A Project of The Annenberg Public Policy Center

Climate Change Review


At the United Nations’ Conference of the Parties in Paris, 195 countries approved an agreement that commits nearly every country to reducing greenhouse gas emissions in an effort to slow global warming. The nations pledged to take action designed “to hold global temperature rise to well below 2 degrees Celsius,” as United Nations Secretary-General Ban Ki-moon announced on Dec. 12.

The agreement had been six years in the making, since the collapse of climate change talks in Copenhagen in 2009. Prior to reaching a final accord, 186 countries already had submitted mitigation contribution plans to the U.N. Under the new agreement, all countries will update those plans by 2020 and revise them every five years thereafter to meet the global climate change goals.

With the climate change announcement, we provide here a recap of false and misleading claims about climate change that we have fact-checked in recent years.

The ‘Hiatus’

Those who reject mainstream climate science often claim that there has been no warming for 17 years — a claim that relies on cherry-picked data, as we have written about before. By starting with 1998, a particularly warm year, the amount of warming over that time period appears smaller than starting with 1997 or 1999. The far more relevant long-term trend, however, is unequivocal: Fourteen of the 15 hottest years ever recorded have occurred this century, and 2014 was likely the warmest year on record. The National Oceanic and Atmospheric Administration says 2015 is “extremely likely” to supplant it.

SciCHECKinsertAs explained by NOAA, the Intergovernmental Panel on Climate Change concluded in 2012 that the “global surface temperature trend from 1998­­-2012 was markedly lower than the trend from 1951-2012.” However, a new report published in the journal Science by NOAA scientists has called that conclusion “no longer valid.”

The researchers updated temperature data sets to better reflect the readings taken from ships and floating buoys, as well as from land-based temperature stations. They found that the warming trend from 2000 to 2014 was 0.116 degrees C per decade – a number that is “virtually indistinguishable” from the earlier and longer period from 1950 through 1999 (0.113 degrees C per decade). Even if they shifted the more recent trend to 1998 through 2014, which features a very warm starting year, the trend was similar — 0.106 degrees C per decade.

Cruz on the Global Cooling Myth and Galileo,” March 27, 2015

Satellite Data

Rep. Lamar Smith, chairman of the House Committee on Science, Space, and Technology, claimed that satellite data in particular “has clearly showed [sic] no warming for the past two decades.” In a Dec. 9 interview on National Public Radio, Sen. Ted Cruz made a similar claim, saying “[f]or the last 18 years, the satellite data … that actually measure the temperature showed no significant warming whatsoever.” This is misleading.

There have been discrepancies between surface and satellite data — but that does not “invalidate the fact that surface temperatures are rising” and global warming is occurring, as NOAA explains on its FAQ Web page.

Satellites have been taking measurements since 1979. The various satellite data sets of the temperature in the troposphere (the lowest atmospheric layer) — including from NOAA, from a research company called Remote Sensing Systems and from a research group at the University of Alabama in Huntsville — disagree. But the UAH data set is the only one to show a lack of warming. Though there is some disagreement on the best ways to adjust and interpret satellite data, studies have indicated that correcting the UAH data in certain ways (specifically, removing a particular source of satellite error known as diurnal drift) would yield similar results to other data sets, indicating more warming.

NOAA says the corrections of “some measurement and calibration problems” bring the satellite record “into better agreement with surface measurements.”

Smith Misfires on Climate Science,” Nov. 5, 2015

Bears and Climate Change

Senate Minority Leader Harry Reid in August made the claim that climate change is causing bears in the Sierra Nevada mountains to change their hibernation patterns. But there is no evidence that climate change is actually having such an effect.

We could find no published evidence regarding changes to black bear hibernation, and biologist Jesse Garcia of the California Department of Fish and Wildlife told us that “we have no data or specific evidence” that black bears in the Sierras have changed their hibernation patterns. Black bears are not “true” hibernators and they “will often display some mid-winter activity,” Garcia said.

The Bear Facts,” Aug. 14, 2015

Climate Consensus

Sen. Rick Santorum in September criticized the oft-cited fact that 97 percent of scientists agree that human activity is primarily responsible for warming, saying that figure is “bogus” and comes from a single study. Several surveys involving thousands of researchers have all found that the level of consensus is about 97 percent.

The 97 percent number comes from several distinct sources. The first was a 2009 survey published in the American Geophysical Union’s Eos magazine. A year later, another study published in Proceedings of the National Academy of Sciences found a similar result.

Most recently, a 2013 paper published in the journal Environmental Research Letters analyzed 11,944 journal article abstracts published from 1991 to 2011 that matched the search terms “global climate change” or “global warming.” From that list of papers, the study authors identified which ones expressed a position on anthropogenic — human-caused — global warming. Of the 4,014 papers that took a position, 97.1 percent endorsed the idea that humans are causing global warming. A second analysis in that same study asked 8,547 authors to rate their papers. Did they think their papers endorsed the consensus on warming? A total of 1,189 scientists responded, rating 2,142 individual papers. The results: 97.2 percent of the papers endorsed the consensus that humans are causing global warming.

Santorum’s Climate Consensus Claims,” Sept. 2, 2015

Glaciers Growing?

In September, former Alaska Gov. Sarah Palin questioned the scientific evidence that human activity causes global warming, and cited the fact that some glaciers in Alaska are expanding. But an individual glacier’s growth does not disprove the existence or causes of global warming. In fact, the vast majority of glaciers in Alaska and around the world are losing ice rapidly.

In a study published in the journal Geophysical Research Letters in July, researchers from the University of Alaska at Fairbanks, the U.S. Geological Survey and the University of Washington in Seattle measured the “mass balance” of 116 glaciers in Alaska — of 616 named and many thousands of unnamed glaciers, representing 41 percent of the total glacial area — and extrapolated the results to the rest of the state. They found that Alaska’s glaciers are losing 75 gigatons of ice every year. A gigaton is equal to 1 billion metric tons of ice.

Palin Off on Glaciers and Global Warming,” Sept. 9, 2015

Volcanoes vs. Human Activity 

Former Arkansas Gov. Mike Huckabee in July said a single volcanic eruption “will contribute more than 100 years of human activity” toward global warming. Actually, it is estimated that humans pump upward of 100 times as much carbon dioxide into the atmosphere every year than all the world’s volcanoes combined.

According to a summary of evidence by the U.S. Geological Survey, the entire collection of volcanoes around the world emits an average of 0.26 gigatons of CO2 per year. (Again, a gigaton is equal to 1 billion metric tons.) Humans today, on the other hand, emit more than 30 gigatons every year, from power plants and factories, cars and airplanes, agriculture, and other activities. According to the Energy Information Administration, humans worldwide emitted 32.3 gigatons of CO2 in 2012, the most recent year for which complete data are available.

So that means humans collectively are responsible for nearly 125 times as much CO2 entering the atmosphere every year as volcanoes.

Huckabees’ Hot Air on Volcanoes,” July 29, 2015

U.S. Carbon Dioxide Emissions

In his State of the Union address in 2014, President Obama boasted that the U.S. “reduced our total carbon pollution more than any other nation on Earth.” That’s accurate in terms of sheer tonnage of emissions reduced, but the U.S. is the second-largest emitter of carbon dioxide emissions. Dozens of countries reduced their emissions by a larger percentage than the U.S.

On ABC’s “This Week” on Dec. 13 — as well as in a press conference on Dec. 12 — Secretary of State John Kerry repeated the president’s claim. “And the fact is, the United States of America has already reduced its emissions more than any other country in the world,” Kerry said on “This Week.”

However, even with the benefit of another year of data, our conclusion remains the same. While the U.S. is the biggest reducer in terms of overall tonnage, there are other countries with a higher percentage reduction than the U.S.

A State Department official told us Kerry was looking at the change between 2003 and 2012, the latest data from the U.S. Energy Information Administration available for international comparison (even though in the press conference Kerry referred to the effect of “President Obama’s plans,” which obviously did not take effect until 2009). Nonetheless, by that measure the U.S. reduced emissions by 583 million metric tons, more than any other country. But that was a 10 percent reduction, while, for example, France (10.7 percent) and the United Kingdom (12.9 percent) saw larger percentage reductions. And while international data are not yet available beyond 2012, EIA data for the United States show emissions increased 2.5 percent in 2013 and 0.9 percent in 2014, mostly due to an increase in the gross domestic product as the country recovers from the Great Recession.

Facts of the Union,” Jan. 29, 2014

‘Zero Impact’?

Santorum falsely claimed in January that U.S. policies aimed at reducing greenhouse gas emissions “will have zero impact” on climate change. The U.S. is the world’s second-largest emitter of carbon dioxide, after China, and while it’s true that the U.S. can’t solve the problem of global warming by itself, emissions reductions by the U.S. could indeed play a role in slowing the rise of global temperatures.

For example, in August 2012, the Obama administration finalized rules that will increase fuel-economy standards for vehicles to 54.5 miles per gallon by 2025. The administration estimated that the new fuel standards could reduce oil consumption by 12 billion barrels through 2025, which would mean a reduction of 5.16 billion metric tons of carbon dioxide through the life of the program.

A study published in the journal Nature suggested that to avoid catastrophic warming, about one-third of all the remaining oil reserves (and higher percentages of coal and natural gas) needs to stay in the ground. A single U.S. policy — such as increasing fuel-economy standards to 54.5 mpg — would represent almost 5 percent of that amount.

The U.S. also could have an indirect impact, climate scientists told us, because its leadership on the issue could spur a global movement to cut down on the carbon dioxide emissions that are warming the planet. The climate agreement struck in Paris may be an example of that, depending on how the U.S. and future governments comply with the agreement and to what extent the agreement is effective in slowing global warming.

Distorting Climate Change Threats, Solutions,” Jan. 28, 2015

Temperature Data ‘Falsified’?

Rep. Gary Palmer, a Republican from Alabama, falsely claimed in February that temperature data used to measure global climate change have been “falsified” and manipulated.

Palmer cited the so-called Climategate episode of six years ago, in which emails written by climate scientists purportedly showed evidence of data manipulation, and a more recent accusation of climate scientists tampering with data from temperature monitoring stations. The Climategate scandal has been subject to several separate investigations, all of which exonerated all scientists involved from any wrongdoing. And the latest data manipulation charges are a mischaracterization of standard, well-validated and peer-reviewed methods for adjusting temperature records to eliminate factors that could produce inaccurate readings.

Palmer’s claim that “we are building an entire agenda on falsified data” has no basis in evidence. Even as these claims of data manipulation have resurfaced, there is now a general consensus that 2014 was likely the hottest single year since temperature record-keeping began. This same conclusion has been reached by NOAA and NASA, the Japan Meteorological Agency, and the World Meteorological Organization. According to NASA, nine of the 10 warmest years have all occurred since 2000, with 1998 the lone exception.

Nothing False About Temperature Data,” Feb. 12, 2015

Was 2014 the ‘Warmest Year’?

In April, President Obama said that 2014 was “the planet’s warmest year on record.” Several major climate monitoring organizations have found that 2014 is more likely than any other year to have been the warmest. But statistical uncertainties inherent to calculating global temperatures make the president’s definitive claim problematic.

Given the margin of error associated with global average temperature calculations, it is possible that 2005 and 2010 were warmer. The president would have been on firmer ground had he said 2014 was “most likely” the planet’s warmest year on record.

Obama and the ‘Warmest Year on Record,’ ” April 20, 2015

Climate Change and Severe Weather

In a Wall Street Journal opinion piece, Rep. Lamar Smith wrote that a connection between worsening storms and climate change has been “widely debunked,” and that the United Nations doesn’t believe that warming is related to “more severe weather disasters.” Both claims are incorrect. There is some evidence linking climate change to worsening hurricanes, droughts and other disasters.

We asked Smith’s office for supporting evidence, and his office sent us a number of links to and quotes from various documents from the Intergovernmental Panel on Climate Change, the United Nations body that releases periodic reports on the entirety of climate change science. Smith’s citations were generally cherry-picked lines from very long and complicated reports. The list ignored other lines from the same reports, as well as evidence published elsewhere.

A 2014 summary published jointly by the U.S. National Academy of Sciences and its British equivalent, the Royal Society, agrees that the science on hurricanes in general is not settled, but that hurricanes are likely to become larger and more powerful as the world warms. There is also evidence that warming will make hurricanes more intense, and extreme weather events — like droughts and heavy precipitation events — worse.

The Extreme Weather-Warming Connection,” April 30, 2015

‘Significant Shortcomings’ in U.N. Climate Reports?

In his op-ed, Smith also misrepresented an InterAcademy Council report as saying the U.N.’s climate reports had “significant shortcomings in each major step” of the U.N.’s assessment process.

The InterAcademy Council is a group made up of major science academies from around the globe — including the U.S. National Academy of Sciences — that provides advice to international bodies such as the United Nations. Its 2010 report did find problems with the methods and structure in U.N. climate reports. But Smith was cherry-picking. The council’s general assessment was that “[t]he Committee found that the IPCC assessment process has been successful overall.”

The Extreme Weather-Warming Connection,” April 30, 2015

Human Contribution to Global Warming

Republican presidential candidate Jeb Bush claimed that the science is unclear as to how much humans contribute to global warming. In fact, the United Nations climate change research organization says it is “extremely likely” that more than half of the observed temperature increase since 1950 is due to human activities.

In response to a question about climate change during an event in New Hampshire, the former Florida governor said that while climate change is occurring, “I don’t think the science is clear of what percentage is man-made and what percentage is natural. I just don’t — it’s convoluted. And for the people to say the science is decided on this is just really arrogant, to be honest with you.”

According to the U.N.’s Intergovernmental Panel on Climate Change’s fifth assessment report that was released in 2013, it is “extremely likely” (meaning between 95 percent and 100 percent certain), that human activities caused more than half of the observed global warming between 1951 to 2010. In its summary for policymakers, the IPCC stated, “The best estimate of the human-induced contribution to warming is similar to the observed warming over this period.” In other words, the best guess is that humans have caused essentially all of the warming that has occurred.

Jeb Bush Off on Contributions to Warming,” May 22, 2015

Editor’s Note: SciCheck is made possible by a grant from the Stanton Foundation.

— compiled by Eugene Kiely and Robert Farley