Summary: An eminent climate scientist gives her summary of the debate about the Climate Emergency. Sadly, much of this repeats the messages given us by the IPCC and the major climate agencies. Few people know this because the major news media misrepresent their messages, since claims by alarmists are more exciting and (to them) politically pleasing.
About climate ‘limits’ and timelines
By Judith Curry at Climate Etc., 16 October 2019.
I received the following questions today from a reporter, related to climate change and ‘timelines.’ These questions are good topics for discussion. My answers are provided below
Q: From your perspective, have the early warnings about how hot the Earth is getting turned out to be accurate? Have they been adjusted higher or lower than expected?
Early predictions of warming were 0.2 to 0.3°C/decade were too high relative to actual observations. Further, blaming all of the recent warming on carbon dioxide emissions is incorrect, in my opinion. Solar indirect effects and multi-decadal oscillations of large scale ocean circulations have been effectively ignored in interpreting the causes of the recent warming.
Q: What is the best figure that explains how we will know when things are really irrevocably bad? Is it the 2ºC limit, as some have reported?
‘Bad’ is a value judgment, and regions are affected differently by climate variations and change. Most of the so-called ‘bad effects’ of climate change relate to the natural variability of weather, and there is little to no evidence that extreme weather events have been worsening, against the large variations of natural climate variability.
The single adverse impact that is unambiguously associated with warming (whatever the cause) is a sea level rise. Since 1900, global sea level has risen about 8″. There are substantial temporal and spatial variations of sea level rise, associated with large scale ocean circulation patterns, glacial rebound, weather, and tides. Projections of a sea level rise by 2100 beyond several feet require: implausible scenarios of the amount of carbon dioxide in the atmosphere, climate models that have implausibly high warming sensitivity to the amount of CO2 in the atmosphere, and the collapse of the West Antarctic ice sheet (from speculative and poorly understood processes).
The 2°C limit relates to expectations for long-term (many many centuries) melting of the Greenland and Antarctic ice sheets. The issue of the 2°C limit is better described as ‘planetary diabetes’ rather than extinction or other dire characterizations. Another way of thinking about the so-called 2°C limit is analogous to a highway speed limit. If the speed limit is 65 mph, exceeding that by 10 or even 20 mph is not guaranteed to cause a crash. But if you exceed the limit by a lot, your risk of a fatal crash certainly increases.
Q: How do the actions (or inactions) of the Trump administration, such as withdrawing from the Paris climate agreement, affect that timeline? If Democrats win the government in 2020, would implementing the Green New Deal (if it even passed) be too little, too late?
The actions of President Trump have made no essential difference to this timeline. Most of the signatories to the Paris Agreement are falling far behind in their commitments {details here} – although the U.S. has been doing relatively well in terms of its emissions cuts. Any future success of the Green New Deal relies on both politics and technology. Overwhelming Democratic control of the U.S. government wouldn’t necessarily help with the needed technology developments.
Afterword
The bottom line: these timelines are meaningless. While we have confidence in the sign of the temperature change, we have no idea what its magnitude will be. Apart from uncertainties in emissions and the Earth’s carbon cycle, we are still facing a factor of 3 or more uncertainty in the sensitivity of the Earth’s climate to CO2, and we have no idea how natural climate variability (solar, volcanoes, ocean oscillations) will play out in the 21st century. Even if we did have significant confidence in the amount of global warming coming, we still do not have a handle on how this will change extreme weather events. With regards to species and ecosystems, land use and exploitation are bigger issues.
Cleaner sources of energy have several different kinds of justifications, but thinking that sending CO2 emissions to zero by 2050 or whenever is going to improve the weather and the environment by 2100 is a pipe dream. If such reductions come at the expense of economic development, then vulnerability to extreme weather events will increase.
There is a reason that the so-called climate change problem has been referred to as a ‘wicked mess.’
Reposted under her Creative Commons license.
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About Judith Curry
Judith Curry retired as a Professor of the School of Earth and Atmospheric Sciences at the Georgia Institute of Technology. She is now President and co-owner of Climate Forecast Applications Network (CFAN). Prior to joining the faculty at Georgia Tech, she served on the faculties of the University of Colorado, Penn State University and Purdue University.
She has served on the NASA Advisory Council Earth Science Subcommittee, the DOE Biological and Environmental Science Advisory Committee, the National Academies Climate Research Committee, and Space Studies Board, and the NOAA Climate Working Group.
She is a Fellow of the American Meteorological Society, the American Association for the Advancement of Science, and the American Geophysical Union. Her views on climate change are best summarized by her Congressional testimony: Policy Relevant Climate Issues in Context, April 2013.
Follow Dr. Curry on Twitter at @curryja. Learn about her firm, CFAN, at their website.
For More Information
Ideas! See my recommended books and films at Amazon.
If you liked this post, like us on Facebook and follow us on Twitter. For more information about this vital issue see the keys to understanding climate change. Also, see all posts about uncertainties in climate science, about Judith Curry, and especially these …
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