Tag Archives: Holocene

What is global temperature?

When I write here about climate change you can be sure one or more trolls will pop up and tell me about the snow in the UK. Or accuse scientists of relying on this year’s New Zealand drought in their claims of climate change. It seems surprising that no matter how many times we point out the climate is not the same as weather, and global climate change is not the same as local or regional weather, some people seem to think such arguments are valid.

I have illustrated the difference before here – but here’s another example I picked up from Real Climate (see Response by Marcott et al.). The illustration is in response to the question of what is meant by global Temperature. Here’s what they say:

“Global average surface temperature is perhaps the single most representative measure of a planet’s climate since it reflects how much heat is at the planet’s surface. Local temperature changes can differ markedly from the global average. One reason for this is that heat moves around with the winds and ocean currents, warming one region while cooling another, but these regional effects might not cause a significant change in the global average temperature. A second reason is that local feedbacks, such as changes in snow or vegetation cover that affect how a region reflects or absorbs sunlight, can cause large local temperature changes that are not mirrored in the global average. We therefore cannot rely on any single location as being representative of global temperature change. This is why our study includes data from around the world.

We can illustrate this concept with temperature anomaly data based on instrumental records for the past 130 years from the National Climatic Data Center (http://www.ncdc.noaa.gov/cmb-faq/anomalies.php#anomalies). Over this time interval, an increase in the global average temperature is documented by thermometer records, rising sea levels, retreating glaciers, and increasing ocean heat content, among other indicators. Yet if we plot temperature anomaly data since 1880 at the same locations as the 73 sites used in our paleotemperature study, we see that the data are scattered and the trend is unclear. When these same 73 historical temperature records are averaged together, we see a clear warming signal that is very similar to the global average documented from many more sites (Figure 1). Averaging reduces local noise and provides a clearer perspective on global climate.”


Temperature anomaly data (thin colored lines) at the same locations as the 73 paleotemperature records used in Marcott et al. (2013), the average of these 73 temperature anomaly series (bold black line), and the global average temperature from the National Climatic Data Center blended land and ocean dataset (bold red line) (data from Smith et al., 2008).

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New “Hockey Stick” but same tired old denial

Ian Wishart is on his climate change conspiracy high horse again (see New global warming scandal hits climate science). His fevered imagination has managed to produce a “scandal” out of the publication of a scientific paper. Of course the scandal is based entirely on his climate change denial echo chamber. His denier mates have ripped into this paper. They are obviously very upset by it – more so than normal. It’s worth asking why?

I think the simplest answer lies with the word “Hockey Stick!” This phrase, together with reference to Dr Michael Mann, usually gets them foaming at the mouth. And it’s amazing what rubbish they can spout once so provoked.

This time they are reacting to a new “Hockey Stick” presented in a recent Science paper by Shaun A. Marcott, Jeremy D. Shakun, Peter U. Clark and Alan C. Mix. (see “A Reconstruction of Regional and Global Temperature for the Past 11,300 Years.”) The earlier research had extended back roughly 1,500 years, and suggested that the rapid temperature spike of the past century, believed to be a consequence of human activity, exceeded any warming episode during those years. This new work confirms that result while suggesting the modern warming is unique over a longer period.

The new work compiled the most meticulous reconstruction yet of global temperatures over the past 11,300 years, almost the entire Holocene. They used indicators like the distribution of microscopic, temperature-sensitive ocean creatures to determine past climate. The plots below compare these new results with those found by previous workers


The temperature reconstruction of Marcott 2013 (past 11,000 years) and a collection of reconstructions (past 1800 years) as presented by Mann 2008. (Credit: The two epochs of Marcott and the Wheelchair).

Wishart says the new paper “claimed to have validated the discredited “hockey stick” graph and proven that modern temperatures were the highest in four millennia.” He then goes on to use the authors’ simple acknowledgement that “The 20th century portion of our paleotemperature stack is not statistically robust” to claim their “story is rapidly unravelling” and that this is a “new global warming scandal.”

Bloody hell – is that all it takes to produce a scandal? For a scientist to point out limitations in part of their data (an area already extensively covered by other work)? What does Ian think – that every piece of scientific work must repeat in depth all the previous work? That no existing information can be used?

No of course not. He is just being dishonest. Using anything he can get hold of to weave a story discrediting honest science – and honest scientists. We have seen it all before in the lies he and his climate change denial mates promoted about Dr Michael Mann’s work – the work producing the original “Hockey Stick.”

For example, Wishart’s reference to “the discredited “hockey stick” graph” is a lie he promotes in his book “Con Air” (see  Alarmist con for my review) and is repeated ad nauseum in the climate denial echo chamber. But it is just not true. Far from being discredited this work has been validated again and again. It’s the critics of this work who have been discredited. Been caught lying.

I summarised this several years ago in my article Climate change deniers’ tawdry manipulation of “hockey sticks”. Have a look at that if you want details.

The climate change denial movement worked extremely hard to discredit the work of Michael Mann which produced the original “Hockey Stick.” Mann has described this campaign in his book The Hockey Stick and the Climate Wars: Dispatches from the Front Lines (see The truth about the hockey stick for my review of the book). Their campaign failed. This work has been discredited in one place only – the  biased mind of the committed climate change denier like Ian Wishart.

Meanwhile, if you wish to learn more about the Marcott (2013) paper and their work here are some links:

A Reconstruction of Regional and Global Temperature for the Past 11,300 Years.
Global Temperatures Highest in 4,000 Years
Response by Marcott et al.
Recent Warming Is Still Unprecedented In Speed, Scale And Cause: A Marcott Et Al. FAQ
Fresh Thoughts from Authors of a Paper on 11,300 Years of Global Temperature Changes

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