Longterm Climate Change Due to Astronomical Cycles

Climate cycles on Earth are directly related to astronomical cycles in the solar system, UC Berkeley researchers have found.

The team of scientists collected evidence of ice ages stored at the bottom of the oceans and found that there is a distinct pattern of cycles - an ice age that lasts approximately 90,000 years is followed by a warm period that lasts approximately 10,000 years.

"Astronomy is responsible for almost all climate changes," said project leader Richard Muller, a UC Berkeley professor of physics and a researcher at Lawrence Berkeley National Laboratories.

In addition, the researchers examined the astronomical cycles caused by variations in the tilt of Earth's orbit. They found that the tilt cycles match the cycles of the ice ages.

"When we look at ancient records of planets, these astronomical cycles appear in the climate record," Muller said.

Due to gravitational forces caused by other planets, the tilt of Earth's orbit changes depending on the position of these other objects.

"The orbit of the earth around the sun is constantly changing due to the gravitational effects of other planets," Muller said.

The law of gravitation is dependent on the distance between two objects. When objects are closer together, they exert stronger forces on each other than when they are farther apart.

Other planets orbit the sun, so their proximity to Earth varies over time. Due to gravitational forces exerted by other planets, the tilt of Earth's orbit changes in a cyclic pattern.

"By using the laws of physics, we can figure out what kind of cycles (other planets) induce on the orbit of the earth," Muller said.

The two planets that most strongly affect the tilt of Earth's orbit are Jupiter and Venus, Muller said. Jupiter is large an massive, so the planet exerts strong gravitational forces on Earth. Venus is relatively close to Earth, so it also has a large effect on the tilt of the orbit.

"Jupiter, which is the biggest planet (in our solar system), is the most important," Muller said. "The other planet that is very important is Venus. Even though it is much smaller, it comes much closer to the earth."

The team of scientists found that the tilt of the earth goes up and down every 100,000 years - the same amount of time required for one ice age-warm age cycle to be completed, he said.

"The history of the ice ages for the last 1 million years shows that they also have 100,000-year cycles," Muller said. "The pattern is an excellent match."

The scientists found that ice ages occur when the earth's orbit is less tilted, although Muller said he did not know which tilt would result in a warm period and which one would result in an ice age when he began the project.

"We did not know which it would be when we started," Muller said. "What we are actually looking at is the sea floor. Every year, another layer of sediment forms. These layers contain (a record of the climate)."

The scientists determined the climate cycles on Earth by collecting sediments at the bottom of the ocean. Every year, a layer of dust is added to the ocean floor. This sediment holds the record of the climate and the atmosphere, Muller said.

The researchers examined the sediments and found that certain periods were characterized by large amounts of oxygen isotopes, which are oxygen atoms with extra neutrons. These isotopes indicate the amount of ice present in the earth's climate at the time the sediment reached the ocean floor.

During ice ages, there are more oxygen isotopes present in the sediment than there are during warm periods.

The scientists are now trying to figure out why the tilt of the earth has such a strong effect on its climate.

An old theory, later proven incorrect, theorized that the climactic cycles on Earth are caused by differential amounts of sunlight hitting the earth's surface.

Although the sunlight theory was found to be wrong in the case of long-term climactic cycles, many researchers continue to believe that climate change is directly related to astronomical cycles.

Muller said his group does not know exactly what causes the cycles, but thinks that changes in the amount of dust in the earth's atmosphere is a likely cause of the cold periods.

"We have lots of guesses and we are trying to figure out which one is correct," Muller said. "The first guess is dust. Dust hitting the Earth has the same cycles as the ice ages."

Although the cycles match, scientists are not sure that dust alone could cause dramatic climate changes.

"The problem (is that) the amount of dust is so small, it does not seem there is enough to affect climate (this much)," Muller said. "Our best guess as of right now is that changes in the dust affect the formation of clouds. Remarkably, cloud formation is not well understood."

Muller said that if the greenhouse effect is not considered in climate analysis, the Earth's climate will soon cycle back to a cold period.

"Ignoring global warming, then the ice age is due back any millennium now," Muller said. "The ice age is coming back."

Muller said the current warm period has lasted approximately 10,000 years. Over the past million years, warm periods have lasted between 5,000 and 20,000 years.

"Our warm period is 10,000 years long," Muller said. "At the beginning of that warm period, humans developed agriculture."

Muller said the question of how the climate cycles is important to study because it directly affects the way human societies function.

"All of civilization has taken place during this short and relatively unusual warm period, which won't last very long," Muller said. "We have been through 10,000 (years of this warm period), so some time in the next 10,000 years, another ice age will arrive."

Although some believe that the coming of an ice age could be averted because of the effects of global warming, Muller said that the two problems occur on very different time scales.

"Many people think that maybe we need global warming (because) it will keep another ice age from coming, but that argument is silly and wrong," Muller said. "These two effects are very unlikely to cancel each other. Global warming (is an effect) for the near future; the ice age relates to the distant future."

He added that the only way for human society to combat these climate problems is to study them.

"Both (global warming and the coming ice age) will likely be disastrous," Muller said. "What we need is not to try to get them to cancel each other - we need to understand them better."

It is important to study ancient climates, Muller said, because the past is often the key to the future.

"What we are really studying are ancient climates in order to give us insight into the future," Muller said. "I can't imagine a more important question."

Scientists must often be detectives to get their job done, Muller said.

"There is a wonderful wealth of data (and) clues," Muller said. "Our role as scientists is analogous to the role of Sherlock Holmes. (We) walk into a room and look at all these clues and then try to find one pattern - the one explanation that answers the question."

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