19 January 2015
Stefan Brönnimann, a professor of climatology and a member of the Oeschger Centre, advocates in Nature Geoscience that paleoclimatologists and their colleagues in dynamical climatology should work together more closely.
In a “News & Views” contribution to Nature Geoscience, Brönnimann states how increasingly, the realms of paleoclimatology – largely based on proxy reconstruction – and the backward extension of methods and interpretations used in modern climatology have started to overlap. “Innovative ideas can develop at such an interface, but with this comes the challenge of combining two different perspectives,” he writes. “Collaboration at this particular boundary is not just about reconciling different data sets, but also about the meeting of different scientific cultures.” Paleoclimatological studies often rely on only a few – sometimes just one – proxy time series, which despite uncertainties, are then used to raise hypotheses. Conversely, dynamical climatologists have a very critical attitude even towards new, comprehensive data sets, particularly when it comes to trends. Their results may be more trustworthy, but with little room for novel interpretations.
Therefore Brönnimann, a climatologist himself, argues that dynamical climatologists could learn from paleoclimatology and think more boldly. Conversely, paleoclimatologists might benefit from a more critical stance towards their data, as taken by dynamical climatologists. “Working in tandem gives both groups the best chance to exchange not only results but also perspectives.”
Linked wind strength and warming rate
Stefan Brönnimann makes his point by commenting on a paper by Diane Thompson and her colleagues in the same issue of Nature Geoscience. In the first decade of the 20th century, the Earth warmed rapidly. In their study, which is mainly based on a coral record from the tropical Pacific, Thompson et al. suggest that this warming was due to more frequent westerly winds over the tropical Pacific. In this situation, the ocean may release heat to the atmosphere. This reverse mechanism – more heat uptake in the Pacific Ocean due to strong easterly winds – has been used to explain the current slow-down of global warming. This shows the relevance of past warming episodes for understanding the present.
“The suggestion of a close relationship between western equatorial Pacific winds and warming rate links the early 20th century climate to the unexpectedly slow warming rates at the beginning of the 21st century,” writes Brönnimann. However, this does not exclude alternative explanations that have been raised previously, such as a similar mechanism in the Atlantic Ocean. Research now needs to reconcile the roles of the Pacific and Atlantic Oceans – both in the early 20th and early 21st centuries. The fast progress at the interface of the worlds of paleo and modern climate science can thus contribute to a better understanding of our climate system. As Thompson’s study on the early 20th century warming shows, the combination of proxy reconstructions with observations and dynamic interpretations will lead to more exciting findings in the future.