Ricky Rood is a professor at University of Michigan and leads a course on climate change problem solving. His articles often come from and contribute to the course.
This article was originally published here.
I am nearing the end of the tenth time I have taught my climate change class. This year we focused on climate change science and the Paris Agreement. In particular, we thought about how climate science would contribute to the execution of the Paris Agreement. Towards the end of class, I do what I call a strategic summary and organize some resources to provide memory cues on how to think about climate change and our responses. At the end of that summary, I present my personal analysis. Here are the bullets.
* It will be difficult to avoid a world that is four degrees warmer.
* We have, in fact, underestimated the impacts of warming.
* We have some control over how fast and how far the warming will go.
* We are committed to irreversible changes, for example, sea-level rise.
* We can “cope” with this. We must. There is opportunity.
This list has been largely the same since 2010, and the class analysis of the Paris Agreement did little to change the list.
Realizing the consistency of the list over the years, I went on a search for another list that I made at the end of 2008. We had a presidential transition in the works, and someone working on that transition asked me what I thought the strategic climate-science issues would be for the new president. Here is the list I put together in late 2008.
2) Because of the underestimation of ice melt, sea level rise has been underestimated. We are committed to sea level rise, and we need to plan accordingly.
3) The terrestrial and ocean sinks of carbon dioxide are likely to be less effective than previously stated.
4) The acidification of the ocean is likely to be more disruptive sooner than expected.
Eight years later, I am satisfied that that was a good list. Also, I am shocked that it has been eight years, but that’s a more existential issue. Going into the Conference of the Parties in Paris, I felt that one of the most defining new science-based results was the evidence of loss of some of the West Antarctic Glaciers. (A brief mention in my September 2014 blog) Loss, here, means that we have reached a point where these glaciers will continue to melt, and there is no identified physical mechanism that will stop this melting.
The primary paper mentioned in the excellent NASA press release is by Eric Rignot et al. Widespread, rapid grounding line retreat of Pine Island, Thwaites, Smith, and Kohler glaciers, West Antarctica, from 1992 to 2011. (I don’t see any reference to the actual paper in an otherwise excellent press release, so I assume this is the correct paper.) Rignot and his research colleagues have many excellent publications on both Greenland and Antarctic ice sheets. I also bring attention to a paper by lead author Jeremie Mouginot entitled, Sustained increase in ice discharge from the Amundsen Sea Embayment, West Antarctica, from 1973 to 2013.
It has long been known that some of the glaciers in West Antarctica are “unstable.” This is, primarily, due to the fact that these glaciers are grounded below sea level. Basically, the glaciers extend into the sea. They can extend to the rock surface at the bottom of the sea; they are grounded on bedrock. Alternatively, they can float in water; that is they have water below them. If there is water below the glacier it melts faster. The combination of warming ocean water and a grounding line below sea level, well, that’s a prescription for continuous melting – instability. Flowing warm water is always available to accelerate melting. Here is an explanation from AntarcticGlaciers.org on Marine Ice Shelf Instability.
At the core of these 2014 papers is the study of the bedrock topography; that is, what is the elevation of the rock surface at the bottom of the sea and the bottom of the glaciers. The bedrock topography is measured with space- and air-based radar. For the glaciers to be stable requires that there be some structure in the bedrock that acts, perhaps, like a dam. A conclusion of Rignot et al. paper is, “Upstream of the 2011 grounding line positions, we ﬁnd no major bed obstacle that would prevent the glaciers from further retreat and draw down the entire basin.”
This brings me to two recent papers that have gotten coverage. The first is Contribution of Antarctica to past and future sea-level rise. The authors are Robert DeConto and David Pollard. This paper concludes that if emissions continue on their current path, then past evidence suggests more than a meter of sea-level rise by 2100. The second paper is Ice melt, sea level rise and superstorms: evidence from paleoclimate data, climate modeling, and modern observations that 2 °C global warming could be dangerous. In this paper Hansen et al. conclude that we can see “nonlinearly growing sea level rise, reaching several meters over a timescale of 50–150 years.” These conclusions come from examination and analysis of observations of the climate at past times when the temperature was determined to be comparable to the 2-degree goal that is the policy definition of avoided dangerous climate change. (See also No Way to Slow Down) Both of these papers come with some controversy; however, taken in concert with alignment of present-day observations, theory, and modeling paint a picture of rising sea-level rise that will be measured in feet over the next several decades and continue into the next century. More than the specifics of these papers, there is little evidence of any moderating influences that slow the melting of ice, and the Earth is far more likely to be set up for rapidly melting ice.
In Things Going Fast, I documented other papers that suggested that the effects of warming had been underestimated than in our consensus climate assessments. My last summary bullet from class, above, is that we can and must cope. Here is how I think of this. We know that sea level is going to rise, and there is increasing knowledge that suggests that sea level will rise at or above the highest levels suggested in assessment reports. This rise will be on the time-scale of decades, and after a few decades, the rise will continue, not stabilize. As we make plans and take actions in the next few decades we will collect more knowledge, improve our predictions, and know how our energy portfolio changes. We are moving into a time where we will be required to consider climate change as an essential part of planning and management. In the best of circumstances, the societal impacts will be enormous. What frightens me more than the technological challenges or the cost of adaptation is the inability of governments and societies to take on new approaches to our valuation and use of resources, property, and services. I suspect that our motivations will ultimately follow from a series of increasingly costly weather disasters and the accumulation of smothering evidence of the impacts of a changing climate.
Here are some useful links on our melting ice.
Antarctic Glaciers . org: A comprehensive collection of information on the Antarctic’s ice.
Figure 1: The Washington Post published this excellent graphic on melting of ice sheets, based on DeConto and Pollard, 2016. For description see Why some Antarctic glaciers are disappearing faster than we thought.