Scientific and Spiritual Dimensions of Climate Change: Class 8


Class 8

Some More Climate Science

Planet Earth will continue to exist despite climate change, although in a much impoverished state, as there will be much less species of plants and animals. In the course of many thousands of years a rich biodiversity will probably evolve again on the Earth and the climate return to its natural cycles. The only question is whether human civilization will survive. Currently we are on a direct course to self-destruction.

Section 1: Historical Perspective

We know from earlier civilizations that the lead indicators of economic decline were environmental, not economic. The trees went first, then the soil, and finally the civilization itself. To archeologists, the sequence is all too familiar. (1)

Two Examples:

The ancient Sumerian civilization flourished on the central floodplain of the Euphrates River in the fourth millennium BC. The Sumerians had the first written language and built the first cities. They had a very productive agriculture with a sophisticated irrigation system. Unfortunately their irrigation system caused salination of the soil because of water evaporation. For a while the Sumerians could survive by planting more salt tolerant crops. However, their civilization collapsed and until today their once fertile land is almost a desert, with only little vegetation. (2)

Easter Island in the South Pacific was settled around ad 400. Its civilization flourished on a volcanic island with rich soils and lush vegetation, including trees that grew 25 meters (82 feet) tall with trunks 2 meters (6,6 feet) in diameter. Archeological records indicate that the islanders ate mainly seafood, principally dolphins—a mammal that could only be caught by harpoon from large sea-going canoes. The Easter Island society flourished for several centuries, reaching an estimated population of 20,000. As its human numbers gradually increased, tree cutting exceeded the sustainable yield of forests. Eventually the large trees that were needed to build the sturdy canoes disappeared, depriving islanders of access to the dolphins and dramatically shrinking their food supply. The archeological record shows that at some point human bones became intermingled with the dolphin bones, suggesting a desperate society that had resorted to cannibalism. Today the island has fewer than 4,000 residents. (3)

In other parts of the world, similar events happened in the past. A culture flourished. Population grew. Demand on the environment increased. Civilization reached a peak, then declined and collapsed because the environment could not sustain it any longer.

The situation today is unique because this time the whole planet is at stake and therefore civilization as we know it. "Our global economy is outgrowing the capacity of the Earth to support it, moving our early twenty-first century civilization ever closer to decline and possible collapse. ... We are consuming renewable resources faster than they can regenerate. Forests are shrinking, grasslands are deteriorating, water tables are falling, fisheries are collapsing, and soils are eroding. We are using up oil at a pace that leaves little time to plan beyond peak oil. And we are discharging greenhouse gases into the atmosphere faster than nature can absorb them, setting the stage for a rise in the earth's temperature well above any since agriculture began." (4)

As mentioned previously, global temperatures of the last 10,000 years have been about the most stable in the Earth’s history which allowed humans to develop a civilization built on agriculture. We are in one of the naturally occurring warm interglacial periods. The Earth did experience warmer temperatures than now, but the last time temperatures were warmer than at present was about 125,000 years ago, at a time when humans survived as hunter-gatherers.

The extremely high concentration of greenhouse gases in the atmosphere, however, is unprecedented in all of human history. Scientists are virtually certain that this commits us to more global warming in the future without us adding more greenhouse gases to the atmosphere. They just can't tell us yet the exact amount of warming still in store. And of course, atmospheric greenhouse gas concentrations are continously increasing as humans are burning fossil fuels. 

Section 2: Future Threats

Best current estimates for temperature rise by the end of this century is 4°C (7.2°F) if we continue with business as usual. It's hard to imagine a 4°C warmer world. Scientist James Hansen explains how our world could potentially look like with 2.8°C (5°F) warming: "Our best information comes from the Earth's history. The last time that the Earth was 2.8°C (5°F) warmer was three million years ago, when sea level was about 24m (80 feet) higher. Twenty-four meters! (Eighty feet!) In that case, the United States would lose most East Coast cities: Boston, New York, Philadelphia, Washington, and Miami; indeed, practically the entire state of Florida would be under water. Fifty million people in the US live below that sea level. Other places would fare worse. China would have 250 million displaced persons. Bangladesh would produce 120 million refugees, practically the entire nation. India would lose the land of 150 million people.

"A rise in sea level, necessarily, begins slowly. Massive ice sheets must be softened and weakened before rapid disintegration and melting occurs and the sea level rises. It may require as much as a few centuries to produce most of the long-term response. But the inertia of ice sheets is not our ally against the effects of global warming. The Earth's history reveals cases in which sea level, once ice sheets began to collapse, rose one meter (3.3 feet) every twenty years for centuries. That would be a calamity for hundreds of cities around the world, most of them far larger than New Orleans. Devastation from a rising sea occurs as the result of local storms which can be expected to cause repeated retreats from transitory shorelines and rebuilding away from them." (5)

More recent studies (July 2015) show an unexpected acceleration of glacial melt all over the world. “Glaciers are now losing mass twice as fast as they were in the period from 1901-1950, three times as fast as in the period from 1851-1900, and four times as fast as in the period from 1800-1850, the researchers found.” (6)

“The rates of early 21st-century mass loss are without precedent on a global scale, at least for the time period observed and probably also for recorded history, as indicated also in reconstructions from written and illustrated documents. This strong imbalance implies that glaciers in many regions will very likely suffer further ice loss, even if climate remains stable.” (7)

As if this was not enough, there are several issues that should prompt us to quick and effective actions:

  • The projected sea-level rise scenario as described in the previous two paragraphs is based on a 2.8°C (5°F) warming. The United Nations Environment Programme (UNEP) stated that national pledges to cut carbon emissions, even if fully implemented, would see temperatures rise by 3°C above pre-industrial levels, far above the "well below 2°C" of the Paris Climate Agreement. (8)
    We should be aware that already an increase of 2°C (3.6°F) would displace people from Small Island States and from low-lying coastal areas including from many heavily populated large cities such as Miami  (9) , Tokyo, Shanghai, and New York (10)
  • Inertia of the Climate System: Even if we could keep carbon dioxide levels stable at today's levels, the planet would continue to warm for decades. It takes a long time for the oceans to warm. As long as they are still in the process of warming, the atmosphere cannot reach equilibrium. Unfortunately we are not even on a path to stabilize CO2 levels. On the contrary, atmospheric CO2 concentrations are continuing to rise every year.
  • The Limit of Carbon Sinks: Almost half of the CO2 which humanity has emitted since the industrial revolution has been absorbed by plants during photosynthesis, especially by trees, and by the water and phytoplankton in the oceans. Without this absorption, the warming we have already experienced would have been stronger. However, this process has already started to change because there is a limit to this carbon sink. Due to warmer temperatures, some old growth forests are now releasing more CO2 than absorbing. The oceans used to be a huge carbon sink as well, but some show signs that they are close to reaching their capacity to absorb CO2. (The absorption of CO2 into the oceans makes the water more acidic. For more information about the harmful consequences of ocean acidification, see Class 3, More Impacts of Climate Change, Section 5.)
  • Aerosol Pollution: The burning of fossil fuels not only emits greenhouse gases, but also toxic air pollutants, especially sulfate aerosols. These aerosols are a serious health hazard (lung disease) and cause acid rain and crop losses. Ironically they have a cooling effect on the local climate as they reflect some of the sun's rays back into space. Of course, we cannot consider them a "solution" to the climate crisis because of their negative effects. Also they remain in the lower atmosphere for only several weeks while greenhouse gases stay many decades and centuries. Cleaning up our air pollution will have some warming effect on the climate.

The inertia of the climate system, the carbon sinks, and aerosol pollution have so far clouded the effects of climate change. Without these factors, the warming we would have experienced so far would have been considerably greater. Now, with the climate system changing to new patterns, carbon sinks reaching their limits, and (hopefully) aerosol pollution diminishing (with pollution control and reduction of fossil fuel burning), the warming will accelerate and its impacts become much more severe.

Feedback Mechanisms:

Many feedback mechanisms can accelerate the warming of the Earth. The following are the most important known feedbacks:

  • Ice - Albedo: Snow and ice are the best reflectors of solar radiation. Water on the other hand is the worst reflector. It absorbs most of the heat. Expansive thawing of ice and snow, therefore, increases the absorption of solar energy. This ice - albedo feedback is believed to be the major reason why the Arctic is warming so rapidly (see Class 4, Section 1).
  • Melting of the Permafrost: When permafrost melts, organic material that has been frozen for thousands, even millions of years, will break down, and in the process release CO2 and methane.  (11)  Once permafrost starts to melt over extensive areas, for example in Alaska or Siberia, it initiates a feedback mechanism that intensifies the thaw. As the huge volume of thawed vegetation breaks down, it will release immense amounts of greenhouse gases. Once the process reaches this point of no return it will continually affect the global climate regardless of whether we reduce our carbon emissions or not. "In most parts of Alaska, the permafrost has warmed by 1.7°C (3°F) since the early 1980s. In some parts of the state it has warmed by nearly 3.3°C (6°F)."  (12)
    Researchers found expansive areas in western Siberia, which have started to melt and turn into mud and lakes. Billions of tons of methane could be released into the atmosphere. Methane is 86 times more potent as a greenhouse gas than CO2 over a 20 year period. Sergei Kirpotin at Tomsk State University in western Siberia who made the discovery said that the situation was an "ecological landslide that is probably irreversible and is undoubtedly connected to climatic warming".  (13)

    A report by UNEP (United Nations Environment Programme) on Policy Implications of Warming Permafrost projects the following. “Arctic and alpine air temperatures are expected to increase at roughly twice the global rate and climate projections indicate substantial loss of permafrost by 2100. A global temperature increase of 3°C means a 6°C increase in the Arctic, resulting in anywhere between 30 to 85% loss of near-surface permafrost. Such widespread permafrost degradation will permanently change local hydrology, increasing the frequency of fire and erosion disturbances. The number of wetlands and lakes will increase in continuous permafrost zones and decrease in discontinuous zones, but will decrease overall as the continuous permafrost zone shrinks, impacting critical habitat, particularly for migratory birds. Risks associated with rock fall and erosion will increase, particularly in cold mountain areas. Damage to critical infrastructure, such as buildings and roads, will incur significant social and economic costs.” (14)
    The most far-reaching implications of the thawing of permafrost is the amplification of anthropogenic climate change caused by the release of huge amounts of methane.
  • Water Vapor: The warmer the air, the more moisture it can hold. As the planet is warming up, there is more water vapor in the atmosphere. Water vapor is a powerful natural greenhouse gas, which magnifies the impact of man-made greenhouse gases.

Any of these feedback mechanisms could bring the Earth's climate system to a tipping point. We don't know where that tipping point is. It's quite likely that the planet will cross over that threshold without humanity noticing. Once we will wake up to that reality, it will be too late because this is an irreversible process. Some scientists think that we are already close to that point. "Computer models of the Earth's climate suggest that a critical threshold is approaching. Crossing over it will be easy, crossing back quite likely impossible." (15) The long atmospheric lifetime of CO2 implies that global warming will last a long time. "20 to 25% of fossil fuel CO2 will still persist after a thousand years, and 10 to 12% will still remain in the atmosphere after ten thousand years." (16)

Section 3: Present Challenges

So far, the approach of political leaders when they consider cutting carbon dioxide emissions has not been effective at all, because their first concern has always been what is politically feasible. There must be a complete turn around: Actions need to be taken according to the reality of the threat, which means that they must be taken in accordance with science. What do scientists say about how much CO2 emissions must be cut to avoid irreversible climate change?

NASA climatologist James Hansen said that if we want to preserve creation, the planet on which civilization developed, CO2 levels need to be stabilized at below 350ppm.  (17)  "Halting the increase in global warming at far below 2°C (3.6°CF) is possible, and lowering global warming as rapidly as possible to below an increase of 1°C (1.8°F) appears critical if there is to be a high probability of preventing dangerous climate change. The emissions reduction actions required to achieve this are massive and appear to be at the outer edge of what is technically and economically feasible. Scenarios that can start to get within reach of these temperature goals require greenhouse gas emissions to peak before 2020 and then to drop toward 85% below 1990 levels by 2050, with further reductions beyond this time."  (18)

It is an enormous task to reduce our emissions and to stabilize atmospheric CO2 levels. The world is moving rapidly towards the threshold of irreversible climate change. (19)  As the threat of reaching a tipping point is becoming increasingly close, Nobel Peace Price winner Al Gore challenged the United States to "produce 100% of its energy from renewable energy and from truly carbon free sources within 10 years.  (20)

Many experts in the field believe that with a concerted effort it is still possible to avoid the worst scenarios of climate change. "It is encouraging to know that we now have the technologies to build a new energy economy, one that is not climate-disruptive, that does not pollute the air, and that can last as long as the sun itself. The question is no longer whether we can develop a climate-stabilizing energy economy, but whether we can develop it before climate change spins out of control."  (21) >

Of course, it is not only the energy system that must quickly be transitioned away from fossil fuels. We also must change our transportation system, agricultural practices, our general land use, waste management, diet, and stop deforestation. The challenges are many and complex.

Section 4: Prospects for the Future

All prospects for the future are only estimates based on certain assumptions. We really don’t know how exactly climate change will play out, how fast temperatures will rise or how specific geographical regions will be affected. The climate system is extremely complex. The two main uncertainties are:

  1. The threshold of numerous feedbacks that will reinforce the warming, how these feedbacks will interact in the very complex climate system, and how sensitive the climate system will react.
  2. Human behavior: we don’t know how much greenhouse gases humans will emit in the future. That’s why climate models calculate different emissions scenarios.

The graph below illustrates that point very well. It is from the most recent report by the Working Group 1 of the IPCC issued on Sept. 30, 2013. (22)  

You can see two emission scenarios. The red curve shows the projected temperature rise under a scenario of business as usual. The reddish field shows the uncertainty in the projections. Temperature rise could be anywhere between about 2.4 and 5.7°C (4.3 and 10.3°F), but the most likely is the mean which is indicated as the red line heading to 4°C (7.2°F).

The blue line indicates a scenario with strong emissions reductions. With this scenario global warming can be stopped below 2°C (3.6°F). The emissions reductions required for that scenario are massive. Currently we are well on the path of the red line. The blue line is much less realistic.

The content of this class is difficult to digest. How can we deal with all this scary information, and how should we response? This will be the topic of the next and last class.

Community Service Project:

Consult about the Community Service Project as needed to carry it forward.


1.  Lester R. Brown, Plan B 2.0: Rescuing a Planet Under Stress and a Civilization in Trouble (NY: W.W. Norton & Co., 2006), From Chapter 1. Entering a New World
2. Information from Lester R. Brown, Plan B 2.0: Rescuing a Planet Under Stress and a Civilization in Trouble (NY: W.W. Norton & Co., 2006), From Chapter 1. Entering a New World
3. Information from Lester R. Brown, Plan B 2.0: Rescuing a Planet Under Stress and a Civilization in Trouble (NY: W.W. Norton & Co., 2006), From Chapter 1. Entering a New World
4.  Lester R. Brown, Plan B 2.0: Rescuing a Planet Under Stress and a Civilization in Trouble (NY: W.W. Norton & Co., 2006), From Chapter 1. Entering a New World
5.  The Threat to the Planet by Jim Hansen, Director of the NASA Goddard Institute for Space Studies and Adjunct Professor of Earth and Environmental Sciences at Columbia University's Earth Institute.
6.  World’s Glaciers Melting Faster Than Ever Before Recorded, Study Finds
7. Historically unprecedented global glacier decline in the early 21st century, by Zemp, Michael; et al, July 30, 2015,
8.  World on track for 3°C of warming under current global climate pledges, warns UN…
11. Information from Field Notes from a Catastrophe, Elizabeth Kolbert p. 21
12.  Field Notes from a Catastrophe, Elizabeth Kolbert p. 20
13. Information from: Ian Sample, science correspondent, The Guardian, Thursday August 11, 2005
14.  Policy Implications of Warming Permafrost, Report by UNEP (United Nations Environment Programme) , Nov. 27, 2012,
15.  Field Notes from a Catastrophe, Elizabeth Kolbert p.3
16.  The Long Thaw, David Archer, p. 123
17.  Global Warming 20 Years Later: Tipping Points Near, Jim Hansen, 23 June 2008, National Press Club, and House Select Committee on Energy Independence & Global Warming, Washington, DC.
18.  A Safe Landing for the Climate by W. L. Hare in State of the World 2009, p. 29, published by the Worldwatch Institute
19.  information from Field Notes from a Catastrophe, Elizabeth Kolbert p. 184/185
20. ] July, 2008
21.  Lester R. Brown, Plan B 3.0: Mobilizing to Save Civilization (New York: W.W. Norton and Company, Earth Policy Institute, 2008) From Chapter 12. Turning to Renewable Energy, THE WORLD ENERGY ECONOMY OF 2020

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Last updated 4 January 2018

© Christine Muller and International Environment Forum