Copenhagen/New Delhi: The pledge of the world’s 17 most powerful nations that they won’t allow temperatures to rise by more than 2 degrees Celsius is unlikely to be met. A leaked United Nations (UN) internal document predicts that even at the most optimistic, current pledges on emission cuts are not enough to protect the planet from warming exceeding this limit.

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The difference in degrees means changes in rainfall patterns, crop yields, water availability and sea levels rising, apart from a surge in the cost of adaptation.

The UN document comes in the wake of a study authored jointly by Nicholas Stern and the United Nations Environment Programme (UNEP), which had reached a similar conclusion (Mint, 8 December). The UNEP report, released just before the beginning of the climate summit, had at the time been hailed as an optimistic statement.

“For those who claim a deal in Copenhagen is impossible, they are simply wrong," UNEP director Achim Steiner had said at the time of the release of the report. “We are within a few gigatonnes of having a deal. The gap has narrowed significantly."

But the more recent UN report has disappointed many as the two-week-long talks drew to an end.

“We are not there," said R.K. Pachauri, who heads the Intergovernmental Panel on Climate Change (IPCC). “The targets are not in line to restrict temperature rise by 2 degrees. We need faster cuts in emissions by 2020 to prevent global catastrophe."

Both the reports say that there is a gap of 2-5.2 gigatonnes between the current estimates and the requirement to contain global warming to 2 degrees Celsius.

“Unless the remaining gap is closed and parties commit themselves to strong action prior and after 2020, global emissions will remain on an unsustainable pathway that could lead to concentrations equal or above 550 ppm (parts per million), with the related temperature rise around 3 degrees Celsius," the UN document said.

IPCC estimates that developed nations will have to cut up to 40% of their emissions below 1990 levels by 2020 if they want the limit to stay unbreached. Current pledges from such nations only add up to 9-17%.

The estimates, however, don’t take into account any mechanism that may come into force later on measuring reduced emissions from avoided deforestation.

The reports urge that both developed and developing nations need to step up their emission cuts if the promise has to be kept. Rich nations also need to pledge financial and technological help for mitigation action more than pledged at present.

A 3 degrees Celsius rise would cause human casualties because of the dramatic changes in climate. Around 170 million additional people will suffer from coastal floods and another 550 million from hunger with the 1 degree Celsius variation. It will hit agriculture in areas such as India, leading to a fall in production of up to 20% by 2050.

The fourth assessment report of IPCC concludes that Asia is a particularly vulnerable region of the world to rising temperatures. “The stresses of climate change are likely to disrupt the ecology of mountain and highland systems in Asia," according to IPCC. “Sea-level rise would cause large-scale inundation along the vast Asian coastline and recession of flat sandy beaches. The ecological stability of mangroves and coral reefs around Asia would be put at risk."

India is especially vulnerable due to its dependence on the river system originating from the Himalayas and because a significant proportion of its population depends on agriculture, for which the main source of water is the monsoon.

A World Bank study released this year estimated that adaptation will cost developing nations up to $90 billion (Rs4.2 trillion) annually from 2010 to 2050, that too only for a 2 degrees Celsius rise till 2050. Out of this, a major proportion of the cost will have to be borne by countries in the Asia-Pacific, to the tune of $25 billion per annum and all countries will have to spend a major chunk of adaptation money on infrastructure and coastal zones ($29-30 billion annually).

India already spends about 2.3% of its gross domestic product on adaptation.

Some scientists are sceptical about the probability of the global warming models. They say there’s far less uncertainty in the relationship between carbon dioxide concentration and temperature, than how well those temperatures correspond to climate change effects.

“I think that the science is well-grounded, of the temperature rise associated with a fixed quantity of carbon dioxide. But does a 1 degree rise mean less severe rainfall over India, or certain islands submerging. That’s still not firmly grounded," said K. Krishna Kumar, a climate scientist at the Indian Institute of Tropical Meteorology in Pune, and a contributor to the IPCC reports.

Others say there’s still uncertainty on the levels of carbon dioxide present in the atmosphere and reported by countries.

In “several parts of the developing world—India and Africa especially—we really don’t know how much carbon dioxide is actually being emitted by say, vehicles", said B.N. Singh, a researcher at the Indian Institute of Technology, Kanpur. “They are highly approximated values."

Singh’s scepticism finds mention even in the latest IPCC reports. A chapter on the uncertainties in climate models says that Asia, with its large climate variability, adds a “further level of uncertainty" in simulating climate change.

“The emission scenarios of greenhouse gases (GHG) and aerosols are strongly related to the socio-economics of the countries in the region and could be strongly dependent on development pathways followed by individual nations," IPCC says. “Inaccurate description on future scenarios of socio-economic change, environmental change, land-use change and technological advancement, and its impacts will lead to incorrect GHG emission scenarios."

Graphics by Sandeep Bhatnagar/Mint

Mint’s Jacob Koshy in New Delhi contributed to this story.