Study compares models to estimate a range of dates
Scientists explore the melting ice of the Arctic. Photo courtesy NOAA.
By Summit Voice
FRISCO— No matter which you slice it, the Arctic Ocean is likely to almost free of summer ice by mid-century, and possibly within the next couple of decades. according to a new study by federal scientists.
By comparing three different predictive models, the researchers came up with a range of dates when most of the Arctic Ocean ice will melt away for at least a couple of months during the northern hemisphere summer.
The most aggressive models, which weigh recent trends more heavily, suggest ice-free conditions could come as soon as 2020. Under a second group of models that rely on weighing the future probability of “extreme” but random ice-melt events, the ice-free date is pushed back to 2030. The most conservative predictions are based on global climate models that use global climate models to forecast atmosphere, ocean, land, and sea ice conditions over time.
“Rapid Arctic sea ice loss is probably the most visible indicator of global climate change; it leads to shifts in ecosystems and economic access, and potentially impacts weather throughout the northern hemisphere,” said James Overland, a scientist with the National Oceanic and Atmospheric Administration’s Pacific Marine Environmental Laboratory.
“Increased physical understanding of rapid Arctic climate shifts and improved models are needed that give a more detailed picture and timing of what to expect so we can better prepare and adapt to such changes. Early loss of Arctic sea ice gives immediacy to the issue of climate change,” Overland said.
“There is no one perfect way to predict summer sea ice loss in the Arctic,” said Wang. “So we looked at three approaches that result in widely different dates, but all three suggest nearly sea ice-free summers in the Arctic before the middle of this century.”
Overland and Wang emphasized that the term “nearly” ice free is important as some sea ice is expected to remain north of the Canadian Archipelago and Greenland.
Overland and Wang surveyed the current scientific thinking on Arctic sea ice loss, and categorized approaches into three groups: “trendsetters,” “stochasters,” and “modelers.” Each group looks at current information in a different way to make predictions for when to expect a nearly ice-free Arctic summer.
- The “trendsetters” approach uses observed sea ice trends. These data show that the total amount of sea ice decreased rapidly over the previous decade. Using those trends, this approach extrapolates to a nearly sea ice-free Arctic by 2020.
- The “stochasters” approach is based on assuming future multiple, but random in time, large sea ice loss events such as those that occurred in 2007 and 2012. This method estimates it would take several more events to reach a nearly sea ice-free state in the summer. Using the likelihood of such events, this approach suggests a nearly sea ice-free Arctic by about 2030 but with large uncertainty in timing.
- The “modelers” approach is based on using the large collection of global climate model results to predict atmosphere, ocean, land, and sea ice conditions over time. These models show the earliest possible loss of sea ice to be around 2040 as greenhouse gas concentrations increase and the Arctic warms. But the median timing of sea ice loss in these models is closer to 2060. There are several reasons to consider that this median timing of sea ice loss in these models may be too slow.
“Some people may interpret this to mean that models are not useful. Quite the opposite,” said Overland. “Models are based on chemical and physical climate processes and we need better models for the Arctic as the importance of that region continues to grow.”
The work was published recently online in the American Geophysical Union publication Geophysical Research Letters.
