IT’S GETTING WARMER!
Welcome to The Deep science and technology column where we cover topics from the deep sea to deep space and beyond.
Greetings everyone! In light of the climate change talks going on right now, and the record snowfall happening on the east coast of the US and in Europe, I figured it was time to talk about everybody’s favorite subject: the weather. And despite that record snowfall, the news isn’t particularly good.
MONITORING THE ICE
In October, a NASA DC-8 airplane loaded with scientists and their instruments began low level passes over the Antarctic coastline where ice sheets are collapsing at a rate far faster than was predicted. The flights, dubbed Operation Ice Bridge, are an effort to determine what’s happening on and under the ice, in order to estimate future sea level rises.
Since 2003, laser measurements of ice surfaces from NASA’s ICESat satellite have shown that the ice caps in Greenland and West Antarctica are thinning and flowing quickly seaward. A report in the journal Nature based on data provided by ICESat showed that some parts of the Antarctica ice shelf have been sinking 27 feet a year. In 2002, one great glacial ice shelf jutting from land over the ocean on the Antarctic Peninsula simply disintegrated and floated away within days. ICESat reaches the end of its life soon, and another ice monitor won’t be launched until 2015. Until that happens, Operation Ice Bridge flights will continue and expand.
In addition to lasers, the plane will carry penetrating radar instruments that measure snow cover and the thickness of ice to bedrock, and a gravity-measuring system that will, for the first time, plot the geometry and depth of ocean waters under the ice shelves. The gravity study is very important because many scientists believe warm ocean currents may be the main force pulling the ice sheets seaward, melting the undersides of ice shelves and thus removing the buttresses that hold back the far greater ice masses on land.
Earlier this year, an icebreaker cruise sent an automated submarine to look under the region’s Pine Island Glacier, which has been moving forward rapidly in recent years. Its bed, where the ice contacts rock, is below sea level, and scientists are concerned about what would happen if seawater poured under the glacier.
The DC-8 is too big for any of the runways in Antarctica, and it will make the 11-hour round trip from Punta Arenas, Chile, with two-thirds of each trip spent getting to Antarctica. Once there, the plane will fly as low as 1,000 feet along sinuous glacial valleys that may test the nerves of both pilots and scientists. Some flights will also investigate the region’s open sea ice, which also seems to be disappearing.
"We learned how fast the ice sheets are changing from NASA satellites," said geophysicist Robin Bell, who is helping lead the project. "These flights are a unique opportunity to see through the ice, and address the question of why the ice sheets are changing."
"A remarkable change is happening on Earth, truly one of the biggest changes in environmental conditions since the end of the ice age," said Tom Wagner, cryosphere program scientist at NASA headquarters in Washington. "It’s not an easy thing to observe, let alone predict what might happen next. Studies like this one are key."
Antarctica’ Larsen Ice Shelf has deteriorated in recent years, and it’s one of the flight targets. (Credit: NASA)
So, if scientists are concerned that the warming seas are causing the coastal melting in both Greenland and Antarctica, what’s causing the warming seas? Despite those snowstorms happening right now, it could be that it’s warmer air temperatures. Read on.
DOES IT SEEM WARMER IN HERE TO YOU?
The combined land and ocean surface temperature for the entire Earth for September 2009 was the second warmest September on record, according to NOAA’s National Climatic Data Center whose records go back to 1880
NCDC scientists also reported that the average land surface temperature for September was the second warmest on record, behind 2005. Additionally, the global ocean surface temperature was tied for the fifth warmest on record for September.
The combined global land and ocean surface temperature was 1.12 degrees F above the 20th century average of 59.0 degrees F. Separately the global land surface temperature was 1.75 degrees F above the 20th century average of 53.6 degrees F.
Warmer-than-average temperatures engulfed most of the world’s land areas during the month. The greatest warmth occurred across Canada and the northern and western United States. There were also warmer than normal temperatures across Europe, most of Asia and Australia.
The worldwide ocean temperature tied with 2004 as the fifth warmest September on record, 0.90 degree F above the 20th century average of 61.1 degrees F. The near-Antarctic southern ocean and the Gulf of Alaska however, had cooler temperatures than average.
Sea ice coverage at the North Pole averaged 2.1 million square miles in September – the third lowest for any September since records began in 1979. The coverage was 23.8 percent below the 1979-2000 average, and the 13th consecutive September with below average Arctic sea ice extent.
Strangely enough, however, the sea ice in Antarctica was 2.2 percent above the 1979-2000 September average and was the third largest ice mass on record, behind 2006 and 2007.
Global surface temperature anomalies (degrees F) for the month of September 2009. (Credit: NOAA)
So . . . . we’ve got all these people monitoring the ice, but the ice is about as far away from us as it can get. I think most people are aware that a grave consequence of global warming will be the land loss for our neighbors here in the Pacific who live on low-lying atolls that are in danger of being completely submerged. But the crisis will hit long before that happens and is already in progress as rising sea levels are salt-contaminating vital food supplies like taro patches.
But are there other ways that global warming can affect us here? If you listen to the weather at all (and who doesn’t here?) you know all about the Intertropical Convergence Zone know familiarly to us as the ITCZ. It’s also called The Monsoon and the capital letters are a nod to just how important it is to us and to all of Asia and India. Well, guess what? Global warming isn’t just affecting the ice!
HEADED NORTH
The rain band near the equator that determines the supply of freshwater to nearly a billion people throughout the tropics and subtropics has been creeping north for more than 300 years, probably because it’s a warmer world.
If the band continues to migrate at just less than a mile a year, which is the average for all the years it has been moving north, then some Pacific islands near the equator – even those that currently enjoy abundant rainfall – may be drier within decades a
nd starved of freshwater by mid-century or sooner.
"We’re talking about the most prominent rainfall feature on the planet, one that many people depend on as the source of their freshwater because there is no groundwater to speak of where they live," says Julian Sachs, associate professor of oceanography at the University of Washington. "In addition many other people who live in the tropics but farther afield from the Pacific could be affected because this band of rain shapes atmospheric circulation patterns throughout the world."
This band of rainfall is, of course, the Intertropical Convergence Zone. It’s created when trade winds from the northern and southern hemispheres collide north of the equator and it’s fueled by the heat of the tropical Sun. Rain clouds 30,000 feet thick in places proceed to dump as much as 13 feet of rain a year in some places. (Guam’s average is around 8 feet a year.) The ITCZ stretches across the Pacific and it’s generally between 3 degrees and 10 degrees north of the equator depending on the time of year. Scientists think that the ITCZ isn’t found in the southern hemisphere because of land mass distribution and the presence of the Andes mountains in South America.
Recent research provides surprising evidence that the ITCZ was originally much farther south and in fact was located on the equator several centuries ago during what’s called the Little Ice Age when Earth’s average temperatures were much cooler.
The scientists analyzed rainfall records in lake and lagoon sediments from four Pacific islands at or near the equator. One of the islands they studied, Washington Island, is about 5 degrees north of the equator. Today it is at the southern edge of the ITCZ and receives nearly 10 feet of rain each year. But drill cores reveal a very different Washington Island in the past: It was arid, especially during the Little Ice Age.
Among other things, the scientists looked for salt tolerant microbes in their sediment cores. On Washington Island they found that evidence in 400- to 1,000-year-old sediment underlying what is now a freshwater lake. Such organisms could only have thrived if there was much less rainfall than there is today. Additional evidence for rainfall changes was provided by hydrogen isotope differences that can only be explained by large changes in precipitation.
Sediment cores from Palau, which lies about 7 degrees north of the equator and in the heart of the modern convergence zone, also revealed that things were also much drier there during the Little Ice Age. In contrast, the researchers present evidence that the Galapagos Islands, which are very dry today were much wetter during the 1400-1700’s.
The researchers write, "The observations of dry climates on Washington Island and Palau and a wet climate in the Galapagos during the time of the Little Ice Age provide strong evidence for an ITCZ located south of Washington Island (5 degrees north) during that time and perhaps until the end of the eighteenth century."
If the zone at that time experienced seasonal variations of 7 degrees latitude, as it does today, then during some seasons it would have extended southward to at least the equator. This has been inferred previously from studies of the ITCZ on or near the continents, but the new data from the Pacific Ocean region is clearer because the feature is so easy to identify there.
The remarkable southward shift in the location of the ITCZ during the Little Ice Age can’t be explained away by changes in the distribution of continents and mountain ranges because they haven’t moved. But the Earth received less solar radiation during the Little Ice Age and that may have caused the shift.
If the ITCZ was 5 degrees south of its present position as recently as 1630, it must have migrated north at an average rate of about a mile a year. If that rate continues, the ITCZ will be more than 75 miles north of its current position by the latter part of this century.
So . . . what does this mean for us? Well, we may get drier. But if the ITCZ is moving north, it may mean that typhoon formation may move north as well, resulting in fewer typhoons, but also less rainfall. Global warming isn’t just happening at the poles!
The band of heavy precipitation the Intertropical Convergence Zone (ITCZ). The new findings are based on sediment cores from lakes and lagoons on Palau, Washington, Christmas and Galapagos islands. (Credit: Image courtesy of University of Washington)
