They say the report has confirmed climate change with greater certainty, but has shed no fresh insights, and it is unclear to what extent it will persuade national governments to reduce emissions of the greenhouse gases that cause global warming.
Portions of the IPCC's draft fifth assessment report (AR5) were leaked online earlier this month.
The AR5 will be released in four phases, beginning with the report of the first working group — which covers the physical basis of climate change — on Monday. Other portions of the report will be released over the next year, with the final synthesis report due in October 2014.
According to New Delhi-based NGO the Centre for Science and Environment (CSE), which discussed the leaked report this week, the document concludes that it is now 95 per cent certain that human activities have caused more than half of the observed temperature increase from 1951 to 2010.
The report says that warming has been particularly marked since the 1970s, and each of the last three decades has been significantly warmer than all preceding decades since 1850. It also says that global seas are set to reach higher-than-expected levels by the end of the century.
It says that there is now less confidence that global average rainfall has increased in the past, but there is greater confidence that it will rise in the future, according to the CSE.
The report says there is no change to the conclusion that heavy rainfall events have increased in the past, but there is greater confidence now that these will increase in the future.
There is also no change to earlier conclusions about a trend of increased flooding, past or future.
“If we do not change our ways, we will be heading towards quite big changes in climate by the end of the century.”
Kirk Smith, University of California Berkeley
In contrast, the report expresses less confidence compared with previous conclusions that drought has increased globally — or indeed that any change is detectable — since 1950. There is also less confidence that the frequency of hurricanes has increased in the past due to climate change.
Saleem-ul-Haq, a senior fellow in the Climate Change Group at the International Institute of Environment and Development, United Kingdom, tells SciDev.Net that the report "makes the climate change case stronger", as it clearly shows that the increased concentration of greenhouse gases in the air is "beyond dispute" and that the world is moving towards the upper end of the range of temperature rises projected by the previous IPCC assessment report of three to four degrees Celsius.
The deputy director of CSE, Chandra Bhushan, says that the first part of the AR5 has built on the IPCC's previous AR4 publication. It now provides higher levels of certainty that climate change has happened and is continuing; that global temperatures have been rising since the 1970s; that rainfall intensity has been increasing and will increase in future; and about sea level rises due to global warming.
More certainty, but little action
The bigger issue, according to Bhushan, is that, despite repeated IPCC reports calling for urgent action to stem global warming beyond the tipping point, "global action on climate change is not going anywhere".
"Maybe the IPCC reports need to be communicated in a different way. Perhaps in much more concrete and simple terms so that a larger audience can understand what the scientists are saying," he says.
A senior scientist at the Mauritius Academy of Science and Technology, who is in New Delhi for a meeting of science academies, says that IPCC reports, in general, are "not radical enough" to force real action by national governments to reduce greenhouse gas emissions.
This is in sharp contrast to reports on the dangers of the growing ozone hole in the atmosphere, which led to the Montreal Protocol in which targets were set for the phasing-out of chemicals that destroy the ozone layer, he adds.
Spurring new research directions
Kirk Smith, associate director of environmental and health sciences at the Center for Occupational and Environmental Health, University of California Berkeley, United States; and a Fulbright chair at the Indian Institute of Technology (IIT) Delhi, tells SciDev.Net that the report confirms what scientists have been saying all along.
"The basic message is the same: that if we do not change our ways in terms of mitigating greenhouse gas emissions, we will be heading towards quite big changes in climate by the end of the century," he says. "Each new report uses more sophisticated models and better data input, but the results do not change in any significant way even if the exact date by which a certain temperature is expected moves forward or back a few decades each time."
Smith, who is the convening lead author of the second working group report on vulnerability to climate change, says: "The new assessment has increased our confidence that the effects for climate change are beginning to be seen, in terms of rise in temperature, sea levels and heavy precipitation events".
He says that, in terms of climate science research, scientists still need to address the remaining uncertainties in the carbon cycle: where and how fast the carbon released into the atmosphere goes, how much stays in the atmosphere, whether there are limits to some natural sinks for carbon and whether there are important new sources of carbon emissions that may be triggered by warming.
Another important issue is what fraction of man-made carbon dioxide emissions will stay in the atmosphere and for how long.
Smith adds that methane emissions are another important case for study, especially to determine if there will be positive feedbacks in which warming will stimulate additional emissions from wetlands and arctic tundra.
Smith and leading climate scientists, including those from India, have stressed the importance of 'downscaling' global models to regional and perhaps even local levels, which requires, among other things, advanced computing power.
Research efforts under way to do so could offer more precise information and help in better planning.
R Krishnan's group at the Indian Institute of Tropical Meteorology in Pune is leading the South Asia component of the World Climate Research Programme's Coordinated Regional Downscaling Experiment (CORDEX) to help develop more-reliable regional climate change models that contribute to the climate research community's understanding of regional climate and monsoon issues under a changing climate, beyond AR5.
Similar CORDEX studies are being done in other regions of the world.
Others, such as the MS Swaminathan Foundation for Research (MSSRF) in Chennai, are working on ground solutions to adapt to a changing climate.
MS Swaminathan, one of India's top crop experts and the father of India's 'green revolution' in the 1960s, expressed particular concern over the AR5 report's projections on sea level rise, which have wide implications for several South Asian countries, including Bangladesh, India, Maldives, and Sri Lanka.
In 2010, his foundation set up in Vedaranyam in southern India a 'genetic garden' of salt-loving plants to help safeguard the livelihoods of coastal communities against a rise in sea level.
The genetic garden provides the raw materials to allow genes for salinity tolerance to be isolated and helps in 'seawater farming': growing crops in coastal areas where sea water is the main water resource. One-third of the world's population are estimated to live in coastal areas.
MSSRF has also initiated studies on the potential of mangroves to act as barriers to protect against rising sea levels. India's West Bengal state and Bangladesh share one of the largest mangrove systems in the world: Sundarbans. At the recent science academies meeting in New Delhi, the Bangladesh Academy of Sciences expressed interest in working with MSSRF in this area.