Is global warming irreversible?

A study published in 2009, led by a scientist with the National Oceanic and Atmospheric Administration, shows that climate change may in fact be irreversible. Instead of it taking a couple hundred years to reverse global warming if we cut emissions right now, it looks like it could take more like a millennium. The issue is the oceans' absorption of atmospheric carbon dioxide.

The world's oceans play a central role in climate control. It's not just plants that absorb CO₂; oceans absorb even more of it. Oceanwatersabsorb CO₂from the air, effectively cooling the atmosphere. The ocean also emits heat from the sunlight it absorbs, warming the atmosphere. This constant cycle of cooling and warming keeps theEarthat a stable temperature. Or at least, that's how it's supposed to work.

The system starts to break down when the amount of CO₂pumped into the atmosphere rises exponentially, as it has in the last couple of centuries. The ocean can only absorb so much CO₂在一段时间内:abs上层的水orb CO₂, and then, as currents move, lower layers of water replace those saturated surface waters, offering new absorption surfaces. The snail-like turnover pace means any actions we take now to curb CO₂emissions won't have any effect for a long, long time.

There are other cycles involved in the problem, too. The loss of sea ice in the Arctic due to global warming creates further warming conditions that are difficult to undo. Sea ice and glacial mass are another big part of the Earth's climate-control system. While water absorbs sunlight, ice reflects it. Glaciers help keep ocean waters at a stable temperature. When glaciers melt, as they've been doing steadily since the United States started recording their levels in 1978, there's less ice to reflect sunlight and more water to absorb it. With more sunlight absorption, ocean temperatures increase. When ocean temperatures increase, more heat is released into the atmosphere, and overall temperatures increase, leading to more melting.

The end result of these combined cycles could be what some experts are calling an irreversible state of global warming. But are we really at that tipping point where there's no turning back climate change?

If climate change is irreversible, does that mean it could take all car off the road and it would never have an effect?

It's not quite that dire. According to the 2009 study, we could be looking at a thousand years of warmer temperatures even if we make dramatic cuts in CO₂emissions right now. So technically, it's not "irreversible" -- any of our descendants born after the year 3000 will be able to reap the benefits of our CO₂cuts (whew!).

We have apparently made it to the point of no timely return.

In terms of sea ice, that point became apparent years ago when Arctic ice stopped replenishing itself. Usually, ice melts to a certain level in summer months and freezes back to a certain level in winter months. Starting around 2003, the ice stopped recovering [source: Connor]. For that year and each year since, the ice melted more than usual in summer, and froze less than usual in winter, resulting in an overall loss of "permanent" ice. For September, the average sea ice coverage has typically been 2.4 million square miles (7 million square kilometers); in September 2007, sea ice covered only 1.65 million square miles (4.27 square kilometers) of the Arctic Ocean, the lowest point on record [source: USA Today]. Some experts believe there may be no summer ice in the Arctic within 10 years [source: USA Today].

The atmospheric CO₂situation isn't much better. We currently have 385 parts per million (ppm) of CO₂in our air; scientists are pushing for CO₂caps that will get us stabilized at 450 ppm in the next few decades [source:New Scientist]. Many people believe this goal isn't politically feasible, and have set 550 ppm as a more reasonable target [source:New Scientist]. But new research suggests it may not even matter. That 2009 NOAA-led study states that at 450 ppm, we're still looking at severe, unavoidable drought conditions in Africa, southern Europe, western Australia and the American southwest. And if we reach 600 ppm, expanding warmwaterscould make ocean levels rise by 3 feet (1 meter) in the next thousand years [source:Modine]. That number gets even higher if you take into account meltingglaciers.

Scientists aren't proposing we stop buying hybrid cars, though. The faster we act to make huge cuts in CO₂, the better the prognosis. If we can make dramatic changes right now, perhaps we could get the atmosphere stabilized at 400 ppm instead of 550 ppm. That would at least increase the chances that the U.S. West Coast will still be above water in 3000. Probably.

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