I recently participated in a mostly two person debate in my Current Events Discussion Group about climate change and whether it is just part of a natural earth cycle or is being caused by humans burning fossil fuels. Another participant and I have polar opposite views on that subject so we agreed to defend our positions on the issue before the other participants. We each prepared a position paper and distributed it to all participants in advance of the discussion.
My friend believes that what the world is experiencing is purely a result of the natural cycle of warming and cooling that the earth has gone through for millions of years. He says that we are in the later stages of a warming cycle that may last for another 3,000 years before a new cooling cycle begins. He discounts human activities as insignificant in the natural earth cycle.
I, on the other hand, am convinced that human activity is disrupting the natural earth cycle and substantially accelerating the warming of the earth. The culprit of course in my mind is excessive release of greenhouse gasses through the burning of fossil fuels. I further fear that if humanity does not take immediate action catastrophic climate change will make large portions of the earth uninhabitable before the end of the 21st century.
Each of us claims the scientific high ground in spite of our radically different perspectives. We are completely in sync on the long history of the earth’s life cycle. We only differ in what has and is happening since the beginning of the industrial revolution. He thinks it’s natural warming which we should accept and that civilization simply must adapt; I think it’s man made and an existential threat to civilization as we know it.
We each produced a document to represent our positions. My friend used an outline format; I used a narrative style. I am copying each position paper verbatim as presented. For the sake of distinguishing the two positions here, I call his presentation “Earth’s Climate History”, and mine “Earth’s Climate Future”. My friend did not provide the scientific sources of his paper. However, from my own sources I agree that his paper represents earth’s planetary physics as well as climate history up until the beginning of the industrial revolution. You draw your own conclusion about what climate change truth is from these and/or other sources.
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Earth’s Climate History
Climate Change Factors
I. Insolation from Sun: Heat from the Sun reaching surface of Earth?
A. Sun Heat Cycles – e.g. 11-year sunspot cycle cools Earth.
1. No measure yet of long-term Sun cycles.
B. Milankovich Cycles, which are astronomical.
1. Changes in orbit of Earth around Sun – Circular vs Elliptical.
Elliptical means cooler climate. It’s now more round. 100,000 year cycle.
2. Changes in tilting of Earth’s axis relative to Sun. It ranges from 21.5 degrees to 24.5 degrees; it’s currently 23.5 degrees. 41,000 year cycle.
3. “Wobble” of tilt of Earth’s axis. A net 21,000 year cycle.
4. Coincidence of cycles increases impact on Earth’s climate.
II. Feedback Conditions on Earth
A. Positive feedback conditions for warming Earth.
1. Warm ocean water absorbs and holds more heat and CO2.
2. Atmospheric CO2 holds in heat on Earth.
3. Ocean surface is dark and has a low albedo, which reflects less heat back into space.
B. Negative feedback conditions for warming Earth.
1. Albedo effect of e.g. clouds and ice reflecting Sun’s energy
back into space. Thereby, a glacier can feed itself.
2. “Silicate weathering” removes CO2 from atmosphere, as silicate rocks (exposed by melting glaciers) are weathered.
3. Volcanic and other materials reflecting Sun’s energy back into space. E.g. the 1815 “Year of Never Summer” after Mt. Tambora volcanic eruption in Indonesia.
C. Ocean currents transfer heat and cold horizontally and vertically around the Earth. E.g. Gulf and Japanese Currents.
D. Man’s rapid mining and burning of hydrocarbons are quickly returning to the atmosphere huge amounts of heat and CO2, which took millions of years to accumulate and store underground.
2,600,000 North and South America join at Isthmus of Panama.
Years Ago Pleistocene Ice Age begins. Since then, continental glaciers advance and retreat over a dozen times.
105,000 Continental glaciers all melted, as warm Inter-Glacial Years Ago Period ends. Average annual temperature approaches 60 degrees. Ocean sea level at max – 25’ higher than now. Latest cold Glacial Period begins.
70,000 Wisconsinan Continental Glacier starts to form in NE
Years Ago Canada, as snow no longer melts in summer and starts
to accumulate. As moisture is transferred from oceans
to continental glaciers, ocean sea level falls. Average annual temperature drops to 33 degrees.
25,000 Wisconsinan Glacier reaches Ohio.
Years Ago
20,000 Wisconsinan Glacier reaches its maximum – 10,000’ thick
Years Ago in Canada, 5,000’ thick in Cleveland, and over 1,000’ thick
in Columbus – extending south to Chillicothe. Ocean sea level down 400’. Glacial Period cooling switches to current Inter-Glacial Period warming.
14,000 Wisconsinan Glacier retreats from Ohio.
Years Ago
10,000 Continental Glaciers all melted, except for Greenland and
Years Ago Antarctica. Ocean sea level rises 375’ to within 25’ of max.
Present Nearing end of Inter-Glacial Period warming. Average annual temperature now over 55 degrees. Over next 3,000 years, Greenland glacier will melt and Antarctic
glacier will partially melt raising ocean sea level another 25’.
3,000 Average annual temperature at 60 degrees. Warm Inter-Glacial Years Period ends, and cold Glacial Period begins.
From
Now
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Earth’s Climate Future
International climate scientists are continuing to study the natural evolution of climate cycles. But today there is a strong focus on better understanding the relatively recent disturbing trend in “Global Warming”.
Global Warming refers to the change of global surface temperature relative to a baseline. Specific global warming levels, such as 1.5°C, 2°C, 3°C or 4°C, are defined as changes in global surface temperature relative to the years 1850–1900 as the baseline; that is the earliest period for which reliable observations are available with sufficient geographic coverage.
Scientific investigation over the most recent several decades indicates that humans burning fossil fuels is destroying the historic natural climate cycles, and left unchecked, will soon produce catastrophic climate consequences for civilization. Here is what they now know:
- Climate is influenced by a range of factors, but there is a nearly linear relationship between cumulative CO2 emissions and increases in global surface temperature. The main human drivers of climate change are increases in the atmospheric concentrations of CO2, other greenhouse gases, and aerosols from burning fossil fuels, land use, and other sources;
- The scale of recent changes in the climate system as a whole – and the present state of many aspects of the climate system – are unprecedented over many centuries to many millennia;
- The current rates of increase of the concentration of the major greenhouse gases (carbon dioxide, methane and nitrous oxide) are unprecedented over at least the last 800,000 years;
- Each of the last four decades has been successively warmer than any decade that preceded it since 1850. Global surface temperature was 1.09°C higher in 2011–2020 than 1850–1900;
- Global surface temperature will continue to increase until at least mid-century under all emissions scenarios studied. Global warming of 1.5°C and 2°C will be exceeded during the 21st century unless deep reductions in CO2 and other greenhouse gas emissions occur in the coming decades;
- Effects of global warming tend to lag measured increases by some decades. The impact of the current global warming state as well as that which has already occurred will continue to show up for decades to come. Therefore, we will likely see the climate impact of temperature increases we are measuring today in around 50 years or so;
- Continued global warming is projected to further intensify the global water cycle, including its variability, global monsoon precipitation and the severity of wet and dry events. The global water cycle also describes the north/south and east/west circulations of ocean currents and their impact on regional temperatures;
- Many changes due to past and future greenhouse gas emissions are irreversible for centuries to millennia in the future, especially changes in the ocean, ice sheets, and global sea level;
- Outcomes, such as ice-sheet collapse, abrupt ocean circulation changes, some compound extreme events, and warming substantially larger than that assessed cannot be ruled out and are part of risk assessment.
The latest international scientific climate change assessment (IPCC AR6) concludes that:
- Humans have played the dominant role in driving recent climate change. That influence has warmed the atmosphere, oceans, and land. Widespread and rapid changes in the atmosphere, ocean, cryosphere and biosphere have occurred as a result. This conclusion is based on a synthesis of information from multiple lines of evidence, including direct observations of recent changes in Earth’s climate;
- Observed increases in well-mixed greenhouse gas concentrations since around 1750 are unequivocally caused by human activities. Since 2011, concentrations have continued to increase in the atmosphere, reaching annual averages of 410 parts per million (ppm) for carbon dioxide (CO2);
- Climate scientists now consider it an established fact that human-induced greenhouse gas emissions have led to an increased frequency and intensity of weather and climate extremes since 1850, in particular for temperature extremes;
- Human-induced climate change is already affecting many weather and climate extremes in every region across the globe. Evidence of observed changes in extremes such as heatwaves, heavy precipitation, droughts, and tropical cyclones are attributed to human influence;
- The dominant effect of human activities is not only in the warming of global surface temperature, but also in the pattern of warming in the lower atmosphere and cooling in the stratosphere, warming of the ocean, melting of sea ice, and many other observed changes;
- Taken together, this evidence shows that humans are the dominant cause of observed global warming over recent decades.
The Intergovernmental Panel on Climate Change (IPCC) is my primary source for quality climate change information. That body was set up and tasked specifically with collecting and consolidating the best scientific evidence about climate change. They are the world’s foremost authority on what climate scientists are thinking and saying, and what scientific research shows about climate change.
The points I make in this document reflect my best understanding of the findings presented in the IPCC’s AR6, Working Group I Report released in August of 2021. I have identified what I think are the central themes of that document. But you need to cut me some slack here on the limited technical details I am presenting. They are all in the Report, but it is long, and I have done the best I can to condense 2391 pages into three.
The IPCC has produced five previous Assessment Reports (AR1-5) since 1988. After the first, each subsequent report has refined the previous assessment with new scientific data and understanding. In each report the evidence for the dominance of human influence on climate change gets stronger.
Note: There are three working groups within IPCC AR6: Working Group I studies the Physical Science Basis of Climate Change; Working Group II focuses on Climate Change Impacts, Adaptation, and Vulnerability; Working Group III considers potential Mitigation of Climate Change. I have not yet explored WG II and WG III in the new Assessment Report 6.