by W. A. van Wijngaarden

The effect of changing greenhouse gas concentrations, most notably carbon dioxide, CO₂, 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 CO₂ 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^oC. However, the GCMs do not account for observed decadal temperature fluctuations and consistently overestimate the warming. Ontario’s contribution to global warming is only 9.2×10−5^oC/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 CO₂ 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 6×10−6 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.

You may download a printable version of W. A. van Wijngaarden‘s publication Impact of Changing Greenhouse Gas Concentrations on Ontario’s Climate here.