The floods that hit Uttarakhand state in northern India in mid-July 2013 were originally thought to have killed 600 people, though the state government was quick to warn that the true number might be much higher because so many were missing. Very few of the latter missing can have survived, and the death-toll is now put at 5,700.

The district subject to the most intense flooding, with its temple towns, is popular with visitors in May and June, though most leave by late July when the most intense period of the monsoon season makes transport difficult. This year, though, the rains came earlier and with a far greater intensity, leading to the catastrophe that has now unfolded.

The events in Uttarakhand closely follow a report from the World Meteorological Organisation (WMO) on weather trends in the first decade of the 21st century, which focuses in part on the increased intensity of severe weather events and their likely link to carbon emissions and climate change. The WMO report - The Global Climate 2001-2010: A Decade of Climate Extremes - is particularly useful because it examine a whole decade and compares it with earlier ones, a process that puts smaller fluctuations in perspective and gives a clearer picture of underlying trends (see Alex Kirby, “Unprecedented climate extremes marked last decade, says UN”, Guardian Environment Network, 3 July 2013).

A basic finding is that in the century from 1901-10 to 2001-10, average temperature rose by 0.88 degrees Centigrade - but more than half of that rise has occurred in the past thirty years, which confirms many other observations that climate change is accelerating. The WMO also confirms its asymmetry, citing the near-Arctic as a region of rapid warming that is affecting not just sea-ice but also the Greenland ice-cap.

The data on sea-level rise contains a surprise. The overall change since the 1880s is 20 centimetres but here too the process is accelerating; the observed trend in the 20th century was an average rise of 1.6 millimetres per year, but a combination of melting and thermal expansion means that in the past decade this has nearly doubled to 3 mm per year.

The WMO puts great emphasis on extreme weather events, highlighting analysis showing that such events - floods, droughts, hurricanes or other phenomena - are indeed becoming more radical in their scale and effects. The wildfires in Russia and the appalling floods in Pakistan are recent examples of disasters of a kind that may not be more frequent than in the past but are much more extreme when they do happen. What might once have been seen as a “hundred-year event” is coming to be more like a twenty- or thirty-year one.

The WMO secretary-general Michel Jarraud says: “Rising concentrations of heat-trapping greenhouse gases are changing our climate, with far-reaching implications for our environment and out oceans, which are absorbing carbon dioxide and heat”. This last point is important, because the current role of the oceans as carbon-sponge and heat-sink may be disguising the impact of increases in carbon-dioxide and methane; there is little understanding, though, of how long this might continue.

The trend also links to the "southern oscillation" (the El Niňo and La Niňa events), a process of ocean-current fluctuations centred primarily on the southern Pacific Ocean but which also has an impact right across southeast Asia and the Indian Ocean through to sub-Saharan Africa. El Niňo events tend to result in higher temperatures, whereas La Niňa events lead to cooling; the fact that the latter were more numerous than the former in the 2001-10 decade may be disguising the rate of climate change. The balance, however, is expected to reverse in the latter part of the current decade, with El Niňo events becoming more frequent. If that happens, human-induced climate change and El Niňo events will be in sync, making for rapid climate change as the 2020s approach.

The price of action

The value of the WMO's work is the way it transcends ordinary timescales. It is easy for climate-change deniers to point to a very warm year like 1998 and argue that since subsequent years were cooler, climate change is a myth. A decade-by-decade approach, and a view that covers the century or more since accurate temperature measurements started, give a much clearer picture of the emerging situation - one, moreover, based on observations not models or predictions.

That is still not enough, though, to persuade policy-makers and others of the urgent need for responsible action. The denial lobby remains very strong and well-funded, not least by fossil-fuel companies and free-market foundations. Its efforts, supported by George W Bush and his fellow deniers, ensured that more than a decade has been lost. As a result there is even more catching up to be done (see "The climate shift: think and prepare", 6 June 2013).

A combination of two factors creates a possible route beyond the impasse: the increased severity of individual weather events, and the expected “warm-up” of the late 2010s. That might just be enough to induce a truly serious shift in political outlooks. By then the steps required will be even more radical than they are now, and there will have been death and suffering on a far larger scale than seen in northern India in recent days. It is a grim reflection on society if, as it appears, the transformation needed can only come in the wake of great misery.