The effect of changing greenhouse gas concentrations, most notably carbon dioxide, CO 2 , on climate was examined. In particular, calculations of the climate sensitivity, the warming of the Earth due to a doubling of atmospheric carbon dioxide, are discussed. Greenhouse gas concentrations, as determined from air bubbles trapped in ice as well as at Mauna Loa, Hawaii are presented. The greenhouse gas amounts generated by Canada and Ontario were used to estimate their respective contributions to global warming. Ontario was responsible for only 0.35% of the world's CO 2 emissions in 2019 and this amount was 20% lower than in 2005. The predictions of Global Climate Models (GCMs) regarding temperature, polar ice caps, oceans, precipitation and extreme events were compared to observations. Records since 1880 show an overall warming of about 1 o C. However, the GCMs do not account for observed decadal temperature fluctuations and consistently overestimate the warming. Ontario's contribution to global warming is only 9.2x10 5 o C/year using the Intergovernmental Panel on Climate Change (IPCC) recommended climate sensitivity value. Measurements of the polar ice caps reveal a decrease in the minimum September Arctic sea ice extent during 1979-2022 but the trend levelled off after 2007; while the average Antarctic sea ice extent slightly increased. Sea level increased slightly throughout the 20th century. Ontario's contribution to anthropogenic sea level rise is about 0.005 mm/year. Sea level along Ontario's Hudson Bay coast is decreasing due to isostatic rebound of the land following the last Ice Age. The change to ocean acidity due to CO 2 absorption from the atmosphere is negligible compared to that due to tides, ocean depth and seasonal effects. Ontario's contribution to ocean acidification is estimated to be 6x10 6 pH/year. No changes in precipitation in North America over the 19th and 20th centuries, nor at Toronto since 1843, were found. The Great Lake levels are remarkably constant over the past century showing no evidence of a change in the incidence of flooding. No evidence was found that the frequency of extreme events such as hurricanes or tornadoes increased during recent decades. The number of forest fires in Canada and Ontario decreased during 1990 to 2020. 1 Climate In March 2019, the warned that only 11 years remain to avert catastrophic climate change stating "we are the last generation that can prevent irreparable damage to our planet" [1]. These concerns were amplified by the latest report issued by the Intergovernmental Panel on Climate Change (IPCC) in August, 2021. "It has been clear for decades that the Earth's climate is changing, and the role of human influence on the climate system is undisputed" said V. Masson-Delmotte, Co-Chair of the IPCC Working Group [2,3,4,5,6,7]. The IPCC report warns that increasing greenhouse gases due to the combustion of fossil fuels have not only caused global warming, but changed the Earth's ice cover, precipitation, sea level and ocean acidity as well as affected climate extreme events such as cyclones [7]. The first question to ask when considering climate change is whether the Earth's climate is constant. The occurrence of Ice Ages indicates the answer is an emphatic No. Ice ages are caused by small changes in the Earth's orbit around the sun known as Milankovitch cyles that have periods of about 100,000 years [8]. The next question is whether the climate has remained constant throughout recorded history. Temperatures in the North Atlantic were warmer during the so called Medieval Warm Period from 900 to about 1300 A.D. This allowed the Vikings to settle in southern Greenland and farm with sheep and goats! Two settlements were established which at their peak had a total population of several thousand inhabitants [9,10]. Trade with Europe was brisk in walrus ivory for several hundred years until the early 14th century. It appears there was a shift to a markedly cooler climate in the Northern Hemisphere in the 1300s that led to the demise of the Viking settlements. Radiocarbon dating of plant material found beneath glaciers on Baffin Island and Iceland shows glaciers began to grow in the late 1300s [11]. The stone ruins of a Church at Hvalsey, Greenland shown in Fig. 1 are a poignant reminder of the power of natural climate change. The period from 1400 to 1700 is known as the Little Ice Age. Temperatures in Europe were cooler. Swiss villagers even offered prayers to stop advancing glaciers from destroying their alpine villages [13,14]. Rivers such as the Thames and Rhine regularly froze during winter, something that has seldom occurred in the last 150 years. ended around 1700. The reasons for the Medieval Warm Period and Little Ice Age are not well understood. An obvious possibility is variation of the amount of heat produced by the sun. Satellite measurements of the solar intensity only exist from 1975 onwards [15]. These NASA data show the sun's intensity varies by about 0.1% in a cyclic fashion having a period of 11 years. This coincides with the well known sunspot cycle recorded over the last 200 years. Sunspots were first observed in about 1600. The sharp decreases in sunspot number in the 1600s and immediately after 1800 are known as the Maunder and Dalton Minima, respectively [16]. Possibly, the sun had fewer sunspots during the 1600s (as opposed to a lack of scientists studying sunspot activity) which corresponded to a reduced solar intensity that contributed to the Little Ice Age. The atmosphere is essential for making Earth habitable. Dry air consists of 78% Nitrogen, 21% Oxygen molecules and 1% Argon atoms. Carbon dioxide (CO 2 ), Methane (CH 4 ) and Nitrous Oxide (N 2 O) are only found in trace amounts with average surface concentrations in 2021 of 415, 1.9 and 0.32 parts per million (ppm) respectively. Water vapour is a very important atmospheric constituent. Its concentration varies considerably from as high as 4% in the warm tropics at high humidity to minuscule amounts in the polar regions during winter. Fig.
2 shows the observed concentration dependence of these trace gases on altitude [17]. The temperature of the Earth's atmosphere for a midlatitude position, where Ontario is located, is shown in Fig. 2 [18]. Weather events occur in the lowest part of the atmosphere called the troposphere. The temperature is observed to decrease rapidly from an average surface temperature of about 15.5 degrees Celsius or 288.7 Kelvins until the tropopause which at midlatitudes occurs at an altitude of 11 km. The temperature increases in the stratosphere located from 11 to 47 km, due to absorption of ultraviolet sunlight by ozone molecules. The temperature drops sharply in the mesosphere located above 47 km. All objects having a finite temperature radiate energy. The sun is very hot and therefore produces visible light. Cooler objects such as the Earth's surface and atmosphere generate heat or infrared radiation. This infrared radiation exists at a wide range of infrared colours, which scientists refer to as frequencies or wavelengths, that the human eye cannot see. In the absence of clouds, most sunlight is transmitted through the atmosphere. In contrast, infrared radiation, is strongly absorbed by the atmosphere. A gas that does not absorb visible sunlight but strongly absorbs infrared radiation is called a greenhouse gas. In the absence of greenhouse gases, radiation emitted by the Earth's surface would pass through a transparent atmosphere to outer space. Greenhouse gases absorb the radiation which is then reemitted in all directions, some upwards and some back to the surface, warm- or heat radiated by the Earth and its atmosphere over the Sahara, Mediterranean and Antarctica [19]. The intensity observed over the Sahara, whose surface temperature is a very warm 47 Celsius or 320 Kelvins, is much higher than the intensity detected over cold Antarctica where the surface temperature is only -83 Celsius or 190 Kelvins. The dashed red curves are the intensities that would be radiated by the surface, for a transparent atmosphere without any greenhouse gases. For Antarctica, very dense cold air sinks to the surface causing the surface temperature to be lower than the atmosphere a few kilometers above the surface. This slightly warmer air causes the satellite to see a higher intensity than one would expect from the very cold surface. ing it. This is called the Greenhouse Effect. For the case of a clear sky, one can compute the amount of heat radiated by the Earth as is shown in Fig. 3 [19]. This shows the heat radiated per unit area by the Earth and its atmosphere to outer space at the various infrared colours or frequencies. This calculation considered the 5 most important naturally occurring greenhouse gases: water vapour (H 2 O), carbon dioxide (CO 2 ), ozone (O 3 ), nitrous oxide (N 2 O) and methane (CH 4 ). The effects of water vapour are very noticeable at frequencies less than 550 cm 1 and in the range of 1200 to 2800 cm 1 . The two noticeable dips in the black and red curves are due to absorption by carbon dioxide at 660 cm 1 and ozone at 1050 cm 1 . The effects of methane and nitrous oxide are barely noticeably because their atmospheric concentrations are over 1000 times smaller than water vapour and more than 100 times smaller than carbon dioxide. One can barely distinguish between the black and red curves which correspond to carbon dioxide concentrations of 400 and 800 ppm, respectively. An important check of this work is to compare modelled results to data observed by satellites that measure the intensity of infrared light radiated by the Earth and its atmosphere as shown in Fig. 4 [19]. The effect of doubling carbon dioxide is shown by the red and black curves in The surface warming T , due to the carbon dioxide concentration increasing from C o to C is given by where S is called the climate sensitivity. The warming predicted by this formula is plotted in A warming of only 1 o C is not a threat to the planet. However, the maximum amount of water vapour that can be contained in a given volume of air increases at a rate of 6% per degree Celsius. Therefore, the water vapour concentration would go up in a warming atmosphere if the relative humidity remained unchanged. This so called water feedback effect would amplify the small warming due to increasing carbon dioxide. Observations are inconclusive that water vapour has increased at the maximum theoretical rate [21]. A study that examined 1/4 billion hourly values of temperature and relative humidity at 309 stations located throughout North America during 1948-2010 found relative humidity decreased at many inland stations [22]. A more sophisticated analysis of surface warming must take into account that the troposphere warms more than the higher atmosphere. S. Manabe, who , originally estimated a climate sensitivity of 1.4 C for the case of constant water vapour concentration [23]. This has been independently confirmed by several subsequent groups including our own calculations [19]. The For the case of methane, we recomputed Fig. 3 for ambient and doubled methane concentrations of 1.8 and 3.6 ppm, respectively. One additional methane molecule is 30 times more effective for global warming than one additional CO 2 molecule. However, 300 times more carbon dioxide is added to the atmosphere each year than CH 4 . Hence, the overall effect of the increasing methane concentration to global warming is less than 1/10 that of carbon dioxide [19]. For the case of nitrous oxide, one additional N 2 O molecule is 230 times more effective for global warming than one additional CO 2 molecule, But the rate of increase of CO 2 molecules is 3000 times larger than that of N 2 O. So the contribution of nitrous oxide to global warming is about 230/300 or about 1/13 that of carbon dioxide [20].
Efforts to construct a realistic mathematical computer model of the Earth's climate are an enormous task that have been ongoing for over half a century [25]. The Earth's surface area of 515 million km 2 is divided into area segments and the atmosphere into vertical slices. For an area element of 100 km 2 and a vertical step size of 100 m, one needs over 2.5 billion points. At each point, one must calculate: temperature, pressure, water vapor concentration, greenhouse gas and aerosol concentrations, wind speed and direction etc. At the surface, one must determine the fraction of sunlight reflected. Evaporation must be taken into account which is very different for an ocean as opposed to a land surface. For the latter case, the vegetation type may be important. Ocean currents such as the Gulf Stream that transport enormous amounts of heat from the tropics to polar latitudes must also be modelled using an additional array of points. Ocean circulation is not well understood and cycling times of deep ocean water are estimated to take up to hundreds of years. Finally, the entire system is time dependent, as the Earth orbits annually about the sun and daily rotates about its axis. Year S ( o C) 1990 [2] 1.5 -4.5 1996 [3] 1.5 -4.5 2001 [4] 1.5 -4.5 2007 [5] 2.0 -4.5 2014 [6] 1.5 -4.5 2021 [7] 2.5 -4.0 Developing a Global Climate Model (GCM) requires a very large team of people and the computer programs easily exceed a million lines of code. GCMs have been developed at large centers such as the [25], UK Meteorological Office [27], Boulder's National Climate Center for Atmospheric Research [28], Max Planck Institut fur Meteorologie [26] and the Canadian Centre for Climate Modelling and Analysis [29]. Even using the world's fastest supercomputers, numerous simplifying approximations are essential. Typically, one tunes a myriad of parameters to ensure the GCM reasonably reproduces the Earth's 20th century climate. One then models future climate considering various scenarios of increasing greenhouse gases. Work is ongoing to make GCMs more realistic. (CMIP) attempts to evaluate and compare the different GCM results [30]. Table 1 lists the estimates for the climate sensitivity. These values have not changed spectacularly over 30 years. In 2021, the IPCC gave a value for S of between 2.5 and 4.0 o C with the best estimate of 3 o C. The 2021 uncertainty is smaller than for previous reports because it is believed the latest GCMs better model clouds. It is very challenging to determine the global warming or cooling effects of clouds, which at any time cover about two thirds of the Earth. Cooling occurs when clouds block the midday sun on a summer day while in winter, cloudy nights are warmer than clear nights. The huge uncertainty due to clouds is the elephant in the room in Climate Science. Carbon dioxide is an odourless, invisible gas. It is plant food. Greenhouse growers routinely add it to promote growth. An example is shown in Fig. 6 where pine trees grow much faster at higher concentrations of carbon dioxide [31]. An increase in global vegetative productivity has been observed by satellites as shown in Fig. 7 [35,36,37]. For the period 1982-2011, more than 30% of the Earth's land area greened for a 14% overall increase in total gross vegetative productivity. This is very beneficial to farmers who provide food for the world's growing population [38]. Fig. 7 shows particularly striking greening in the region bordering the Sahara desert. Plants extract carbon dioxide from the atmosphere through small holes in their leaves called [35]. The increase of plant growth is especially noticeable in arid regions such as south of the Sahara desert. At higher CO 2 levels, the stomata in plant leaves are smaller, reducing the loss of water [32]. stomata. At higher carbon dioxide levels, the stomata become smaller, reducing water loss from the plant [38,32]. This is believed to be part of the reason for the notable greening of the Earth's arid regions. The response of plants to higher atmospheric carbon dioxide levels depends on plant type [32]. So called C3 plants such as soybeans and wheat, use an enzyme, rubisco, to convert CO 2 to simple carboyhydrate molecules having 3 carbon atoms. These molecules are subsequently converted into more complex molecules such as sugar. Rubisco evolved when atmospheric CO 2 levels were several thousand ppm rather thn 415 ppm in 2021. At today's low CO 2 level, the leaf uses up much of the CO 2 when the sun shines. If there is insufficient CO 2 , then rubisco uses an O 2 molecule which produces toxic bypoducts such as hydrogen peroxide [32] C4 plants such as corn evolved during the past tens of millions of years when atmospheric CO 2 levels were relatively low. These plants developed special structures within the leaf to prevent the reaction of rubisco with oxygen. CO 2 molecules are ferried into the protective leaf structure by molecules having 4 carbon atoms. It is reasonable to expect that C3 and C4 plants would respond differently to increased CO 2 levels. There has been a huge increase in agricultural productivity in the last century. American soybean and corn yields since 1940 have increased three and six fold respectively [33]. Most of this increase is due to better farming techniques including improved genetics, irrigation and the use of chemical fertilizers. The effects of increased atmospheric CO 2 however are not negligible. A recent paper states "a 1 ppm increase in CO 2 equates to a 0.5%, 0.6% and 0.8% yield increase for corn, soybeans and wheat respectively. Viewed retrospectively, 10%, 30% and 40% of each crop's yield improvements since 1940 are attributable to rising CO 2 " [33]. Other studies have also found higher atmospheric CO 2 levels increase plant growth.
For example, a review by Poorter and Navas showed doubling CO 2 increases growth of C3 plants by an average of 45% while the response of C4 plants is about 12% [34]. 3 ? Atmospheric carbon dioxide levels have varied throughout Earth's history. They were as high as 4000 ppm 500 million years ago in the Cambrian period and dropped to 180 ppm at the peak of the last ice age [39]. Carbon dioxide concentrations of the last several hundred thousand years are shown in The increase of carbon dioxide is due primarily to the combustion of fossil fuels such as oil, coal and natural gas that resulted from the industrial revolution that began in about 1750. There are significant other sources of greenhouse gases. As much as 20% of the annual anthropogenic production of carbon dioxide has been estimated to result from clearing forests by burning vegetation [45,46]. The most notable deforestation has occurred in Brazil where about 10% or 400,000 km 2 of the Amazonian rainforest was destroyed during 1988-2013 [47]. A detailed look at Canada's emission from 1990 to 2019 is given in The contribution of Ontario to global warming is given in Table 2 for climate sensitivity values S = 1 and S = 3 o C, the value recommended by the 2021 IPCC. Ontario's contribution is estimated by multiplying Ontario's 2019 22% fraction of Canada's CO 2 production by 1.6%, Canada's fraction of global CO 2 emission, giving 0.35% of the world total CO 2 emission The curve shows a temperature increase as one would expect from Figures 5 and 9. However, there are notable differences. 1. From about 1900 to 1940, there was a warming of about 0.5 o C during which CO 2 increased from 296 to 311 ppm [51]. Using equation ( 1), this gives a climate sensitivity of S = 7 which greatly exceeds the values given in The failure of the GCMs to predict the hiatus in global average temperature after 2000 is illustrated in The excessive warming projections continues to be a problem for the latest IPCC 2021 report. A study compared the observed average surface temperature increase between 1980 and 2021 of 0.56 o C to that given by the 38 GCMs [57]. Every GCM having a climate sensitivity greater than 3.0 o C predicted a higher temperature increase than was observed Only the GCMs having the lowest sensitivity between 1.8 and 3.0 o C agree with observations. This indicates that the 2021 IPCC's estimate of 3 o C for the climate sensitivity is likely too high. The largest global warming is expected to occur at the tropopause, the boundary of the troposphere and stratosphere [19]. For midlatitudes, the tropopause occurs at an altitude of 11 km where atmospheric pressure is about 300 to 200 hPa. Atmospheric pressure at the Earth's surface is just over 1,000 hPa. Fig. 15 compares the results of the latest (CMIP6) to observations. It should be emphasized that these were the climate models used in the latest IPCC 2021 report. The modelled temperature trend for 1979-2019 is more than twice what was observed. The observed temperature anomaly, given by the green curves in Fig. 15b as well as in Fig. 16 for the period 1979-2023, is also much less than predicted by nearly every GCM. This shows GCMs systematically overestimate global warming [58]. The observed data do show the Earth's average temperature has warmed since 1880. Warming trends are especially pronounced if one compares temperatures to the period 1950 to 1980 when the average temperature did not increase. The warming of the Earth is not evenly distributed but is somewhat larger in the Arctic [60,61]. This is not surprising given that ice reflects more sunlight than water. However, a reduction in summer Arctic ice of 2 million km 2 as will be discussed in the next Section, represents less than 0.4% of the Earth's surface and therefore has primarily a regional as opposed to a global impact. For Ontario, global warming since 1980 is reflected in a slightly longer growing season and undoubtedly a slightly increased incidence of heat waves. The latter should be most pronounced in large urban areas. The contribution of increased greenhouse gases to heat waves is difficult to study as metropolitan regions, such as the Golden Horseshoe, have expanded enormously in recent decades replacing pristine meadows and farmland with asphalt, buildings etc. that heat up much more in the summer sun. This so called urban heat island effect can increase temperatures by as much as 1 o C [62]. The world's largest glaciers are located at the North and South Poles. The largest volume of Arctic ice is contained in the Greenland ice sheet. It has a volume of 2.6 million km 3 and covers an area of 1.7 million km 2 with a thickness ranging from 1 to 3 kilometers [65]. The remaining Arctic ice is floating. So called multiyear ice has a typical thickness between 3 to 4 meters while single year ice is only about 1 meter thick [63]. The extent of the polar ice caps has been monitored since 1979 by satellites. Fig. 17 shows the Arctic ice cap has been steadily shrinking since 1979. The reduction of the Arctic ice cap has been especially noticeable north of Siberia and in Greenland in recent years [65]. This is not surprising given that Arctic temperatures have increased during that period [60,61]. The minimum sea ice extent has been decreasing faster than the maximum sea ice extent. This can be explained by a decrease in the ice thickness which has also been observed by analyzing data recorded by submarines [63]. A reduction of ice thickness may in part be due to storms that have dislodged multiyear ice in recent decades [64]. Extrapolation of the September red solid trendline, leads to a prediction of no ice in September, 2077.
If however, one extrapolates the dashed red trendline obtained using data for 2007 to 2022, an ice free Arctic must wait until 4729. These ice free projection dates can change significantly as one obtains additional years of years. For example, the trend line obtained using 1979-2021 (2007-2021) data predicts an ice free Arctic in September 2073 (2585). In recent years, there have been a number of reports of dramatic summer melting of the Greenland icecap [68]. Over a century of data exists for a few stations in Greenland and is shown in Scientific investigations have been carried out in the Arctic for about a century. An interesting article describes a Norwegian expedition to Spitzbergen [71]. It states: "The Arctic seems to be warming up. Reports from fishermen, seal hunters and explorers who sail the seas about Spitzbergen and the eastern Arctic all point to a radical change in climatic conditions, and hitherto unheard of high temperatures". It adds: "where formerly great masses of ice were found there are now often moraines, accumulations of earth and stones. At many points where glaciers formerly extended far into the sea, they have entirely disappeared. ... Great shoals of white fish have disappeared and seals are few in number". The waters formerly "held an even summer temperature of about 3 o C; this year recorded temperatures up to 15 o C and last winter the ocean did not freeze over even on the north coast of Spitzbergen". A very famous glacier is located in Glacier Bay Alaska, at a latitude just below the Arctic circle. This glacier has retreated dramatically over the last two centuries as shown in The Antarctic ice sheets are the world's largest with a volume of about 27 million km 3 [67]. The Antarctic ice sheet is nearly all on land although part of it is below sea level. The ice thickness averages several kilometers with a maximum thickness of just under 5 kilometers. Fig. 17 shows the maximum September Antarctic ice sheet has gotten slightly larger during 1979 to 2022. The September 2014 ice area was the largest ever recorded since observations began. The trendline for the minimum ice extent in February for 1979-2022 is nearly flat with a slope of -0.13 million km 2 per century. This trend changes to +0.15 million km 2 per century using only the 1979-2021 data. The ice sheet appears to be increasing everywhere around the continent with the exception of the Antarctic peninsula that juts northward toward South America [66]. The obvious result of melting glaciers would be to increase sea level. Various IPCC scenarios predict increases as high as 2 meters by 2100. An increase of about 6 meters would occur if the entire Greenland ice sheet melted while the demise of the Antarctic ice sheets would increase ocean levels by over 60 meters [65]. This would inundate coastal areas displacing hundreds of millions of people. It is important to realize that sea levels only go up if glaciers located on land melt. The melting of the entire floating Arctic ice cap would have no effect. The reason is that floating ice displaces a volume of water that nearly equals the volume it would occupy if the ice were converted to water. Fig. 20 shows sea level has risen over 100 meters since the end of the last ice age. The rate of sea level rise 10,000 years ago exceeded 10 mm/year. Ancient sea levels can be estimated using fossil coral reefs. Coral reefs grow vertically as sea level increases such that the distance to the ocean surface remains approximately constant. The age of successive levels of coral can be determined by measuring the concentration of radioactive isotopes such as 14 C [75,76]. Modern sea level measurements are determined by averaging over low and high tides. Fig. 20 shows that sea level rose at an average rate of 2 mm/year between 1880 and 2000 [77]. This increased to 3.5 mm/year for data covering the period 1994 to 2008. Extrapolating the rate of 3.5 mm/year from 2021 to 2100 results in an average global sea level rise of 28 cm. A significant complication in this determination is that land may be subsiding or rebounding. The region bordering Hudson Bay is rising at about 10 mm/year [78]. This so called isostatic rebound occurs because the land no longer is depressed by the weight of kilometer thick ice sheets that existed during the last ice age. The increase in sea levels are caused not just by additional water supplied by melting glaciers but also by the thermal expansion of water. The maximum density of water occurs at 4 o C. This is approximately the ocean temperature at depths below 1000 meters. Most of the ocean's heat is contained in the top few hundred meters. A 200 meter column of water whose temperature changes from 20 to 21 o C would increase in height by 14 mm. Sea level should increase as the ocean absorbs heat from a warming atmosphere. Estimates vary but it appears that this so called thermosteric contribution is responsible for a sea level increase throughout the 20th century of about 1 mm/year [79]. This effect is difficult to estimate, Ontario's contribution to global sea level rise is found by multiplying the fraction of global CO 2 emitted by the province, 0.35%, by the anthropogenic rate of sea level rise. The latter can be estimated assuming it to equal the entire change in the rate of sea level rise observed during 1994 to 2008, 3.5 mm/year relative to the rest of the 20th century, 2.0 mm/year. One finds Ontario is responsible for 0.005 mm/year sea level rise. This is minuscule when one compares to tides whose amplitudes are as high as 16,000 mm in the Bay of Fundy and occur about twice each day. An especially dramatic concern is that climate change may be acidifying oceans which is being blamed for threatening the future of coral reefs [82].
Acidity is measured using the pH scale. Distilled water is neutral and has a pH of 7. Substances such as baking soda, ammonia and bleach have a pH > 7 and are called bases while coffee, orange juice and stomach acid have a pH < 7 and are called acids. Sea water is slightly basic due to various impurities, most notably salt while rain is acidic. About half of the carbon dioxide emitted into the air by burning fossil fuels is believed to be absorbed into the oceans [83]. A small fraction of these carbon dioxide molecules react with sea water to generate carbonic acid [84]. The ocean acidity dependence on the atmospheric concentration of CO 2 has been calculated and is shown in Fig. 22 [85]. It is the presence of carbon dioxide that prevents seawater from being very basic and makes the oceans habitable. Doubling CO 2 from 400 to 800 ppm, reduces the seawater pH by 0.27. This is less than changes as high as 1 pH per day that occur in some coastal regions due to the influx of inland fresh water caused by tides. No adverse impact on the ecosystem has been detected [86]. Fig. 23 shows the observed pH dependence on depth and time in Santa Monica Bay during 2003 to 2008. A sunbathing seal who decides to dive 50 meters to catch a fish experiences a pH change comparable to that resulting from doubling atmospheric CO 2 . Similarly, the pH decrease due to the increase of CO 2 since the start of the Industrial Revolution is only 0.1. Ontario's contribution to ocean acidification can be estimated by multiplying the province's fraction of global CO 2 emissions, 0.35%, by the reduction in pH, 0.27, that would result if atmospheric CO 2 were to double. A CO 2 doubling time of 166 years is found by dividing the 2021 CO 2 concentration of 415 ppm by the observed rate of increase of 2.5 ppm/year. This gives Ontario's contribution to ocean acidificiation of 6 x 10 6 pH/year. The maximum amount of water vapour in the atmosphere increases 6% per degree Celsius. It is therefore reasonable that precipitation should increase in a warmer world [88]. Indeed, it is hot humid summer days that produce torrential downpours. The 2007 IPCC report stated that precipitation has increased in some regions by as much as 1% in each decade of the 20th century [5,89]. Several studies have examined precipitation for the last part of the 20th century. The results range from a globally averaged precipitation trend that has changed by: -1 mm/year [90]; +3.5 mm/year [91]; and +0.1 mm/year [92]. These differences are not entirely surprising given that precipitation varies considerably over time scales of decades [93]. Data is also very sparse for large regions of the Earth including the Sahara, Amazon, Oceans etc. over most of the 20th century. Hence, the resulting trends frequently are not statistically significant. The need to be cautious about concluding precipitation has changed significantly is illustrated in The data shown in Figures 25 and 26 do not address whether once in a century downpours are becoming more common. It is difficult to study the frequency of such events because several centuries of data are needed to make any meaningful conclusions. Data for such extended times do not exist for Ontario. That is not to say that heavy rainfall events do not produce greater flooding than in the past. Such flooding, with extensive associated damage, invariably occurs in urban settings where the land surface has been greatly modified to accommodate concrete roadways, parking lots, buildings, etc. that make the surface impervious to water [96]. Whereas before it was developed, the land was able to soak up much rain like a sponge, the water now runs off into creeks turning them into raging torrents. That may be a serious problem, but not one caused by climate change. The Great Lakes watershed is the most important for Ontario as it contains the province's largest metropolitan areas. Fig. 27 shows the water levels of the Great Lakes relative to sea level measured by the U.S. Army Corps of Engineers from 1920 to 2020 [97]. The water levels depend not only on the amount of precipitation but also are affected by various dams comprising the St. Lawrence Seaway. Even so, there is no trend for any Great Lake. This supports the conclusion that in Ontario neither precipitation nor flooding due to high Great Lake water levels have changed significantly over the past century. A claim of the IPCC is that climate change is warming the oceans which has increased the severity and frequency of powerful storms. This would make sense for hurricanes that develop in tropical regions and get their energy from warm surface water. However, this prediction may be simplistic. An important driver of the Earth's climate is the temperature difference betweeen the equatorial and polar regions. Weather systems transfer energy away from the tropics. Global warming will be largest in the Arctic. Hence, the temperature difference between the Arctic and the equator will be reduced, with presumably a subsequent weaking or shift of wind patterns such as the Jet Stream [98]. Hurricanes, with the exception of Hurricane Hazel in 1954, seldom strike Ontario. Another extreme weather event is tornadoes. Most of the world's tornadoes occur in the United States. They originate when a warm air front from the Gulf of Mexico collides with cooler air from Northern Canada. The damage caused by a tornado depends on the wind strength and is categorized by the Enhanced Fujita scale shown in The number of tornadoes recorded has increased over the past 50 years as improved technology, especially Doppler radar, has been introduced [103]. Fig. 29 shows the number of tornadoes observed in the U.S. from 1995 to 2020. There is no significant trend in either the total number of tornadoes or the number of strong tornadoes, defined as having a rating of EF2 or greater. Fig.
30 shows the number of tornadoes recorded in Ontario from 1950 to 2007 [104]. There were fewer tornadoes in the period 1950 to 1975 than in later years. This is readily explained by the introduction of better observing technology. There seems to be a decreasing trend after 1978. A significant negative effect of decreasing precipitation and/or higher temperatures would be an increased risk of forest fires. It should be pointed out that forest fires caused by lightning are a natural part of the ecosystem. The concern is that climate change is increasing drought severity making fires more numerous and larger. Fig. 31 shows a small decrease in the number of wildfires in Canada and Ontario from 1990 to 2020. There is no clear trend in the number of hectares burned. This is somewhat surprising given that mankind has strongly interfered with the forest ecosystem. Policies to extinguish fires have allowed a build up of flammable material in North America's forests during the 20th century. Hence, one would expect fires to be much larger. In addition, man has all too frequently been careless, inadvertently starting fires. The 0. Ontario's contribution to global warming can be estimated using its fraction of world CO 2 production. Using the 2021 IPCC recommended climate sensitivity, S = 3 o C, gives a contribution of 9.2 x 10 5 o C or 92 microdegrees C per year to global warming. This is dwarfed by that of other countries, especially China, U.S. and India. There has been a significant reduction in the Arctic ice cap since satellite measurements began in 1979. However, the extent of minimum sea ice in September appears to have stabilized after 2007. Extrapolating the 1979-2022 data to determine when there will be an ice free Arctic Ocean gives a date of 2077. Using the 2007-2022 data changes the ice free year to 4729. Records of Greenland suggest that the warming of the last few years is less than that experienced in the first part of the 20th century. The dramatic retreat of glaciers such as in Glacier Bay, Alaska during the 1800s and early 1900s occurred when greenhouse gas emissions were relatively low and is likely due to warming fo the Earth following the end of the Little Ice Age. For Antarctica, there has been a slight increase in average sea ice extent since 1979 although a slight reduction in recent years. Sea levels have continued increasing throughout the 20th century at a rate of 2 to 3.5 mm/year. This is likely a continuation of a natural process that began at the end of the last ice age. Ontario's contribution to anthropogenic global sea level rise is only 0.005 mm/year. For Ontario's sea coast bordering Hudson Bay, sea level will likely continue a significant decline due to isostatic rebound of the land in response to the end of the last ice age. The acidity change due to absorption of CO 2 by the oceans is small compared to tidal and season effects as well as the pH change experienced when one dives below the surface. Ontario's contribution to ocean acidification is a minuscule 6 x 10 6 pH/year. North American precipitation records show no change over the past two centuries. Precipitation recorded at Toronto from 1843 to 2020 is remarkably stable. Over a century of measurements show no significant change of flooding caused by high Great Lake water levels. The frequency of extreme events was examined. No change in either the number of total hurricanes or severe hurricanes during 1981 to 2021 was found. Similarly, tornado observations using modern Doppler radar show no change for either the number of total tornadoes or strong tornadoes from 1995 to 2020 in the U.S. The number of Ontario tornadoes shows no overall trend from 1950 to 2007 but there appears to be a decrease from 1978 to 2007. The annual number of forest fires decreased in Canada and Ontario from 1990 to 2020 and the area burned shows no clear trend. In conclusion, the author wishes to emphasize that application of well tested physics shows an increase of greenhouse gases will cause some global warming. However, contrary to the United Nations claim, there will not be catastrophic climate change within 10 years [1], nor should one overlook the beneficial aspects of increased carbon dioxide for promoting plant growth. The impact of Ontario's anthropogenic emissions of greenhouse gases on global climate is minuscule. We are grateful for the financial support of the Canadian Natural Science and Engineering Research Council. We are grateful for the financial support of the Canadian Natural Science and Engineering Research Council.