The report assesses available scientific evidence for seven major climate phenomena. Looking at historical patterns, it assigns a likelihood to whether a change in trend has taken place since 1950 and whether this is the consequence of human actions. Looking ahead, it makes a judgement on the prospects of these trends being reinforced over two time horizons - early 21st century and later 21st century.

Looking back over the past six decades, two out of the seven phenomena are seen to have had a high likelihood of intensification. These are "warmer and/or fewer cold days" and "warmer and/or more hot days" over land areas. Further, the human contribution to both these changes in trend is seen to have been very likely. The scientific evidence apparently is far less persuasive on the other five phenomena. Some are likely to have seen a change in trend over this period, while there is low confidence in reaching this inference in others. In one, "increase in intense tropical cyclonic activity", while the global trend is indiscernible, it is virtually certain to have happened in the North Atlantic - last year's Hurricane Sandy offers a vivid illustration of this!

Does the historical pattern matter? In particular, are predictions of future trends critically dependent on the precision with which models have explained past dynamics? This is always a dilemma in forecasting, whatever the domain of variables. Be that as it may, the mandate of the report is to assess the likelihood of these trends being reinforced over the course of the current century and this has been done. Keeping in mind all the caveats about forecast accuracy, there is a striking pattern to the forecasts. For the early 21st century time horizon, the highest probability classification for trend reinforcement is "likely" - as opposed to "virtually certain" or "very likely". Four of the seven phenomena are assigned this - besides the two mentioned above relating to daily temperatures, "heavy precipitation events" and "increased incidence/magnitude of extreme high sea level". Of the other three, one - "warm spells/heat waves" - was not formally assessed, while the remaining two - "increase in intensity/duration of drought" and "increase in intensity of tropical cyclone activity" - are phenomena for which there is relatively low confidence in an inference about intensification.

However, this pattern changes dramatically when the forecast horizon shifts to the late 21st century. Over this time frame, the two phenomena relating to daily temperature variations - fewer cold days and more hot days, respectively - are judged to have a virtual certainty of trend reinforcement. Three of the remaining five - heat waves, heavy precipitation events and higher sea levels - are seen to be very likely to see an intensification. The intensification of drought incidence is seen to be likely, while that of tropical cyclonic storms is seen to be more likely than not. Of course, as one drills deeper into the assessments, there are some regional differentiations that the scientific literature clearly highlights, but those are for future discussions. Let's look at some implications of this broad risk assessment for India.

The first significant issue is the horizon itself. The report suggests that the more dire consequences of climate change will manifest later in the century. This immediately introduces a demographic divide in the global debate on mitigation costs and who is to bear them. Obviously, the farther into the future the consequences are, the greater the stake that countries with young populations have. At the same time, the burden is to fall hardest on generations yet unborn. It is a truism that democratic politics always prioritises the interests of those who are "present and voting". Assuming that as a society we have a responsibility to not leave a scorched earth (literally!) behind for future generations, how do we institutionalise the effective protection of the interests of these generations?

Two other trends should also cause concern. The increase in the frequency of heavy precipitation events underscores the need for building infrastructure that can withstand heavy floods in areas that are prone to them. We saw just how much damage such flooding can do in the recent experience of Uttarakhand. Presumably, the hill states are going to be the most likely victims of more such events and every episode threatens to wipe out infrastructure constructed over decades. But hill regions are not the only ones vulnerable; flooding in river basins can also cause enormous damage and long-term disruption of livelihoods. Should we be thinking of significantly ramping up the disaster management mechanism?

The assessment does not specifically refer to rainfall trends, but we need to worry about the potential impact on spatial and temporal distribution. Our agricultural sector is struggling to meet the demand for many food products and the growing demand-supply imbalance has significant macroeconomic impacts. Are one or more of these climate phenomena going to exacerbate the problem through their impact on overall water availability?

The increase in sea levels has obvious significance for an economy with a long coastline. Apart from the direct physical impact, including freshwater contamination, there is a very significant issue of migration. This is not just a national issue; it has to be seen from a regional perspective, as significant coastal populations find it necessary to relocate, some, presumably, across national boundaries. Do we need to consider a regional mechanism that can anticipate the likely movements and propose measures that make them as less painful as possible for the affected people?

The most dire judgement of the report is that, no matter what is done from now on, the cumulative impact of previous emissions will be the predominant driver of the late 21st century outcomes. In other words, there is nothing we can do to stop the burn; at best, we can keep it on simmer. Everything now seems to rest on adaptation and mitigation.