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Global Warming: Too Much Energy
by Henry Robertson
The concentration of greenhouse gases in the atmosphere is increasing and the temperature is rising along with it. This phenomenon is usually called either global warming or climate change. Neither name is adequate to convey the danger and the challenge. Global warming, says Bill McKibben, “is better thought of as excess energy trapped in the atmosphere, which will express itself in every possible way.” [1]
Climate change is caused by forcings and feedbacks. A forcing is a process or event that alters the energy in the system. [2] Human activities like deforestation and burning fossil fuels are anthropogenic climate forcings. We have it in our power to reduce them. But sometimes global warming triggers other events that reinforce it. These are positive feedback loops, and it may not be possible for us to stop them or even foresee them. Is there a tipping point beyond which global warming will be out of our control?
Greenhouse Earth
Water vapor is a greenhouse gas (GHG). It lets sunlight reach the Earth but prevents some of the long wavelength, infrared radiation that rebounds from the planet’s surface from escaping to space, trapping its heat energy in the atmosphere. We need GHGs. They act like the panes of a greenhouse to warm the Earth, which would otherwise have a surface temperature of 0°F or below instead of 57°. [3]
Clouds play a dual role. High, thin clouds warm the planet while low, thick ones cool it. Next in importance as a GHG, and less ambivalent in its effect, is carbon dioxide, which only heats the atmosphere. Methane, the main component of natural gas, is 21 times more potent than CO2 in warming the Earth, but it is less abundant and only stays aloft for 12 years, not a century like CO2. [4]
Human activity is increasing the amount of CO2, methane and other trace GHGs. Scientists have reconstructed the history of CO2 in the atmosphere from air bubbles trapped in ice cores drilled deep into the Antarctic ice cap. For 650,000 years the concentration of CO2 in the air stayed in a band of 180–290 parts per million (ppm) by volume. [5]
Then, 200 years ago, the Industrial Revolution began, achieving unprecedented levels of production by burning fossil fuels, first coal, then oil, then natural gas. Industrialized economies are free from the constraints of direct solar radiation. They mine the solar energy of the past in the form of buried organic matter subjected to heat and pressure over a period of 300 million years. Burning combines the fossil carbon with oxygen to make CO2. Economic growth accelerated this mining; half of all fossil fuel consumed since the Industrial Revolution was burned in the last 20 years. [6]
In 1958, when measurements began on Mauna Loa, Hawai’i, specifically to track global warming, the CO2 concentration was 315 ppm. Now it’s 382 ppm and rising by 2 ppm per year. [7]
Many doubt that human actions could affect the vast sky, but the atmosphere is more fragile than it appears. Compared to the Earth, it’s like the skin of an onion. Half of all its gases reside in the lowest third of the bottom layer of the atmosphere, the troposphere, a level that tops out well below the peak of Mt. Everest. [8] Then consider the rate at which we are burning fossil fuels.
Half of all fossil fuel consumed since the Industrial Revolution was burned in the last 20 years.
The US accounts for 25% of the world’s human CO2 emissions. Every year American motorists burn 150 billion gallons of gasoline. Every year our power plants burn over a billion tons of coal, and this is one area where the US does not lead the world in pollution — China burns more coal. Each year the US burns over 20 trillion cubic feet of natural gas for industrial processes, heating, electricity generation, etc. [9] Burning natural gas (methane) as fuel creates CO2; methane is also added directly to the atmosphere by rice paddies and livestock raising, among other things. Is it really hard to believe that we can alter the composition of the atmosphere and change the climate?
Carbon sinks
Any medium that relieves the air of some of its carbon burden is known as a carbon sink. Nature has provided three — the oceans, the soil and plants.
The oceans take up half the extra CO2 we generate, but evidence is already coming in that they can no longer absorb this much. [10] Moreover, they have become more acidic in the process, and this reduces the amount of calcium carbonate in the sea, which corals, plankton and shellfish use in making their shells. [11]
Soils already store vast amounts of carbon, and they can hold more with practices like no-till agriculture. But global warming evaporates soil moisture. Deserts are expanding and croplands are losing their productivity. [12] As soil warms, bacterial decomposition accelerates and the soil becomes a source, not a sink, of CO2. [13]
“Global warming is good for you,” say the deniers who have given up on denying the fact of climate change. Since plants breathe CO2, they assume that global warming will increase plant growth and crop production. This turns out not to be true.
Doubling CO2 experimentally only slightly increased wheat and rice yields. Plants in CO2-enriched environments have less nutritional value, tougher leaves and more defensive chemicals. Through breathing holes called stomata, plants take in CO2 and release water vapor in the process of transpiration. With higher CO2 levels the stomata remain shut longer and less water vapor is transpired. As a result, less rain falls. [14]
These sinks must eventually fail, not only because their absorptive capacity is limited but because forests and soils give back their carbon by the decomposition of plants and bacteria. Burning fossil fuels transfers buried carbon to the biosphere’s carbon cycle. In that cycle it is only temporarily removed from the atmosphere by the perishable bodies of organisms.
Consequences
The heating of the atmosphere has other direct effects that are becoming familiar.
Glaciers and the polar ice caps are melting. The disappearance of the Greenland ice cap alone could raise sea levels by 20 feet or more. Not only will this inundate coastal areas, but salt water will infiltrate drinking water supplies. [15] Himalayan glaciers supply half the drinking water for 40% of the world’s population as they feed the seven major river systems of southern and eastern Asia. [16] In the US the annual melting of mountain snow provides a steady flow to the rivers on which we depend, but snow is no longer falling as before. [17]
Global warming increases the heat energy and the amount of water vapor in the air. Storms become more intense, as Hurricane Katrina attested. The number of storms may increase as well; 2004 saw a record number of tornadoes in the US and the first hurricane ever recorded in the south Atlantic. [18] And, as more precipitation falls as rain rather than snow, flooding worsens. [19]
Global warming expands the range of disease vectors — microbes and insects that are kept in check by winter at higher latitudes and altitudes. [20] Not all species benefit from climate change, however. As many as 30% of plants and animals could go extinct as their habitats shift from under them, heat overstresses them, or early springs desynchronize the birth of their young from the availability of the food supplies they need. [21]
One potentially catastrophic outcome is the destruction of the Amazon rainforest. This great ecosystem, built on poor soil, cycles water between the tree roots and the forest canopy, creating its own climate. With the decline of transpiration and the drying of the soil, the forest may die and its unparalleled biodiversity give way to dry grassland or even desert. [22]
Feedback
The human effect on climate is not merely additive. It can trigger positive feedbacks by which global warming becomes self-reinforcing. Water vapor feedback is one example. The heat added to the atmosphere by GHGs evaporates more surface water; water vapor is itself a GHG, and with more in the air the warming accelerates. [23] The drying out of soil sets off another positive feedback loop, fueling more wildfires that hurl forest carbon into the sky. [24]
In a few decades, the Arctic may be ice-free in summer. The ice cap, being white, reflects 90% of the sunlight hitting it back into space. Open water, being dark, reflects only 5–10% and absorbs the rest as heat. [25]
This albedo effect poses a problem for those who see reforestation — offsetting our CO2 emissions by locking up the carbon in trees — as our salvation. Regenerating the tropical rainforest is unequivocally a good way to counter global warming. Planting trees in higher latitudes, however, may have the opposite effect. The point is controversial, but some scientists think that dark trees overshadowing ice and snow on the ground will actually worsen global warming by absorbing heat, negating the benefit they provide by storing carbon. [26]
At the end of the last ice age 11,000 years ago, a million square miles of peat bog was frozen in the Siberian permafrost. It may contain 70 billion metric tons of methane. About the turn of this century the permafrost began to thaw. Even if it takes 100 years to melt, it could add 700 million tons of methane to the atmosphere every year, doubling the amount contributed by wetlands and agriculture. [27] The prospect is terrifying — a runaway feedback that we are helpless to stop.
Is there a tipping point beyond which global warming becomes uncontrollable? Prediction is inherently uncertain and consistent numbers are hard to come by, but many climate scientists believe that at some level between 450 and 550 ppm of CO2 the climate could destabilize and enter a state never before seen by the human species. If you add the other GHGs, converted into CO2 equivalent, then by some calculations we are already close to, or even over, 450 ppm. [28]
There is only one conclusion: we must drastically curtail our GHG emissions. The most commonly cited reduction targets are between 60% and 80% by 2050; some say 90% by 2050 or even 90% by 2030. [29] The change will be wrenching, but the sooner we start the easier it will be.
Henry Robertson is a member of the Green Party of St. Louis/Gateway Green Alliance.
Notes
1. McKibben, Bill, Year One: Climate Chaos Has Arrived, Sierra, Jan./Feb. 2006, p. 34.
2. Kolbert, Elizabeth, The Climate of Man, New Yorker, May 2, 2005, p. 68.
3. Kolbert, ibid., April 25, 2005, p. 66; Flannery, Tim, The Weather Makers, Atlantic Monthly Press 2005, 23–4.
4. Flannery 23–4; Houghton, John, Global Warming: The Complete Briefing, Cambridge Univ. Press 2d ed. 1997, p. 34. (1997).
5. Gore, Al, An Inconvenient Truth, Rodale Press 2006, 66–7.
6. Flannery, 167.
7. Flannery, 29.
8. Flannery, 20.
9. Figures in this paragraph are from the US Energy Information Administration, eia.doe.gov.
10. Flannery 33, 35; Los Angeles Times, Study: Ocean failing as CO2 buffer, St. Louis Post-Dispatch, May 18, 2007. 11. Gore, 168; Flannery, 16, 186; Union of Concerned Scientists, Summary of Intergovernmental Panel on Climate Change (IPCC) Report on Climate Impacts (IPCC Fourth Assessment Report, 2007), http://ucsusa.org/.
12. Flannery, 256; Gore, 118, 121.
13. Flannery, 196.
14. Monbiot, George, Heat: How to Stop the Planet from Burning, South End Press 2007, pp. 7–8; Flannery 175, 197, 207.
15. Monbiot 8; Gore 190; Flannery 143–4.
16. Gore 106–7.
17. http://ucsusa.org/, Summary of IPCC Report on Climate Impacts.
18. Gore 84–106; Monbiot 8–9.
19. Gore 106–7.
20. Gore 172–5; Monbiot 6.
21. http://ucsusa.org/, Summary of IPCC Report on Climate Impacts.
22. Monbiot 9–10; Flannery 196–8.
23. realclimate.org, Glossary, “Water vapor feedback;” Kolbert, New Yorker, May 2, 2005, p. 69; Flannery 24, 28, 123.
24. Gore 227–9.
25. Kolbert, New Yorker, April 25, 2005, p. 64; Flannery 144–5.
26. Jha, Alok, Planting trees may worsen global warming, Guardian Weekly, April 20, 2007.
27. Sample, Ian, Warming hits “tipping point,” Guardian Weekly, August 19, 2005.
28. Monbiot 15–6; Flannery 167–8.
29. Monbiot 16.
[7 jan 08]