The melting of Arctic ice may divert a large undercurrent in the ocean, which in turn may cause cold weather in Europe and North America
18.3.2004
From: NASA's Science News website - Translation: Dikla Oren
Global warming may put North America and Western Europe into a "deep freeze", possibly within a few decades.
Many climate scientists are beginning to believe this paradoxical possibility. The melting of the ice in the Arctic sea may divert and even stop large currents in the Atlantic Ocean. Without the tremendous heat that these currents provide - the power of which is roughly equivalent to the power of a million nuclear power plants - the average temperature in Europe would probably drop by about 5 to 10 degrees Celsius. Also, parts of North Africa will also cool, although to a less dramatic extent. Such a decrease in temperatures will result in a situation where the temperatures will be close to the average global temperatures towards the end of the last ice age about 20,000 years ago.
There are scientists who believe that the change in the course of the currents in the ocean may come sooner than expected - within about twenty years, says Robert Gagosian, president and chairman of the "Wood Hall" Oceanographic Institute. Other scientists are not sure that this will happen at all. However, the Pentagon does not ignore the matter. Andrew Marshall, a veteran planner at the Department of Defense, recently released an unclassified report on how shifting ocean currents in the near future could put national security at risk.
"It's not easy to predict what will happen," warns Donald Cavalieri, senior scientist at NASA's Goddard Space Flight Center. "The reason for the difficulty lies mainly in the fact that the Pole and the North Atlantic Ocean are extremely complex systems that have many interactions with the land, the sea and the atmosphere. However, the facts do raise the possibility that the changes in the pole we are witnessing may affect currents that raise the temperatures in Western Europe, and this certainly worries many people."
There are several satellites that continuously monitor the ice cover in the Arctic region. NASA's Aqua satellite, for example, carries a Japanese sensor called the ESO Advanced Microwave Scanning Radiometer (E-AMSR). The E-AMSR, which uses radio waves rather than visible light, can penetrate through clouds and get a good view of the ice, even at night, explains Roy Spencer, director of the E-AMSR facility at the Center for Climate and Hydrology in Huntsville, Alabama. Other ice observation satellites operated by NASA, NOAA (National Oceanic and Atmospheric Administration) and the Department of Defense use similar technology.
The images from the satellites clearly reveal that over time the "frozen ice" surfaces (the ice that remains frozen even in the hot summer months) are shrinking. Giuseppe Commisso, a climate scientist at NASA's Goddard Space Flight Center, published a paper in 2002, which claims that these ice sheets are retreating at an average rate of 9% per decade since the satellite began operations in 1978. Studies, which have looked at more recent data, put the rate of retreat at fourteen percent per decade, suggesting that the rate of retreat is accelerating.
Some scientists worry that the melting of the Arctic ice will flow a lot of fresh water into the North Atlantic, and the water will change the course of various currents in the ocean. Some of the fresh water will originate from the thaw itself, but most of it will come from the increased rain and snow in that area. The retreat of the ice exposes more water surfaces to the sun, so more moisture evaporates into the atmosphere, leading to increased precipitation.
Since salt water is denser and heavier than fresh water, following this addition of fresh water to the ocean the upper layers of the water will be more encrypted. This matter is a problem, since in order to set in motion a main circulation pattern in the ocean, known as the "great ocean mover", the upper layers of water must sink. Water that has sunk flows south over the ocean floor toward the equator, while warm water from the upper layers from tropical regions flows north to replace the sunk water. This is how the big carrier continues to work. An increased amount of fresh water may prevent the deposition of water from the surface waters in the North Atlantic Ocean, which will lead to the slowing down and even stopping of the circulation.
E-AMSR is collecting data, which will help scientists test this possibility. One thing is for sure, the satellite provides better ground resolution than any other weather satellite before it. The images from it reveal smaller cracks and fissures in the ice, when it hatches in the spring. These details allow scientists to better understand the dynamics of the ice sheets, says Cavalieri, a member of the E-AMSR team.
"The E-AMSR reveals other important pieces of the puzzle, such as rainfall, water surface temperatures and ocean winds. "Looking at all these variables together will help scientists gauge the likelihood of a change in currents in the Atlantic Ocean," Spencer added.
While in the past the concept, that the climate can change rapidly, was not accepted, today it is gaining more and more supporters. Robert Gagosian is quoted in a 2003 report "There is evidence [tree trunk rings and ice cores] that Earth's climate changed suddenly and dramatically in the past." For example, when the world began to warm towards the end of the last Ice Age about 13,000 years ago, melting ice shelves apparently caused the Great Conveyor to stop abruptly, putting the world back into 1,300 years of Ice Age-like conditions, a period called the "Younger Dryas." .
Will it happen again? Researchers are struggling to find out the answer.
On the thirteenth of February, a delegation sailed from Great Britain to put current measuring sensors in the Atlantic Ocean, which will check the Gulf Stream and look for signs of a slowdown in its flow. The expedition is part of a joint research project for Great Britain and the United States, called Rapid Climate Change, which began in 2001. Another international project, called SEARCH (Study of Environmental Arctic CHange) began its operation in 2001, when its goal was to accurately assess the changes in the thickness of the ice in the North Pole.
Computer simulations of Thomas F. Stocker and Anders Schmittner from the University of Bern state that the rate of warming of the Arctic region is of enormous importance. According to their models, rapid warming may stop the Atlantic Ocean's Central Current entirely, while slower, more moderate warming may only slow it down for a few hundred years.
And of course, what about humans? Does human industry play a role in the warming of the Arctic? Can we reverse the warming trend if we wanted to? Not all scientists agree on this. Some claim that the changes taking place in the Arctic region are part of slow and large cycles in the behavior of the ocean. Others attribute to humans a more significant role in the changes.
"The melting of the ice is consistent with the warming we have witnessed in the last century," notes Spencer, "but we do not know how much of this warming is due to natural climate fluctuations and how much of it is due to human-made greenhouse gases."
If the flow of the great ocean carrier were to stop, the cause would not matter much. The Europeans will have to worry about other things - for example, how to grow crops in the snow. Now it's time to find out what will happen.
