Washington, June 28 : Climate experts have warned that the world might have already reached the tipping point of climate change, where immediate actions needed to be done to reduce the effects of global warming.
According to a report in Discovery News, the scientist who first put forward this theory is NASA climate scientist James Hansen.
Though Hansen had earlier warned about the dangers of climate change in 1988, his latest theory determines that "we have used up all slack in the schedule for actions needed to defuse the global warming time bomb."
Hansen's message painted a stark and urgent picture of a world already past the point where significant damage would occur.
According to Hansen, the safe level of atmospheric carbon dioxide should be no more than 350 ppm (parts per million), and it may be less.
This recommended level is less than the amount currently in the atmosphere - 385 ppm.
Already, arid lands are expanding, glaciers are receding, and Arctic sea ice is shrinking, driven by cycles of positive feedback, where melting leads to more warming of the exposed dark ocean water, which leads to more melting, according to Hansen.
"As a result, without any additional greenhouse gases, the Arctic soon will be ice-free in the summer," he added.
When Discovery News got in touch with other scientists, they more or less agreed with Hansen on his hypothesis.
While other scientists agree that 350 ppm is a safer target that increases the likelihood we will avoid many of the negative effects of climate change, some also think it's unrealistic.
"Three hundred and fifty is impossible. We're going to overshoot 350 and 450 and probably 550, though I sure hope not," according to climatologist Stephen Schneider of Stanford University in Palo Alto, California.
"My cynical scenario is that there will be more Katrinas, massive fires, melting of the Arctic, and people will say, 'Oh my God, what have we done. We'd better undo this'," he said.
"Such catastrophes could finally spark the dramatic change that's needed, if we don't take action sooner of our own accord," he added.
"My view is that we've probably passed some tipping points. We've entered some realms of irreversibility. There are probably many more, but we don't know where they are," said John Harte of the University of California, Berkeley.
Many scientists have agreed that the problem is urgent and that not doing anything will lead to disaster, which includes rising sea levels, food shortages, spread of infectious diseases and extinctions.
"We know that if we don't take action, it will be a disaster. That's all we need to know," said Harte.