Global Warming and the “Greenhouse Effect”

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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:

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 1.5oC to 4.5oC 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 4oC 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 1oC 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:

Without the greenhouse effect, the earth would be about 33oC 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 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.


This site last updated April 14, 1998.