Assembly Bill 1493: Scripps Scientist Answers Questions


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Answers to common questions concerning Global Warming, in the context of Assembly Bill 1493 (Fran Pavley, Agoura Hills), with regard to the desirability of the reduction of carbon dioxide from automobiles in California

by W. H. Berger, Ph.D.
Professor of Oceanography and Climate Researcher,
     Scripps Institution of Oceanography, UCSD
Director of the California Space Institute, University of California
Fellow of the American Geophysical Union

22 July 2002

(1) How will the planned reduction in emissions in California help with the reduction of greenhouse gases in the atmosphere?
Greenhouse warming is a global problem and must be attacked on a global scale. California's action is an important first step in the right direction and will get this vital process started in a serious manner. Automobiles produce more than half of the carbon dioxide emissions. Once California requires that emissions be cut, other states will (hopefully) follow California's lead. In addition, a focus on the question of what tail-pipe emissions do to the environment is a very healthy thing. It is to be hoped that the efficiency of power generation will be further increased across the board and that alternative energy sources, such as a combination of solar power and use of hydrogen, will become more important. For this to happen, we need the public to support the appropriate measures.

(2) What causes global warming?
Global warming is caused by addition of certain trace gases to the atmosphere, notably carbon dioxide (more than half of the effect), methane, chlorofluorocarbons and nitrogen oxide (the rest). An important effect is the increase of water vapor in the atmosphere that results from the warming. Water vapor is a powerful greenhouse gas itself and greatly amplifies the effect caused by the addition of the trace gases mentioned. The bulk of the carbon dioxide added to the atmosphere is from combustion of fossil carbon fuels (coal, petroleum, natural gas).

(3) Is global warming real, or only theory and speculation?
Global warming is real, and has been with us for some time (increasingly during the past two decades, but gradually for more than a hundred years). The reality of the warming is seen in direct temperature measurements and also in the melting of glaciers in low latitudes, permafrost decay in Alaska, and the decrease in sea-ice cover in the Arctic Sea, among other effects.

(4) Is the warming due to human activity, and specifically to emission of greenhouse gases?
By far the bulk of the energy needs of a growing population on Earth are met by burning fossil carbon fuels, resulting in emission of carbon dioxide. The amount emitted each year is close to one percent of that already present in the atmosphere. Carbon dioxide is now about 30 percent higher than it was before the Industrial Revolution. As far as we can tell, this is significantly beyond the concentration ranges for the past million years or so. Scientists generally agree that greenhouse gases in the atmosphere keep the Earth pleasantly warm at the surface. It is thus reasonable to assume that adding greenhouse gases will warm the Earth's surface further. From geophysical principles, there is no problem in attributing all the warming experienced in the last century to emissions of greenhouse gases. However, because climate change is complex, and the natural temperature of the Earth fluctuates, this explanation is not certain except for warming that occurred during the last two decades.

(5) What about the apparent discrepancies between expectations and actual observations, regarding the warming?
A few vocal critics of the statement that human activity has caused (and is causing) substantial global warming keep emphasizing the well-known uncertainties involved in making the relevant calculations. Indeed, actual warming is somewhat less than we would expect based upon the measured increase in greenhouse gases. The reasons for this are not entirely clear, but probably are associated with an increase in air pollution, with heat absorption by the ocean, and with an increase in shading by clouds - all of which tend to reduce the effects of greenhouse gases. What these discrepancies demonstrate is that we do not understand the system as well as we should. What they do not demonstrate is that there is nothing to worry about. (Ignorance is not bliss, in this instance.)

(6) Is Global Warming a major problem for society, or can we live with it?
This is difficult to evaluate. Answers depend on who is asking and are characteristically imprecise. Some will suffer, some won't. Many effects are too poorly understood to make the call. An increase in temperature at high elevations affects snow cover and consequently the water supply - something that is of special interest in California. In general, warming will increase the amount of water vapor in the atmosphere and hence the amount of available energy to make storms and winds. Shifts in the great centers of low and high pressure will change the distribution and strength of winds and therefore the patterns of evaporation and precipitation. Some areas will experience more drought, others will benefit from more rainfall. Hurricane and winter storm activity has increased greatly in the last 50 years and might increase further. The productivity of the California Current (and the production of fish) has decreased over the last 25 years ¾ but this could be part of a cyclic change. Growing-seasons in mid- and high latitudes are getting longer ¾ this change could be for the good in many countries. Coastal fisheries, on the whole, may be expected to suffer, if California is a good example. If sea level rise becomes a problem (from melting ice on Greenland and Antarctica), low-lying countries will suffer, but those without lowlands will not be significantly affected. Milder winters will save energy for heating. But the absence of harsh freezing will allow the spreading of opportunistic plants and animals (including disease vectors). Plant communities depending on freezing will tend to get "out of alignment" with the new climate; their defenses will weaken, allowing pests to thrive, and providing fuel for fires. We are now living with global warming and we have no choice but to continue living with it. The real question is whether we can slow it down, so we (and the entire biosphere) gain some time to make the adjustments.

(7) Are there potential catastrophes lurking?
The point has been made that the climate system resembles the stock market, in that it apparently follows well-defined rules, but also is quite unpredictable. A "crash" in such a system is a sudden jump to a new mode of operation. Such jumps have been observed in a time span centered on about 12,000 years ago, when the system became unstable because of the large-scale melting of glacial ice (in North America, Scandinavia and around the Eurasian Arctic). Potential problems ahead include a major change in the deep circulation (and heat budget) of the ocean (which could greatly change wind fields and precipitation patterns), and large-scale release of methane from the sea floor (which would lead to unprecedented, unstoppable warming). In California, a possible increase in the frequency and severity of El Niño events is of concern.(8) What is the University of California doing to help with these problems?Research at the University of California is concerned with the role of energy in the State's economy, the technical and system-inherent opportunities for increased efficiency, and the feasibility of increased use of alternative energy. (For more information, contact the UC Energy Institute, and the UC Energy Efficiency Institute). Hopefully, these projects will show that we can save money and simultaneously help the environment, by taking an intelligent long-term view of the problem. Putting to work the considerable resources of UC, of industry, and of the State government, in a concerted effort to decrease our dependence on fossil carbon fuels, will emphasize California's leadership role in attacking one of the most important environmental problems of our new century.


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