Climate Models Biases and Limits

 Regional climate signals pose new challenges for climate science | News | Physical Sciences Division | The University of Chicago

Microsoft Word - _09-09-13_ Chapter 1 Models.doc

Local predictions of climate change are hazy. But cities need answers fast | Science | AAAS

The article below is excerpted from the University of Chicago press release and the other published articles linked above. 

Climate models are good at the big picture of global warming, but at a regional level they have blind spots. Climate science has correctly predicted many aspects of the climate system and its response to increased atmospheric carbon dioxide concentrations in the past one hundred and seventy-five years. However, those are very broad strokes. Recently, discrepancies between the real world observations and expectations for regional climate changes impacts have emerged and been acknowledged.  With decades of observations in hand, researchers can now identify local climate trends the models failed to predict.

• Some of the published examples to emerge are:
• Because warmer air can hold more moisture, models predict rising humidity in many arid places. But such changes have not occurred in the U.S. Southwest and elsewhere.
• Models fail to capture rising rainfall in South America and Australia and drying in East Africa, Europe, and northern India.
• Unforeseen shifts in wind patterns have led to more stalled, sunny weather over Greenland.
• Unforeseen shifts in wind patterns have also strengthened the jet stream over the Atlantic Ocean and intensified storm tracks over the Southern Ocean.
• Europe has faced unexpected summer heat, whereas the Southern Ocean; eastern, tropical Pacific Ocean; and U.S. Midwest have stayed cooler than predicted.

As scientific fields evolve, dominant paradigms emerge and is considered the settled science. When discrepancies or anomalies also arise, they are at first seen as a denial of the “scientific truth,” and often the current framework tries to explain away the anomalies.  However as the anomalies begin to accumulate, the dominant paradigm can be called into question creating a fracture in the scientific consensus. For example, at the beginning of the 20th century, classical physics underwent such a fracture that resulted in the development of quantum physics to understand and explain the anomalies. We may have arrived at such a point in climate science.

According to an analysis by University of Chicago Professor of Geophysical Sciences Tiffany Shaw and Max Planck Institute for Meteorology (MPI-M) Director Bjorn Stevens, published in Nature this month, such a process may be underway in climate science. What the authors describe as the dominant paradigm or “standard approach” of climate science has been developed over the past 60 years by applying fundamental laws of physics to the climate system under the assumption that small-scale processes are determined by statistical averages dependent on large scales (parameterization). This has allowed researchers to uncover the relatively simple physics governing the behavior of the complex climate system.

“The standard approach has been extremely successful in explaining general features of the climate system and certain aspects of its response to increased carbon dioxide concentrations,” said Tiffany Shaw. For example, it does an excellent job of describing and explaining the vertical structure of the atmosphere and some aspects of the spatial pattern of warming of the Earth due to an increase of atmospheric carbon dioxide.

However, Drs. Shaw and Stevens point out that the accumulating discrepancies are exposing knowledge gaps related to assumptions about how large- and small-scale processes and climate system components connect and interact. If these regional discrepancies persist, climate scientists might have to revisit the dominant paradigm.

Given the acknowledged limitations of the current climate models, many climate scientists eschew regional projections. While it may be in foolish to try to use the current regime to make hyperlocal projections, nonetheless there are groups attempting just that because there is little hope at this point of preventing the climate from changing in response to the still ever increasing concentration of carbon dioxide in the atmosphere; our only hope is to know where and how to use our resources to survive.