Nicholas Stern argues that the time for debate on climate change is over | Environment | The Guardian

Nicholas Stern argues that the time for debate on climate change is over | Environment | The Guardian:

The point of no return

In an exclusive extract from his new book, Nicholas Stern argues that the time for debate on climate change is well and truly over

• Nicholas Stern
• The Guardian, Monday 30 March 2009

How is it that, in the face of overwhelming scientific evidence, there are still some who would deny the dangers of climate change? Not surprisingly, the loudest voices are not scientific, and it is remarkable how many economists, lawyers, journalists and politicians set themselves up as experts on the science. It is absolutely right that those who discuss policy should interrogate the science, because the implications for action are radical. However, they should also take the scientific evidence seriously and recognise the limitations on their own abilities to assess the science.

Contrary to the narrative that some have tried to impose on the debate, climate change is not a theory struggling to maintain itself in the face of problematic evidence. The opposite is true: as new information comes in, it reinforces our understanding across a whole spectrum of indicators. The subject is full of uncertainty, but there is no serious doubt that emissions are growing as a result of human activity and that more greenhouse gases will lead to further warming.

The last 20 years have seen special and focused attention from the Intergovernmental Panel on Climate Change (IPCC), which has now published four assessments, the most recent in 2007. With each new report, the evidence on the strength and source of the effects, and the magnitude of the implications and risks, have become stronger. Some people accuse the IPCC of having institutional and procedural structures which predispose it to alarmism. In fact, the IPCC is structurally conservative and requires very tight consensus among scientists from many backgrounds and nationalities.

As a result, statements are muted and it is likely that risks are understated. It mostly confines attention to the period until 2100, when the lags are such that still bigger damages appear later; and it leaves out effects which are likely to be important but on which strong, detailed quantitative evidence has yet to accumulate sufficiently.

Some of the marginally more sophisticated attempts at obfuscation focus only on mean expected temperature increases in the short term, rather than looking at a longer horizon or at the very real possibility of much higher increases. Look, they argue, the IPCC does not expect a temperature increase of much more than 2.5-3C by the end of the century; we can cope with that. This is a classic example of the misuse of evidence to divert attention from the main point - how to control the risk of bigger increases. By focusing on the limited time period and suppressing the uncertainty, the deniers deliberately miss the point: temperature increases of 4-5C and above are likely to be catastrophic. If we act strongly and effectively in the next decade, we can radically reduce the probability of those temperature increases at modest cost.

More recently, others have tried to argue that the warming has stopped because 1998 (a so-called El Niño year, with warmer surface temperature of oceans) was a little warmer on average than 2007 (a La Niña year, with cooler surface temperature of oceans). This confuses cycles with trends, peaks with troughs and sea temperatures with land temperatures. Further, it ignores that the last decade was the hottest since records began and that the trend is clearly upwards. But this is the kind of nonsense that some would try to peddle. There are many more half-baked attempts to try to naysay the science, but they always unravel on careful inspection. And the same has been true of more sophisticated attempts, such as those involving changing structures of humidity in the atmosphere.