Earth is roughly 4.5 billion years old and many climate changes occurred over that extended period of time. Warm, tropical periods were interspersed with ice ages on the timescale of millions to hundreds of thousands of years ago. Those types of climate changes occurred \u201cnaturally,\u201d long before humans impacted the earth. In fact, humanity has only existed on Earth for a fraction of that time, with Homo Sapiens emerging in the geological record approximately 300,000 years ago.<\/p>\n\n\n\n
Over long periods of geological history, both the global temperature and CO2<\/sub> levels fluctuated for natural reasons. Figure 10 taken from the Massachusetts Institute of Technology\u2019s recent climate primer (Emanuel, 2020) illustrates those fluctuations over the past 800,000 years.<\/p>\n\n\n\n Source: Emanuel, 2020, p. 22.<\/p>\n\n\n\n The jagged lines are expected on climate graphs and show variability over a shorter timeframe, but the longer-term ups and downs are of interest when explaining how fast climate is changing. The more pronounced \u201cpeaks\u201d and \u201cvalleys\u201d illustrate that CO2<\/sub> (green) and temperature (purple) rose and fell in conjunction with one another every 100,000 years or so. The peaks reflect tropical periods and the valleys reflect ice ages.<\/p>\n\n\n\n This 100,000-year cycle can be attributed to a natural cause: the amount of sunlight the Earth received. The Milankovi\u0107 <\/a>theory explains that the timing of Earth\u2019s tilt, wobble and orbit around the sun creates a predictable cycle of heating and cooling that repeats approximately every 100,000 years. When more of Earth\u2019s surface is exposed to the sun and the Earth is closer to the sun, hotter global temperatures result, and vice versa. These pre-historical ups and downs in CO2<\/sub> and temperature have been confirmed with very high confidence from chemical analysis of arctic ice cores (Masson-Delmotte et al., 2013). What has happened in more recent history, is a much faster change than the pre-historic 100,000-year cycle. For example, the rapid increase in CO2<\/sub> over the past 70 years is illustrated by the green star on the right side of Figure 10.<\/p>\n\n\n\n In addition to the speed of the change, the relationship between CO2<\/sub> and temperature is also important to understanding natural versus human-induced climate change. In pre-historic times, CO2<\/sub> lagged temperature, meaning temperature was the driving force for CO2<\/sub> levels, but since the industrial revolution, the reverse is true. In prehistoric times, when temperature increased due to the Milankovi\u0107 cycles, the oceans warmed and glaciers melted. When oceans are warmer, they store less CO2<\/sub> gas in the water and release it to the atmosphere. Melting glaciers elevated sea levels, thereby reducing land and vegetation cover for photosynthesis also resulting in higher atmospheric CO2<\/sub> levels. Less sunlight in cooling periods resulted in cooler oceans absorbing more CO2<\/sub> and growing glaciers dropping sea levels, which exposed more land for vegetation that removed more CO2<\/sub> from the air (Hausfather, 2020). This pre-historic temperature-driven relationship lasted for hundreds of thousands of years, but was reversed relatively quickly during the industrial revolution. Starting at the end of the 1800\u2019s, more fossil fuels were burned with the invention of machines and vehicles, releasing CO2<\/sub> into the atmosphere and a noticeable effect in temperature was observed. This increase was due the greenhouse effect, which occurs when gases at Earth\u2019s surface, especially CO2<\/sub>, trap heat and radiate it back to Earth causing more warming. Figure 1.2 from the International Panel on Climate Change\u2019s (IPCC) 2018 report, shows the impact of the industrial revolution on global temperature.<\/p>\n\n\n\n Figure 1.2 Evolution of global mean surface temperature over the period of instrumental observations<\/p>\n\n\n\n Source: IPCC, 2018, p.71.<\/p>\n\n\n\n The grey jagged lines in Figure 1.2 illustrate the variable monthly temperatures and the red line indicates the average Earth temperature. In the \u201cpre-industrial\u201d period (1850 to 1900), temperature remains relatively constant, but starts to increase at approximately 1900. This is the same time that the industrial revolution led to a significant increase in burning of coal, oil and gas. The temperature has continued to increase with even more intensity around the middle of the century, with warming reaching approximately 1.0 degree Celsius above pre-industrial levels in 2017 (IPCC, 2018, p. 51).<\/p>\n\n\n\n If humans fail to curb emissions, we may reach a mean global temperature increase between 2.5\u00b0C and 4.5\u00b0C by 2100 (Emanuel, 2020). The size of this temperature increase is extraordinary considering the Milankovi\u0107 cycles should be causing a cooling phase that would continue for several thousand more years, leading to the next ice age. Instead, what has occurred is a strong uptick in both temperature and CO2<\/sub> since about 1900, which is quite unusual and does not correspond to the trends of the last few thousand years (Emanuel, 2020). <\/p>\n\n\n\n The rate that CO2<\/sub> and temperature have increased over the past 100 years is much faster than pre-historic changes. The industrial revolution led to higher CO2<\/sub> emissions, which started global temperature on an upward trend. CO2<\/sub> and temperature are now at higher levels than humanity has ever experienced and are projected to increase even further. The temperature increase is especially unusual considering Earth\u2019s orbital cycle, which should be cooling Earth and moving us towards the next ice age.<\/p>\n\n\n\n The IPCC has recently communicated the cause of climate change more clearly than ever before. They concluded, \u201cIt is unequivocal that human influence has warmed the atmosphere, ocean and land. Widespread and rapid changes in the atmosphere, ocean, cryosphere and biosphere have occurred\u201d (IPCC, 2021, p. 5). It is unequivocally clear that climate change is no longer naturally-occurring. Humans are the cause, and global warming will increase unless CO2<\/sub> emissions are significantly reduced. <\/p>\n\n\n\n Did this blog help you understand the difference between natural and human-caused climate change? Please feel free to comment, or connect with me on social media.<\/p>\n\n\n\n References<\/strong><\/p>\n\n\n\n Emanuel, K. (2020). Climate science, risk & solutions. Massachusetts Institute of Technology. https:\/\/climateprimer.mit.edu\/climate-science-risk-solutions.pdf<\/a><\/p>\n\n\n\n Hausfather, Z. (2020). How the rise and fall of CO2<\/sub> levels influenced the ice ages. CarbonBrief. 2 July 2020. https:\/\/www.carbonbrief.org\/explainer-how-the-rise-and-fall-of-co2-levels-influenced-the-ice-ages<\/a><\/p>\n\n\n\n IPCC (2018). Global Warming of 1.5\u00b0C.An IPCC Special Report on the impacts of global warming of 1.5\u00b0C above pre-industrial levels and related global greenhouse gas emission pathways, in the context of strengthening the global response to the threat of climate change, sustainable development, and efforts to eradicate poverty [Masson-Delmotte, V., P. Zhai, H.-O. P\u00f6rtner, D. Roberts, J. Skea, P.R. Shukla, A. Pirani, W. Moufouma-Okia, C. P\u00e9an, R. Pidcock, S. Connors, J.B.R. Matthews, Y. Chen, X. Zhou, M.I. Gomis, E. Lonnoy, T. Maycock, M. Tignor, and T. Waterfield (eds.)]. In Press. https:\/\/www.ipcc.ch\/site\/assets\/uploads\/sites\/2\/2019\/06\/SR15_Full_Report_Low_Res.pdf<\/a>. <\/p>\n\n\n\n Revised Blog September 1, 2021 As Canadians, we see a lot of variation in the weather and it is normal to wonder if it is typical or if the climate is changing for the worse. If global warming is real, why does it get so cold sometimes? If humans have caused climate change, why did […]<\/p>\n","protected":false},"author":945,"featured_media":0,"comment_status":"open","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[26],"tags":[],"class_list":["post-270","post","type-post","status-publish","format-standard","hentry","category-cals-500","has-post-thumbnail"],"_links":{"self":[{"href":"https:\/\/webspace.royalroads.ca\/kchomlak\/wp-json\/wp\/v2\/posts\/270","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/webspace.royalroads.ca\/kchomlak\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/webspace.royalroads.ca\/kchomlak\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/webspace.royalroads.ca\/kchomlak\/wp-json\/wp\/v2\/users\/945"}],"replies":[{"embeddable":true,"href":"https:\/\/webspace.royalroads.ca\/kchomlak\/wp-json\/wp\/v2\/comments?post=270"}],"version-history":[{"count":7,"href":"https:\/\/webspace.royalroads.ca\/kchomlak\/wp-json\/wp\/v2\/posts\/270\/revisions"}],"predecessor-version":[{"id":352,"href":"https:\/\/webspace.royalroads.ca\/kchomlak\/wp-json\/wp\/v2\/posts\/270\/revisions\/352"}],"wp:attachment":[{"href":"https:\/\/webspace.royalroads.ca\/kchomlak\/wp-json\/wp\/v2\/media?parent=270"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/webspace.royalroads.ca\/kchomlak\/wp-json\/wp\/v2\/categories?post=270"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/webspace.royalroads.ca\/kchomlak\/wp-json\/wp\/v2\/tags?post=270"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}![\"\"](\"https:\/\/webspace.royalroads.ca\/kchomlak\/wp-content\/uploads\/sites\/897\/2021\/09\/Emanuel-2020.png\")
<\/figure>\n\n\n\n![\"\"](\"https:\/\/webspace.royalroads.ca\/kchomlak\/wp-content\/uploads\/sites\/897\/2021\/09\/IPCC-2018.png\")
<\/figure>\n\n\n\nIPCC (2021). Summary for Policymakers. In: Climate Change 2021: The Physical Science Basis. Contribution of Working Group I to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change [Masson-Delmotte, V., P. Zhai, A. Pirani, S. L. Connors, C. P\u00e9an, S. Berger, N. Caud, Y. Chen, L. Goldfarb, M. I. Gomis, M. Huang, K. Leitzell, E. Lonnoy, J.B.R. Matthews, T. K. Maycock, T. Waterfield, O. Yelek\u00e7i, R. Yu and B. Zhou (eds.)]. Cambridge University Press. In Press. https:\/\/www.ipcc.ch\/report\/ar6\/wg1\/downloads\/report\/IPCC_AR6_WGI_SPM.pdf<\/a><\/h1>\n","protected":false},"excerpt":{"rendered":"