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February 23, 2004 | A version of this story appeared in Volume 82, Issue 8

The greenhouse gas debate

"Climate Change" by bette hileman provides an informative, far-ranging overview of the science and potential practical impacts of global warming (C&EN, Dec. 15, 2003, page 27). However, the statement "Hansen suggested controlling soot, tropospheric ozone, and methane, and stabilizing CO2 emissions rather than trying during the next 50 years to make large reductions in CO2 emissions," followed immediately by "Holdren, on the other hand, says there is no way to avoid controlling CO2 in any strategy to limit global change," leaves an inaccurate impression of the "alternative scenario" for climate forcings that I have proposed as a means to keep additional global warming from exceeding 1 ºC [Proc. Natl. Acad. Sci., 97, 9875 (2000); Hansen, J., Can we defuse the global warming time bomb?,].

The latter goal, which I believe is needed to avoid "dangerous anthropogenic interference" with global climate, requires absolute reductions in air pollution (soot, ozone, and methane) in addition to, not instead of, reductions in CO2 emissions. The 75-ppm growth of CO2 between 2000 and 2050 in the "alternative scenario" is achieved by annual growth declining from 1.7 ppm per year to 1.3 ppm per year in 2050, with more rapid slowing in the second half of the century, such that the CO2 amount peaks at about 475 ppm in 2100 (time series for CO2, CH4, N2O, and CFCs for the alternative scenario are given at

The most important actions needed to achieve this scenario are aggressive efforts in energy efficiency in the near term and long term and development of technologies for eventual CO2-free energy and/or CO2 capture and sequestration. These air pollution and CO2 goals are more feasible than generally realized, but they are ambitious and require "an unprecedented level of international cooperation" (Hansen).

Others have suggested that 2 ºC global warming may be acceptable. Such a scenario, also defined on the above website, with CO2 peaking at 560 ppm in 2100, allows continued near-term CO2 emissions growth. I argue, however, that the "2 ºC" scenario would likely set in motion unstoppable long-term ice sheet changes leading to an eventual large sea level rise. Strategies and goals must be adjusted as our knowledge of climate sensitivity improves, but available evidence suggests that something along the lines of the "alternative scenario" will be needed.

James Hansen
New York City


I was shocked to find the box titled "Myths About Past Temperatures in Greenland and England." "One myth is that Greenland was much warmer during the so-called medieval warm period than it is today. ... The truth is that a few hundred Norse settled in the fjord region of southwest Greenland in 986. ... The settlements collapsed totally by 1500, not primarily because of climate change, but because of social factors."

There is a large and growing body of literature on Viking-era life in Greenland and Iceland. That includes saga, Vatican, and other documentary evidence and analysis of large numbers of archaeological samples, Greenland ice core samples, and north Iceland shelf marine sediment core samples, to give a partial list. In 986, Eric the Red arrived in Greenland in 14 ships with some 450 settlers. Various estimates give the peak population of the several settlements as 3,000 to 5,000. More than 400 farms have been identified, along with 20 churches. In 1124–26, Greenland became a diocese of its own, with its own bishop. In 1261, the Greenlandic Parliament acknowledged the supremacy of the king of Norway and the right of Norway to claim taxes (Greenland had a parliament). The last written record is of a wedding in 1408. The Norse settlements survived for more than 400 years.

Norse society was one of traditional dairy farming. Excavations show that in the later days of the settlements there was a sudden switch to a marine diet and the eating of cows and even dogs (the former a violation of Norse law), and graves were much more shallow. The GISP2 ice core analysis suggests a series of cold spells, the longest from 1343 to 1362, corresponding to the abandonment of the Western Settlement. Norse society hung on, amassing fodder and food surpluses to survive long winters. Once ice-free trade routes became ice-clogged, necessitating changed routes. There is little doubt that in Greenland and Iceland there was a significant weather change. Would today's climate permit a traditional European dairy society to exist in southwest Greenland? No.

If the facts of Norse settlements in Greenland trump those who wish to say that today's global temperatures are the highest in 1,000 years, so be it. In today's discussion of climate change, one needs comprehensive science. Climate is more than temperature. One does not define as a myth data which do not support a particular conclusion; that is politics, not science.

Gordon L. Nelson
Melbourne, Fla.


I was disappointed in the very biased recent article "Climate Change." Those disagreeing were not given voice, only dismissive statements. There is, however, real basis for disagreement.

The graph of the temperature versus time showing a warming trend omitted the needed correction for the heat island effect. The corrected data look far less dramatic and even show a period of cooling from about 1940 to 1970. Proxy temperature data from the Sargasso Sea show medieval temperatures to be much warmer than currently. Whether current hybridized grapes grow in England or not is really irrelevant. If the Sargasso Sea temperature proxy is correct and not Mann's tree ring proxy data, then there was a much warmer period, during which there was not a corresponding global ecological disaster.

The Vostok ice core from Antarctica, which goes back more than 400,000 years, shows periodic warming trends along with periodic increases in CO2 concentration of the atmosphere. In that data, CO2 concentration always lags the temperature increase; it does not precede it. That certainly does not fit the espoused model.

There are other things too numerous to detail, such as sea level measurements in the South Pacific showing no consistent trend either up or down (for example, New Guinea dropping, Tonga increasing), the report that Antarctic ice extent is increasing at 1.3% per decade, an apparent greening of some northern regions of sub-Saharan Africa, tropospheric temperatures not increasing like those on land, etcetera. I have read that the only way current global circulation models can accurately track what good records we do have is when the forcing factors are arbitrarily adjusted (fudged would be a better term) to make it come out right, suggesting that perhaps we still are not fully aware of all that causes changes.

The global warming folks are really arguing for a static climate for Earth. The Maunder minimum was associated with the 1700s mini-ice age. Is solar radiation output constant or does it vary, sometimes unpredictably? Does Earth wobble on its axis, and does that affect climate? And what of the infrequent impact of a small asteroid, or when a volcano like Krakatoa or Pinatubo erupts and cools us off for a while? Our system is chaotic and unpredictable, is it not? That implies a fundamental lack of ability to control the system.

If the global warming folks have their way, CO2 emissions will be highly restricted only in developed countries. If CO2 is bad, then Chinese-generated CO2 is just as bad as U.S.-generated CO2, isn't it? Legislating against CO2 emission here but not curbing worldwide emissions amounts simply to moving all industrial production to China and India, not to solving some supposed problem.

David R. Fagerburg
Kingsport, Tenn.


I had hoped that C&EN would be more scientific when addressing global climate change, especially the possible anthropological causes. This article better reflects the mass media mire that engulfs politicized science issues rather than a scientific method. The author and many of the quoted scientists follow preconceived conclusions; as stated in the article: "The aim of the 1992 UN Framework Convention on Climate Change is to prevent dangerous anthropogenic interference with climate." What scientific approach draws a conclusion before doing the research?

This explains my experience as an observer at a United Nations Intergovernmental Panel on Climate Change (IPCC) workshop in the mid-1990s. The organizers had written the workshop position paper before the workshop started. Only one scientist was vocal enough to ask why the workshop was even convened. Unless their approach has changed, one should be skeptical about conclusions that IPCC presents.

No one can state unequivocally whether the current climate changes are man-made or natural. It is likely a combination of the two. That is where the difficulty begins. Which has the greater impact? The following question would be one of the first to answer in that regard:

If anthropogenic greenhouse gases are the cause, what would explain the global surface temperature cooling period from 1939 to 1979 (as depicted in the "Heating Up" chart on page 33)? When did man-made greenhouse gases trend down, leading to such cooling? This trend indicates that natural changes overpowered all anthropogenic effects for 40 years. That seems to swing the causal balance toward natural effects--since some unspecified natural climate change could so easily overpower man-made emissions for four decades.

There are some nagging questions regarding the current technical approach:

* How can a scientist specify historic global average surface temperatures without having worldwide data from previous centuries? Looking at current micro-climate data for our region (which often show air temperature differences of several °C within a few kilometers) makes one wonder how the surface temperatures for the entire globe can be modeled so "precisely" hundreds of years later based on data from limited parts of the globe.

* Little is said about water vapor as a greenhouse gas. Is this because it would be unpopular to attack increased irrigation as a source of a greenhouse gas, or is it because it truly has a minimal impact on global climate change?

One needs to maintain his or her scientific mentality and not get caught up by politicized science. We need healthy skepticism and debate among equally funded researchers--not conclusions from those who obtain funding because of their preconceived views.

Peet M. Sööt
Lake Oswego, Ore.


Hileman responds: Climate-change science is very complicated and involves unresolved issues.

For example, over relatively brief periods, such as from 1940 to 1970, the cooling influence of aerosols and perhaps natural variability overwhelmed warming from the gradual buildup of greenhouse gases in the atmosphere. Over even shorter times, such as two years, volcanic aerosols have produced significant cooling. But if emissions keep rising over the 21st century, most climate researchers expect the buildup of greenhouse gases in the atmosphere will be the 800-lb gorilla, causing average global warming that far exceeds cooling from aerosols and from slight decreases in solar radiation.

This does not mean that every region on Earth will be warmer. Nor does it mean that sea level will rise uniformly over the globe. If current salinity trends for the North Atlantic continue, temperatures in Northern Europe may even fall for a time. One challenge is to gain a much more precise understanding of regional climate changes.

Out of order

Your articles in the Jan. 26 issue of C&EN about the decline in U.S. fine chemicals businesses ("Informex Displays Tough Times," page 11) and at Lonza in particular ("Lonza Results Tumble Badly," page 13), and the opposite findings reported in the same issue on China ("Prospering South of Shanghai," page 18), tell the all-too-familiar story of fine chemicals and many similar businesses in the U.S.

The situation is analogous to your out-of-sequence picture on the cover of the same issue, where laundry soap is being poured after the laundry in the background is cleaned and folded. The U.S. needs to get it's industrial labs in proper sequence again, with more focus on R&D (as the Chinese are doing now), rather than worrying about short-term or profit programs that only result in temporary stockholder approval.

Gus Gutman
Austin, Texas


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