Discussions on global warming By S.M. Enzler MSc
The discussion between skeptics and climatologists
An enormous amount of research has been conducted on the enhanced greenhouse effect. The IPCC has brought out reports showing modelling results about expected temperature change and consequences for the next century. There are however skeptics and scientists that argue with the results of the IPCC. Some do not even believe that an enhanced greenhouse effect exists at all.
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1. The discussion on skeptical environmentalism
1.1 Bjorn Lomborg
Lomborg argues that 'the limitations of computer modelling, the unrealistic nature of basic assumptions made about future technological change and political value judgments have distorted the scenarios being presented to the public'.
Lomborg does not disagree with today's explanation of the greenhouse effect mechanism. He also does not deny that there must be some kind of anthropogenic addition to the greenhouse effect. He agrees with the idea that the centuries before 1900 where much colder than current times. He does however mention that this is mainly because of the Little Ice Age, which lasted from 1400-1900. There is no disagreement to the so-called Medieval Warm Period, when temperatures were 2-3 degrees warmer.
1.1.2 Proxy indicators
Lomborg does comment on the use of tree ring records by Mann to determine temperatures in the centuries before the thermometer was invented. He argues that only North American tree ring data were used and that the data only cover land surface temperatures during summer. Additionally, disturbances in measurements by other factors influencing tree ring development were not corrected. Data of different origin has a lack of spatial scale coherence, causing Lomborg to question whether there is even enough temperature proxy data. This is an important finding, because the results of Mann's tree ring research has already been taken up in the 2001 IPCC report.
1.1.3 Greenhouse gases and temperature change
When it comes to greenhouse gas emissions Lomborg states that we should not ask ourselves whether greenhouse gases emitted by human activities have an impact, but how much effect these emissions have on temperature. This requires an adequate prediction of climate development in the future, which is very hard because of the complexity of the climate system. Current computer models are already relatively complex but do not even represent all important factors and processes yet. Scenarios (projections of future events) may not always be based on reasonable assumptions and some data may still be missing. How much CO2 impacts climate is strongly dependent on the representation of crucial areas in models, such as sulphur aerosols, water vapour feedback and clouds. These areas are briefly explained here.
1.1.4 Other causes of temperature change
Lomborg also states that we should ask ourselves whether greenhouse gas emissions are the real causes of temperature change. It is the question whether temperature change really leads to the catastrophic events that have been predicted by the IPCC models.
1.1.5 IPCC scenarios
Lomborg has some concrete comments on the scenarios made in 1992 by the IPCC. He states that their predictions of population growth may be too high, as they are much higher than those of the UN today. He also disagrees with their expectation of 82% tropical forest disappearance in 2100 and with their expectation of a CO2 emission doubling in 109 years. Sustained growth at the observed rate would mean a doubling in no less than 154 years. Computer simulations use a very high growth rate for CO2, namely 1%. A measure of 0,6% would be more accurate according to Lomborg. Measuring other gases and expressing them as CO2 equivalents also cause the estimated rates to be way above the estimates based on current rates. Lomborg argues that all greenhouse gases should be expressed separately. All these overestimates of emissions cause a prediction of much more warming in a given time. This is repeated by the press without mentioning the applied overestimates in the computer models.
In the new scenarios constructed in 1996 the IPCC abandons the idea of predictions and starts using the term projections. The emissions estimates for sulphur dioxide in different scenarios are now lower than those made in 1992. This has an important impact on the greenhouse effect because sulphur aerosols in the atmosphere may decrease global warming, as was explained before.
1.1.6 Consequences of global warming
Many consequences of global warming have been predicted and modelled by the IPCC. In agriculture a severe decrease in crop yield is expected which will eventually cause overall production to fall. But Lomborg finds that even the most pessimistic evaluation of UK Met Office experts expects crop production to grow dramatically over the next 50 years, so that overall production will not fall. Most plants grow better at higher atmospheric CO2 concentrations and higher temperatures, because of an enhanced fertilizer effect. This effect will cause production declines to be much smaller. Global warming may enhance the difference between developed and developing countries, because developed countries can adjust their farming methods more effectively and a longer growing season may not have as much of a negative impact. However, by the time the impact of global warming will be visible developing countries may be much more developed. The IPCC scenarios are only based on current development records. The IPCC also does not take into account the possibility of development of stronger crop varieties resistant to global warming impact.
Lomborg states that it is important to decide what considerations we should employ to determine whether or not and how we should take action. No matter what we decide, it will be a costly operation. And all measures should be based on reliable evidence, which is hard now that we still rely on inadequate model data. These considerations will cause the global warming debate to continue far into the future.
1.1.7 Costs of Kyoto
The IPCC has estimated the costs of global warming by aggregating the total cost if CO2 concentrations would double instantly and than stabilize. Lomborg comments that this is not likely to occur and that this cost estimate does not take into account possible future adaptations to climate change. He also states that the higher end of the IPCC estimated range of temperature rise (1,4-5,8oC) is not very likely. Not all important sectors have been included in the IPCC estimates of costs of the consequences of global warming. The transport sector and the question of political instability have not been included. Costs are the costs of adaptation and the costs of consequences of non-adaptation taken together.
1.1.8 Action or inaction
Finally, Lomborg emphasizes that we need to be careful in our choice of how to act. He claims that if we reduce CO2 emissions more than 11% or stop using fossil fuels totally, this will cause great economic losses. Apparently the optimal policy calls for a relatively modest level of control of CO2. Lomborg states that it would be better to simultaneously invest in cleaner technologies such as solar power. He also wonders why reports on global warming do not treat the consequences of major emission cut-backs for the economy and society. If the costs of cuts outweigh the eventual costs of global warming, economy may be negatively affected. Lomborg admits that we can afford the cut-backs, but he wonders whether postponing GDP growth for a couple of years after 2050 is really worth it.
Source: Lomborg, B., The Skeptical Environmentalist - Measuring the Real State of the World. Cambridge University Press 1998, United Kingdom, CH24: Global Warming (258-324)
1.2 Schneider's opposing view
Stephen Schneider, a leading expert on global warming and leading author of several IPCC chapters and IPCC guidance papers un uncertainties, contests Lomborg's account on the topic in the 'Scientific American'.
1.3 Lomborg replies
Bjorn Lomborg states that many of the arguments used by Schneider are incorrect. He finds that the information he used is of fine quality because he has taken it from top international world organizations and existing statistics. He does not state that things will all be fine as Schneider mentions, but rather that we should not act on myths of doom as they are sometimes represented about global warming and its consequences.
Source: The Scientific American, 2001. For the full reply by Lomborg see http://www.lomborg.org and for other replies by authors, see http://www.sciam.com/search/index.cfm?QT=Q&SCC=Q&Q=lomborg
1.4 Greenpeace vs. Lomborg
Not only Greenpeace protests Lomborg's views. As was shown above, scientists also try to discredit him. Stuart Pimm and Jeff Harvey in Nature magazine:
Lomborg has written a chapter on global warming that questions the seriousness of the problem and criticizes our methods of dealing with it. This does not mean Lomborg does not believe a greenhouse effect exists. In other chapters however, he takes matters one step further by claiming certain environmental problems really are not as serious as we think and acting on it as we do today may be unnecessary. He claims that the world is not running out of resources and species are not rushing to extinction at the rate that is claimed. Greenpeace highly contests this view.
Lomborg's thesis is not meant to be anti-environmental. He simply wants to point out that environmental protection today is based to much on scaremongering and ideology, whereas it should be based on rational analysis and risk-assessment.
The Daily Telegraph calls Lomborg 'a marked man', because of threats he now receives from enraged environmentalists consequential to the claims in his book. In September 2001 one environmentalist even hit Lomborg in the face with a baked Alaska pie for claiming Arctic wildness is not dying out.
Source: Thomas, D., Anti-Christ of the Green movement, Daily Telegraph 20/1/2002
2. The three that call climate change a 'dogma'
CO2 and other greenhouse gases can trap heat and thereby enhance the greenhouse effect. This heat-trapping may result in warming but this is a hypothesis, not a simple truth.
The writers state that a substance so crucial to all life forms would not be likely to cause climate change beyond what naturally occurs in the climate system. They think that it has been greatly exaggerated in order to safeguard donations of people to environmental organizations that depend on them. All media attention the greenhouse effect has received has given green parties and environmental NGO's the opportunity to keep convincing people to support them.
Source: Labohm, H., Rozendaal, S. and Thoenes, D, Man-made Global Warming: Unraveling a Dogma. Multi-Science Publishing 2004, Essex, United Kingdom
3. The Hockey Stick theory by Mann
The two Mc's went through the same database Michael Mann and others had used for the earlier paper and used a similar calculation. However, the outcome was completely different and led to the belief that Mann and others manipulated their data. According to their calculations the 15th century was warmer than the 20th century. They stated that Mann's records contained ' collation errors, unjustifiable truncation or extrapolation of source data, obsolete data, geographical location errors, incorrect calculations of principle components and other quality control defects'.
The theory of Mann was also contested by Lomborg (see earlier). Labohm, Rozendaal and Thoenes use similar arguments to discard the theory. Von Storch has attempted to reconstruct current climate by entering Mann's tree ring record into a climate reconstruction model. The reconstruction appeared far from correct. Bradley and others commented in Science that Mann had too few calibrated data for the tropics and the southern hemisphere. This makes the extrapolation of the results to global scales implausible.
This critique on Mann's records does not necessarily mean that the theory of current climate change being unique and therefore anthropogenic is disregarded. The evidence is still too narrow to really alter our beliefs. Other scientists have also shown current warming patterns to be unique and so far they have not been proven wrong by the skeptics.
- Labohm, H., Rozendaal, S. and Thoenes, D, Man-made Global Warming: Unraveling a Dogma. Multi-
- NRC Handelsblad, 6 februari 2005: 'Herrie om een Hockeystick'
4. Mark Maslin on what skeptics say
4.1 CO2; cause or consequence?
Some skeptics claim that ice-core data suggests that global CO2 responds to global temperature. They therefore conclude that CO2 is a consequence, rather than a cause of global temperature change. Maslin argues that examination of ice-core CO2 data suggests that increases in atmospheric levels occurred at the same time as the gradual warming in Antarctica. Step-wise warming of the northern hemisphere occurred in a later period. Time-series analysis by a professor of Cambridge University has pointed out significant atmospheric CO2 levels 5000 years before global variations in ice caps. All this evidence leads Maslin to believe that global CO2 levels increased before overall global temperature rises and ice cap melting.
4.2 Data manipulation
A well-known and often recurring critique of skeptics is that global warming data is manipulated to gain a desired outcome. This causes many discussions on whether global warming really exists. Labohm et al. have for example used this argument (see above). Maslin argues that this is a misunderstanding that is created because all global warming data requires some adjustment. Not all insights into data sets concerning global warming were immediately present. Accordingly, changing the data sets is all part of the scientific process. Constant questioning of the data adds to the confidence climatologists have in their results. The IPCC tries to make sure they verify their results by checking them through different studies and by using very different sources.
4.3 Solar activity
Bjorn Lomborg is one of the skeptics that mentions that solar activity, not CO2 concentrations, is mainly responsible for past temperature ranges. Both skeptics and non-skeptics agree that this has some impact. Scientists state that not only solar activity but also volcanoes have an important impact on past temperatures. However, Maslin states that the skeptics may put too much weight on the solar activity hypothesis. Even though there are still some major uncertainties in this area, it is clear that a combination of solar activity and greenhouse gas concentrations together have been able to simulate a global temperature curve for the past 130 years. Moreover, evidence suggests that solar activity and volcanic eruptions have been similar for the last millennium. This means that not only natural forcing causes global warming. An anthropogenic effect by greenhouse gases is certainly present.
4.4 Satellite data
Satellite data has suggested that over the past two decades there has been a slight cooling. However, re-examination of data and examination of the source demonstrated that there are some inconsistencies in satellite data. Altitude adjustments, friction with the atmosphere and inter-instrumental comparisons casted serious doubts about whether the obtained data were consistent. Moreover, two decades is too short a time to find any usable temperature trend. Al temperature cycles together take much longer than 20 years. Which of the cycles is present at the time of satellite operation remains to be seen.
4.5 Cloud feedback
Clouds can have both a positive and a negative feedback on global warming. Skeptics have claimed they may reduce the impact of global warming to a negligible amount. The role of clouds in the climate process is still one of the major uncertainties acknowledged by the IPCC. Clouds can both absorb and emit radiation, thereby either cooling or warming the surface. Which of the to effects takes place is largely dependent on the location and characteristics of clouds. This largely depends on the atmospheric distribution of cloud forming particles. Cloud representation in climate models has improved, yet uncertainties still remain. Climate models so far have shown that the cooling effect of clouds does not have a large enough impact to counter global warming trends.
4.6 Climate model reliability
A question that has been asked by skeptics many times is whether or not we can trust climate models. Climate models often give different results, they fail to predict abrupt weather conditions, they fail to reconstruct natural variability, deep ocean circulation and past climate trends and proxy data may be more extensive than model outcomes.
Source: Maslin, M., Global Warming, a very short introduction. Oxford University Press, Oxford 2004, page 60-65, 78-82
5. The NOAA/ IPCC contradiction on methane
The IPCC uses climate change models for its predictions and projections. The IPCC expects that methane (CH4) emissions will increase in the next century. Increases are most pronounced in regional wealth SRES scenarios where emissions may rise to between 549 and 1069 Mt CH4 by 2100, compared to 310 Mt CH4 in 1990. In globalized scenarios, the CH4 emissions level off and subsequently decline sooner or later in the 21st century.
The National Oceanic and Atmospheric Climate Administration (NOAA) reports on the basis of satellite images that the atmospheric build-up of methane has slowed greatly (figure 1). It is claimed that if current trends continue, it may reach zero within a few decades (Dlugokencky et al., 1998). This finding was however not reported on major news broadcasts or websites, for some reason. It may lead to an IPCC overestimate of global warming by 5%. This was also mentioned by Lomborg in his book (see earlier).
Figure 1: contrast between findings of the IPCC and NOAA
Even in the globalized scenarios of the IPCC methane emissions were not expected to decrease as fast as predicted by the NOAA. The author of the IPCC chapter dealing with future methane concentrations has admitted that the assumptions about methane of the IPCC were based on an understanding of methane build-up that was five to 15 years old. This may explain the differences between IPCC and NOAA scenarios.
Source: National Oceanic and Atmospheric Climate Administration (NOAA)
6. Specific data discussions
All data that are produced on global warming are discussed on many occasions as this continues to be a topic subject to large uncertainties. Some of the current discussions are mentioned here.
6.1 Documentation of temperature measurements
Critics have claimed that average earth temperatures may not be accurate because there can be local variations around the world of up to 100 degrees between two locations. This means that average global temperature can only be valuable when it is expressed as an anomaly, for example the difference between the current average global temperature and a period of reference, being the last 25 years for example. But even these anomalies are lacking in precision.
- Labohm, H., Rozendaal, S. and Thoenes, D, Man-made Global Warming: Unraveling a Dogma. Multi-Science Publishing 2004, Essex, United Kingdom
- Various internet articles
6.2 CO2 emissions and temperature change
Astrofysica Sallie Baliunas claims that at least 80% of anthropogenic CO2 emissions have entered the atmosphere after 1945. This means that the significant global warming caused before 1945 (0,45 degrees Celcius between 1910 and 1945) is not necessarily caused by an increasing CO2 concentration in the atmosphere. After 1945 CO2 concentration significantly increased, whereas temperatures started to decrease. This makes extrapolation of the CO2 impact on temperatures very difficult. This claim has caused some critics to even state that temperature rises cause an increase in atmospheric CO2 concentrations; not the other way around. Other critics point out that human contribution to CO2 emissions is relatively small, compared to some natural sources, such as volcanic eruptions. Humans cause an annual 8 billion tons of CO2 emission, whereas natural emissions are as high as 200 billion tons annually.
Labohm et al. state that CO2 only absorbs infrared radiation in a small part of the spectrum. They therefore doubt that an increase in CO2 content would have a significant effect on the heat balance of the earth. They claim that the comparison of the earth to a greenhouse is unjust because the earth system is much more complex than simply an incoming and outgoing flow of radiation. Many factors may positively or negatively influence this flow and it may come from different angles. A net radiation in a region therefore does not automatically mean that temperatures will rise. In the IPCC reports this mechanism, known as 'radiative forcing' is stated true. According to the writers this concept is fundamentally wrong. They also state that no significant temperature rise has been noted in the past 70 years, whereas CO2 concentrations have significantly increased. They do not consider climate change unlikely, but they doubt whether it will always manifest as a change in temperature.