If The Climate Scientists Don’t Know Then The Politicians Certainly Won’t

The latest satelite data confirms that the trend in global temperatures has been flat for 17 years. Graphic: courtesy WoodForTrees.org

The latest satellite data confirms that the trend in global temperatures has been flat for 17 years. Graphic: courtesy Paul Clark of WoodForTrees.org. Click to enlarge.

This week’s leak of the doom-laden second instalment of the report from the Intergovernmental Panel on Climate Change (IPCC) coincided with the publication of the latest satellite data on global temperatures showing a continuation in the so called global warming pause.

These two items neatly summarise the dilemma facing policy makers over the climate. On the one hand, there are warnings of food shortages, heat waves and death resulting from future climate change and on the other is data showing that the trend in global mean atmospheric temperatures has been flat for 204 months or 17 years.

For the world as a whole there are huge economic costs involved in avoiding the dangers of climate change; and potentially deadly consequences if we fail to act and the climate warms catastrophically. In Britain this issue is crystallising around the debate on energy policy and the cost of decarbonising electricity generation that is currently contributing to higher consumer energy bills. UK tabloid daily newspaper The Sun has started a petition to “cut the hated green levies” while the coalition government is showing signs of being split along party lines on this issue.

Leaked report predicts food shortages

Last week saw the completion of the draft Summary For Policy Makers of the second instalment of the IPCC’s fifth assessment report – the AR5 WGII report entitled Climate Change 2014: Impacts, Adaptation and Vulnerability. This report due for publication in March follows on from the draft of the IPCC’s science report that was published in September. The draft of the second instalment was leaked by climate sceptic website nofrakkingconsensus.com.

The leaked report, which could well be edited before publication in March, looks at the potential impacts of future climate change. The leaked document does not beat about the bush in its scary forecasts. Here is what it says about food crop production: “climate change will reduce median yields 0 to 2% per decade for the rest of the century, as compared to the baseline without climate change. These projected impacts will occur in the context of rising crop demand, projected to increase by about 14% per decade until 2050,” it says. Read that as higher food prices, food shortages and famine.

Meanwhile, satellite data has just been published for global mean atmospheric temperatures for October. The data shows that the trend in global mean temperatures has been flat for 17 years. Now to be fair, there is some debate about when exactly the pause started depending on the data that is used and how it is analysed. The IPCC dates the pause from 1998 while MIT atmospheric physicist and climate sceptic Richard Lindzen has stated: “There has been no warming since 1997 and no statistically significant warming since 1995”.  There is no debate that this millennium there has been a pause in the global warming trend that accelerated in the late 20th century.

There is a significance to the 17 year figure as some of the climate sceptics are already pointing out. In an important scientific paper published in 2011 climate scientists analysed what is known as signal-to-noise ratio in the climate system – the effects of all those awkward natural swings and variations that send temperatures up and down and confuse our attempts to understand what is happening. They determined that the minimum period necessary to spot a human impact on the climate was 17 years – the implication of the latest data is clear: we have had 17 years with no detectable human impact on global temperatures.

So what is going on? Why has the IPCC and most of the climate science community been forecasting that temperatures would rise for almost a quarter of a century while global mean temperatures appear to have flat-lined since the mid-1990s. The short answer is that the climate scientists do not know.

IPCC implicitly acknowledged greater uncertainty by increasing its range of forecasts

In its latest science report the IPCC implicitly acknowledged that it was less certain about what would happen in the future than it has been in the past by widening its range of projected future temperature increases. Science should be about working to reduce uncertainties not increasing them and yet the closer the IPCC scientists have looked at the data, the less certain they have become about the future. But the tone of IPCC statements and publications, such as the new document on the impacts of global warming, continues to sound as certain as ever.

There is no shortage of potential explanations for the hiatus in temperature. There is a suspicion among some scientists that natural variations in climate may play a bigger role than has been admitted until now even though the IPCC insists that the warming seen during the second half of the 20th century is entirely due to human emissions of carbon dioxide. There are uncertainties about the role of volcanic dust and other aerosols in the atmosphere and also about the role of the solar magnetic field.

The oceans – which account for nine-tenths of the energy in the climate system – are soaking up a proportion of the heat but the sums do not yet add up sufficiently well to explain the pause. There is “insufficient data” on the uptake of heat into the ocean system to fully  explain the current observed pause in atmospheric temperature, is how it was put by Professor Thomas Stocker, the Co-Chair of the committee that wrote the IPCC science report, speaking in September.

The truth is that we do not know what is happening. If we fully understood these processes then our understanding would have been programmed into our computerised climate models and they would have been able to provide accurate forecasts. The fact is that they can not. As the IPCC tacitly admitted in its September science report: “There are, however, differences between simulated and observed trends over periods as short as 10 to 15 years”. The trouble is that the period of the difference continues to grow.

Do computer models over-estimate the carbon sensitivity of the atmosphere?

The suggestion is that computer models consistently over-cook the heating impact of carbon dioxide – the so called sensitivity of the atmosphere. Climate scientist Dr Roy Spencer, a leading sceptic, analysed the performance of climate models against real observations and found that most of them get it wrong most of the time. In a typically combative blog post he wrote: “In my opinion, the day of reckoning has arrived. The modellers and the IPCC have willingly ignored the evidence for low climate sensitivity for many years”.

Climate models warm faster than reality. Courtesy: Dr Roy Spencer. Click to enlarge.

Climate models warm faster than reality. Graphic: courtesy: Dr Roy Spencer. Click to enlarge.

Now many who are not climate sceptics will take the view that he would say that, wouldn’t he? And that, in a sense, goes to the heart of the political dilemma. There is a split on views about the climate that seems curiously to break along political lines. In general terms, climate sceptics tend to be on the right of the spectrum and those who believe in dangerous human-driven climate change tend to be on the liberal left of the political spectrum.

An objective scientific reality exists irrespective of what you want to believe

This is senseless. Why should your politics affect what is happening in the climate? Physics is not political. The climate is not political. Climate change is not political. It does not matter to the laws of physics whether you personally believe in the dangers of human-driven climate change or not. For there is an objective scientific reality out there that exists irrespective of any of our political beliefs and irrespective of whatever we individually choose to believe about the climate.

And the fact is that right now we do not fully understand what that objective scientific reality is – and the evidence for saying this is the failure of the computer climate models to explain observations.

This means that any politician who makes a definitive statement about the state of the climate and the inevitability or not of climate change is talking rubbish and that any attempt to set policy on the basis of such statements is at best misguided.

If the climate scientists don’t know what is happening – the politicians certainly won’t.


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The link to the leaked IPCC ART5 WGII SPM report “Climate Change 2014: Impacts, Adaptation and Vulnerability” is here.

The link to the satellite temperature data set is here. A link to WoodForTrees.org analysis is here and a discussion of the significance on the sceptical website wattsupwiththat.com here.

The links to Dr Roy Spencer’s climate model blog posts are here and here

The link to the paper on signal-to-noise ratios in the climate system is here.

Citation: Santer, B. D., et al. (2011), “Separating signal and noise in atmospheric temperature changes: The importance of timescale”, J. Geophys. Res., 116, D22105, doi:10.1029/2011JD016263


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