The IPCC Assessment---An Overview

Bert Bolin
Intergovernmental Panel on Climate Change

The IPCC is just completing its second assessment. The first one, as you all know, was completed in 1990. By now, the three Working Groups, One, Two and Three, have all approved their policy makers' summaries and have accepted the underlying material from the scientific community as the basis for their conclusions.

What remains now is the approval of a synthesis report, which will provide the basic knowledge to assist in the political process of trying to see what to do in view of what is said in the second article of the Climate Convention. That is, we must aim for a stabilization of greenhouse gasses in the atmosphere in order to avoid undue changes of the environment, and do it in a manner that does not jeopardize sustainable development for the world as a whole.

That report is up for final consideration in Rome in December 1995 and we shall see how that goes. I will have to be a little restrained with regard to what I am going to say on that matter, because it is essential that I keep to the key findings as finally reported in the IPCC document, and do not go beyond that in individual speculation.

Of course, the joint effort of the scientific community as reflected in the IPCC report is of fundamental importance in this context. Frankly, I don't think there has been that serious an effort internationally before to try to express the knowledge of the scientific community in a comprehensive and a careful manner to serve a political process.

It is not perfect, but it is indeed a very major effort. You should know that the present report, the second assessment report, will consist altogether of 50 chapters, each one of them of quite some length and each one of them with some 300 or 400 references. Altogether, there are probably 10,000 references in these documents, which probably will be somewhere between 1,500 and 2,000 pages.

One may wonder why we do all that, because no politicians will ever read it all, and of course they shouldn't. What it is supposed to do is provide the basis for the conclusions contained in the Summary for Policy Makers that are based on a careful, comprehensive and well-reviewed report, consistent with the common view of the scientific community.

You can never agree fully on single numbers in an effort of this kind. The ranges of uncertainty as they appear are supposed to reflect the kind of uncertainties that exist in the problem, and also the different scientific judgments that necessarily must go into a complex issue of this kind. Still, there are some that do not accept the IPCC report, at least not all of the details. I welcome comments and critics, because that will only add to the status of the report, provided it is scientifically founded. I regret to say, this is not always the case.

It is to be remembered also that the bulk report, those 2,000 pages, is not approved by the IPCC. It remains as the scientific responsibility of the key authors. That is very essential, because it is impossible to approve documents of that kind. It should be reflecting the scientific community as well as can be worked out between scientists. The lead authors, and there are about 300 or 400 of them that are engaged in writing these chapters are obliged to consider carefully the reviews and comments produced by other scientists, and also, in the final round, by government representatives.

Thus, when you see in the newspaper that the IPCC must say so-and-so, there are no IPCC models. What we provide is the synthesis of all available models that are credible, to see what they altogether tell us with regard to present knowledge. That is quite a different story. I am afraid this is not recognized fully by the public, and is used occasionally to discredit some of the work of the IPCC.

Within the setup as we have it, we indeed try to accommodate different views as they are brought forward.

There was an indication, I think it was in a committee in Congress, that IPCC withheld information. That is completely wrong. A paper that was published in Nature wasn't available but we have 10,000 pages of reference. The IPCC has nothing to do with the way publication is handled by the individual authors, certainly not. It is important to distinguish the true roles of the IPCC.

The Policy Makers' Summary is a proposal by the IPCC Working Group bureaus to these plenary sessions in which representatives of government participate, of what scientists think might be of interest to the politicians. In the final sessions of the Working Groups, which approved the Summary for Policy Makers, there are a number of changes. The outcome is occasionally colored also to some extent, but not too badly, by non-scientific views as they are brought forward by individual countries. After all, it is difficult for all of us, for you and for me, to completely separate scientific comments and value judgments. But hopefully, the outcome is reasonably clear.

I am sure, it is useful for the policy makers. As a matter of fact, it is very clear since the special committee that was appointed in Berlin to negotiate possible reinforcements of the original Climate Convention agreed that present commitments by nations are inadequate. This is a formal statement by the parties of the Convention.

Therefore, they appointed a committee to negotiate what possible further agreements could be reached on this issue. The Convention has a subcommittee, the Subcommittee on Science and Technology, which is the linkage to the pure political process of final negotiation.

The IPCC is requested to report both to the Berlin mandate committee and to the subcommittee subsidiary body for science and technology. In that sense it is serving in an advisory function to the Convention.

But remember, we do not propose one or the other policy principle to be adopted. The IPCC role is to expose alternative possibilities and what they imply. For example, we have requirements for stabilization, depending upon whether we wish to stabilize at 350, 450, 550, 750, or 1,000 parts per million of carbon dioxide concentration in the atmosphere. Of course, these requirements differ very much. Which level to stabilize at is a policy issue based on knowledge of impacts, and not only of impacts of Climate Change, but also possible economic consequences of taking drastic action. We do have two sides of this coin, and we recognize that fully.

Well, after this preaching on how good the IPCC is, which it is not in all regards, let us turn now to some more specific issues. I will now briefly try to bring home some of the key things as they are reported on by the three Working Groups. I will put most of my emphasis on Working Group One, because it is closest to my own competence, but I will address the other two to a certain degree.

There are a lot of things which are reconfirmed with regard to the climate system and its behavior, and also with what man is doing with regard to emissions into the atmosphere and the consequences. But there are some very important things which are a considerable step forward in our present understanding of the system and its way of responding to man's interventions.

The greenhouse gasses are the same as they have always been. Of course, there are a few added of a more exotic nature, but I think those are not crucial for a conclusion, except a substance like CF-6 is mentioned now for the first time by some policy makers as having a lifetime of 50,000 years, which means that it will be there from our point of view forever. These kind of absolutely irreversible processes, as far as we can judge, are important to point out, although play no role whatsoever with regard to the amounts presently in the atmosphere.

There are other aerosols emitted by burning, particularly grassland and forest burning. The indirect effects are unspecified as of a year ago, but I should say that by global climate change models, one of the present values for the joint effects of this, is somewhere between .5° and 1.0°C for the global average effect, even though one should remember that the effect of these aerosols is very regionally different. When including aerosols, you get a forcing picture with very clear, almost negative forcing in areas of industrialization, where sulfur is emitted by burning fossil fuels, that is, oil and coal particularly. Gas of course has hardly any sulfur in it. This forces the atmosphere of the climate system in a patchy manner.

It is to be remembered, however, that the effect of these aerosols is not reflected in patterns of climate change that are corresponding more or less exactly to this forcing. The climate system is a dynamic one, and the patchy forcing sets up interactions dynamically in the Climate Change system. The final effect can be considerably different.

It is however clear that of sulfate aerosols, 90 percent are emitted in the Northern Hemisphere. There is therefore to be expected a clear difference between the two hemispheres in man's emissions of greenhouse gasses and aerosols into the atmosphere.

The greenhouse gasses on the other hand have lifetimes of more than ten years. We can assume they are essentially homogeneously distributed over the globe and because there are different effects dependent upon the prevailing climate, there is more warming due to greenhouse gasses in the tropical regions, or more forcing in tropical regions than in north polar and south polar regions.

There are the patterns here. In the report from 1990 there is a clear change of somewhere between 0.3 and 0.6 degrees Celsius over the last 100 to 130 years. We also said that this could be partly a result of man's interventions.

But in order to draw that conclusion, we must know something about the temporal variability of the climate, the natural variability of the climate system. We do not know the natural variability on the time scales of half a century to a century or more with the precision to exclude, simply and directly, that this is not a natural variability. But we say it is not in conflict with the idea that some of it, at least, might be caused by man.

Now, this is this question about detection and attribution. Let me only very briefly summarize what is expressed now in the Working Group One Policy Maker Summary.

The question is to see if there are characteristic features of climate change due to man's intervention as compared with the natural variability: to see if there are particular patterns that emerge that could not be viewed as natural variability, or rather, is unlikely to be natural variability. That is what is now being recognized.

In the 20-year period from 1964 to 1984 there was generally some warming, probably about three-tenths of a degree, but there is a very clear patchy nature of the change over those 20 years.

Now, this is observed. We can run the climate models in the transient mode in the two centers, the Hadley Center in Britain and the Max Planck Institute in Hamburg, beginning in the 19th century, 1850 or so, to see the pattern of the known emissions of the various greenhouse gasses and estimated sulfate emissions during this period.

You get the correlation of about .3, which is not big but still, it is not significantly different from zero, but there are similarities between the observed pattern and what models predict.

The fact that the correlation is not bigger to a considerable degree depends upon natural variability. But the similarity here means that there are similarities in the models and the actual observed changes in the last 30, 40,or 50 years.

It is interesting to see that in the course of time, this similarity improves, so it is better in 1990 than in 1960.

Now, there is one more thing which is interesting. There are other so-called characteristics of the change due to the emissions of greenhouse gasses, which is illustrated by the cross-section of temperature changes during the latter part of this century. There is not only carbon dioxide in the model, but the models also include greenhouse gasses and sulfate aerosols. There is a difference between the two hemispheres with regard to the distribution.

There are similarities, particularly if you take the Northern Hemisphere and Southern Hemisphere and the stratosphere troposphere. None of these similarities would exist if the observed changes were due, for example, to volcanic eruptions or changes of variation, which are the two prime contestants here to explain the variability in the past. Of course, there is a major component of natural variability, which is stochastic, and is in principle unpredictable. At least so far, we have not been able to reproduce that in a model, except in a statistical sense.

The change of precipitation is also defined in the report in terms of grid point values all over the land surfaces; there are inadequate observations over the sea. There are definite differences between the hemispheres but we cannot yet use these data for validation or verification of models. There is, on the whole,some intensification of the hydrological cycle. But even that is marginally detectable.

Now, this fact that there is some correspondence permits us draw conclusions. I think I would like to read out precisely what is said here, in order to really be careful in what I say, and not be accused of anything.

The last paragraph with which we are concerned here says, our ability to quantify the human influence of global climate is currently limited because the expected signal is still emerging from the noise from natural variability, and because there are uncertainties in key factors. These include the magnitude and patterns of the long term natural variability and the time evolving pattern of forcing by and a response to changes in concentrations of greenhouse gasses and aerosols and land surface changes.

Nevertheless -- and that is the final concluding sentence -- the balance of evidence suggests that there is a discernible human influence on global climate.

This is an exceedingly important conclusion. First of all, you introduce more realism into the temperature achievements. Secondly, it is also implicitly a first validation of climate models against observed changes. You also can trust the models a little better. I wouldn't say they are perfect in any way, but they are somewhat more reliable. Therefore, projections for the future become somewhat more reliable. There is a lot more to be done to see where in the uncertainty range we actually are.

The 1990 report said that the sensitivity of the global climate system is such that a doubling of carbon dioxide would yield a change of the equilibrium surface temperature average around the globe of somewhere between 1.5 and 4.5 degrees Celsius. There is considerable uncertainty in the range, and that was fully justified at that time. It may still be so, but there are some answers that may be important.

It is to be remembered that none of the models that were run at that time showed a smaller value than 1.9. But there were actually two that were above 5.2, about 5. The fact that we chose a little lower range and also a central value of 2.5, and there was just one out of four of the models that showed less than 2.5, was the discrepancy between this range and what had happened so far regarding temperature changes, which indicated that maybe after all we should be in the low range.

Now it seems to become clear that the slower increase which has been observed may well be due to aerosols. This then means that the sensitivity of the climate system maybe is more properly between 1.5 and 4.5, and some may even wish to say the central value should be three rather than 2.5. This is not included in the report, but you can sense the way we change somewhat the view of the sensitive characteristics of the climate system to man's impacts.

I now would like to mention some information reported in the IPCC report from transient runs by the Max Planck Institute and the Hadley Center.

As a result of increasing carbon dioxide concentrations in the atmosphere by 2100 there will be a rise of about three and a half or a little more than three degrees increase from the present. But there has been an increase on the order of half a degree from the middle of last century.

But if you include aerosols, both these drop down. The two models show about the same temperature changes. It is just a coincidence, because they use different assumptions about some of the parameters, particularly cloud, there is more of a range of uncertainty than is shown by these two models, for sure. So don't take this as a proof in any way that we now know the change of the average temperature of the globe over the next hundred years; by no means. I'll come back to that in just a moment.

Thus, this is a step forward. Now, how we wish to use that is another matter, and what conclusions do we draw?

There is also this, by the year 2050 only 70 percent of the potential effect of increased carbon dioxide will actually be realized because of the inertia of the climate system. It takes time to heat ocean waters.

With respect to the change of response of the sea level due to the emissions and the heating, the values are reduced, as compared to previous estimates, from an average of about 65 centimeters to about 50, with an uncertainty range of between 10 and 15 centimeters only, up to 95, a huge range of uncertainty.

But one should remember in this context that the lower ranges to which the IPCC referred in its conclusions here refer to scenarios of the future which are called C and D, with low values of change of temperature or sea level over the next century, brought about by having population increases to nearly 6.3 billion people during the next century. It is likely that we will pass that number just a little after the turn of the century. The population numbers are very low in these scenarios, trying to show lower limits of what might happen in the future.

Finally, very briefly with regard to Working Group One, stabilization. We may need to stabilize carbon dioxide. How much and when is to be decided by others in the IPCC. There are alternative scenarios in which we end up with stabilization between 350 and 750 ppm.

The question is how quickly can we turn around, 450 requires emissions below present within about 35 years, and a rather quick turnaround. That is my personal view. It is not very likely that a 450 stabilization of carbon dioxide will be possible, unless very drastic measures are taken. I am simply doubtful. There are no signs at present that such attitudes to the issue are evolving.

Let us turn to the two other Working Groups which have already completed their work, the important conclusions in their Summaries for Policy Makers. It will be very superficial. Working Group Two will deal with that more in detail.

With regard to sea level rise, there are of the order of a hundred million people living in the regions which will be directly influenced by sea level rise of the magnitude that is being foreseen here. There is some time for them to move. It is not like they are staying there and drowning. But the realization of this rise in sea level is a slow rise, it is sensed that ten years from now or 40 years from now, major storms cause more flooding into regions which were not flooded before. The extreme events associated with such stormy weather are the crucial things in judging what the impacts of the sea level rising might be.

Secondly, with regard to agriculture, the IPCC says very clearly that there is no reason to think there needs to be a very drastic negative change of the total productivity of land on earth, because of the Climate Change. As a matter of fact, it would be possible to maintain present agricultural production or even increases. But there may be considerable changes over where you can grow and where you can't grow, where present patterns might change, and where some countries might be very badly off, others might gain, which is in itself a disturbing factor for the global society to experience.

When it comes to forests, forests are at present being diminished, or have been, due to man's use of forest products. It is likely that there will be more warming over continents and also drier climate in middle latitudes, not high latitudes, which might well affect forests, because forests grow on land that would otherwise be grassland, provided there is adequate precipitation.

How much this will change, or particularly where, is impossible to say. But there are indications that two degrees change of temperature and associated precipitation changes might lead to a situation where about one-third of the land area would preferably not have the present ecosystem there, but another one. Present ecosystem distribution is tuned over the centuries and millennia to present climate, and if climate changes, the ecosystems also will change. But they are unable to change as quickly as the change of climate is expected to occur, and there will be thus pressures on these systems, maybe not so that existing forests die out, but the regeneration of forests may be difficult in areas where climate is suitable for forests. But we cannot tell where, and we cannot tell either how quickly this will come about, because it still depends upon whether we choose a lower sensitivity of climate response or a higher sensitivity of climate response to man's interventions.

Health is another issue which is influenced, in the sense that vector-borne diseases are very much dependent upon temperature and precipitation or humidity conditions. It is likely that tropical diseases would have the possibility to spread into larger regions. To the extent that is a real danger for humanity depends upon how well we are able to protect ourselves against such diseases. Malaria, for example, is not found in all of the regions in which malaria could exist, because of precautionary actions by man in the health domain.

There are a number of things of this kind, for example, energy provisions. To emphasize, our use of energy is not at all very efficient. There are some 10, 20, 30 percent increases in efficiency of energy use which will not cost very much, or in some cases will even be profitable. The technical potential is a lot bigger. There, costs come into the picture. Again, to optimize or minimize costs, the rate with which society can change is indeed very constrained. To disband existing infrastructure is very costly. So investment policy for the future, if changes are required, must pay very much attention to the way capital investments for the future are actually coming about.

Finally, I will conclude what Bob Watson pointed out so clearly in the introduction. There is a difference between developed and developing countries in this matter, a very major difference. We know that the mitigation actions will primarily concern carbon dioxide emissions, fossil fuel use. Almost 80 percent of the world energy supply is fossil fuels right now. If developing countries use energy as we have been able to with fossil fuel we will then certainly double or triple concentrations in the atmosphere.

Therefore, even though efficiency in energy use can be enhanced considerably and provide us breathing space, we must take stronger action in the longer perspective. The need for new sources of energy is becoming a most urgent issue to develop over the next decades or half century.

The climate change issue is not an issue that we can resolve over a day or a year or over a decade, as was the case with the chlorofluorocarbons and the ozone issue, although these are not completely settled as yet. It is rather an issue over half a century. To have a long term perspective of this is most essential. It does not mean that we take drastic, not well- thought-through, actions now, right away, but we need to learn about this. We need to do the things that are cheap and can be done for other reasons, and that contribute to limit emissions.

In the meantime, we may learn more. We may be able to settle more clearly where in the uncertainty range are we heading, and in that sense, gradually approach the issue of what do we need to do in the long term perspective.

These are the views as expressed in Working Group Three of the Summary for Policy Makers, the issues that we bring to the politicians, in order for them to try to see what the climate impact in the future might imply.

For example, there is no value you can put to natural ecosystems. It is a question of how we as human beings value our environment, which means that cost benefit analyses of the future become very questionable. The question about intergenerational expertise is an issue that cannot be easily taken care of by deciding on a discount rate. Although one may choose very low discount rates in other to value the future more than the discount rate usually used in industrial investments actually implies, implying that, beyond 20 years, nothing we do today is worth anything.

This is the concluding comment I wish to make here. It is a long term issue. We need to approach it gradually on a sound temperature knowledge basis, and try to iron out the political controversy. But I am happy that I need not address that question specifically.

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