Wednesday, August 12, 2020
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Global Warming Grounded in Science

Scientists overwhelmingly agree that human activities have caused global warming. The Feb. 5 opinion article by Jesse Nickles, ‘Global Warming Not Proven by Science,’ is an example of how information about global warming and climate science is commonly misrepresented and manipulated. The graduate students in UC Irvine’s Earth System Science Department find this a ripe opportunity to accurately explain the facts and common misconceptions about climate change and global warming.
What are climate change and global warming? The Earth’s climate has fluctuated naturally over its history on both long and short timescales. This natural climate variation differs from the observed increase of Earth’s average temperature in recent decades, global warming, which is attributed to human activities.
How do we know global warming is happening? The U.N.-sponsored Intergovernmental Panel on Climate Change is made up of over 2,500 top climate scientists from around the world. A consensus statement in their most recent report, ‘The IPCC Fourth Assessment Summary’ (released last week), reads, ‘Warming of the climate system is unequivocal, as is now evident from observations of increases in global average air and ocean temperatures, widespread melting of snow and ice, and rising global average sea level.’ Specifically, 11 of the last 12 years have been among the 12 warmest years since 1850, and the global average temperature is now more than one degree Fahrenheit warmer than at the beginning of the industrial period.
What is the cause of this warming? The same report states with greater than 90 percent confidence that the current warming trend is caused by human activity. The observed increase in human-produced greenhouse gases (e.g., carbon dioxide and methane) in the atmosphere is the primary cause of this warming, which enhances the Earth’s natural greenhouse effect. The burning of fossil fuel and changes in land use are the main human sources of these gases in the atmosphere. The carbon dioxide concentrations in the atmosphere are higher today than they have been in the past 650,000 years.
What are the consequences of global warming? For many people around the world, global warming is predicted to have negative social and economic effects. Sea-level rise, increases in the intensity of tropical cyclones, heavy precipitation events and droughts are all predicted in the 2007 IPCC report. Additionally, these negative effects will have greater impact on those that don’t have the ability to rapidly adapt to climate changes, and are least responsible (i.e., developing countries).
Scientifically, what was wrong with Nickles’ article? Almost everything. To support his views, Nickles cites a letter to an editor, a 1975 Newsweek article, the 1990 IPCC report and Sen. Inhofe (R-Oklahoma), a politician with no scientific background and little support even among politicians for his opinion that humans are incapable of altering Earth’s climate. Of these references, only the 1990 IPCC report should be considered a scientific source, and there have been three such reports since then, each conveying progressively greater confidence that human activity is the cause of global warming. Nickles jokes about not including termite and rice paddy contributions to emissions of methane, yet these sources have long been quantified by scientists (see Table 4.2, IPCC 2001: The Scientific Basis). He accurately states that the plants and oceans are taking up about half of our fossil fuel emissions, but failed to comprehend the implications of the other half accumulating in the atmosphere each year. Overall, Nickles cherry-picked information in an attempt to create controversy where it no longer exists among scientists.
What can be done? The argument has been made that it is not in our economic interest to combat global warming, yet the potential economic impacts of doing nothing may be far greater. With the discovery of the human-caused ozone hole, we have already demonstrated that scientists (including several here at UCI) can accurately identify environmental problems, and with the cooperation of the public and politicians, enact worldwide policies to remedy them. This can be done for global warming too. The first step to implementing policy on global warming is public acknowledgement of the facts.
For further information about the science we recommend the following resources: the IPCC 2007 report ( and the non-profit organization Real Climate ( We invite the public to discuss issues regarding climate change, and have set up an email address for this purpose ( We look forward to hearing from you.

Mariah Carbone
Mark Flanner
Ray Anderson
Chris Doughty
Aaron Fellows
Adrian Rocha
Erin Benoy
Mike Tosca
Fengpeng Sun
Hsun-Ying Kao
Laura Marshall
Nicole Nowinski
Fuu-Ming Kai
Scott Capps
Eun Young Kwan
Neeta Bijoor
Lori Ziolkowski
Steve Beaupre
Mike Lawler
David LeBauer
Tim DeVries
Minhui Lo

Graduate Students,
Department of Earth System Science