New research, published in the journal Climatic Change in November, suggesting that humanity may have to remove carbon dioxide (CO2) from the atmosphere on a large scale, the emissions increase after 2020.
The series of articles which provide scenarios that form the basis of the forthcoming report of the Intergovernmental Panel on Climate Change (IPCC) in 2013 and 2014.
Currently, the emission levels of less than 20 years, the sky would be full of reality, that is, each additional ton of carbon dioxide (CO2) should be eliminated to stay within the limits of the climate safer, one of the lead author says.
This so-called "negative emissions" approach, which removes the excess carbon dioxide in the atmosphere, is a less radical step than the direct manipulation of the climate, called geo-engineering, which includes blocking the sunlight using mirrors or artificial clouds in space.
Both approaches are thinking more seriously, reflecting the increase in emissions and a target of interest in the hands of governments worldwide to keep global average below 2 degrees Celsius compared with preindustrial levels.
Some scientists say that the limit of 2 degrees is too arbitrary and has not been shown to be linked to dangerous weather phenomena.
And 'calculated as part of the border, beyond which the Greenland ice may melt irreversibly, increasing the global sea levels by seven meters over the centuries.
"If you want to stay below 2 degrees, and possibly reach 1.5 in the 22 century, so we have no intention to circumvent these negative emissions", says an author, Malte Meinshausen of Germany, Potsdam Institute for Climate Impact Research.
"This is a fundamental change in the perception that there is a point and is very close to when, if we put the CO2 in the atmosphere for future generations need to take him out."
Strong reduction of emissions now could prevent or delay the time until the end of this century.
NEGATIVE
In its next report, the IPCC for the first time to assess what the world is likely to have a chance to keep long-term warming below 2 degrees Celsius. The temperature has already risen about 0.8 degrees Celsius since pre-industrial times.
Meinshausen study calculates that the world would stop the rise of global greenhouse gas emissions by five years.
By 2070, people should have a power output of less than 3.5 billion tons of CO2 per year to reduce the temperature continues to rise below 2 degrees of long-term, and then a slow rise in sea level.
The scientists say that emissions continue to grow after 2020 would require passing 2 degrees in the middle of the century.
After that, the only way back is the removal of CO2 from the atmosphere on a large scale - a net outflow of 18 million tons of CO2 per year over the next century and for 100 years, is calculated in the new series of studies.
This compares with actual emissions of 33 million tons of CO2 last year by the burning of fossil fuels. Emissions have increased by 3.2 percent annually in recent decades.
Considering that extreme measures are needed, we are still accepted.
"If you really want to avoid a warming of 2 degrees, or are watching the Sun signs in geo-engineering sense in space, or negative emissions by type of geo-engineering of the second half of this century," said the University of Oxford climate scientist Myles Allen.
"It is increasingly thought."
Technologies that drive negative emissions of CO2 include the burning plant materials known as biomass and sequestration of carbon emissions and bury them underground.
This results in a net negative effect on emissions because the plants self-absorption of CO2 from the air. But the idea is there only in the laboratory and pilot projects.
Other techniques could be crushing limestone, which absorbs CO2, but it seems unlikely, because the vast amounts of ore to be mined. Engineers have also proposed using artificial plants to mimic photosynthesis.
Instead of absorbing CO2 is an alternative geo-engineering approach to screen sunlight, for example by spraying sulfur in the upper atmosphere. This causes water droplets to form and create hazy clouds and will be tested by British engineers next month.
The problem is a threat of incalculable consequences.
"It is not the same as just twisting things back to where we were in terms of greenhouse gases. You will be the second change, which are likely to get the return temperature, but can lead to less rain," said Peter Stott of the University of Reading.
CONCERN
Some climatologists are concerned about how the predictions were confirmed or exceeded since the last IPCC report.
Other experts say it is not clear to what extent the specific changes that result in emissions or natural effects.
"There is a final decision," said the Potsdam Institute Vladimir Petukhov.
For example, last week revealed that the Arctic sea ice melted this summer at a record low extent, or second place. Natural atmospheric effects were partially explained by the previous record in 2007, the researchers say, and may help to explain this year, said Petoukhov.
Other changes in climate research last week, temperatures will rise quickly found the North-East Atlantic, driving major changes in fish stocks.
And scientists say they can now detect a human footprint on trends in global precipitation.
"What is clear is that the changes do not seem to occur in line with expectations," said Stott reading.
"This shows that the climate is already changing, not only global temperatures, but precipitation patterns. So we come to things that actually affect people. "
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