U.S. NAS and U.K. Royal Society: Atmos. CO2 has increased 40% since industrial revolution, climate has warmed 0.8°C since 1900 (most of which has occurred recently), substantial warming in store if GHG emissions continue unabated. [For fact checking or general commentary]
POSTED FOR COMMENTARY BY SCIENTISTS
Today the U.S. National Academy of Sciences (NAS) and the Royal Society (RS) released a joint publication titled “Climate Change: Evidence & Causes.” The publication is around 30 pages in length and is highly readable (click on the image below for the full report in PDF). Dr. Ralph J. Cicerone, President of NAS, explained on the Royal Society’s website that the NAS and RS are two of the world’s leading scientific bodies, and, therefore, had “a responsibility to evaluate and explain what is known about climate change, at least the physical side of it, to concerned citizens, educators, decision makers and leaders, and to advance public dialogue about how to respond to the threats of climate change.”
The document begins with the following summary on the science of climate change and its causes:
GREENHOUSE GASES such as carbon dioxide (CO2) absorb heat (infrared radiation) emitted from Earth’s surface. Increases in the atmospheric concentrations of these gases cause Earth to warm by trapping more of this heat. Human activities—especially the burning of fossil fuels since the start of the Industrial Revolution—have increased atmospheric CO2 concentrations by about 40%, with more than half the increase occurring since 1970. Since 1900, the global average surface temperature has increased by about 0.8 °C (1.4 °F). This has been accompanied by warming of the ocean, a rise in sea level, a strong decline in Arctic sea ice, and many other associated climate effects. Much of this warming has occurred in the last four decades. Detailed analyses have shown that the warming during this period is mainly a result of the increased concentrations of CO2 and other greenhouse gases. Continued emissions of these gases will cause further climate change, including substantial increases in global average surface temperature and important changes in regional climate. The magnitude and timing of these changes will depend on many factors, and slowdowns and accelerations in warming lasting a decade or more will continue to occur. However, long-term climate change over many decades will depend mainly on the total amount of CO2 and other greenhouse gases emitted as a result of human activities.
After the summary, the document provides answers, each around one-to-two pages in length, to 20 common questions about climate change. Here are the questions with links to the answers on the Royal Society’s website:
1. Is the climate warming?
2. How do scientists know that recent climate change is largely caused by human activities?
3. CO2 is already in the atmosphere naturally, so why are emissions from human activity significant?
4. What role has the Sun played in climate change in recent decades?
5. What do changes in the vertical structure of atmospheric temperature – from the surface up to the stratosphere – tell us about the causes of recent climate change?
6. Climate is always changing. Why is climate change of concern now?
7. Is the current level of atmospheric CO2concentration unprecedented in Earth’s history?
8. Is there a point at which adding more CO2 will not cause further warming?
9. Does the rate of warming vary from one decade to another?
10. Does the recent slowdown of warming mean that climate change is no longer happening?
11. If the world is warming, why are some winters and summers still very cold?
12. Why is Arctic sea ice reducing while Antarctic sea ice is not?
13. How does climate change affect the strength and frequency of floods, droughts, hurricanes and tornadoes?
14. How fast is sea level rising?
15. What is ocean acidification and why does it matter?
16. How confident are scientists that Earth will warm further over the coming century?
17. Are climate changes of a few degrees a cause for concern?
18. What are scientists doing to address key uncertainties in our understanding of the climate system?
19. Are disaster scenarios about tipping points like ‘turning off the Gulf Stream’ and release of methane from the Arctic a cause for concern?
20. If emissions of greenhouse gases were stopped, would the climate return to the conditions of 200 years ago?
Here’s a sample (Question #7):
Is the current level of atmospheric CO2 concentration unprecedented in Earth’s history?
The present level of atmospheric CO2 concentration is almost certainly unprecedented in the past million years, during which time modern humans evolved and societies developed. The atmospheric CO2 concentration was however higher in Earth’s more distant past (many millions of years ago), at which time palaeoclimatic and geological data indicate that temperatures and sea levels were also higher than they are today.
Measurements of air in ice cores show that for the past 800,000 years up until the 20th century, the atmospheric CO2 concentration stayed within the range 170 to 300 parts per million (ppm), making the recent rapid rise to nearly 400 ppm over 200 years particularly remarkable [figure 3]. During the glacial cycles of the past 800,000 years both CO2 and methane have acted as important amplifiers of the climate changes triggered by variations in Earth’s orbit around the Sun. As Earth warmed from the last ice age, temperature and CO2 started to rise at approximately the same time and continued to rise in tandem from about 18,000 to 11,000 years ago. Changes in ocean temperature, circulation, chemistry and biology caused CO2 to be released to the atmosphere, which combined with other feedbacks to push Earth into an even warmer state.
For earlier geological times, CO2 concentrations and temperatures have been inferred from less direct methods. Those suggest that the concentration of CO2 last approached 400 ppm about 3 to 5 million years ago, a period when global average surface temperature is estimated to have been about 2 to 3.5°C higher than in the pre-industrial period. At 50 million years ago, CO2 may have reached 1000 ppm, and global average temperature was probably about 10°C warmer than today. Under those conditions, Earth had little ice, and sea level was at least 60 metres higher than current levels.
The document then provides a 10 page summary on the basics of climate change and a one page conclusion.
In the report’s conclusion, the authors state that the “physical mechanisms by which changes in amounts of greenhouse gases cause climate changes” are well understood and “most of the recent [warming] is almost certainly due to emissions of greenhouse gases caused by human activities.” The authors recognize that there “remains a range of estimates on the magnitude and regional expression of future change” but state with certainty that “[f]urther climate change is inevitable” and “if emissions of greenhouse gases continue unabated, future changes will substantially exceed those that have occurred so far.”
In the report’s final paragraph, the authors state that this information leaves citizens and governments with a choice:
[T]hey can change their pattern of energy production and usage in order to limit emissions of greenhouse gases and hence the magnitude of climate changes; they can wait for changes to occur and accept the losses, damage and suffering that arise; they can adapt to actual and expected changes as much as possible; or they can seek as yet unproven ‘geoengineering’ solutions to counteract some of the climate changes that would otherwise occur. […]
Our description of the science of climate change, with both its facts and its uncertainties, is offered as a basis to inform that policy debate.
The event commemorating the release began with introductions by NAS President Dr. Ralph J. Cicerone and RS President Sir Paul Nurse and was followed by a discussion with the lead authors moderated by PBS science correspondent Miles O’Brien. The video of the official release and moderated discussion will be available on the Royal Society’s website after March 3rd (see link).
The primary writers for the document were:
- Eric Wolff FRS (UK lead), University of Cambridge
- Inez Fung (NAS, US lead), University of California, Berkeley
- Brian Hoskins FRS, Imperial College London and University of Reading
- John Mitchell FRS, UK Met Office
- Tim Palmer FRS, University of Oxford
- Benjamin Santer (NAS), Lawrence Livermore National Laboratory
- John Shepherd FRS, University of Southampton
- Keith Shine FRS, University of Reading
- Susan Solomon (NAS), Massachusetts Institute of Technology
- Kevin Trenberth, National Center for Atmospheric Research
- John Walsh, University of Alaska, Fairbanks
- Don Wuebbles, University of Illinois
According to the document, the reviewing team was made up of “individuals chosen for their diverse perspectives and technical expertise, in accordance with procedures approved by the RS and NAS.” The document also mentioned that the reviewers provided comments and suggestions, but “were not asked to endorse the views of the writing team, nor did they see the final draft before its release.” The reviewers were:
- Richard Alley (NAS), Department of Geosciences, Pennsylvania State University
- Alec Broers FRS, Diamond Light Source and Bio Nano Consulting (Former President of the Royal Academy of Engineering )
- Harry Elderfield FRS, Department of Earth Sciences, University of Cambridge
- Joanna Haigh FRS, Imperial College London
- Isaac Held (NAS), NOAA Geophysical Fluid Dynamics Laboratory
- John Kutzbach (NAS), Center for Climatic Research, University of Wisconsin
- Jerry Meehl, National Center for Atmospheric Research
- John Pendry FRS, Imperial College London
- John Pyle FRS, Department of Chemistry, University of Cambridge
- Gavin Schmidt, NASA Goddard Space Flight Center
- Emily Shuckburgh, British Antarctic Survey
- Gabrielle Walker, Journalist
- Andrew Watson FRS, University of Exeter
Finally, the document stated that oversight of the review process was provided by the RS Council, with representation by John Pethica (FRS), and the NAS Council, with representation by Dr. Jeremiah Ostriker (NAS).