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Climate in Context: August 19, 2010

By Michael D. Lemonick and Alyson Kenward

And Now: Antarctic Sea Ice Update

Yesterday we told you that the sea ice coverage in the Arctic is currently running well below average, although not quite in record territory. Today, let’s flip the world upside down and look at Antarctica – what’s going on with sea ice down there? (Keep in mind that although it’s summer in the Arctic, it’s winter in the Southern Hemisphere). 

Well, according to a recent paper in the Proceedings of the National Academy of Sciences, an increase in Southern Ocean sea ice area that has been going on for three decades might come to an end, soon-ish; computer models project that global climate change could lead to declining sea ice surrounding Antarctic by the end of the century, if not earlier.

That Antarctic sea ice coverage has grown during the last 30 years doesn’t contradict the global trend of rising temperatures. In fact, warmer global temperatures have brought more moisture into the air, which has consequently increased precipitation in some parts of the world. And near the South Pole, of course, the temperatures are still cold enough that the extra precipitation falls as snowfall, which accumulates onto ice cover and helps shield it from solar radiation. Other air and ocean cycles have combined to build up Antarctic sea ice, in stark contrast to conditions in the Arctic.

As global temperatures climb even higher, however, much of that Antarctic precipitation is bound to start coming down as rain, rather than snow, according to the new study conducted by Jipling Liu and Judith Curry, atmospheric scientists at the Georgia Institute of Technology. The combination of rainfall and warmer ocean temperatures could be fatal for Antarctic sea ice by the end of this century, they found.  

Chart showing Antarctic sea ice projections for the next 100 years, based on three different greenhouse gas emissions scenarios. Credit: PNAS

Curry discussed her findings with Houston Chronicle reporter Eric Berger at his Sciguy blog, telling him:

"Sea ice can melt from both above and below, either heating from the ocean below or the atmosphere above. In the case of the Arctic most of the melting is driven from the warmer atmosphere above. In the Antarctic most of the melting has been driven from the ocean below. What our study has identified is that there's been increased precipitation over the last few decades that has freshened the upper ocean, which makes it more stable so the heat below doesn't make it up to the sea ice to melt it."

"What happens in the 21st century projections is that the global warming signal begins to dominate. We still have the freshening of the upper ocean, but the upper ocean is getting warmer because of a warmer atmosphere. And the precipitation starts to fall more as rain than snow. Rain falling on ice speeds the melting from above."

Putting the Pakistan Floods in Perspective

It’s a bit too easy to put the Pakistan floods in the back of our minds these days; it’s a country halfway around the world from us, the reports of the death toll (about 1,600 people so far) are relatively low compared to other recent natural disasters like the Haiti earthquake, and we’ve got the Rod Blagojevich trial and Manhattan Mosque controversy to keep cable news networks occupied for the moment. The reports that do trickle through about the overwhelming problems in Pakistan, however, should give us pause.

United Nations officials are calling this the worst natural disaster to date that can be attributed to climate change, according to a ClimateWire story that ran online in the New York Times yesterday. Such framing goes against much of the other coverage we’ve heard in the past few weeks, which, in so many words, says that although climate change may have contributed to the floods, as well as the historic heat wave in Russia, we can’t say for certain that climate change has directly caused this summer’s severe weather. 

Somewhere between 15 and 20 million people have been displaced from their homes in Pakistan since the floods began in late July. This is equivalent to the entire state of New York (or almost the entire country of Australia) having to abandon their homes due to flooding.

According to NASA, the Indus River, which is normally one to two kilometers wide, has swelled to 24 kilometers in places, inundating areas along its banks.

Satellite image of flooding near Kashmor, Pakistan on August 12. Credit: NASA.

In other words, this is a huge problem, particularly for a country with limited disaster response capabilities.

The Pakistan floods raise the issue of what constitutes a “climate refugee,” which is a term that is frequently bandied about in discussions about the potential national security ramifications of climate change.

There has been debate over who the first climate refugees were. Some of the leading contenders are victims of Hurricane Katrina, residents of Papua New Guinea who have been affected by sea level rise, and more than 500,000 Bangladeshis who were forced to move due to flooding. Now, those in Pakistan have been added to the list, even though it’s still unclear exactly how significant of a role climate change played, as opposed to natural weather variations, in instigating many of these events. In the near term, as foreign aid finds its way to Pakistan, these refugees are probably more concerned with finding food, water and shelter than how they can best be labeled to help raise awareness of climate change.

Today the U.S. announced the creation of a Pakistan Relief Fund. Secretary of State Hillary Clinton stated in a video message, “the enormity of this crisis is hard to fathom, the rain continues to fall, and the extent of the devastation is still difficult to gauge.”

New Version of Widely Used Computer Model Unveiled

We know the Earth is warming thanks to actual measurements—especially over the past half-century, but with at least vague accuracy (despite what you may have heard) dating back for the last several hundred years at least.

What we can say about future warming is less precise, since the climate system is complex, and you can’t do lab experiments on it (unless you classify our emissions of greenhouse gases an experiment, which many do). Scientists’ best projections, therefore, come from sophisticated simulations that try and capture the climate system inside a supercomputer.

Since computers keep getting more powerful — and since scientists’ understanding of the actual climate keeps getting more detailed — the models are updated every so often to make the projections that much more accurate.

As part of the preparations for the next major report from the U.N. Intergovernmental Panel on Climate Change (IPCC), the National Center for Atmospheric Research (NCAR) in Boulder, Colorado has just announced its latest upgrade to a key academic computer model in the United States, called the Community Earth System Model (CESM). According to the NCAR press release, the new version of the model will help climate scientists refine the answers to some key questions, including:

  • What impact will warming temperatures have on the massive ice sheets in Greenland and Antarctica?
  • How will patterns in the ocean and atmosphere affect regional climate in coming decades?
  • How will climate change influence the severity and frequency of tropical cyclones, including hurricanes?
  • What are the effects of tiny airborne particles, known as aerosols, on clouds and temperatures?

The model won’t be perfect, but even the previous generation of models has done a reasonable job of “predicting” the climate of the past, which gives some confidence about their ability to project (roughly) the future.

NCAR’s new, improved model, whose output, along with that of other models, will end up in the IPCC’s Fifth Assessment Report in 2013, should presumably do even better.

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