New models still give Arctic summer ice 30 years

A thin sheet of sea ice reflects the rising sun off the east coast of Greenland on Apr. 14, 2012, with thicker sea ice and icebergs in the background. On average, the most up to date climate models that accurately simulate recent Arctic ice melting predict a nearly ice-free September by 2035. Credit: NASA/Jefferson Beck

A thin sheet of sea ice reflects the rising sun off the east coast of Greenland on Apr. 14, 2012, with thicker sea ice and icebergs in the background. On average, the most up to date climate models that accurately simulate recent Arctic ice melting predict a nearly ice-free September by 2035. Credit: NASA/Jefferson Beck

Predictions from a collection of the latest climate models on average say that ice will be nearly gone from the Arctic by the 2030s. But when you don’t include man-made – or ‘anthropogenic’ – CO2 emissions’ ‘forcing’ effect, those models show a much icier picture.  “This clearly shows that if you don’t consider anthropogenic forcing, the ice won’t decline that fast,” said Muyin Wang from the University of Washington. “It should be oscillating around a much higher level.”

These findings echo some that Muyin and her Seattle colleague James Overland, from the US National Oceanic and Atmospheric Administration (NOAA) Pacific Marine Environmental Laboratory, made in 2009. Then, James and Muyin used climate models that formed the basis for the Intergovernmental Panel on Climate Change’s fourth assessment report, which was published in 2007. “Because of this report’s success a lot more modelling groups around the world started doing simulations,” Muyin told me. Scientists are now bringing their improved old models together with new ones in a project to compare them. Having found the old models bad at reproducing measured shrinkage of Arctic ice at the end of the 20th century, James and Muyin wanted to see if the new and improved ones could do any better.

It’s important to be able to reproduce real data to be confident in models’ predictions, Muyin said. “If you are interviewing someone for a job, you look at their resumé, to see if they did a good job in the past,” she explained. “Then you know that they can do the job going forward. It’s a similar idea here, if models can simulate the past climate, then they’re the models we want to use in the projection.”

In a paper published in the scientific journal Geophysical Research Letters on Tuesday, they started from 32 different models, and compared them with satellite data on sea ice coverage. Overall, their resumés were slightly better than the older models: For the period from 1981-2005, the average of all these models was near the ice coverage actually seen, whereas the older models had overestimated the values.  But the highest and lowest estimates in both groups were still very similar.

Frozen out

Satellite data reveal how the new record low Arctic sea ice extent, from Sept. 16, 2012, compares to the average minimum extent over the past 30 years (in yellow). Sea ice extent maps are derived from data captured by the Scanning Multichannel Microwave Radiometer aboard NASA's Nimbus-7 satellite and the Special Sensor Microwave Imager on multiple satellites from the Defense Meteorological Satellite Program. Credit: NASA/Goddard Scientific Visualization Studio

Satellite data reveal how the new record low Arctic sea ice extent, from Sept. 16, 2012, compares to the average minimum extent over the past 30 years (in yellow). Sea ice extent maps are derived from data captured by the Scanning Multichannel Microwave Radiometer aboard NASA’s Nimbus-7 satellite and the Special Sensor Microwave Imager on multiple satellites from the Defense Meteorological Satellite Program. Credit: NASA/Goddard Scientific Visualization Studio

When James and Muyin looked at the entire group of new models, some showed that there would still be Arctic ice in 2100. So the scientists did what they had done in 2009 – only looked at the models that successfully simulated recent ice loss. “We analysed only 7 models that performed better at simulating the sea ice extent,” Muyin said. “If you want to look at the Arctic you should concentrate on these models, rather than looking at the whole group of 32 models.” Those seven, in a scenario where climate-change causing greenhouse gas emissions stayed very high, showed a rapid decline. The average time until the minimum sea ice area in the Arctic fell below a million square kilometres was 28 years from 2007, with predictions ranging from 14-36 years.

Muyin and James write that they are ‘discouraged’ that the models aren’t better at reproducing the Arctic melt we’ve seen. But Muyin said that there are reasons why it’s difficult. “There are still a lot of things we don’t fully understand about the Arctic climate system,” she explained. “We still need to find out which are the most important processes that control the sea ice growth and disappearance. That’s very challenging for us to do. Also, for the Arctic, observational data are short and sparse. That makes the modelling harder than if we had more than several decades of continued, systematic observations.”

However, by pointing out which ones are the best at simulating the Arctic, Muyin is helping make sure predictions for the area are as reliable as they can be. With a record minimum coverage reached this year, that’s more important than ever for areas where Arctic ice affects society, the environment and the economy. “When I go to meetings, other researchers do recognise that these models are better at simulating the ice, so it does have an impact,” she said. “They are still useful, and they are the only tools we have.”

Journal Reference:

Muyin Wang and James E. Overland (2012). A sea ice free summer Arctic within 30 years: An update from CMIP5 models Geophys. Res. Lett. DOI: 10.1029/2012GL052868

About these ads

4 Responses to “New models still give Arctic summer ice 30 years”

  1. Richard Hanson Says:

    It would interesting to know how these 7 chosen models did in simulating other aspects of the global climate, such as, did they correctly simulate the global temperature trend, especially since 1997 and did they simulate the growth of the Antarctic Sea Ice Sheet? Was this Cherry Picking?

    • andyextance Says:

      This study solely concerned the Arctic – I don’t think clearly defining their question is cherry picking. You can read the entire paper to see what they did in more detail yourself – either click on the hyperlinked word “paper” to go direct to the full text, or the link in the DOI will take you to the abstract, and there you can click on and read the full text link free of charge.

  2. Another Week of GW News, September 30, 2012 – A Few Things Ill Considered Says:

    […] 2012/09/29: SinmpleC: New models still give Arctic summer ice 30 years […]

  3. Can we trust climate models? « Simple Climate Says:

    […] shrinking Arctic ice. That’s what Muyin Wang from the University of Washington did in September, finding clear evidence that human greenhouse gas emissions are speeding its loss. “It’s important to be able to reproduce past climate and variations to be confident in […]


Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s

Follow

Get every new post delivered to your Inbox.

Join 195 other followers

%d bloggers like this: