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Dealing with Uncertainty

When scientists use the word "uncertainty," they mean something slightly different than just not being sure about something. When it comes to climate science, uncertainty has to do with a range of possibilities that could happen in the future, depending on whether humans decrease greenhouse gas emissions, and takes into account that climate systems are variable and difficult to predict. Watch "Uncertainty in Climate Change Modeling" which explores this type of uncertainty with regard to climate change.

Such uncertainty is confusing to those not trained in how to "do" science. Scientists habitually working at the edge between what is known and what is yet unknown are trained to deal with uncertainty. While scientists are still not confident in estimating how much sea level rise we will see within the next century, the rate of sea level rise we will see is uncontroversial. Widely varying estimates of sea level rise published in the press, as well as the unwillingness of the Intergovernmental Panel on Climate Change (IPCC) to make estimates of projected sea level rise in their 2007 assessment contributed little to public confidence in climate change science. Some think that the IPCC's effort to make their report more understandable to the public by using the descriptors Likely, Very Likely, Extremely Likely, and Virtually Certain to describe quantitative probabilistic statements was a further gaffe, because the general public uses these terms regularly in other contexts, confusing what they mean in this scientific context. Do you think the descriptors make the findings of the report more or less confusing?

While the municipalities of New York City and Seattle have chosen to take steps to adapt and mitigate the impacts of climate change on the basis of scientific evidence, others see reported scientific uncertainty as an excuse for discounting the reality of climate change and continuing business as usual.

Part of public perception of scientific uncertainty relates to how non-scientists understand and evaluate data. Why is it that scientists find data to be so compelling? Is there really a conspiracy among scientists who want their research funding to continue despite highly equivocal evidence?

The answer to the last question is no, of course not. Scientists examine a single line of evidence within the context of other evidence, sometimes found in totally different kinds of data using different procedures. Independent lines of evidence that reach the same conclusion can be highly persuasive in a scientific research setting. If many lines of evidence support the same conclusion, even if each line of evidence carries some degree of uncertainty, scientific confidence increases overall. A good example can be found in our reconstructions of past climate. For instance, tree ring data may provide evidence of a change in moisture balance affecting plant growth, but stable hydrogen and oxygen isotope data from the same tree ring sequence can provide independent evidence of a temperature change.

Sea Level Change

Here is where there is a cultural difference between how scientists approach data, and how the public tends to evaluate information outside their area of expertise. Henry Pollack, a scientist on the IPCC and a 2007 Nobel Peace Prize recipient along with Al Gore, summarized this difference succinctly (2007):

"There is a tendency to focus on the weakness of the parts rather than the strength of the whole, supposing that if a single piece of evidence can be discredited the entire construct will fall like a house of cards. In fact, discrediting a single line of evidence is more like snipping a strand in a net hammock-the hammock continues to be supported by the many strands that remain intact. The scientific evidence for climate change in the natural world is compelling in its totality although individual pieces of the story may indeed be open to some question."

As humans, we have all witnessed the immense energy of the Earth's system. We have seen the devastation of earthquakes, tsunamis, volcanoes, hurricanes, and tornadoes, recently with Japan's 9.0 earthquake and tsunami in 2011. In these situations, we feel powerless. It is difficult for many of us to accept that the powerful world around us, making us feel so insignificant, is vulnerable to our seemingly innocuous activities and responds with changes in climate. This predisposes many of us to discounting climate change evidence simply because it flies in the face of our worldview and our role in it.

In summary, one of the benchmarks for grades 9-12 from the Benchmarks for Science Literacy (2007) states:

  • The lack of acceptance of scientific arguments for natural selection by some members of the general public has been affected by their discomfort with its implications, such as the relation of humans to other animals, and their religious beliefs about when and how the world and living things in it were created (10H/H6c).
Do you see any parallels with this statement and with the situation we are confronting as we try and educate our students and the public about climate change?