Claim: 0.7C / Century is Exceptional

Guest essay by Eric Worrall

A new study published in SAGE claims that 0.7C / century warming is exceptional, because on average temperature change over the last 9500 years, after smoothing away short term wobbles, was 0.1C -0.01C / century.

The Anthropocene equation

Owen Gaffney, Will Steffen

The dominant external forces influencing the rate of change of the Earth System have been astronomical and geophysical during the planet’s 4.5-billion-year existence. In the last six decades, anthropogenic forcings have driven exceptionally rapid rates of change in the Earth System. This new regime can be represented by an ‘Anthropocene equation’, where other forcings tend to zero, and the rate of change under human influence can be estimated. Reducing the risk of leaving the glacial–interglacial limit cycle of the late Quaternary for an uncertain future will require, in the first instance, the rate of change of the Earth System to become approximately zero.

Read more: http://journals.sagepub.com/doi/full/10.1177/2053019616688022

The money quote;

… From 9500 to 5500 years BP global average temperature plateaued, followed by a very slight cooling trend (Marcott et al., 2013). Over the last 7000 years the rate of change of temperature was approximately −0.01°C/century. Over the last hundred years, the rate of change is about 0.7°C/century (Intergovernmental Panel on Climate Change (IPCC), 2013), 70 times the baseline – and in the opposite direction. Over the past 45 years (i.e. since 1970, when human influence on the climate has been most evident), the rate of the temperature rise is about 1.7°C/century (NOAA, 2016), 170 times the Holocene baseline rate. …

Read more: Same link as above

What is wrong with this picture?

Marcott himself explained in an interview with Real Climate that his data has been heavily smoothed – that any short term warming trends in the past, which were similar to late 20th century warming, could have been eliminated from the climate record by his methodology.

Q: What do paleotemperature reconstructions show about the temperature of the last 100 years?

A: Our global paleotemperature reconstruction includes a so-called “uptick” in temperatures during the 20th-century. However, in the paper we make the point that this particular feature is of shorter duration than the inherent smoothing in our statistical averaging procedure, and that it is based on only a few available paleo-reconstructions of the type we used. Thus, the 20th century portion of our paleotemperature stack is not statistically robust, cannot be considered representative of global temperature changes, and therefore is not the basis of any of our conclusions. Our primary conclusions are based on a comparison of the longer term paleotemperature changes from our reconstruction with the well-documented temperature changes that have occurred over the last century, as documented by the instrumental record. Although not part of our study, high-resolution paleoclimate data from the past ~130 years have been compiled from various geological archives, and confirm the general features of warming trend over this time interval (Anderson, D.M. et al., 2013, Geophysical Research Letters, v. 40, p. 189-193;

Read more: http://www.realclimate.org/index.php/archives/2013/03/response-by-marcott-et-al/

The instrumental record itself provides evidence of short term warming periods comparable to the modern warming – including warming periods which occurred well before anthropogenic CO2 could have had a significant effect.

The following is from an interview with one of the stars of the Climategate Emails, Dr. Phil Jones, former director of the Climatic Research Unit;

…

A – Do you agree that according to the global temperature record used by the IPCC, the rates of global warming from 1860-1880, 1910-1940 and 1975-1998 were identical?

An initial point to make is that in the responses to these questions I’ve assumed that when you talk about the global temperature record, you mean the record that combines the estimates from land regions with those from the marine regions of the world. CRU produces the land component, with the Met Office Hadley Centre producing the marine component.

Temperature data for the period 1860-1880 are more uncertain, because of sparser coverage, than for later periods in the 20th Century. The 1860-1880 period is also only 21 years in length. As for the two periods 1910-40 and 1975-1998 the warming rates are not statistically significantly different (see numbers below).

I have also included the trend over the period 1975 to 2009, which has a very similar trend to the period 1975-1998.

So, in answer to the question, the warming rates for all 4 periods are similar and not statistically significantly different from each other.

…

Read more: http://news.bbc.co.uk/2/hi/8511670.stm

There is no evidence of anything exceptional about the rate of post 1970 warming, compared to pre-1970 warming. The suggestion by the authors that warming is currently occurring at an unusual rate is nonsense.

Update (EW): Corrected the first paragraph, the authors claim an average trend of -0.01C / century over the last 7000 years, not 0.1C / century.

Update 2 (EW): ClimateReason provided a link to an excellent post he provided in 2013, which uses the Central England Temperature record to demonstrate how dramatic an impact smoothing of historic data has on the representation of the temperature data.