Humans are dominant cause of climate change

As the IPCC delivered their fifth assessment report on climate change they were very keen to stress that despite the vast amount of media coverage it will no doubt generate, their role was one of sober scientific analysis – not headline makers.

That is admirable, and as the press conference held at launch of the report went on it was obviously something that they were keen to stick to. However, when one of the key messages of the report is that ‘human influence has been the dominant cause of the observed warming since the mid-20th century’, then they’ll be only too aware that headlines is exactly what they’ll get.

The 36-page report (http://www.ipcc.ch/report/ar5/wg1/), which has 259 authors from 39 countries, is perhaps the most comprehensive statement on climate change yet. And they find that: "The atmosphere and ocean have warmed, the amount of snow and ice has diminished, the global mean sea level has risen and that concentrations of greenhouse gases have increased," summarised Qin Dahe, co-chair of IPCC working group one, who produced the report.

One of the biggest challenges said co-chair Dr Thomas Stocker was to put their findings into everyday language. Not only for the benefit of members of the public but also, and perhaps more importantly, for the policy makers around the world. This was something that the IPCC have ‘proudly achieved’ according to Dr Stocker After a week of intense negotiations, in the form of a ‘summary for policy makers’ on the physical science of global warming.

But a larger challenge is of course the uptake of the advice. The IPCC has suffered criticism in the past over both its methods and its conclusions, something that has surfaced again recently due the wide reporting of the ‘global warming hiatus’. This is something that is downplayed in this report, but slowing of global warming has, at least in public opinion, caused some damage to the IPPC. At worst climate change deniers have used it to fluff up their feathers and cry wolf; at best people have questioned why the models used by the IPCC couldn’t foresee this.

Yet this is a problem of understanding say the IPCC – their methods and models are not designed to take into account short term anomalies, but rather long term trends. The 15 year hiatus is they say nothing more than natural short term variability – likely to be caused by the ability of the oceans to act as a heat-sink. In terms of longer term trends however the IPCC models are robust and confer a high level of confidence to climate scientists around the globe.

At the press conference the IPPC stressed that there may well be other short term changes which they haven’t ­– and indeed didn’t seek to – predict, but we must distinguish the ability to predict long term trends from the ability to predict specific anomalies. Let’s hope that the governments of the world take note of that and begin to legislate accordingly.