AAAS: Earth’s climate on path to warm beyond anything experienced in “past millions of years”; action needed to lower costs & risks of catastrophic and irreversible impacts. [General Commentary]
POSTED FOR COMMENTARY BY THE CCNF SCIENTIST COMMUNITY
The American Association for the Advancement of Science (AAAS) — the world’s largest non-governmental and general scientific society and the executive publisher of the respected peer-reviewed journal Science — released a report on global warming on Tuesday. The report, titled “What We Know,” is meant to serve as an accessible assessment of current climate science and impacts “for every American.” According to the AAAS press release, the report “emphasizes the need [for the public] to understand and recognize possible high-risk scenarios.” Speaking on behalf of the Society, AAAS CEO Dr. Alan Leshner, stated that “[w]e believe we have an obligation to inform the public and policymakers about what science is showing about any issue in modern life, and climate is a particularly pressing one. […] As the voice of the scientific community, we need to share what we know and bring policymakers to the table to discuss how to deal with this issue.”
The report intends to communicate what the authors call “the three R’s of climate change.” These include the “reality” that human-caused climate change is happening, the “risks” posed by climate change, and our possible “response.” Here is an excerpt from the summary on the AAAS website:
1. Climate scientists agree: climate change is happening here and now. Based on well-established evidence, about 97% of climate scientists have concluded that human-caused climate change is happening. This agreement is documented not just by a single study, but by a converging stream of evidence over the past two decades from surveys of scientists, content analyses of peer-reviewed studies, and public statements issued by virtually every membership organization of experts in this field. Average global temperature has increased by about 1.4˚ F over the last 100 years. Sea level is rising, and some types of extreme events – such as heat waves and heavy precipitation events – are happening more frequently. Recent scientific findings indicate that climate change is likely responsible for the increase in the intensity of many of these events in recent years.
2. We are at risk of pushing our climate system toward abrupt, unpredictable, and potentially irreversible changes with highly damaging impacts. Earth’s climate is on a path to warm beyond the range of what has been experienced over the past millions of years.[ii] The range of uncertainty for the warming along the current emissions path is wide enough to encompass massively disruptive consequences to societies and ecosystems: as global temperatures rise, there is a real risk, however small, that one or more critical parts of the Earth’s climate system will experience abrupt, unpredictable and potentially irreversible changes. Disturbingly, scientists do not know how much warming is required to trigger such changes to the climate system.
3. The sooner we act, the lower the risk and cost. And there is much we can do. Waiting to take action will inevitably increase costs, escalate risk, and foreclose options to address the risk. The CO2 we produce accumulates in Earth’s atmosphere for decades, centuries, and longer. It is not like pollution from smog or wastes in our lakes and rivers, where levels respond quickly to the effects of targeted policies. The effects of CO2 emissions cannot be reversed from one generation to the next until there is a large- scale, cost-effective way to scrub carbon dioxide from the atmosphere. Moreover, as emissions continue and warming increases, the risk increases.
By making informed choices now, we can reduce risks for future generations and ourselves, and help communities adapt to climate change. People have responded successfully to other major environmental challenges such as acid rain and the ozone hole with benefits greater than costs, and scientists working with economists believe there are ways to manage the risks of climate change while balancing current and future economic prosperity.
As scientists, it is not our role to tell people what they should do or must believe about the rising threat of climate change. But we consider it to be our responsibility as professionals to ensure, to the best of our ability, that people understand what we know: human-caused climate change is happening, we face risks of abrupt, unpredictable and potentially irreversible changes, and responding now will lower the risk and cost of taking action.
In terms of substance, length, and intended audience, “What We Know” is strikingly similar to “Climate Change: Evidence & Causes,” a similar plain-language summary recently released by the National Academy of Sciences and the U.K.’s Royal Society. One difference between the two reports is that “What We Know” focuses more on the potential worst case scenarios in the current projections. The report’s authors state that the reason for this is “[g]iven the high stakes, it is valuable to understand not just what is most likely to happen, but what might possibly happen to our climate.” [UPDATE: For more on the need to understand and communicate this “tail risk” of climate change, see Dr. Kerry Emanuel’s recent post on CCNF, titled “Tail Risk vs. Alarmism.”] Part two of the report, titled “Climate Risks,” identifies the following as “high-side” projections:
- 8˚ F increase in temperatures by 2100 which would be irreversible for hundreds of years (the report notes that 8˚ F is almost the same difference in temperature between the ice age and our modern time);
- massive shift in precipitation patterns and concentrations;
- sea level rise of up to 6 to 7 feet by 2100, which would “rende[r] many cities and communities uninhabitable as is,” and a rise of up to 16 feet in the distant future;
- ecosystems collapse due to climate change and ocean acidification; and
- abrupt climate change occurring “over periods as short as decades or years,” which could be brought on by positive feedbacks triggered by such events as ice sheet collapse on a large scale, the collapse of part of the Gulf Stream, dieback of the Amazon forest, or coral reef die-off. The report also states that abrupt climate change could result from the “very unlikely” but still possible disruption of the Gulf Stream/Atlantic Meridional Overturning Circulation or a rapid release of methane from the sea floor.
The climate science panel that generated the report was chaired by Nobel laureate Dr. Mario Molina, distinguished professor of chemistry and biochemistry at the University of California, San Diego and Scripps Institution of Oceanography. Dr. Molina won the Nobel Prize in Chemistry in 1995 for discovering that chloroflourocarbons (CFCs)—then common in refrigerators, air conditioners, and hair spray—were destroying the protective layer of ozone in the stratosphere. (Note: Ozone is a good thing high up in the stratosphere, where it is naturally produced and blocks ultraviolate (UV) rays from harming life on Earth, but a bad thing in the troposphere, where it acts as main ingredient of smog and is harmful to breath and damages crops). This led to the international treaty called the Montreal Protocol, which has phased out and banned CFCs and other ozone-depleting substances. The treaty was incorporated in Title VI of the Clean Air Act and has proven successful in reducing the size of the ozone hole according to a recent post by CCNF science columnist Dr. Mauri Pelto. See “Do We Understand the Atmosphere Enough to Identify Problems and Solve Them? Heck Yes, We are Two-for-Two“. The co-chairs of the panel were Dr. Diana Wall, distinguished professor of biology and director at Colorado State University’s School of Global Environmental Sustainability, and Dr. James McCarthy, Alexander Agassiz Professor of Biological Oceanography at Harvard.
The other scientists on the panel included:
- Richard Alley, Pennsylvania State University;
- Kim Cobb, Georgia Institute of Technology;
- Julia Cole, University of Arizona;
- Sarah Das, Woods Hole Oceanographic Institution;
- Noah Diffenbaugh, Stanford University;
- Kerry Emanuel, Massachusetts Institute of Technology;
- Howard Frumkin, University of Washington;
- Katharine Hayhoe, Texas Tech University;
- Camille Parmesan, University of Texas, Austin and University of Plymouth, UK; and
- Marshall Shepherd, University of Georgia.