What Scientists Have to Say About Global Cooling

Tue, 2009-04-28 14:04Jeremy Jacquot
Jeremy Jacquot's picture

What Scientists Have to Say About Global Cooling

Scientists have been quietly gnashing their teeth in frustration over deniers’ latest attempts to pervert their research on global warming. Until now.

In an article published in the latest issue of the journal Geophysical Research Letters (sub. required), David R. Easterling of NOAA’s National Climatic Data Center and Michael F. Wehner of the Lawrence Berkeley National Laboratory set out to refute the “global cooling” lies peddled by Fox News, The Washington Post, and the Republican Party once and for all.

They start off by pointing out that periods of no trend or even slight cooling in the globally averaged surface air temperature record have been quite common in the last 34 years and in climate model simulations of the 20th and 21st centuries so the most recent trend is nothing new. In fact, given the natural variability inherent in the climate, they say that it is highly likely that we will experience several more periods of a decade or two where there is no trend, or slight cooling, “in the presence of longer-term warming.”

The myth of “global cooling” has largely been perpetuated by deniers who zealously cherry pick the data, fitting linear trend lines to particular decadal temperature records, to “reinforce their point of view,” the authors say. Indeed, deniers often single out the 1998 – 2008 period, during which there was no significant trend, to argue that global warming has stopped, for instance.

That’s a red herring because one could just as easily fit the trend to the 1999 – 2008 period and obtain a statistically significant positive trend (1998 having been an unusually warm year because of the strong El Niño).

Or take the 1977 – 1985 and 1981 – 1989 periods: Looked at individually, they both show no trend but, when embedded in the 1975 – 2008 period, they become part of a larger, substantial warming trend (the top left graph in the image is a close-up of the 1977 – 1985 period and the top right one is a close-up of the 1981 – 1989 period).

While it may seem easy to fixate on these short-term trends, there’s a very simple reason for why scientists do not do so: they don’t matter. Easterling and Wehner:

Climate scientists pay little attention to these short-term fluctuations as the short term “cooling trends” mentioned above are statistically insignificant and fitting trends to such short periods is not very meaningful in the context of long-term climate change.”

To further disprove the deniers’ claims, the authors ran a series of climate model simulations to look for both positive and negative decadal trends in the projected temperature record for the 21st century. One of their simulations, while predicting an overall warming trend of about 4°C by the end of the century (in line with most IPCC models), showed that the 2001 – 2010 and 2016 – 2031 periods would not see a clear trend, or, at most, see a small, statistically insignificant cooling trend.

Because the model was run without any simulated volcanic eruptions or solar variability (which could result in prolonged periods of cooling), Easterling and Wehner attributed the observed trends entirely to natural internal variability.

Overall, they found that there was about a 5% chance of a negative decadal trend occurring during the 21st century; if they restricted their timeline to only the first half of the 21st century, the probability of a negative decadal trend rose to 10%.

Their simulations also demonstrated that, as greenhouse gas forcing increases, the percentage of statistically significant positive trends increases – from 26% for the first half of the century to 47% for the entire century – while that of statistically significant negative trends decreases.

They conclude by stating the obvious: though the natural variability of the climate will likely produce several more periods of slight cooling or no change, the overall trend is one of significant, and sustained, warming.

Claims that a global warming is not occurring that are derived from a cooling observed over such short time periods ignore this natural variability and are misleading.”


Previous Comments

I think I get the point about natural variability over periods of years and even decades not adding up to a meaningful trend.

If thats true, and I think it is, then what do we have really in the temperature record? We have a hundred years of natural variability that doesn’t mean much and as we go back further in time the record becomes increasingly unreliable.

I understand the point, but I think it works both ways. If short term information is meaningless, then we really don’t have much.

I was going to post a long list of examples in which short term trends can mislead regarding the long term.  You don’t need me to do that, do you?  I’ll just provide one:  Look at the inexorable declines in alpine glaciers. 

Some people seem to think that the variability around the warming trend means we don’t have to worry about it so much.  Bizarre.  The variability around the trend means that wildlife will have a harder time adapting to the warming (e.g., I study sockeye salmon and selection for the ability to migrate up warmer rivers occurs only once every four years).  The variability around the trend means that we’ll have a harder time predicting and adjusting to the warming.  It’s a great failing that we (collectively) allow the reality of variability to stifle our efforts to recognize and mobilize to deal with long term problems.

“…Climate scientists pay little attention to these short-term fluctuations…”

Swanson and Tsonis 2009, postulated on a possible climate shift at 2001/2002. That would make the current non-warming trend, short as it it, important in that it supports the hypothesis of climate shifts occurring at the synchronizing of assorted oceanic climate oscillations. If they are right then this current episode is more than just decadal variability.


Money isnt important when its the nature who punishes the people. Bad credit loans are also good for small amount short term financing as well. So if you need some fast financing, an installment loan for bad credit might do the trick – you may want to go ahead and apply now!

COP20 UNFCCC DeSmog Canada

How to finance a global shift away from toxic greenhouse gases caused by burning fossil fuels was one of the key talking points during the first week of the annual United Nations climate change conference held this year in Lima, Peru.

The conference, which began Monday and is scheduled to end next Friday, started with a ...

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