Climate Change: “Uncertainty” and the Hottest Year on Record

By Roberta Attanasio, IEAM Blog Editor

Over the last month, much has been said about 2014 being the hottest year on record. The first announcement came from the Japan Meteorological Agency during the first week of January. Later, a joint announcement by NASA and NOAA reinforced the finding: 2014 was the hottest year in more than 120 years of record keeping. The joint announcement underscored the significance of two major scientific branches of the US government reaching the same conclusion through separate data analyses. Gavin Schmidt, Director of NASA’s Goddard Institute of Space Studies, said: “This is the latest in a series of warm years, in a series of warm decades. While the ranking of individual years can be affected by chaotic weather patterns, the long-term trends are attributable to drivers of climate change that right now are dominated by human emissions of greenhouse gases.”

“Long-term trend” is the buzzword here. The World Meteorological Organization (WMO) called 2014 the hottest year on record, as part of a continuing trend. However, it specified that 2014 was warmer than other recent years by only a few hundredths of a degree and, therefore, there is minimal difference between the three hottest years ­– 2005, 2010 and 2014. In contrast, the UK’s national weather service, the Met Office, announced that 2014 was one of the hottest years on record globally, but declined to call it the hottest year. Colin Morice, a climate monitoring scientist at the Met Office, said: “We can say with confidence that 2014 is one of ten warmest years in the series and that it adds to the set of near-record temperatures we have seen over the last two decades.” He added that uncertainties in the estimates of global temperature are larger than the differences between the warmest years, thus limiting what can be said about rankings of individual years.

Uncertainty is the impossibility to exactly describe an existing state. In a recent National Geographic article, Joel Achenbach pointed out: “Scientists rarely proclaim an absolute truth or absolute certainty. Uncertainty is inevitable at the frontiers of knowledge.” To the non-scientist, uncertainty is “not knowing,” but to scientists, it is “how well something is known.” Uncertainty is an inherent component of the scientific process—in most cases, science reduces uncertainty without eliminating it.

Climate science is observational; it does not rely on controlled laboratory experiments. It is based on projections made with sophisticated computer codes, modeling a large part of the system. In the name of transparency, climate scientists like to point out the level of uncertainty associated with their model projections. For example, an event is deemed “very likely” if it has a 90% chance of occurring. In other words, uncertainty means risk, and an understanding of this risk is necessary for its management and for decision-making.

The focus on risk plays a major role in guiding discourse on climate policy and can lead to effective solutions. The interest is not only on what is most likely to happen, but also on what might possibly happen.

Unfortunately, when risk is seen as “uncertain,” its role in terms of policy and solutions sometimes shifts—uncertainty then appears to justify inaction. For example, people who doubt climate change often use uncertainty to justify their position, and the statement given by the Met Office provides them with one more chance to point out disagreements between climate scientists.


Photo credit: Rhutu Mantri

But is there real disagreement between the reports from NASA, NOAA, WMO and the Met Office? They all agree on the “long-term trend” of increasing temperatures, and they all acknowledge that the differences between 2005, 2010 and 2014 are minimal. The data certainly shows that 2014 is one of the hottest years on record. More importantly though, the uncertainty about whether 2014 takes first prize should not detract from what we know: carbon dioxide levels keep following an upward trend, polar ice sheets and glaciers are melting, sea levels are rising, oceans are more acidic, and floods, heat waves and droughts are more frequent. Climate change is happening here and now due to human activities. We need to act soon. There is much we can do. Responding now will lower the risk of unpredictable and potentially irreversible events caused by climate change.

7 thoughts on “Climate Change: “Uncertainty” and the Hottest Year on Record

  1. Ray Kinney

    • There are lot of engineers, scientists, and naturalists floating around in this big pot of frogs… I for one smell smoke, makes me suspect a fire somewhere. Maybe we could get a few more firefighters into this stew before we get too warm to think straight, or measure straight.
    How many accurate measurements will it take to look a little harder for the fire? I don’t live in Australia but my toes feel a lot warmer than they used to… here, stick your toes down a little deeper… do you feel it too?

  2. Wayne Landis

    I enjoyed the article and the discussion regarding how models work and that there are differences between them. All of the models that we are now working with regarding climate change point to a warmer environment but there are difference in the exact predictions. Thanks for pointing out how uncertainty is a specific term in science for describing how well we know something as compared to an emotional state regarding how confident a person feels about a topic. I have begun to use certitude instead of uncertainty when describing scientific predictions.

    However, uncertainty is not synonymous with risk and does not generate risk. Risk in the terminology of Integrated Environmental Assessment and Management is the probability of an unwanted effect to a feature of the environment valued by the culture. So that even with no uncertainty about the probability of exposure to the feature of interest and no uncertainty (complete certitude) about the probability of an effect, the resulting probability would be risk.

    There is also a scientific consensus regarding that the current rapid change in climate is do to humans and there has been since 2005. Naomi Oreskes (2004) demonstrated that even with the uncertainty in the models available in the mid-2000s that a consensus was already in place among climate scientists that the observed change was due to human activities. Oreskes is a social scientists and historian of science, particularly qualified for this type of study.

    Thanks for bringing this discussion to our blog.
    Oreskes N. 2004. The Scientific Consensus on Climate Change. Science 306:1686.

  3. Larry Kapustka

    Though the points Wayne makes are mostly valid, one argument he makes and one that is routinely voiced in climate debates, that of consensus among scientists, is not valid. A cursory examination of the history of science reveals many examples in which there was not only consensus, but near unanimous agreement only to be proven wrong later. Consensus does provide comfort, but it is not confirmatory.

    1. wayne Landis

      Please note that I make a distinction between consensus and truth. Consensus is now reached among climate scientists regarding climate change and anthropogenic causation. As scientists, and as I teach my students, we make a clear distinction between consensus and truth. There is now a consensus that the hypothesis that human and their activities are causing climate change has not been falsified although there have been numerous attempts. Popper back in the 1950s codified the idea that we what do as scientists is not define truth but instead focus on falsification. Even when a hypothesis is confirmed by experiment or observation that does not mean truth but not yet falsified, an important distinction.

  4. Simon Suarez

    Granted, uncertainty is an inherent feature of the scientific method. However, there is no consistency among different disciplines. You can look at uncertainty with different lens: the mathematical, philosophical or statistical lens, for example. Governments and businesses often make important decisions taking into account uncertain scientific advice. Because of this, do we suffer the consequences of uncertainty on a daily basis? We need cross-fertilization of ideas for how to represent and communicate uncertainty, especially to government bodies. The methods by which different scientific disciplines communicate these concepts are rarely compared. Uncertainty in global health is not uncertainty in economics and is not uncertainty in climate change.

  5. Melissa M

    Since these reports first appeared there has been good discussion and insight on the situation. NASA should be more careful with public statements. The NASA public statement referenced in the post did not include the error bars when representing the data however the original studies did. The authors of the studies made clear that the difference of only 0.02 degrees Celsius “is within the uncertainty of the measurement.” Thus, the actual scientific study reported in the NASA public statement had the proper error bars in, as unfortunately happens quite often problems derive from news releases that are not accurate and rushed out.


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