Lennart Bengtsson has prepared this statement for a discussion in the Swedish Riksdag.
That the Earth's energy balance is slowly changing due to increasing greenhouse gases and anthropogenic aerosols is not questioned by the scientific community. This is physically well understood and based on fundamental physical principles known since at least the middle of the 19th century.
What is not as well understood is to what degree this is changing the climate of the Earth and how fast this will happen. Furthermore, any change in climate might have a very long perspective and might be virtually irreversible at least on time scales from several hundred years and longer.
If the changes are as large as indicated by many modelling studies there are reasons to be concerned as rising sea level, changing precipitation patterns and the risk of more extreme weather events as these are serious business for an increasingly populated planet. It is thus no surprise that the world community has to consider such a perspective a priority issue. This is the background why the International Panel on Climate Change was set up in 1988. One reason behind the establishment of IPCC was the apparent success with the Montreal agreement to reduce constituents damaging the stratospheric ozone layer. The Montreal agreement and following protocols was successful and during the last decade or so a gradual reduction of CFCs has been confirmed from satellite observations. However, there are still sufficient ozone destructive constituents in the atmosphere to create an ozone hole every spring over Antarctica but it appears gradually to becoming less extreme.
The IPCC has been around for more than two decades and four major reports on the state of the climate have been issued. The next is expected by 2014. While most aspects on the science of climate and climate change are not controversial, at least among the majority of active scientists in the field, the issue is becoming increasingly emotive in the public debate and gradually so in the political community. The main reason to this are the potential consequences for the world economy and the society at large of major reductions in the use of fossil fuels as this is seen as the main culprit behind an anticipated climate warming.
These political and economical aspects have led to a polarization of the political debate that indirectly has affected the science of climate change.
The problem is the following. Climate warming over the last century has been rather modest amounting to about 0.6-0.8 C in a global average. In many parts of the world such a warming is hardly noticeable towards a background of natural climate variations that in many parts of the world is significantly higher. The representativeness of some of observations over land has also been questioned due to urbanisation influences. However, a long-term warming is supported by a number of other estimates such space observations (at least from 1978) a deep-sea heat accumulation, glacier retreats etc.
To prevent an ongoing climate warming would require enormous resources and sacrifices and is probably not even then possible to be achieved within a time scale of several decades. This situation has led to the mobilization of many interests and pressure groups.
Different fundamentalist- and environmental activist groups see possibilities to save the world from sin and have not spared a moment to paint a future world in the darkest colours of collapse and disaster that reminds us of religious activists through the history. Economical and technical interests developing alternative techniques for energy generation are another supporting force for a clear climate policy as significant public subsidies are generally needed to develop alternative non-fossil fuel based energy systems based on solar, wind and bio-energy. Some of the scientists involved in IPCC are likely to be influenced by such arguments and in addition are concerned to maintain governmental support for their research programs. Such views are not uncommon in a social context and do exist in this case as have been apparent from recently reported events.
As a counter force has been a group of so called sceptics, deniers or contrarians. Among those there are many senior scientists often with a broad understanding of physics but only in exceptional cases well informed about modern climate research as it has evolved since the mid 1950s. Many of their contributions have unfortunately been scientifically weak, some of them substandard on the border of being truly scientifically embarrassing. However, there are also cases where publications have been refused not on grounds of science but rather as it appears of the opinions of journal editors and individual reviewers. It is essential for a healthy science debate that such contributions are not to be ignored but to be scientifically analyzed and openly discussed.
It should also be mentioned that there are strong economical interests from the fossil fuel industry on all levels to counteract activities that are seen as a threat in this context. It can therefore not be excluded that there are side issues of a corresponding nature that at least inadvertently are influencing the critics of climate change. It is also clear that countries that presently are in a stage of rapid development towards a modern society are clearly unwilling to be caught up in a web of policy commitments that will hamper their economical development. This is certainly the case with China and India. This was the main cause of the failure at the Copenhagen meeting and it is surprising the EU did not foresee such an obvious fact.
So there is no doubt that there are political and social issues that have distorted the climate science debate and led to the most absurd claims and counter claims. Unfortunately, many of the individuals caught up in this have tried to make use of proxy scientific arguments as support for their case. The more absurd once such as the CO2 records were irrelevant or falsified have fortunately disappeared. Present critical statements include:
1. Present warming has little to do with increasing greenhouse gases, as it is just a recovery after the little ice age.
2. There can be no effect from greenhouse gases as there have been similar warming trends in the past such as between 1920 and 1945 without any noticeable change in the greenhouse gases such as CO2.
3. There has hardly been any warming over the last some 50 years as the present temperature records are not representative due to the rapid urbanization.
4. There was less sea ice in the Arctic Ocean in the 1940s than presently
5. Sea level has not changed generally, present observations are unreliable.
6. Climate models are unreliable as they warm the upper tropical troposphere where there in reality is no warming at all.
Typical of these statements is that they 1) cannot generally be confirmed or questioned as we lack observational data or 2) the proponents implicitly sees the climate system as essentially linear and that there exist a direct relation between forcing and response to forcing.
Let us now analyze these claims in more details
1. This is a clever statement as it brings up the little ice age as an anticipated fact, known and recognized by scientists and public at large. It is politically very clever as it can well be used even if warming were to accelerate in the future. It assumes without any reliable evidence that climate for the last several 1000 years was warmer than now until that nasty little ice age appeared in the 14th century due to some unknown cause, such as a fluke of the sun or whatever. There does not seem to be a need for a proof in this case. However, this does not at all have to be the case. A more likely mechanism is internal chaotic variations superimposed on a slow cooling trend (Milancoviç effect) from the climate optimum 6000 years ago. This view is supported from observations and theory.
2. and 3. This is a very popular argument but a likely explanation is again the greenhouse effect but not the concentration of CO2 but the radiative effect of the sum of all the greenhouse gases. As shown by Schwartz et al (2010) the curve of forcing and that of temperature follow each other assuming a climate sensitivity of ca. 0.3°C/Wm-2. This is a very modest warming but the most likely explanation is that anthropogenic aerosols mask the warming from greenhouse gases. The small deviations up a down can effect global temperature trends over some 20 years and are essentially due to chaotic processes of the general circulation of the atmosphere and the oceans (such as El Nino) as well as the effect of occasional volcanic eruptions. It should be noted that the cold winter in northern Europe 2009/2010 coincided with a warm global temperature similar to what happened during the cold winters in Europe during World War II such as the winter 1941/42.
4. The Arctic sea ice undergoes periodic changes that might have time scales of several decades. As far as can be judged from limited Arctic data the temperature was as high there in the 1940s as it was in the 1990s, but in all likelihood not as warm as in the last decade 2000-2009. Because of the close relation between Arctic sea ice and surface temperature this suggest correspondingly less sea ice when temperature of the Arctic is high.
5. Sea level is a very complex issue as there are large regional and local variations. This is due to wind patterns and ocean currents as well as tectonic processes. Space observations such as sea level altitude measurements from Topex-Poseidon and recent gravity measurements from GRACE supports a mean sea level rise of presently around 3 mm/year. Future rise is very difficult to estimate, as there are competing factors such as more snow accumulation on Antarctica and higher altitudes on Greenland and increased ablation on coastal areas of Greenland. The probability of a rapid change in mass losses of the land ices is to be considered as minor during the next several decades but will gradually become more serious.
6. Present global models used in climate assessments have been developed from models used for weather prediction and have inherent limitations due to the fact that the models cannot be satisfactory verified on time scales of climate variations. However, this is by far the best tool we have and if used sensibly can be very helpful. An overly naïve belief in climate models is regrettably detrimental in particular in so called limited area models used by many national services. There is also an increasing risk that the many users of climate models have little idea about their limitations due to lack of insight in the constructions of general circulation models. Some users almost completely lack the knowledge in mathematics and atmospheric physics and dynamics to judge the reliability of the climate models.
In conclusion I can summarize my views as follows:
1. The recent statement by the Royal Swedish Academy of Sciences for example is considered as balanced and sensible and could preferably be used as guidance by the political community. There is in essence no deviation from the 2007 basic science report by IPCC that does not include the summary for policy makers.
2. Recent events related to IPCC are problematic and should be urgently dealt with by the governing international bodies UNEP and WMO. If IPCC is to be effective in the future its scientific and ethical standard can never be compromised. My personal view is that individuals, and there are apparently some that have acted unethically, shall be removed from future work.
3. One particular problem has been the limited access to basic climate data. This is partly due to the policy of several European meteorological services that because of commercial interests refuse access to some data free of charge. Many European scientists must therefore turn to USA where information is free as it is financed by public money. That the same is the case in Europe does not appear to bother those involved the slightest. This is in my opinion unacceptable and should be changed forthwith. An additional factor has been limited resources and lack of technical competence in the small climate groups that have put together climate databases for users. A third factor is the there are still scientists that are sitting on data due to the worries they might have that someone else could use it before he/she himself can do so.
4. It would further be helpful for the society at large if all amateur activities on climate and climate change either from fundamental environmental activists or from equally unscientific claims that greenhouse gases have no climate effect could at least be commented on by professional experts and not left to the self-proclaimed expertise among the journalists. The present situation is simply embarrassing in a society that calls itself educated. It might be a consequence of the falling standard in science and mathematical education in recent decades in several countries and the corresponding lack of respect for the hard and demanding work of many scientists.
25 February 2010
Lennart Bengtsson is now with the University of Reading (UK), and was earlier director of the European Centre for Medium Range Forcast (ECMWF) and of the Max-Planck Institute of Meteorology in Hamburg.