What is the right diagnosis?

Published: 5:09 AM GMT on April 21, 2014

What is the right diagnosis?

April 22, 2014 is Earth Day, and I will be giving a talk at an Earth Day event in Ann Arbor, Michigan. I was asked to talk about the weather and if it is changing due to human-caused climate change. Yes it is. There are some safe conclusions about climate change due to increasing carbon dioxide: the planet is warming, ice is melting, sea level is rising and the weather is changing. All of these changes are occurring and all will continue. The more specific question that was posed to me by the meeting organizers was whether or not the changes in Arctic sea ice were leading directly to recent weather-climate events in the U.S. Perhaps even more specific, will people in Michigan see more winters like the winter of 2013-2014 in the future? Thanks to a small snowfall last week, Southeast Michigan set a record.

Thinking about recent news as a possible starting point for my talk, the last few weeks have seen the release of both the IPCC Working Group II and Working Group III assessment reports. Briefly, Working Group II assesses the impacts of global warming and Working Group III focuses on how to limit the impacts through reduction of greenhouse gas emissions. For each of these reports there was a very short flurry of press coverage. The one sentence takeaways: Working Group II - The impacts are large and emerging faster than expected. Working Group III - We still have the wherewithal to avoid dangerous climate change if we reduce greenhouse emissions by an enormous amount in the next few decades.

Also in the last few weeks there has been more discussion in the blog-press about changes in Arctic sea ice leading to changes in the atmospheric jet stream leading to California drought and the very cold and snowy winter in the eastern half of the United States. (We just don’t mention Alaska enough – so let’s add the absurdly warm winter in Alaska.) (Rood’s summary a few weeks ago)

On Climate Progress there is an entry Study Ties Epic California Drought and “Frigid East” to Manmade Climate Change. Joe Romm’s blog entry reports on a paper by Wang et al. on probable causes of the California drought. Indeed Wang et al. state (in an early publication release), “Therefore, there is a traceable anthropogenic warming footprint in the enormous intensity of the anomalous ridge during winter 2013-14, the associated drought and its intensity.”

This paper stands in contrast to an opinion piece in the New York Times by Martin Hoerling entitled Global Warming, Not Always. In this piece Dr. Hoerling states, “At present, the scientific evidence does not support an argument that the drought there is appreciably linked to human-induced climate change.” Hoerling argues that there are analogues of the current drought in the historical record; hence, human-induced climate change is not necessary for severe drought. The current drought is distinguished by the huge demand for water that comes from a large population and high-demand water requirements. Hoerling concludes that as far as attribution of the cause of the drought “the correct diagnosis matters” because it informs how to respond to the drought.

If I think about what to say to an audience at Earth Day, I don’t think that my opinion on whether or not this past winter is “caused” by climate change matters a lot. In my talk I will try to frame the reports and discussion that I mentioned above.

What the recent work on sea ice and the jet stream suggests is plausibility that the recent weather in the U.S. is influenced by changes in the Arctic. The changes in the Arctic are enormous. The spatial extend of the reduction of sea ice is continental and would be expected to have some consequences. In fact, if there is any magical thinking, then it would be to expect there to be no consequences. I admit that there is a lot to be untangled in our understanding, but minimally, that the changes in sea ice might have an impact because it influences patterns of variability is important for planning. It is also important for research because it suggests a relationship between weather, climate and climate change that is traceable.

The argument suggested by the Hoerling piece and Romm’s blog on the Wang et al. paper is a continuation of an argument about event attribution that I consider flawed both scientifically and rhetorically. We live on a planet that is warming. We do not have weather events occurring in a “natural” climate and a “natural plus human changed” climate. The existence of drought analogues in the historical record does not exempt the current drought from influence by human-induced climate change. A similar argument might be that the existence of lung cancer prior to the use of tobacco excludes tobacco as a cause of lung cancer. If there were an absence of drought in past centuries and the presence of drought today that would be compelling. However, if there were no history of drought followed by the onset of drought, then that would suggest that our knowledge and understanding of weather and climate would be profoundly deficient. One of the anchors of our confidence in science-based knowledge of climate change is the ability to look at past analogues and provide nuance related to a warming planet, and for that matter, increased stress on resources by an increasing population.

When I started my climate change class in 2006, a stated goal was to move beyond polarized arguments. Polarization exists as a tactic in political and rhetorical arguments. However, we also see polarized arguments when we look at the relation of climate change to other disciplines: climate-policy, climate-agriculture, climate-ecosystems, climate-population, climate-energy, climate-economy … . We are not, however, at a point where we can separate climate change from population, from consumption, from economics and from energy. The only solution to the mitigation of climate change that we allow as viable is that we find sources of energy that are less damaging to the climate – or really to the environment.

The conclusions of the recent IPCC reports are another brick in the wall. The impacts of climate change are broad and significant. It is hard to argue that we will avoid dangerous climate change when we look at the Arctic. This is especially true if the changes in the Arctic might have an amplified affect on lower latitudes by changing the patterns of weather variability. Even with a magical explosion of existing capability and new technologies to reduce carbon dioxide emissions, we will not return to the Arctic that denied a Northwest Passage to the explorers of the Renaissance.

My message will be that the weather is changing. Also, the relation of weather with people and countries and economies is changing. Weather, what people do and how many people there are – all are changing. Currently, all in a way to increase people’s vulnerability. In the short term, we can make decisions to improve our resilience and reduce our vulnerability. If we think that the weather in the future will be the same as the weather of the past, then that will be wrong. There is no world in which we live that is uninfluenced by our emissions of many pollutants, including carbon dioxide, as well as our changes to the land and oceans. We make a mistake if we dismiss human-induced climate change as not influencing the weather each and every day.


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About The Author
I'm a professor at U Michigan and lead a course on climate change problem solving. These articles often come from and contribute to the course.

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