By Dr. Sebastian Lüning and Prof. Fritz Vahrenholt
(German text translated/edited By P Gosselin)
Slowly people are realizing that not everything in the climate modeling world is as rosy as once claimed for years. It’s bit like the Tour de France, where racers were once celebrated as heroes, but later the doping reality came to light. Are we on the verge of the same realization in the field of climate modelling?
Recently we saw a worthwhile editorial in Nature, 3 May 2017, where the global warming hiatus and communication errors were admitted on both sides:
Increased scrutiny of climate-change models should be welcomed
The apparent slowdown in global warming has provided a spur for better understanding of the underlying processes. […] Some background: the El Niño weather event in 1997 and 1998 belched a great bolus of heat from the ocean into the atmosphere, a release that was entirely consistent with expectations — as was the heady spike in global mean surface temperature that followed. From the top of the Himalayas, the rest of Earth is downhill. And, in a similar way, the 1998 peak in temperature offered an easily visualized time that climate sceptics could cherry-pick as a starting point for a ‘hiatus’, ‘pause’ or ‘slowdown’ in climate change. It’s true (of course) that the next few years saw a reduced rate of warming, or maybe even a slight cooling. And it’s also true that, soon after, some analyses showed that these observations were beginning to diverge from the suite of projections made by climate models. A few responses emerged. First: yawn — “This is nothing more than the sort of normal variability one should expect in the climate system, and models should not be expected to predict any specific dip or peak.” Second: hysteria — “Climate scientists have no idea what controls the climate system.” Third: interesting — “Let’s figure this out.” Happily, most of the climate-science community adopted the third option. The result was a flood of publications on the topic, and the only half-joking suggestion that Nature’s publisher should launch a new journal called Nature Hiatus.
Continue reading in Nature.
Already in March 2016 Nature was looking at the topic:
Where climate models fall short
Climate models tend to overestimate the extent to which climate change contributes to weather events such as extreme heat and rain. Omar Bellprat and Francisco Doblas-Reyes at the Catalan Institute of Climate Sciences in Barcelona, Spain, used an idealized statistical model to compare the frequency of weather extremes in simulations with and without climate warming. Extreme events seemed to be more closely linked to climate change when the model was forced to run at low levels of reliability than when the model error was kept to a minimum. To account for models’ biased representation of climate variability, studies should rely on calibrated model ensembles, which are commonly used by weather forecasters, the authors suggest.”
There was also welcome realism in a press release from Lawrence Livermore National Laboratory in December 10, 2015. Climate models systematically overstated the increase in precipitation by 40%:
Climate models overestimate rainfall increases
Lawrence Livermore researchers and collaborators have found that most climate models overestimate the increase in global precipitation due to climate change. Specifically, the team looked at 25 models and found they underestimate the increase in absorption of sunlight by water vapor as the atmosphere becomes moister, and therefore overestimate increases in global precipitation. The team found global precipitation increase per degree of global warming at the end of the 21st century may be about 40 percent smaller than what the models, on average, currently predict. The research appears in the Dec. 10 edition of the journal Nature.
Evaluation of model-predicted global precipitation change with actual precipitation observations is difficult due to uncertainties arising from many sources, including insufficient spatial and historical data coverage. As an alternative approach, the team, made up of LLNL scientist Mark Zelinka and colleagues from the University of California, Los Angeles, including lead author Anthony DeAngelis, evaluated model-simulated global precipitation change through consideration of the physical processes that govern it.
The team found that the increase in global precipitation simulated by models is strongly controlled by how much additional sunlight is absorbed by water vapor as the planet warms: Models in which more sunlight is absorbed by water vapor tend to have smaller increases in precipitation. They demonstrated that model-to-model differences in increased absorption of sunlight were not controlled by how much their humidity increased, but by how much additional sunlight was trapped in the atmosphere for a given increase in humidity. Conveniently, this quantity can be measured from space, allowing the team to assess how well the models capture the physics controlling changes in global precipitation.
“This comparison with observations allowed us to see quite clearly that most models underestimate the increased absorption of sunlight as water vapor increases,” Zelinka said. “Because this acts as such a strong lever on global precipitation changes, the models are likely overestimating the increase in global precipitation with global warming.”
Paper: Anthony M. DeAngelis, Xin Qu, Mark D. Zelinka, Alex Hall. An observational radiative constraint on hydrologic cycle intensification. Nature, 2015; 528 (7581): 249 DOI: 10.1038/nature15770
There was also model failure in the simulation of wildlife space. The animals of the last ice age stubbornly resisted the requirements of the computer simulation and instead showed an expansion that was completely unexpected. Press release by the University of Oregon from November 2014:
Fossils cast doubt on climate-change projections on habitats
Mammals didn’t play by the rules of modeling on where they migrated to survive last ice age, says UO researcher
Leave it to long-dead short-tailed shrew and flying squirrels to outfox climate-modelers trying to predict future habitats. Evidence from the fossil record shows that gluttonous insect-eating shrew didn’t live where a species distribution technique drawn by biologists put it 20,000 years ago to survive the reach of glaciers, says University of Oregon geologist Edward B. Davis. The shrew is not alone. According to a new study by Davis and colleagues, fossil records of five ancient mammalian species that survived North America’s last glacial period point to weaknesses in the use of ecological niche models and hindcasting to predict future animal and plant habitats. As a result, Davis says, the modeling needs to be fine-tuned for complexities that might be harvested from fossils.
Ecological niches use modern habitat distributions and climate; hindcasting adds predictive power by adding major past climate shifts into the models. That modeling combination — as seen in a 2007 study led by Eric Waltari, then of the American Museum of Natural History in New York — had the short-tailed shrew surviving the last ice age in mostly Texas and the Deep South. Conclusions drawn in other studies, Davis noted in the new study, also are biased toward southern locations for ice-age surviving mammals of the Pleistocene Epoch. Short-tailed shrew, according to fossil records, did not live in the predicted ranges. Instead they lived across north central and northeast United States, closer to the glaciers and where they are widely found today.
“It’s almost as though it is living in all of the places that the model says it shouldn’t be living in and not in any of the places that the model says it should be living in,” said Davis, who also is manager of the paleontological collection at the UO Museum of Natural and Cultural History. “This suggests to me that whatever the model is keying on is not actually important to the shrew.” Nor to the American marten (Martes americana), two species of flying squirrels and the Gapper’s red-backed vole (Myodes gapperi), all of which lived mostly outside of predicted ranges, according to the fossil record. Northern (Glaucomys sabrinus) and southern (Glaucomys volans) flying squirrels, the Davis study found, shared a compressed geographic region. It may be, Davis said, that some species tolerate competition under harsh conditions but separate when abundant resources are available.
Davis noted that an important but under-cited 2010 paper on rodents by Robert Guralnick of the University of Colorado and Peter B. Pearman of the Swiss Federal Research Institute also showed problems with hindcast projections. Those for lowland rodents in the last ice age did not hold up, but those for a higher elevation species did. “Our findings say that we need to pay more attention to the potential problems we have with some of our modern methods, and the way that we can improve our understanding of how species interact with the environment,” said Davis, who added that his study was inspired by Waltari’s. “The way to improve our forecasting is to include data from the fossil record. It can give us more information about the environments that species have lived in and could live in.” The findings appear in the November issue of the journal Ecography. In a special section of the journal, the Davis paper is packaged with four papers on research initially presented in a symposium on conservation paleobiogeography in 2013 at a biennial meeting of the International Biography Society. The Davis paper is co-authored by Jenny L. McGuire, now at Georgia Tech University, and former UO doctoral student John D. Orcutt, who is now at Cornell College in Iowa.”
Paper: Edward Byrd Davis, Jenny L. McGuire, John D. Orcutt. Ecological niche models of mammalian glacial refugia show consistent bias. Ecography, 2014; DOI: 10.1111/ecog.01294