Is the climate changing in eastern ontario discussion paper final

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Is the Climate Changing in Eastern Ontario?

Prepared by Robert B. Stewart, PhD Eastern Ontario Model Forest, Forest Science Committee Member and Retired Climate Change Science Advisor Canadian Forest Service, Natural Resources Canada

SUMMARY Climate data from the Central Experimental Farm in Ottawa covering the period 1890 to 2011 are analyzed in terms of 30‐year averages to determine if the climate is changing in Eastern Ontario. Results indicate that the present climate is quite different from the climate a century ago. The current climate is warmer and wetter than any other period on record. The current 30‐year average annual temperature (1981‐2010) is 1.2°C greater than the 30‐year average a century ago. Much of the warming is due to the increase in minimum temperatures which have increased by 1.9°C, while the average maximum temperature has increased by 0.5°C. Analysis further suggests the rate of warming may be accelerating with 9 of the 10 warmest years occurring since 1991 and 6 of the 10 warmest years occurring since 2002. The 30‐year average annual precipitation levels have increased by about 60 mm per year ; the form of precipitation has changed with more rainfall (121mm) and less snowfall (61cm) being received; and the average number of precipitation days has increased by 31 days a year. Contrary to the warming that has occurred over the last century extremes in hot days with temperatures >20, 25 and 30°C , rather than increasing, have declined over the last century by 4 to 6 days per year. On the other hand, the number of extreme cold days with minimum temperatures <‐10, ‐20 and ‐30°C has declined considerably ‐ roughly 19 days for temperatures <‐10°C, 11 days for temperatures <‐20°C, and 3 days for temperatures <‐30°C. The current 30‐year average growing season length has increased by 10 to 22 days from 140 to 160 days per year; the start of the growing season has advanced by 7 to 14 days while the end of the growing season has been extended by 1 to 8 days. The average mean growing season temperature at present is relatively the same as it was a century ago except that the average maximum temperature has declined by 0.9°C, while the average minimum temperature has increased by 0.9°C. The difference in growing season average day and night‐time temperatures has declined by 1.8°C over the last century. The quantity of heat available for crop and plant growth has increased by 170 to 220 Degree Days >5°C (about 10%). This increase has not occurred because of increased daytime temperatures, but rather, the increase in the growing season length. The average number of days per growing season year with temperatures >20°C and 25°C is relatively the same today as a century ago. However, the average number of hot days >30°C has declined by about 5 days per year from a century ago. Average growing

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season precipitation levels have increased by 80 to 100mm over the last century and the number of rain days has increased by 13 to 19 days per year. Extremes in growing season precipitation appears to be increasing with the number of days with >10mm, >20mm, >30mm and > 40mm precipitation increasing by 0.4 to 3.6 days per year. From a moisture perspective eastern Ontario is getting wetter with the increase in growing season precipitation more than offsetting the increase in growing season temperatures.

From a climate perspective Eastern Ontario is currently warmer and wetter than at any other period over the last 120 years. From a global warming or climate change perspective, although the record is not conclusive, the observed change in temperature and moisture conditions experienced in Eastern Ontario over the last century suggests it may be happening.

Introduction We read in the news and hear every day on the radio and TV about global warming and climate change.

This was brought home in the summer of 2012 with record temperatures and drought being observed in much of North American including Eastern Ontario. In Ottawa the weather for the 12‐month period for July 1, 2011 to June 30, 2012 was the warmest and nearly the driest on record. The average temperature for the period was 2.3°C above the average, 0.3°C above the previous warmest period in 2005‐06. Over the same period 619mm of rain and snow fell, roughly two‐thirds of the normal, which was 12mm short of the previous record low set in 1960‐61. The question is ‐‐ is global warming really happening or are these record setting weather conditions just part of the natural variability in the global and regional climate systems? Although there are many scientists who believe it is all natural variability the majority of scientific opinion is that the evidence clearly indicates global warming is real and happening.

What about Eastern Ontario? Are the recent record setting temperature and precipitation conditions harbingers of global warming? Is the climate changing, and, if so, how is it changing? In this article using the climate data for the Ottawa CDA station (Agriculture and Agri‐Food Canada Experimental Farm) I will attempt to answer these questions in the context of Eastern Ontario.

For the purposes of this paper Eastern Ontario is defined as being the triangle in Southern Ontario bordered by Pembroke in the north, Cornwall in the east, and Gananoque in the west. For my analysis only data from the Ottawa CDA station are used as it is the only station in Eastern Ontario with a continuous record covering 100 years or more. As well, it is the only site in Eastern Ontario with data available up to the end of 2011. The only other city available for comparison was Brockville, but data were only available up to the end of 2006. Comparing the overlapping weather records for both Ottawa and Brockville showed that the trends and patterns were similar so the weather record for Ottawa is a good indicator of what is happening in Eastern Ontario.

The Ottawa CDA station has the longest continuous climate data set existing in Eastern Ontario covering the period November 1, 1889 to December 31, 2011. Available data include maximum and minimum

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daily air temperature, daily rainfall and snowfall amounts, and measured potential evaporation. With these data one can get a pretty good idea of heat and moisture conditions for the region. Having a data set that is 121 years in length also provides a good base for identifying trends and patterns especially in the context of comparing past weather to the present. The Ottawa CDA data have been corrected for instrument and site location changes so the data provides a reasonable basis for determining whether the climate is changing or has changed.

In this article I will discuss the data in the context of 30‐year averages or what climatologists and meteorologists refer to as “normal.” When you hear the term normal or average in the media, it refers to a 30‐year average. The current normal period covers the years 1981 to 2010 and it is this average that is used to describe the present weather or climate. Every 10 years the 30‐year average shifts. By this I mean prior to 2010 the normal period was 1971‐2000, prior to 2000 it was 1961‐1991 and so on.

In 2021 the normal period will shift to cover the years 1991‐2020. The climate normal is used as the basis for comparing today’s weather to the average over the last 30 years. In the context of comparing weather over short periods of time – 30 years or less – it is a very useful indicator to use. However, in the context of global warming and climate change it is not very useful because it is a shifting average.

However, if one looks at the change in the normal periods themselves over time you can get a very good idea as to whether the climate is, or is not, changing.

Changes in Annual Values Figures 1, 2 and 3 show the change in the average annual average (Tave), maximum (Tmax) and minimum (Tmin) temperatures over the period 1890 to 2011, respectively. In each Figure a 10‐year moving average is used to show the trend in the data over the 121‐year record. Table 1 shows the 10 warmest years for each. Results indicate that since 1890: 

Average annual temperatures have increased by about 1.8°C – increasing from roughly 5.5°C to 7.3°C with values declining by about 0.5°C from 1890 to 1945 ( from about 5.5°C to 5.0°C), then increasing to the present by about 2.5°C (from 5.0°C to 7.3°C).

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TAve(oC)

Fig. 1 Annual Average Temperature (oC) Ottawa CDA 1890‐2011 10.0 9.0 8.0 7.0 6.0 5.0 4.0 3.0 1880 1900 1920 1940 1960 1980 2000 2020

Annual Average Daily T (C) 1890‐2011 10 per. Mov. Avg. (Annual Average Daily T (C) 1890‐2011)

Year

 

Nine of the 10 warmest years have occurred since 1991 (Table 1), with 1998 being the warmest year.

Six of the 10 warmest years have occurred since 2002. The record clearly shows the climate in Ottawa has been warming over the last century and because of the large number of record warm years occurring within the last 20 years it appears the rate of warming is accelerating.

TABLE 1 Ottawa CDA ‐ 10 Warmest Annual Tave, Tmax and Tmin Years Over the Period 1890‐2011 Annual Tave (°C ) Rank Year 1 1998 2 2010 3 2006 4 1999 5 2001 6 2011 7 1953 8 2002 9 1991 10 2005



Tave 8.63 8.45 8.12 8.03 7.99 7.94 7.63 7.44 7.4 7.39

Annual Tmax (°C ) Rank Year Tmax 1 1998 13.39 2 1999 13.09 3 2010 13.05 4 2001 12.93 5 2006 12.74 6 2011 12.7 7 1991 12.43 8 1913 12.41 9 2005 12.3 10 2002 12.09

Annual Tmin (°C ) Rank Year Tmin 1 1998 3.87 2 2010 3.85 3 2006 3.51 4 2011 3.19 5 2001 3.06 6 1999 2.97 7 2002 2.79 8 1953 2.63 9 1990 2.6 10 1973 2.53

Average annual Tmax has increased by about 1.2°C (from 10.8°C to 12.0°C) remaining relatively constant over much of the period 1890 to 1985 at about 11°C then increasing by approximately 1.2°C from 1985 to 2011. Associated with this rise is a sharp rise in record temperatures with 9 of the 10 warmest annual average Tmax years over the 121‐year record occurring since 1991.

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Fig. 2 Annual Tmax(C) Ottawa CDA‐ 1890‐2011 14.00 Annual Tmax(C) Ottawa CDA‐ 1890‐2011

13.00 12.00 11.00 10.00 9.00

8.00 1880 1900 1920 1940 1960 1980 2000 2020



10 per. Mov. Avg. (Annual Tmax(C) Ottawa CDA‐ 1890‐ 2011)

Average annual minimum temperatures have increased by about 2.3°C since 1890 with Tmin declining slightly (0.1°C to ‐0.1 °C) from 1890 to 1942 then increasing steadily from ‐0.1°C to more than 2.3°C in 2011. Associated with this rise is a sharp rise in record temperatures with 8 of the 10 warmest annual average Tmin years over the 121‐year record occurring since 1991.

Fig. 3 Annual Average Tmin (C) for the Ottawa CDA ‐ 1890‐2011 5.00 4.00 3.00 2.00 1.00 0.00 ‐1.00 ‐2.00 ‐3.00 1880 1900 1920 1940 1960 1980 2000 2020



Annual Tmin (C) Ottawa CDA ‐ 1890‐ 2011 10 per. Mov. Avg. (Annual Tmin (C) Ottawa CDA ‐ 1890‐ 2011)

The major portion of the warming that has taken place in Ottawa has been due to the increases in Tmin which have increased at about twice the level of Tmax.

Changes in Annual 30‐Year Averages In looking at the change in average annual temperatures shown in Figures 1 to 3 over the last 121 years it is evident the climate is different today from a century ago. How different is it? To answer this question the annual average data for Ottawa were broken down into a series of 30‐year averages

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covering the 120‐year record from 1890 to 2010. Table 2 shows the change in 30‐year average annual temperature, degree days greater than 5°C, rainfall, snowfall, total precipitation (P) and potential evaporation (PE) in Ottawa over the period 1890 to 2011.

Degree Days greater than 5°C (DD>5°C) is used as a means of quantifying the amount of heat available for crop and plant growth. This term is very important to farmers, florists and foresters because it is often used to determine where crops, plants and trees can be grown and to select specific varieties to be grown in an area. The daily DD>5°C is calculated by taking the average daily temperature and subtracting 5°C. If the value for the day is less than zero the value is set at zero. Annual DD > 5°C is then calculated summing the daily DD>5°C values for the year. PE is defined as the maximum amount of evaporation from a surface given an unlimited water supply. P and PE are very important components of a region’s water balance or hydrologic cycle. They are often used in the form of a ratio (P/PE) or index to quantify or describe the moisture conditions of an area. A P/PE ratio of 1 means that the amount of precipitation balances the amount of evaporation. If the ratio is <1 it means that the amount of precipitation is less than the amount of evaporation that could have taken place and is typified by a shortage of water. A desert is a good example of a very dry area where P is considerably less than the PE. Values of 0.3 or less would be typical for desert regions. On the other hand if P/PE is greater than 1, P exceeds PE and the result is a surplus of water. A water surplus typically shows up as runoff in streams and/or an increase in the water table and water levels in lakes. A rainforest is a good example of where the P/PE ratio is typically much greater than 1. Values of 4 or higher are typical for these areas.

Key points emerging from the results shown in Table 2 can be summarized as follows:    



The perception of average climate is quite different today from what it was 50, 75 and 100 years ago.

Over the last century the 30‐year average annual temperature has increased by about 1.2°C. The majority of the warming has resulted not from the increase in daytime maximum temperatures (0.5°C) but rather from the increase in night‐time minimum temperatures (1.9°C).

DD>5°C totals have increased over the last century in response to the increasing temperatures.

The record shows that DD>5°C values declined in the first half of the 20th century by about 66 DD>5°C. From the middle of the century to the present, DD>5°C values have steadily increased, increasing about 176 DD>5°C or 8.8%.

Thirty‐year average temperatures and heat levels are greater today than at any point over the last 120 years.

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Table 2 Year Range 1891‐1920 1901‐1930 1911‐1940 1921‐1950 1931‐1960 1941‐1970 1951‐1980 1961‐1990 1971‐2000 1981‐2010

Ottawa CDA – 30‐Year Annual Average Data for the Period 1891‐2010 Tmax DD>5 Tmin Tave Rainfall Snowfall Total Precip PE (°C ) (°C) (mm) (cm) (mm) (mm) P/PE (Annual) (°C) 11.0 10.9 10.7 10.7 10.8 10.9 10.8 10.8 11.0 11.5

0.1 0.0 0.0 0.1 0.5 0.8 1.1 1.3 1.6 2.0

5.5 5.4 5.4 5.4 5.6 5.9 5.9 6.0 6.3 6.7

638.3 641.4 649.1 683.1 670.6 662.7 668.4 700.5 733.4 760.0

239.1 231.2 218.5 203.6 194.9 192.5 205.3 197.4 202.6 178.3

877.4 872.6 867.6 886.7 865.5 855.2 873.7 897.9 936.0 938.3

697.5 699.7 688.5 684.7 677.8 669.1 647.4 635.0 629.0 638.2

1.26 1.25 1.26 1.30 1.28 1.26 1.31 1.37 1.45 1.45

2074 2030 2016 2008 2038 2055 2066 2087 2127 2184

Table 2 also shows the change in 30‐year average annual rainfall, snowfall, precipitation (P) and potential evaporation (PE) over the period 1890 to 2010. Key points emerging from the changes in 30‐year average annual moisture conditions can be summarized as follows:   



Ottawa is wetter today than a century ago. Average annual precipitation is greater today than at any other point in the 121‐year record.

Average annual precipitation has increased by about 45mm per year over the last century.

The form of precipitation, rainfall versus snowfall, appears to be changing. Average annual rainfall has increased approximately 122mm/year while snowfall levels have decreased by about 61cm/year today.

Average annual potential evaporation for Ottawa has decreased by about 50mm/year from a century ago.

The decline in average annual PE values is a major surprise as one would have expected the PE values to increase in response to the increased warming. The reason for the decline in PE values is explained in Table 3 in terms of the change in the average number of rain days per year. As shown the number of rain days has increased in Ottawa by about 30 days a year. The impact of the increase in the number of rain days has been to reduce the potential evaporation as the PE on a rainy day is much less than on a non‐rainy day.

In terms of change in overall moisture conditions over the period 1890 to 2010, the data outlined in Table 2 suggest Ottawa is getting wetter. The increased warming in the region, reflected in the increase in temperature and DD>5°C values, is being more than offset by the increase in precipitation with the 30‐year average annual P/PE ratio increasing from about 1.25 to 1.45.

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The historical record clearly shows that Ottawa is getting warmer and wetter on an annual basis. What about extremes in temperature and moisture? Are we experiencing more hot days in summer and less cold days in winter? Are we getting more precipitation in the form of severe rain storms or winter storms? The answer to these questions can be found in Table 3.

Table 3 shows the change in the 30‐year average number of hot and cold days per year over the period 1890 to 2010. Hot days are days in the summer with maximum temperatures greater than 20, 25 and 30°C while cold days are days in the winter with minimum temperatures less than ‐10, ‐20 and ‐30°C.

Key points emerging from the data outlined in Table 3 for hot and cold day extremes can be summarized as follows: 

Contrary to the warming that has occurred over the last century extremes in hot days with temperatures >20, 25 and 30°C, rather than increasing, have declined over the last century by 4 to 6 days per year.

Table 3 Change in 30 year Average Extremes in Temperature and Precipitation for Ottawa CDA Over the Period 1890‐2010 Number of Hot Days Year Range

Number of Cold Days

Number of Rain Days (R)

Days Days Days Days Days Days Rain >20°C >25°C >30°C <‐10°C <‐20°C <‐30°C Days

1891‐1920 1901‐1930 1911‐1940 1921‐1950 1931‐1960 1941‐1970 1951‐1980 1961‐1990 1971‐2000 1981‐2010

122.8 121.4 120.2 119.8 118.5 117.5 116.7 115.9 116.1 118.9

66.8 64.8 64.7 65.2 66.0 63.4 60.5 58.5 59.4 62.8

19.2 17.9 17.1 15.7 16.1 14.8 12.7 11.9 12.0 13.3

84.0 82.9 81.8 79.8 76.3 73.1 72.5 72.0 69.4 65.4

28.4 27.9 28.1 28.1 26.3 23.9 22.0 21.8 20.3 17.4

2.9 2.9 3.5 3.7 3.5 2.3 1.5 1.1 0.9 0.6

130.6 134.4 134.8 138.1 140.1 140.7 149.3 157.0 163.6 161.3

R>10mm #Days 29.7 28.5 27.7 27.6 26.0 25.8 26.0 26.9 28.5 29.0

R>20mm R>30mm #Days #Days 8.7 8.2 8.0 8.2 7.7 7.2 7.5 8.1 9.1 8.9

2.6 2.3 2.1 2.5 2.7 2.6 2.5 2.6 2.9 2.9

The data indicate the number of hot days with temperatures >20, 25 and 30°C declined by 7 to 9 days over the first eight 30‐year periods (1891‐1920 to 1961‐90). However, over the last two 30‐year periods the number of hot days has increased an average 2 to 4 days per year. 

The number of extreme cold days has decreased significantly.

R>40mm #Days 1.0 0.7 0.7 1.0 1.1 1.1 0.8 0.8 0.9 1.0

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The number of cold days <‐10, ‐20 and ‐30°C has steadily been declining over the eleven 30‐year average periods ‐ roughly 19 days for temperatures <10°C, 11 days for temperatures <‐20°C, and 3 days for temperatures <‐30°C. 

Winters in Ottawa have warmed significantly over the last century with a considerable decrease in number of extreme cold days in winter. Comparing summer to winter the record also clearly shows that the majority of the warming that has taken place over the last century has taken place during the winter period.

In terms of extreme precipitation values Table 3 shows the change in the 30‐year average number of rain days (R) per year, and the change in average number of days per year with precipitation amounts greater than 10, 20, 30 and 40mm per day over the period 1890 to 2010. Key points emerging from the data can be summarized as follows:  



The average number of rain days has increased by 30 days a year.

Extremes in precipitation days with greater than 20mm, 30mm and 40mm per day have increased slightly. Although the extremes in precipitation are slightly higher they are not high enough to suggest that extremes in precipitation have changed significantly.

Ottawa is getting more precipitation annually today than at any point over the last century or so and the increase is largely due to the increase in the number of annual rain days.

Changes in 30‐Year Average Growing Season Conditions Table 4 Change in 30‐year Average Growing Season Start (GSS), End (GSE) Dates, the Growing Season Length (GSL), and Growing Season Tmax, Tmin and Tmean, Degree Days >5°C , and Number of Days with Temperatures > 20, 25 and 30°C for Ottawa CDA Over the Period 1890‐2010

Period

GSS Date

GSE Date

GSS GSE GSL Tmax Tmin Day Day Days (°C ) ( °C )

Tave (°C)

DD>5°C

Number of Growing Season Days >20°C >25°C >30°C

1891‐1920 May‐06

Oct‐04

126

277

152

23.5

11.1

17.3

1867

115.2

65.0

18.8

1901‐1930 May‐10

Oct‐03

130

276

147

23.6

11.1

17.3

1805

112.8

62.6

17.5

1911‐1940 May‐12 1921‐1950 May‐14

Oct‐01 Oct‐01

132 134

274 274

143 140

23.6 23.6

11.2 11.4

17.4 17.5

1770 1744

110.2 108.8

62.1 62.0

16.7 15.5

1931‐1960 May‐13

Oct‐02

133

275

143

23.4

11.5

17.5

1776

107.9

63.1

16.0

1941‐1970 May‐10

Oct‐04

130

277

148

23.0

11.5

17.3

1807

107.8

60.9

14.7

1951‐1980 May‐05 1961‐1990 May‐02

Oct‐07 Oct‐07

125 122

280 280

155 159

22.6 22.4

11.5 11.6

17.0 17.0

1864 1903

109.6 110.1

59.3 57.8

12.7 11.9

1971‐2000 Apr‐29

Oct‐05

119

278

160

22.5

11.8

17.2

1945

111.5

59.0

12.0

1981‐2010 Apr‐30

Oct‐08

120

281

162

22.7

12.0

17.3

1992

113.8

62.1

13.3

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As shown above the annual climate of Eastern Ontario has changed over the last century with increased temperatures and precipitation. In the context of these changes what has happened to the growing season values which are important to agriculture and forest operations as well as recreational and everyday activities? For the purposes of this article the growing season is defined as the frost free period during the year when minimum temperatures are greater than 0°C. Table 4 shows the change in average 30‐year growing season conditions. The growing season start date (GSS) was determined annually as starting 5 days after the last killing frost (‐2°C) day in the spring or the next day after the last frost day of or 0°C or less, which every day was later. The growing season end date (GSE) was determined as the first day in the fall when Tmin falls below 0.0°C. The growing season length (GSL) was determined as the number of days between the GSS and GSE. The growing season Tmax and Tmin were then calculated as the average over the period from the start and end of the growing season, while the DD>5°C was calculated as the sum of degree days between the GSS and GSE dates.

Key findings in the data illustrated in Table 4 can be summarized as follows: 



    



The growing season length has increased by 10 to 20 days per year. The increase is associated with an advance in the spring GSS date by 7 to 14 days and extension of the fall frost date by 1 to 8 days. The surprise in this case is that the majority of the increase in GSL has resulted from the advance in the spring start date (GSS).

The growing season length, temperatures, degree days and numbers of hot days basically declined from the 1891‐1920 period to the 1921‐1950 period and since then have been increasing.

Average mean growing season temperatures have changed little over the last century, Average Tmax has declined by 0.8 to 0.9°C while Tmin has increased by 0.9°C. The amount of heat available for crop growth has increased by 170 to 220 DD>5°C. The increase in DD>5°C is due largely to the increase in growing season length as opposed to increased temperature.

Present day summers are longer and warmer than a century ago, but, are not as hot as summers of the past experiencing about 5 fewer days a year with daily maximum temperatures exceeding 30°C. The number of hot days decreased over the first six 30‐year periods for temperatures extremes > 20°C; declined for the first eight 30‐year periods for temperature extremes >25°C; and declined for the first nine periods for temperature extremes >30°C. The decline averaged 4, 5 and 6 days, respectively. Over the last 3 to 5 periods, however, temperature extremes appear to be on the increase, increasing by 6, 4 and 1 days for extremes of >20°C, >25°C and >30°C, respectively.

Table 5 shows the change in 30‐year average growing season precipitation, potential evaporation and rain days and rain day extremes over the period 1890 to 2010.

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Table 5 Change in 30‐year Average Growing Season Rainfall (P), Potential Evaporation (PE), and Rain Days (R), Rain Days > 10, 20, 30, and 40 mm for Ottawa CDA Over the Period 1890 to 2010 Period

GSL rainfall PE Rain Days (mm) (mm) P/PE DD>5°C #Days

R>10mm R>20mm R>30mm R>40mm #Days #Days #Days #Days

1891‐1920

152

381

592

0.64

1816

57.1

13.3

4.8

1.6

0.7

1901‐1930

147

377

589

0.64

1805

55.2

12.7

4.4

1.3

0.4

1911‐1940

143

363

572

0.63

1770

51.5

12.2

4.3

1.3

0.5

1921‐1950

140

375

559

0.67

1744

49.3

12.5

4.5

1.6

0.8

1931‐1960

143

376

559

0.67

1776

50.3

11.9

4.2

1.8

0.9

1941‐1970

148

390

558

0.70

1807

53.2

12.5

4.1

1.8

0.9

1951‐1980

155

414

562

0.74

1864

60.5

13.5

4.6

1.8

0.6

1961‐1990

159

442

562

0.79

1903

65.4

14.7

5.3

2.0

0.6

1971‐2000

160

455

565

0.81

1945

68.5

15.1

5.6

2.1

0.6

1981‐2010

162

466

566

0.82

1992

68.2

15.5

5.5

2.1

0.8

Key changes observed in growing season moisture over the last century can be summarized as follows:

 

Rainfall (P) has increased by 80 to 100mm per year.

Potential evaporation (PE) has declined by 20 to 30mm per year. Even though growing season temperatures have increased the increase in the number of rain days has more than offset the increased warming impact on evaporation.



The average number of rain days during the growing season has increased by 11 to 18 days per year.



The ratio of P/PE has increased indicating the growing season is getting wetter in Eastern Ontario.



The number of rain days with more than 20, 30 and 40mm of rainfall has increased.

The results outlined in Table 5 indicate growing seasons in Ottawa are wetter than a century ago. This is largely due to the increase in the number of rain days. At the same time extremes in rainfall appear to be increasing suggesting more rainfall is being received in more intense storms.

Summary and Conclusions Overall, the results of the discussion above clearly show that temperatures in Eastern Ontario are warmer today than a century ago. The record shows that temperatures basically declined from 1890 to about 1945 and then began to increase to the present day. Results suggest the increase in regional temperatures may be accelerating with 9 of the 10 warmest years occurring in the last 20 years and 6 of the 10 warmest years since 2001. In spite of the increased warming the number of annual hot days

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>30°C has declined over the last century. On the other hand there has been a significant decline in the number of cold days (<10°C).

Although annual mean temperatures are increasing it is not because of the increase in maximum temperatures or increases in summer temperatures. Rather the increase is happening largely because of the increase in minimum temperatures particularly winter temperatures. Over the last century the annual and growing season difference in maximum and minimum temperatures has decreased. In the context of global warming it is clear that Eastern Ontario is warming. However, because of the nature of the warming that has occurred a more realistic view would be to say the region is not getting “warmer” but rather is getting “less cold” in terms of climate.

On an annual basis precipitation patterns appear to be changing with both the precipitation amounts and the number of rain days increasing.

The growing season in Eastern Ontario is 2 to 3 weeks longer than a century ago. The growing season has been advanced by 1‐2 weeks in the spring and extended by about a week in the fall. Although, the growing season is longer the average growing season temperatures have not changed appreciably.

Despite this, temperatures have changed. Daily maximum temperatures have declined by about 0.9°C while daily minimum temperatures have increased by about 1°C. Consequently, the difference in day and night‐time temperatures has decreased by about 1.9°C. Because of the perceived warming, growing season heat units received by the region have increased by 170 to 220 DD> 5°C per year over the last century. The increase in heat units is not the result of increased temperatures, but rather, appears to have increased because of the increase in the growing season length. In terms of heat extremes summers today appear to be less extreme with the number of hot days >30°C experienced by Eastern Ontario being about 5 days less per year than a century ago.

Summers today because of the increase in minimum temperatures may be generally warmer than a century ago, but are not hotter.

Precipitation patterns appear to be changing in Eastern Ontario. The region is experiencing more rain days and more precipitation during the growing season than a century ago. At the same time extremes in growing season precipitation appear to be increasing. From a moisture perspective the growing season is wetter today than a century ago with the increased precipitation more than making up for the increased heat being experienced.

From a climate perspective Eastern Ontario currently is warmer and wetter than at any other period over the last 120 years. From a global warming or climate change perspective, although the record is not conclusive, the change in temperature and moisture conditions experienced in Eastern Ontario over the last century suggests it may be happening.

Acknowledgement The author would like to extend his appreciation to Dirk Anderson, Agriculture and Agri‐Food Canada, for providing the Ottawa CDA climate data.