Even though scientists have uncovered a great deal of information about the climate system and how it works, there are still some uncertainties, and because of them, some misconceptions. Some have stated that abrupt changes in climate are natural, that they have occurred throughout history. The reality is that while natural climate change has occurred and still does, a large component today is attributed to human interference. According to the American Geophysical Union, "It is scientifically inconceivable that—after changing forests into cities, putting dust and soot into the atmosphere—humans have not altered the natural course of the climate system." Greenhouse gases are being added at an alarming rate due to the burning of fossil fuels and deforestation.
Another misconception is that the ocean does not play an important role in climate. The ocean stores roughly 1,000 times more heat than the atmosphere; but because the atmosphere has the capability to move the heat more quickly, they equal each other out. The ocean does play a critical role in transferring heat; it is what keeps Europe warm in the winter, for example.
There is also some confusion when scientists talk about global warming on one hand and a cooling of Europe on the other hand. Although they seem contradictory, they are not. As global warming melts ice cover in the Arctic, it adds freshwater to the North Atlantic, which could threaten to slow, or stop, the North Atlantic conveyor belt, which supplies warmth to Europe, thereby putting the continent into a cold freeze. But it would not completely stop the Gulf Stream. It is also important to note that although global warming could lead to regional cooling such as this, it cannot cause a global ice age. Physical conditions are different now compared to the last Ice Age. For instance, the shape of Earth's orbit is different now than it was during the last Ice Age, as is the tilt of Earth's axis. There is also a much higher concentration of CO2 in the atmosphere.
Global warming will affect the hydrologic cycle, however. As global warming heats the atmosphere, more water is evaporated, which traps additional heat. In theory, the hydrologic cycle should accelerate as a result of global warming, which will then accelerate the process. There is still a lot of uncertainty about the role of the hydrologic cycle, however. Many models have been developed, and a wide variety of results have been obtained.
According to Environment News Service, a study conducted by Ruth Curry of the Woods Hole Oceanographic Institution; Bob Dickson of the Centre for Environment, Fisheries, and Aquaculture Science in Lowestoft, United Kingdom; and Igor Yashayaev of the Bedford Institute of Oceanography in Dartmouth, Nova Scotia, Canada, found that an acceleration of Earth's global water cycle—caused in part by global warming—may affect global precipitation patterns that determine the distribution, severity, and frequency of droughts, floods, and storms. They caution that a water cycle acceleration would intensify global warming by adding more water vapor to the atmosphere, which could continue to freshen the North Atlantic Ocean waters to the point that it could disrupt the ocean conveyor belt, triggering abrupt climate change.
Elise Ralph, associate director of the NSF (which funded the research) said, "This study is important because it provides direct evidence that the global water cycle is intensifying. This is consistent with global warming hypotheses that suggest ocean evaporation will increase as Earth's temperature does." Their models showed that the properties of Atlantic water masses have been changing radically over the past 50 years. The water at the poles is becoming fresher, while the water, in the tropical oceans is becoming saltier. The scientists involved in the study said that "these results indicate that freshwater has been lost from the low latitudes and added at high latitudes at a pace exceeding the ocean circulation's ability to compensate."
The scientists also noted that an accelerated water cycle is causing increasing rain and snow in higher latitudes, which is also contributing to the freshening of the North Atlantic Ocean waters. As a result of their study, the scientists stated: "Monitoring Earth's hydrological cycle is critical because of its potential near term impacts on Earth's climate."
In general, scientists know that in polar areas, the surface and deep waters have been increasing in freshwater for the past 40 years. In the Tropics, surface waters have been losing freshwater due to increased evaporation. These conditions could cause an accelerated hydrological cycle.
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