LE FastCounter
So what if global warming occurs?

The Earth's climate has changed radically many times in our planet's history. The Cretaceous era, during which dinosaurs reigned supreme, was considerably hotter and moister than today's globally-averaged climate; on the other hand, Quaternary ice ages formed the glaciers that carved much of the world's most spectacular scenery. Interglacial warm periods allowed, for example, the Vikings to grow grapes in Iceland, as well as their settlement of Greenland and Newfoundland – which were abandoned as the climate once again cooled.

Climate change has been, and will continue to be, an integral part of the Earth's climate system. The principal reason for humanity to be concerned about global warming is that it is now occurring during our lifetimes, rather than at the geological timescales of the past.

While some regions of the globe will benefit from a warmer climate, many will not – and overall, the losses will most likely outweigh the gains. A list of costs includes:

• Sea-level rise: As the planet's ice sheets and glaciers melt, global sea level will rise. Many of our largest cities will be threatened as coastlines are eroded, and the prospects for saltwater flooding will always be present.
• Atmospheric gases: As the concentration of anthropogenic gases, particularly carbon dioxide (CO₂), increases, competition between C₄ plants – all the cereals that constitute the majority of our food supply – and C₃ plants – the “weeds” – will increase. In general, C₃ plants fare better under higher CO₂ concentrations. In many parts of the world already threatened by food insecurity, the results may be severe.
• Soil moisture deficits: Climate modeling undertaken by the United Kingdom's Meteorological Office for the southern African region indicate that while rainfall may increase by 10 percent in a 720 parts per million (ppm) CO ₂ scenario (roughly double today's concentration), the warmer temperatures will induce evaporation to be 15 percent higher than at present. Such net losses in soil moisture may well threaten rainfed crops in many parts of the world.
• Nutrient recycling: While nobody has an adequate understanding of the interaction between soil microorganism communities and global change, there will be an effect. For example, soil organic matter is crucial in many of the world's drylands, not only for plant growth but also for its moisture-retaining capacity. If carbon is more-rapidly recycled to CO₂, moisture retention in the soil will be reduced.
• Precipitation amount and timing: Rainfed crops need moisture at critical periods during the growing season. Climate models indicate that storms will be less frequent but more intense in many parts of the world. In the Sahel, where I conducted my doctoral research, crops need fairly consistent rain during the season. Once germinated, millet dies after 17 days of no rain. Maize requires adequate soil moisture as it sets its cobs – yet too much moisture late in the season can lead to the development of aflatoxin, a potent and dangerous fungal carcinogen.
  Climate models also suggest that severe storms, such as winter blizzards or summer hurricanes, will also be more intense. In the United States, over the past decade we have been struck by unprecedented snowstorms, hurricanes, and tornadoes, with damages mounting into the billions of dollars and considerable loss of life. Intense storms in the world's drylands can damage crops and sheet-erode the precious topsoil, paradoxically resulting in desertification.
• Heat waves: It should be hardly surprising that a warmer world must endure intensified heat waves. Once such heat wave led to the deaths of approximately 700 people in Chicago in the summer of 1995.
• Agroecozones: Today's highly-productive agricultural areas will migrate toward preferred conditions. For example, the United States' corn belt will eventually be positioned in southern Canada. Fruiting trees that require winter dormancy and cold temperatures will suffer. Today's winter-killed diseases and pests may thrive in more clement conditions, potentially damaging large sectors of the temperate zones' agriculture.
• Shifting ecosystem boundaries: The effect on the world's biodiversity is unlikely to be benign. Many of today's plant and animal reserves are established as islands surrounded by oceans of human populations. Under global warming conditions, many species will be unable to contend or compete, and will also be unable to migrate to more-optimal climates because no connecting corridors exist through the human ocean.

Is global warming real?

Indicators such as cyclonic storm intensities, tropical cyclone frequencies, heat waves, warmer average seasonal temperatures, and measurable sea-level rise as witnessed by eroding coastlines, together strongly suggest that global warming is indeed occurring. Untutored critics of global warming who point to the enormous blizzards striking the United States and Europe during the past several winters as “proof” that warming is not occurring miss the real point: such storms are simply intense precipitation in a frozen state – and these are precisely the storms predicted by global climate models for a warmer world.

Indeed, the warming signal has been diluted during much of the past three decades through the cooling trend induced by industrial particulates, such as sulfate aerosols. Now that industrialized nations are reducing these emissions, the patterns associated with global warming are reasserting themselves.

Global climate models show the warming phenomenon to be more-intense in the polar regions than elsewhere. Recent evidence of an overall thinning and seasonally-earlier break-up of the vast Antarctic sea-ice sheets strongly supports such model results. In the figure below, I show global anthropogenic CO₂ emissions for fossil fuels and cement, as billions of tonnes of carbon (C), from 1860 to 1982 (green); the Mauna Loa observatory's mean annual CO₂ concentration measurements from 1958 to 1990 (red); the mean annual surface temperature for all Antarctic stations near sea level having continuous data records from 1958 to 1987 (elevation given in parentheses after the station name): Halley Bay (32 m), Faraday (9 m), Mawson (16 m), Dumont D'urville (43 m), Mirny (30 m), and Casey (15 m). The temperature data have been increased to equivalent sea-level temperatures using the dry adiabatic lapse rate (blue). The yellow line is the temperature data after smoothing by a 100-year cubic spline; the black curve is the temperature data after smoothing by a 20-year cubic spline. (I obtained all data from the Carbon Dioxide Information Analysis Center [CDIAC], Oak Ridge National Laboratory.) Note how the yellow line shows a persistent temperature increase, then judge for yourself whether global warming is a real phenomenon. . . .

Based on data from global climate models, the Intergovernmental Panel on Climate Change projects that global temperatures will rise by 1.5^oC to 4.5^oC under the scenario of a doubling of CO₂ from preindustrial levels, a level likely to be reached by about 2030. While such a temperature rise may not seem particularly significant, consider that the last major ice age was globally only about 4^oC colder than the present; the “little” ice age of the 1700s, which destroyed settlements in Iceland and froze European rivers, is estimated to have been globally just 1^oC cooler than today.

The Greenhouse Effect

The term “greenhouse effect” is a misnomer for the real problem – an intensification of the greenhouse effect that is resulting in global warming. Global warming is due to the buildup of the gases that trap heat in the atmosphere. These gases are largely anthropogenic in origin.

The greenhouse effect is the sum of the interactions between:

• the heat that is attempting to escape from earth to space;
• the molecules of various gases that trap this heat, impeding its loss to space;
• reradiation of this heat within the atmosphere.

Without the greenhouse effect, the earth would be about 33^oC cooler than it is – that is, for all practical purposes, uninhabitable.

Below, I show anthropogenic greenhouse gas emissions for 1985, expressed as carbon dioxide equivalents. Emission categories (top), as billions of tonnes of carbon; percentage as carbon dioxide equivalent (bottom).

When narrowed down, the sources of global warming are:

• the production of carbon dioxide through (a) the burning of fossil fuels and biomass, and (b) land use modification or disturbance;
• the production of methane that results from (a) the intensification of the livestock industry, and (b) the extension of rice paddies;
• the industrial production of gases such as chlorofluorocarbons, which are also implicated in the reduction of stratospheric ozone (the ozone hole);
• release of nitrous oxide, mainly via the application of fertilizer to arable lands;
• the production of tropospheric ozone (the highly-irritating constituent of smog); and
• another 30 or so greenhouse gases, which play very minor roles.

The Greenhouse Gases

The graphic below depicts the five main anthropogenic greenhouse gases, lists their sources, illustrates their projected increase until 2030, and shows their effectiveness compared to carbon dioxide. Note that while the concentration of chlorofluorocarbons (CFCs) is in the parts per billion (or 10⁵ time less than the concentration of carbon dioxide), its effectiveness per molecule is 10⁴ greater than CO₂. In global terms, CFCs contributed 15% - 17% of the total warming effect in the 1980s; these are also the compounds known to be destroying the planet's stratospheric ozone layer.

The correct citation for this document is:
Milich, L., 1997. Global Warming and the Greenhouse Gases. http://ag.arizona.edu/~lmilich/globwarm.html.

---

Back

This site last updated April 14, 1998.