According To the intergovernmental panel on climate change (IPCC).they have predicted 21st century climate changes, and they are expecting a sudden and wholly climatic discontinuities .
There are several reasons to think that our journey into threshould or tipping point to exist, what there reports telling us is the severe warning of Global temperature rise by more than 2.7 C , and which can cause to meltdown the Greenland glaciers and distabilise the tropical rain forest .

Once the temperature rose upto 4 C the earth possibly could lose its cooling mechanism .
We may have ignored the cosequences or forgot how different the climate was in last ice age . Most of the united kingdom and North – western Europe including Scandinavia , had been buried beneath 3000 meters of ice , Glaciers as thick as that Greenland now ,north America was similarly glaciated, despite all this ice it was probably healthier world than now and More vegetation grew, both on land and sea.

The scientists believe this because abundance of carbon dioxide in the air had been below 200 parts for million .
It takes a lot of life to pump it down that low .

They reckon the sea level was 120 meters lower than now, which may explain why Australia was reached by human during the ice age .
The changes likely in the world to come will, in their different ways, be as greater as or greater than this . The sea cannot rise more than another eighty meters, the amount of extra water which would be released to if the ice of Greenland and Antarctica melted, but world wide torrid conditions would reduce the productivity of the remaining land and sea, and loss of vegetation would slow the rate of removal of Carbon dioxide and so sustain the hotter age for 100.000 years or more .

In 1800, we only had 1 billion people , this amount may not be incapable of lessening the consequences of global heatings but would have limited the damage by stopping carbon dioxide and methane emmisions ,the temparature rise would then be slower.

However, now we are in a situation of hopeless, as all seem too late , we have already 7 billion people right now, and it it keep rising further, therefore a huge quantity of Aerosol particals and green house gases releasing to the atmosphere has become inevitable .
It also suggest to not to forget large and disastrous changes in fresh water abundance, including floods and droughts . It is still far from clear weather the observed rise of sea level of the past fifty years is due mainly to the expansion of ocean water as it warns or mainly to the melting of glaciers. The 2001 IPCC report suggested that expansion was the principal cause of sea level rise, but a 2004 Nature paper by scientists at the national Ocenic essay by Jim Hansen in climate change in 2005, both suggest the increase of Ocean volume is mainly from the melting of land based ice .
If Hansen is right , then rapidly rising sea levels , will be the greater threats .

The reason devastations such as New Orleans , and Sandy in newyorkcity reminds us the damage that temporary flooding can cause.excessive rains and surges of sea water driven by storms can be as disturbing as a permanant slow rise in sea level.all these changes in their turn alter the distribution of forest and deserts and the availability of land on which to grow food.
Although we have much to learn, it does appear probable that in few years , when the carbon dioxide abundance passes 500 ppm ,we will enter the zone where temperature will rise to a new steady state,perhaps six to eight degrees hotter than now.
But the scientists not known whether this new regime will be stable inthe long term.
However the theory is now robustly supported by evidence from the earth and it suggest that we have very little time left if we are to avoid the unpleasant change of climate .

I see science and technology as traits possess by humans that have the potential for great good and great harm.
Evolution is iterative, mistakes are made, blunders committed , but in time that great correctors And erasers ,natural selection, usually keeps a neat and tidy world. Perhaps our greates error was the conscious abuse of fire. Cooking meat over wood fire may have been acceptable , but the deliberate destruction of ecosystems by fire merely to drive out the animals within was surely our first great sins against the living earth .