degree. Volcano eruptions can also have short term (2-3 years) effects on the climate. However, scientists account for these natural changes in their climate models to show the difference between natural changes and human activities over long time-scales.
(IPCC 4th Assessment Working Group I, FAQ 2.1. The Royal Society’s Climate change: a summary of the science.)


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“Global temperatures have been high in the past. The current temperature increase is nothing new or unique, but just natural variation.”

Description: Drought Conditions Experienced on August 28 in the Contiguous United States
Drought Conditions Experienced on August 28 in the Contiguous United States
Source: U.S. Drought Monitor.

The world’s average temperature has varied naturally throughout the earth’s history, and has been higher at times than today. However, the rate at which greenhouse gases and temperatures are increasing is unique, and points to human factors. Increases in global CO2 concentrations and temperature that occurred over thousands of years in the past are now happening in decades. As the IPCC points out, “there is no evidence that this rate of possible future global change [upper end projections of 5C (41F) by the end of the century] was matched by any comparable global temperature increase of the last 50 million years.” Furthermore, climate models that only take natural processes into account cannot reproduce the level of warming the planet has experienced over the past century. When they factor in human activities, however, the models accurately match the level of observed warming.
(IPCC 4th Assessment Working Group I, FAQs 6.2 and 9.2. The Royal Society’s Climate change: a summary of the science.)

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“Climate models are unreliable.”

Actually, climate models are very good at modeling climate. They are less accurate when used to predict local and specific details. The models are designed to be computer representations of how our climate works. Of course, computer models have limits based on our level of scientific knowledge and computer capacity. That is true of all models, from the simplest to the most complex. Scientists are very confident in their climate models because those models have accurately reproduced past global temperature observations. They are based on physical laws, and different models over several decades have shown a similar and unambiguous picture of significant climate warming resulting from greenhouse gas emissions. Models remain valuable and essential tools for simulating, understanding, and predicting climate.
(IPCC 4th Assessment Working Group I, FAQ 8.1.)

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Description: Map of Changes in Areas Burned for a 1C Increase in Global Average Temperature
Map of Changes in Areas Burned for a 1C Increase in Global Average Temperature (Shown as the Percentage Change Relative to the Median Annual Area Burned During 1950-2003).
Source: National Research Council / Rob Norheim.

“We can’t even predict next week’s weather. How can future climate predictions be accurate?”

This relates to the idea that climate is “average weather” over time. While the weather on any particular day can be chaotic and difficult to predict, we still know long-term averages in temperature and rainfall. For example, we know that in California, that it is likely that a day in August each year will be warmer than a day in January in each year, even if we can’t predict the exact temperature for a day two weeks away. Climate science is not trying to predict the weather on a given day in the future. Rather, its focus is on how general trends will change over time. All indications are that the average global weather will get warmer in the future.
(IPCC 4th Assessment Working Group I, FAQ 1.2.)

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“There isn’t a scientific consensus on climate change. Lots of scientists have signed a petition against it.”

In fact, there is a very strong scientific consensus that climate change is occurring and is caused by humans. Recent studies have shown that about 97% of active climate researchers agree that climate change is human-caused. And the few who disagree have substantially less climate expertise than the 97%. Some years ago, a petition rejecting a consensus on climate change garnered press attention, with its proponents claiming they had collected thousands of signatures from scientists. In truth, the signatories largely had training irrelevant to climate science such as veterinary medicine or no scientific expertise at all.
(Anderegg et al. (2010). Doran and Zimmerman (2009).)

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“Scientists are out for personal gain, publishing alarmist studies to capture research grants.”

There is no evidence to support this argument. Scientists who participate in the IPCC climate assessments are not paid, nor are those who participate in panels for the National Academy of Sciences. Career advancement in the sciences is not based on holding popular views, but on publishing original research. By contrast, many deniers have received funding from entities with a financial stake in fossil fuel-based energy system.

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“Dissenting scientists are stifled and can’t publish their research.”

There is no evidence to support this either. All research goes through a peer review process in which it is evaluated for quality and relevance by other experts. Research that doesn’t pass muster is sent back to the author to be corrected and improved. Research that is not published does not meet the standards of good science.

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“The Climategate scandal showed that scientists have manipulated data to invent the climate problem.”

“Climategate” was coined to refer to a series of hacked emails from climate researchers at the University of East Anglia in 2009. No evidence of scientific wrongdoing was ever found. No fewer than seven committees, including bodies from the U.S. and British governments, looked into the emails and all reached the conclusion that the scientists committed no research misconduct, their results were accurate, and nothing in the emails refuted the overwhelming evidence of climate change.
(House of Commons Science and Technology Committee, March 24, 2010; University of East Anglia, April 12, 2010; Pennsylvania State University, June 4, 2010; The Independent Climate Change Emails Review, July 2010; U.S. Environmental Protection Agency, July 29, 2010; U.S. Department of Commerce, February 24, 2011; National Science Foundation, August 15, 2011)

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“Maybe greenhouse gases will cause warming, but the presence of more clouds will have a cooling effect and minimize warming.”

Clouds are a complex piece of the climate system. They may have either a cooling or warming effect, either reflecting sunlight away from the earth (cooling) or trapping heat close to the planet and preventing it from escaping to space (warming). As the earth begins to warm, the amount and properties of clouds could change. The nature of this change is still uncertain. While the effect of clouds on the climate is genuinely an area where more research is needed, there does not appear to be much evidence that we will be saved by clouds.
(The Royal Society’s Climate change: a summary of the science. Chambers et al. (2002). Hartmann and Michelsen (2002). Trenberth et al. (2010).)

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“So what if it gets warmer? More CO2 and warmer weather might be beneficial.”

Description: Projected Impacts on Coral Reefs as a Consequence of an Increase in Ocean Acidification due to a Rising Atmospheric CO2 Concentration.
Projected Impacts on Coral Reefs as a Consequence of an Increase in Ocean Acidification due to a Rising Atmospheric CO2 Concentration.
Source: World Bank / Hare et al. 2011, Rogelj et al. 2010, Schaeffer et al. 2012.

Climate change will create winners and losers. Some temperate regions will benefit from warmer weather and longer growing seasons. However, the negative impacts will be far more extensive and far more devastating. Sea level rise will threaten coastal areas and island nations, severe weather events like droughts, floods, and hurricanes will become more frequent and intense, and water supply will be affected by declining snowmelt, to name a few. These impacts have severe economic, environmental, and public health and safety implications. Furthermore, the Department of Defense has recognized the likelihood that climate change will have national security implications, contributing to instability and conflict in the world. This could include conflict over food and water scarcity, exacerbated poverty, and further weakening of unstable governments.


Several scientific studies document the adverse impact that climate change is likely to have on crops and the food supply.  Agriculture is a major industry in California: there are approximately 81,000 farms and ranches.  California agriculture is nearly $43.5 billion dollar industry and it generates at least $100 billion in related economic activity.  The state has a diversity of highly nutritious specialty crops that are susceptible to increased pests, limited water resources, and numerous other effects in what is predicted to be a warmer future climate in California. The United States produces a significant amount of the world's corn and soybean supply.  While slightly higher temperatures are initially beneficial to these two crops, overall higher temperatures are very harmful.  Increases in temperatures and CO2 may benefit some crops in certain regions.  But, to realize these benefits, plant nutrient levels, soil moisture, water availability, and other conditions for optimum yields must also be met.
(IPCC 4th Assessment Working Group I, FAQs 3.2, 5.1, and 10.1.
Department of Defense. Quadrennial Defense Review (2010). p. 85.
Wolfram Schlenker and Michael J. Roberts, Nonlinear temperature effects indicate severe damages to U.S. crop yields under climate change (2009). California Department of Food and Agriculture, CDFA History. Stephen P Long, Elizabeth A Ainsworth, Andrew D.B Leakey, and Patrick B Morgan, Global food insecurity. Treatment of major food crops with elevated carbon dioxide or ozone under large-scale fully open-air conditions suggests recent models may have overestimated future yields (2005). United States Environmental Protection Agency, Agriculture and Food Supply Impacts & Adaptation (2012). Long SP, Ainsworth EA, Leakey AD, Nsberger J, Ort DR, Food for thought: lower-than-expected crop yield stimulation with rising CO2 concentrations (2006).)
Hogy P., Wieser H., Kohler P., Schwadorf K., Breuer J., Franzaring J. 2009. Effects of elevated CO2 on grain yield and quality of wheat: results from a 3-year free-air CO2 enrichment experiment. Plant Biology. 11: 60-69.
Seneweera S., Makino A., Mae A., Basra A.S. 2005. Response to rice to CO2 enrichment: the relationship between photosynthesis and nitrogen metabolism. Ecological Responses and Adaptations of Crops. 13: 31-53.
Luedeling E., Steinmann K.P., Zhang M., Brown P.H., Grants J., Girvetz E.H. 2011. Climate change effects on walnut pests in California. Global Change Biology. 17: 228-238.
Luedeling E., Zhang M., Girvetz E.H. 2009. Climate change lead to declining winter chill for fruit and nut trees in California during 1950-2099. PLoS ONE 4: e6166. doi:10.1371/journal.pone.0006166.)

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“Ok, maybe climate change is happening, but it’ll cost too much to mitigate it.”

Of course it will cost money to reduce our pollution and switch to clean energy. It will require investment in new technology, a requirement to pay the true price of dirty energy, and a shift in how we do business. However, the cost of inaction will be far higher. The Organization for Economic Cooperation and Development estimated that mitigating climate change would slow world Gross Domestic Product (GDP) growth by about 0.2 percentage points per year, costing 5.5% of global GDP in 2050, but that climate change impacts would be as high as 14% of GDP, almost triple the cost of effective action. The Stern Review, conducted for the British Government, estimated the cost of inaction could be even higher. That report pegged the cost of effective mitigation at about 1% of global GDP annually by 2050, and the cost of climate change impacts at as high as 20% of global GDP.
(OECD Environmental Outlook to 2050: The Consequences of Inaction (2012). Stern Review on the Economics of Climate Change (2006).)

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