UK Temperatures are no higher now in February & April-July than they were in the 18th & 19th Centuries: how exceptional is recent global warming?

COMPARING temperatures today with those of the last few hundred years is a comparison with a period science recognises as being cold, both in the UK and globally: the so-called Little Ice Age (LIA). The various paleoclimate global temperature reconstructions in Figure 1 show a range of values for the magnitude of global warming over the last 300 years or so but they all agree that there was a LIA and that the coldest part of it was the 17th Century: In the case of Mann99 (Figure 1) (the so-called 'hockey stick'), the warming since the 17th Century is about 0.5 C whereas other reconstructions such as Esper02 and Moberg05 show greater warming of about 0.8 C. Therefore it is expected that today's temperatures should appear warm relative to the LIA but this is not how recent global warming is being presented. The IPCC TAR says "Relatively colder hemispheric or global-scale conditions did appear to set in after about AD 1400 and persist through the 19th century, but peak coldness is observed during substantially different epochs in different regions. By contrast, the warming of the 20th century has had a much more convincing global signature. This is consistent with the palaeoclimate evidence that the rate and magnitude of global or hemispheric surface 20th century warming is likely to have been the largest of the millennium, with the 1990s and 1998 likely to have been the warmest decade and year, respectively, in the Northern Hemisphere". So the IPCC view is that the global warming in the 20th Century is unusual in the context of the last Millennium and that it is much more dramatic than a simple case of the global temperature re-bounding since the end of the LIA and that there is no doubt that this warming includes a significant Man-made component.

Figure 1 A selection of paleoclimate reconstructions for the last Millennium showing a warming over the last few hundred years of 0.5 to 0.8 C

How much warming in the UK does a 1 C global warming cause?

PERHAPS the best paleoclimate reconstructions are those based on the global borehole datasets because the sites contributing data are more global in extent and because the measurements depend on a physical process (conduction) rather than the very variable processes of biological growth as in the case of tree rings (Pollack & Huang, 2000). Global Temperatures of the last Five Centuries shows a rise in global temperature since 1500 of 1 C based on global boreholes (Figure 2) which is greater than the paleoclimate reconstructions shown in Figure 1.

SO according to Figure 2 there has been a global warming of about 0.9 C since 1700 when the earliest temperature records in the UK commenced: it is called 1 C for the purposes of this study.

THE Central England Temperature (CET) is the longest temperature record in the world commencing in 1659. A previous study by the author examined the CET from 1700-2004 and compared 1970-2004 data with nine earlier 30 year periods using t-tests on monthly, seasonal and annual data. The interesting and surprising result was that the warming trend over the 300 year period was seasonal being greatest in autumn and early winter while five months of the year showed very little warming. The results of these t-tests are shown in Table 1 below:

Table 1 Mean values of CET for 1971-2004 compared with nine preceding 30 year periods commencing 1700-1729: monthly, seasonal and annual values and results of t-tests comparing 1971-2004 values with earlier 30 year periods


			Mean CET (C) for each 30 year period and result of t-tests comparing 1970-2004 mean with earlier periods
				^* significant at 5% level ^ significant at 1% level ^* significant at 0.1% level
	__________________________________________________________________________________________

	Jan	Feb	Mar	Apr	May	Jun	Jul	Aug	Sep	Oct	Nov	Dec	Win	Spr	Sum	Aut	Ann
__________________________________________________________________________________________________
1700-29	3.1^*	3.7	5.0^**	7.9	11.3	14.4	15.9	15.8	13.5	9.5^***	6.2^**	4.0^**	3.6^**	8.0^**	15.4	9.7^***	9.2^***
1730-59	3.4	3.8	5.2^**	7.7	11.2	14.5	16.1	15.8	13.8	9.5^**	6.0^**	4.1^*	3.8^*	8.1^**	15.5	9.7^**	9.3^**
1760-89	2.3^***	3.6	4.8^**	8.0	11.5	14.6	16.2	15.8	13.4	9.2^***	5.5^***	3.8^**	3.2^***	8.1^*	15.5	9.4^***	9.1^***
1790-19	2.7^**	4.2	5.2^**	7.9	11.2	14.2	15.9	15.7^*	13.1^*	9.6^*	5.5^***	3.2^***	3.4^***	8.1^*	15.2	9.4^***	9.0^***
1820-49	2.6^**	3.8	5.5^*	8.0	11.6	14.6	15.7^*	15.3^**	13.0^**	9.7^*	6.3^**	4.5	3.6^**	8.4	15.2^*	9.7^***	9.2^***
1850-79	3.7	4.2	5.2^**	8.3	10.8^*	14.3	16.0	15.6^**	13.2^*	9.7^*	5.4^***	4.0	4.0	8.1^**	15.3	9.4^***	9.2^***
1880-09	3.4	3.9	5.1^**	7.7	10.8^*	14.1	15.8^*	15.2^**	13.2^*	9.1^***	6.3^*	3.9^**	3.7^**	7.9^***	15.0^**	9.6^***	9.1^***
1910-39	4.4	4.4	5.7	7.8	11.5	14.2	15.9	15.6^*	13.3^*	9.7^*	6.1^*	4.7	4.5	8.3	15.2^*	9.7^***	9.4^**
1940-69	3.2^*	3.6	5.8	8.5	11.4	14.5	16.0	15.7^*	13.7	10.5	6.5	4.4	3.7^*	8.6	15.4	10.2	9.5^*
1970-04	4.2	4.3	6.3	8.1	11.5	14.2	16.5	16.3	13.8	10.5	7.0	5.0	4.5	8.6	15.7	10.4	9.8

					Number of significant t-tests at each level (Maximum 9)

__________________________________________________________________________________________________
5%	2	0	1	0	2	0	2	3	4	4	2	1	2	2	2	0	1
1%	2	0	6	0	0	0	0	3	1	1	3	3	3	3	1	1	2
0.1%	1	0	0	0	0	0	0	0	0	3	3	1	2	1	0	7	6

Totals	5	0	7	0	2	0	2	6	5	8	8	5	7	6	3	8	9
___________________________________________________________________________________________________

Figure 3 shows the three different records and the overlapping periods do not indicate any significant discontinuities so no corrections for homogeneity were required. These three records provide 236 years of data enabling a comparison between recent data and temperatures in the latter part of the Little Ice Age. In the following analyses, a continuous temperature record for Edinburgh from 1764 to 1999 was created by utilising the full 1764-1896 dataset of Mossman, 1897-1960 from Edinburgh Observatory and 1961-1999 from Edinburgh Airport.

Figure 3 Timeseries showing the three Edinburgh annual mean temperature records: Mossman, 1764-1896; Observatory, 1880-1960; Airport, 1951-99.

T-TESTS (two-tailed, unpaired) were used to compare monthly values of Edinburgh mean temperature from 1970-1999 with seven preceding thirty year periods commencing 1764-89 (just 26 years in this first case) and comparative tests were done for seasonal and annual values. Table 2 shows the results which can be summarised as follows:

Table 2 Mean values of Edinburgh Temperature for 1970-1999 compared with seven preceding 30 year periods commencing 1764-1789 (only 27 years in this first period) : monthly, seasonal and annual values and results of t-tests comparing 1970-1999 values with earlier 30 year periods


			Mean Temperature for each 30 year period and result of t-tests comparing 1970-1999 mean with earlier periods
				^* significant at 5% level ^ significant at 1% level ^* significant at 0.1% level
	__________________________________________________________________________________________

	Jan	Feb	Mar	Apr	May	Jun	Jul	Aug	Sep	Oct	Nov	Dec	Win	Spr	Sum	Aut	Ann
__________________________________________________________________________________________________
1764-89	2.0^***	3.2	4.1^***	7.1	10.2	13.1	15.1	14.6	11.7^**	8.1^***	4.6^***	3.3^*	2.8^***	7.1 ^*	14.3	8.2^***	8.1^***
1790-19	2.5^*	3.5	4.5 ^**	7.0	10.1	13.2	15.0	14.6	12.1	8.7^*	4.6^***	2.6^***	2.9^**	7.2^*	14.3	8.5^***	8.2^***
1820-49	2.4 ^*	3.5	5.1	7.2	10.2	13.2	14.6	14.0 ^*	12.0	8.7^*	5.5 ^**	4.1	3.4	7.5	13.9	8 .7^**	8.4 ^**
1850-79	3.2	3.7	4.6 ^**	7.2	9.7	13.3	14.9	14.4	12.0	8.6 ^{* *}	5.0 ^**	3.9	3.6	7.2 ^*	14.2	8.6 ^***	8.4 ^**
1880-09	3.5	3.8	4.8 ^*	7.1	9.8	12.9	14.5	14.3	12.4	8.6 ^*	6.0	3.8	3.7	7.2 ^*	13.9	9.0	8.5 ^*
1910-39	4.1	4.2	5.1	6.9	9.8	12.8	14.7	14.4	12.3	8.9	5.8	4.5	4.2	7.3 ^*	14.0	9.0	8.6
1940-69	3.0	3.2	5.1	7.5	9.8	12.9	14.5 ^*	14.1 ^*	12.5	9.7	6.0	4.2	3.4	7.5	13.8 ^*	9.4	8 5
1970- 99	3.6	4.0	5.6	7.3	10.1	13.0	14.9	14.8	12.5	9.5	6.0	4.3	4.0	7.7	14.2	9.4	8.8

					Number of significant t-tests at each level (Maximum 7 )

__________________________________________________________________________________________________
5%	2	0	1	0	0	0	1	2	0	1	2	1	0	5	2	0	1
1%	0	0	2	0	0	0	0	0	1	1	2	0	1	0	1	1	2
0.1%	1	0	1	0	0	0	0	0	0	3	0	1	1	0	0	3	2

Totals	3	0	4	0	0	0	1	2	1	5	4	2	2	5	3	4	5
___________________________________________________________________________________________________

IN addition to the t-tests, the monthly, seasonal and annual data for 1970 to 1999 are also compared graphically with the data from the seven preceding 30 year periods in Figures 3 to 19. A few comments are presented for each graph. Equivalent graphs for the CET can be found here.

Figure 3 Comparison of Edinburgh January mean temperature from 1970 to 1999 with data from seven preceding 30 year periods

Figure 4 Comparison of Edinburgh February mean temperature from 1970 to 1999 with data from seven preceding 30 year periods

Figure 5 Comparison of Edinburgh March mean temperature from 1970 to 1999 with data from seven preceding 30 year periods

Figure 6 Comparison of Edinburgh April mean temperature from 1970 to 1999 with data from seven preceding 30 year periods

Figure 7 Comparison of Edinburgh May mean temperature from 1970 to 1999 with data from seven preceding 30 year periods

Figure 8 Comparison of Edinburgh June mean temperature from 1970 to 1999 with data from seven preceding 30 year periods

Figure 9 Comparison of Edinburgh July mean temperature from 1970 to 1999 with data from seven preceding 30 year periods

Figure 10 Comparison of Edinburgh August mean temperature from 1970 to 1999 with data from seven preceding 30 year periods

Figure 11 Comparison of Edinburgh September mean temperature from 1970 to 1999 with data from seven preceding 30 year periods

Figure 12 Comparison of Edinburgh October mean temperature from 1970 to 1999 with data from seven preceding 30 year periods

Figure 13 Comparison of Edinburgh November mean temperature from 1970 to 1998 with data from seven preceding 30 year periods

Figure 14 Comparison of Edinburgh December mean temperature from 1970 to 1998 with data from seven preceding 30 year periods

Figure 15 Comparison of Edinburgh winter mean temperature from 1970 to 1998 with data from seven preceding 30 year periods

Figure 16 Comparison of Edinburgh spring mean temperature from 1970 to 1998 with data from seven preceding 30 year periods

Figure 17 Comparison of Edinburgh summer mean temperature from 1970 to 1998 with data from seven preceding 30 year periods

Figure 18 Comparison of Edinburgh autumn mean temperature from 1970 to 1998 with data from seven preceding 30 year periods

Figure 19 Comparison of Edinburgh annual mean temperature from 1970 to 1998 with data from seven preceding 30 year periods

SO in summary of Table 2 and Figures 3 to 19, the Edinburgh climate has certainly warmed since 1764 as you would expect from the rise in global temperature shown in Figure 2 but like the CET, this warming has been seasonal being greatest in autumn and early winter while the April-July period has warmed only slightly.

IT is relevant here to identify both similarities and differences between the t-test results for the CET and Edinburgh temperatures.

THE general consistency in the results at both sites is not surprising as they are only 300 or so miles apart (correlation coefficient between annual values 1764-1999 is +0.847, P<0.001) but the results corroborate each other confirming the seasonality in the warming trend in the UK over the last 300 years. Both Table 2 and Figures 3-19 clearly show that compared with the background noise in the Edinburgh temperature data which is a result of the large variability in weather patterns, the warming introduced by the rise in global temperature of 1 C is relatively small and not exceptional: mean annual temp in Edinburgh rose 0.6 C from 8.2 C 1764-1849 to 8.8 C 1970-1999. The CET shows similar results with a rise of 0.6 C from 9.2 C in the 18th Century to 9.8 C from 1970-2004. So yes, the UK climate has certainly warmed since the LIA but this warming is not earth-shattering. And the answer to the question, how much warming in the UK does a rise in global temperature of 1 C cause is 0.6 C.

What are the implications of these results for the UK climate?

THIS surprising result that five months of the year have warmed little since the latter part of the LIA (the 18th & 19th Centuries) means:

The UKCIP02 predictions of climate change for the UK do suggest that warming is likely to be somewhat seasonal with summer and autumn months warming the most but warming in in all seasons is expected. The seasonal warming of autumn and early winter over the last 300 years is consistent with a rebound from the LIA as cold winters were characteristic of this climate anomaly. The fact that annual temperatures in the UK have warmed less than the global average (0.6 as opposed to 1 C) is also consistent with UKCIP02 which predicts a warming of between 2.0 & 3.5 C for the UK by the 2080s while maximum warming for the globe is put at 5.4 C. But UKCIP02 does not mention in Chapter 2 which is called, "Recent Trends in Global & UK Climate", that the warming over the last 300 years has been seasonal with little warming in five months of the year. However, the marked autumn warming of the CET relative to other seasons can be seen in Figure 1 of UK Weather & Climate.

THESE results do have implications for wildlife as apart from March which has warmed significantly recently owing to strong & persistent westerly winds in the 1989-2002 period, late winter, spring and early summer temperatures have changed little over the last 300 years so climate change at these times of years cannot be blamed for any population declines in those species which are currently under threat. In the case of insects, spring and summer temperatures have big effects on the rate of development and subsequently on the number of generations which may occur in a year and as insects have a minimum temperature for flight, warming and cooling can influence the ecology by increasing or decreasing the number of days suitable for flight. But the little warming from April to July over the last 300 years suggest such effects are unlikely. However, spring phenology is the result of temperature over long periods of time, usually a combination of winter and spring months, and recent years have certainly seen early springs as a result of consecutive months of above average temperature. A future article will use the same analytical approach for combinations of consecutive winter/spring months to see if the earliest springs today are any warmer than the earliest springs of the 18th and 19th centuries in central England & Edinburgh.

THE CET has been analysed in several ways in articles on this website and the unanimous conclusion is that any warming introduced by higher global temperatures is small and the overriding factor dictating variations in the CET is weather patterns/regional atmospheric circulations.

THE conclusion of the first two studies listed above which is that a high incidence of warm weather patterns accounts for most of the post 1988 warming in the UK has been confirmed by the CET over the last six months (November 2005 to April 2006) which has suddenly flipped back to fluctuating around the 1961-90 average (Figure 20) giving southern Britain its coldest winter since 1996. If this recent trend persists, the UK will cool relative to the post 1988 warmth to which we have become accustomed

Figure 20 Monthly anomalies of mean Central England Temperature (CET) relative to 1961-90 average: January 1981 to April 2006.

What are the implications of these results for the magnitude of recent global warming?

THE Millenial temperature reconstructions in Figure 1 suggest that global temperatures during the latter half of the 20th Century are significantly higher than in the LIA and annual values of CET (Table 1) and Edinburgh temperature (Table 2) since 1970 are indeed significantly higher than annual values in the 18th & 19th Centuries. Yet five months of the year have warmed very little which is inconsistent with a significant rise in global temperature. A change in regional atmospheric circulation is a far more plausible explanation and we know that since the LIA ended around 1850, cold easterly winds in winter have been less frequent and that since 1988, persistent mild westerly winds in winter have been characteristic. Indeed it is very clear from studies of the CET that a high incidence of warm weather patterns all year round is the overriding factor causing the post 1988 warmth and not higher global temperatures. It is this successive run of month after month of above average temperatures caused by a high incidence of warm weather patterns that accounts for the significant warming of the seasonal and annual data post 1970 in the CET and Edinburgh temperatures. Therefore changes in atmospheric circulation certainly account for a major part of the warming in the UK since the LIA and the direct effects of the 1 C rise in global temperature are relatively small in comparison. This of course is inconsistent with the claims made by the IPCC about the magnitude of recent global warming which is based on the Millennial temperature reconstructions shown in Figure 1. Their view is that late 20th Century global temperatures are in the unusual category and are outliers relative to most of the last Millennium. Is this the truth or is the magnitude of recent global warming being over-hyped and exaggerated? The CET and Edinburgh temperatures over the last 300 years suggest the latter. Temperature recorded at a single site can be used to measure global temperature over a long period like several hundred years because the warming/cooling effects of weather patterns cancel out over such a long periods and any long term trend is then likely to be due to variations in global temperature. But in the case of the CET and Edinburgh, we know that a decrease in the incidence of cold easterly winters since the LIA accounts for a major part of the long term warming trend and we also know that a high incidence of warm weather patterns post 1988 accounts for the anomalous warmth of recent years. This leaves a modest amount of residual warming over the last 300 years which can be attributed to the 1 C rise in global temperatures. So in conclusion, a 1 C rise in global temperature is unlikely to be an earth-shattering magnitude of global warming in the unusual category as its effects in the UK have been quite modest. These results suggests that there is indeed a great deal of hype and exaggeration about the magnitude of recent global warming by the IPCC and climate change scientists and good quality observational data like the CET amd the Mossman's Edinburgh data are being swept under the carpet and ignored. Instead very dodgy global paleoclimate reconstructions (Figure 1) are being raised on a pedestal in spite of the large uncertainties associated with them and are being used to claim that late 20th Century temperatures are in the unusual category.

Pollack, H, N & Huang, S. (2000). Climate Reconstruction from Subsurface Temperatures. Annual Review of Earth Planet Sciences, 28, 339-65.

Mossman, R. (1896). The meteorology of Edinburgh. Transactions of the Royal Society of Edinburgh, 103, 63-207.