The report issued on September 27 by the UN's intergovernmental panel on climate change (IPCC) may sound similar to the one issued five years ago - after all, it says that humanity is causing climate change, though with more certainty. But on two key aspects this report has categorically said what was never said before.
The first is that the carbon accumulation in the atmosphere and resulting global warming have blown away the 2 degree Celsius tipping point that was earlier set. The present report says that to limit warming to a rise of 2 degrees Celsius above pre-industrial levels, 1,000 gigatons (trillion metric tons) is the outer limit of carbon dioxide that can be emitted. However, by 2011 humans had already emitted 531 gigatons. That leaves very little wiggle room. According to climate change experts, the 1,000-gigaton limit may well be crossed in the next 25 years.
The world has a total of 2,795 gigatons worth of carbon in the form of fossil fuels and reserves. Burning just 10% of these would take the earth over the tipping point. That's the stark message coming from the IPCC report.
The report makes the second categorical assertion regarding sea level rise. It says that sea levels are projected to rise by 28-97 centimetres by 2100. This is over 50% more than the previous projection of 18-59% over the same period. This increase is mainly because of better estimation methods and more observations. By the year 2300, it is projected that seas will be higher by up to a cataclysmic 3 meters.
Buried in the dense Summary for Policymakers, the report issued this week, is a series of future global scenarios. If you look at India, in the worst case scenario, temperatures will rise by up to 4 degrees Celsius and rainfall will increase by up to 20% over most of the sub-continent. Coupled with sea level along India's long coastline - on which are located megapolises like Mumbai, Chennai and Kolkata - this spells a dire picture by the turn of this century. Of course, this is the worst case scenario, in which carbon dioxide concentrations in the atmosphere have more than doubled from the present in the next 80-odd years.
How scientific and robust is the IPCC's statements and predictions? The whole process involved 9,200 scientific studies, reviewed by 1089 experts from 55 countries working in a multistage process. They received 54, 677 comments from scientists across the world. Over 2 million gigabytes of numerical data was analyzed before 209 authors put together the draft report. Then representatives of 195 countries went over it word by word.
Most scientists agree that the IPCC's reports are on the conservative side because they are forced to accommodate everybody, including governments that are wary of sounding too alarmist. In the present report, for instance, two observed facts leading to increasing carbon dioxide release are not fully taken aboard - the melting of permafrost and ocean acidification. Scientists have observed that both these on-going processes will cause an even greater amount of carbon dioxide to be released (or remain unabsorbed) than before. But these are not fully spelt out yet. Similarly warming of the deep sea (beyond 700 feet) is also not fully described or accounted for as the IPCC stopped collecting evidence 6 months ago, in order to start the consultation process.
