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would be expected to have had cooling influences on the troposphere. Dr. Michaels had to adjust the model results for a number of reasons: (i) the original simulation was not for any particular year, (ii) the actual rate of increase of carbon dioxide is less than that assumed in the simulation; and (iii) other greenhouse gases were not simulated. The approach used by Dr. Michaels to adjust the model results is highly questionable. Finally, given the natural variability of the climate, Dr. Michaels should know that comparing the results for a particular observational period and a particular model simulation is not statistically appropriate. It is essential, if a comparison is to be made, for there to have been an ensemble of simulations, each including the variety of factors influencing the global temperature Trends in surface temperamine may be different from friends in mid-moposphere temperature: Dr. Michaels next contends that the surface temperature trends should be the same as the MSU trends. However, before noting a number of reasons for why these records may not be identical I would note that the trends deduced from satellite data over land are not too dissimilar from the rends deduced from land-surface observations. The lack of an observable trend in the satellite record is because there is a warming over land areas and a cooling over the oceans.

would also like to note that if the affects of El-Nino and the Mt. Pinatubo eruption are taken out of the record them even the satellite data shows a warming trend. There are a number of reasons why these records may not be directly comparable. First, recent analyses by Hurdle and by Jones and Santer confirm that, at particular locations, temperature variations at the surface and in the middle troposphere can be quite different. While tropospheric and surface temperatures are connected under many weather regimes, they become disconnected under the many weather regimes when a remperature inversion forms (c.g., on quiet winter nights when the surface temperature cools well below the temperature of the overlying air and throughout the subtropics where the descending air in the troposphere creates a near surface inversion). Analyses of the global patterns of these differences suggest that the differences are largest for just those circulation patterns when warming due to greenhouse gases is most likely. Second, differences occur because sca surface temperatures are relatively stable. Under wintertime conditions over the oceans, the mid-tropospheric temperature measured by the MSU instrument can vary strongly (c.g., in the region of the Aleutian low pressure system where Pacific storms form), while the sea surface temperatures vary only fairly slowly. Thus, whereas land surface temperatures can vary more than tropospheric temperatures, sea surface temperatures will vary only a little. Along with the finding that over land, especially in the winter and on summer evenings, the surface temperature can vary much more than the air temperature, these differences mean that surface and tropospheric temperature measurements are recording quite different quantities. Third, lower stratospheric ozone depletion is likely to have affected the mid-tropospheric temperature trends more than the surface temperate trends. The counter-arguments of Dr. Michaels on this issue are again highly questionable because the geographic region of maximum ozonc depletion does not have to coincide directly with the geographic region of

maximum affect on tropospheric temperatures. I are quite confused about why Dr. Michaels plots the two curves with an offset-he somehow seems not to have adjusted to a common reference level. If this is to show that there is an offset between greenhouse gas only simulations versus the new simulations including sulfate accosols, I agree. Wisca the cooling influence of acrosols is accounted for, the two curves come into broad agreement (recognizing the differences in the two quantities discussed earlier). To more properly investigate the accuracy of model simulations, I would invite Dr. Michaels to prepare a comparison of an ensemble of the newest model simulations with the extended record of surface temperature changes. It is such a comparison that has been relied upon by the IPOC and led to their conclusion that the agreement between model results and observations is suggestive of a "discernible human influence on the climate." I concur with this IPCC finding.

2. During the course of the bearing, Dr. Michaels provided a chart which purported to show that all of the temperature change from 1965 to 1994 occurred in one year, a feature which models cannot predict. Dr. Michaels implied that the inability of models to predict such behavior called into question their use for policy purposes. Please provide your own views on the methodology and interpretation used in this chant and its significance, if any, to the validity of climate models. Answer: Both the simple climate models and the General Circulation Models used by POC are suitable for policy formulation. The fact that they do not simulate every bump and wiggle in the observational record is not surprising given they do not attempt to simulate every natural phenomena that affects the Earth's climate on short time scales. First, I want to note that the record that Dr. Michaels showed was of the radiosonde record, which is a measure of the free troposphere temperatura. As indicated in my answer to the previous question, this record may not be exactly the same as the surface temperature record and it has likely been affected by the cooling influence of the lower stratosphere ozone depletion suppressing warming in the last part of the record. With respect to the statistical analysis, as Dr. Michaels frequendy points out, there is considerable natural variability from one year to the next, hence one needs to be very careful of creating break points at particular time periods, because this can diston the interpretation of the record. Interestingly, this is precisely what Dr. Michaels has done in his analysis of the chart in question. What is interesting is that the temperatures stayed elevatedunlike natural fluctuations, the average did not return to its pre-jump level, hinting that this is likely a human-induced warming. Given that many factors influence the Earth's temperature, and most models do not attempt to simulate all of them, temperature discontinuities should not be unexpected. Observations suggest that major changes in circulation can occur over short periods and persist for some years. Thus, the climatic regime can shift into drought a high precipitation conditions in California, the Sahel, and other regions and last for many years or more. There are suggestions that these shifts result mainly from changes in occan circulation, which can shift rather dramatically over short periods (c.g., ET Nino events in the Pacific Ocean and interruption of the thermohaline circulation in the North Adantic Ocean). Therefore, at certain times a number of factors (c.g., onset of an ENSO cvent, recovery for a volcanic eruption, etc.) could all affect temperature in the same direction. These factors would be superimposed on the long-term warming trend caused by greenhouse gases. It is true that climate models that include only the atmosphere do not reproduce large interanoval shifts in the climate, but the new models that include a fully dynamic occan representation are showing rather significant shifts in the climate are possible over short periods. That the natural climate can seemingly relatively easily shift modes should not, bowever, make us complacent, rather, we should be very concerned that human influences on the climate might lead to shifts in the climate of the future into new modes to which society is not well adapted.

3. You testified that the IPCC assessment finds that aggregare global food production under projected climate change conditions should be able to keep pace with population growth and nutritional needs. In making this -vjection, how does the IPCC make into account the increasing air pollution in many developing countries, soil erosion and degradation, competing demands for land and water, growing populations, the need for fertilizers, sca level rise onto productive river delta lands, and other factors that may limit the availability of agriculture to shift or increase production? What is the range of uncertainty of this projection and what are the chances that the actual consequences could be much worse?

Answer: The IPCC's rather optimistic assessment that overall global food production can risc sufficiently to provide for axpected population and economic growth over the next few decades is based on a combination of factors, including improved varictics and management as a result of scientific research, plus the physiological benefits to crops a C, carichment. The POC chapter concluded that on the whole, new studies of climate change impacts an agriculture "support the evidence presented in the first IPCC assessment in 1990 that global agricultural production can be maintained relative o baseline production in the face of climate changes likely to occur over the next century (ie, in the range of 1.0 to 4.5 C) but that regional effects will vary widely." This broad conclusion was specifically focused on the marginal effects of climate change aa baseline production; that is, climate change, itself, was not judged to prescat a major problem for overall global production providing that thosc regions that become more suitable for agricultural production are able to expand production even as production in other regions contracts. Further, all areas will need to make adjustments in the varieties of crops planted, livestock raised, and the techniques and practices used in production (c.8, the timing of field operations, amount of inigation, tillage practices). However, the key issue may not be global food production, but regional food production. Areas where climate change reduces food production potential may face production declines even if all economically practical adaptations are made. As the IPCC emphasizes, poorer populations in regions negatively affected by climate change are most vulnerable to the more serious consequences of hunger and famine. Thus, there will be losens as well as winners in the process of climate change. The likely winners will be some of the industrialized countries of the northern hemisphere's

cool temperate zones (including such countries as Canada and Russia). The likely losers, as the other hand, will be countries in the tropics and subtropics, particularly those with semiarid and arid regions located inland. In such areas, increasing frequency, duration, and severity of drought as well as of heat spells may cause instability and crop failures. The areas in question include not only most of Africa and parts of Asia and South America, but also the Southern Great Plains of the USA. The regional effects could be very strong even in the United States, with some current farming areas becoming unproductive without major new investments in irrigation (and assuming water supplies are available). Hence, America may lose its capacity to produce large grain surpluses, and to offer them to the hungry nations. This is particularly important because the economic gap between the developed industrialized) countries, and the developing nations (especially in Africa) is likely to widen. The developing nations may well suffer more episodes of famine, thereby generating, greatly increased numbers of cavironmental refugees. As a consequence, the developing nations will become increasing dependent on the largess of the rich nations just when their production may be somewhat limited due to climate change. An important limitation of the IPCC effort was that it was not able to independendy assess the many cavironment, resource, and tochnology factors that may lead to either increases a greater constraints an production in the future. However, climate changes will certainly exacerbate warrisome trends of denudation and land degradation (including crosion) in most semiarid and arid regions, where population growth exerts increasing pressure on fragile and limited soil and water resources. Sez-level rise will threaten the productivity of low-lying coastal zones such as the Nile Delta of Egypt, Bangladesh, island nations, and even parts of the US (Florida and the Mississippi Delta). The IPCC also noted that the baseline agricultural production for their estimates (what agricultural production will be in the future if climate change did not occorr) is widely debated. The PPCC reviewed the studies of agricultural experts from the Waris Jank, the UN Food and Agriculture Organization, and the International Food Policy Rescarch Institute that project world food production into the future. Each of these projections show, in the absence of climate change, increasing world food availability in the future with production expanding faster than population and world commodity prices falling. A limitation of these studies is that they only extend to the year 2010 a 2020. Other studies are less optimistic, citing limits oa further land expansion and

irrigation, resource degradation, and reduced confidence that the historical rates of increase in yield will continue. Factors that will determine whether agricultural supply can keep pace with demand include: (1) how fast demand grows in response to population and economic factors, (2) the future availability and quality of land, (3) the future availability of water, and (4) whether improvements in technology will continue to result in rapid yield growth. Further, economic growth and development are closely tied to demand growth and, in many developing countries, we also dependent on agricultural development. Considering each at these issues separately:

Demand growth. Between 1950 and 1990, world population grew at 1 2.25% compound

annual rate. Through 2025, population is projected to grow u a compound annual rate of between 1.13% and 1.55% (high and low UN variants). The decade of the 1990s is projected to have the largest absolute population addition, with declining additions in subsequent decades. Thus, growth in food supply could slow by 40 to 50 percent from recent decades while maintaining per capita food production levels. Income growth will likely cause demand to grow more rapidly than population and will change the composition of demand, most likely away from food grains and toward meat, fruits, and vegetables. The shift to meat is likely to increase the demand for grain for livestock foed. Increased demand generated by increased income growth would allow more and higher quality food to be consumed per capita but this depends on bow food consumption is distributed. Beyond 2025, population growth is generally projected to be reduced because world population is

projected to stabilize by around 2075, but this is an assumption that may be optimistic. • Land quantity and quality. Some estimates suggest that there is much potentially-available

land, but the cost of bringing it under production may be high with attendant adverse
environmental impacts limiting expansion. Intensification de production on existing cropland
may worsen land degradation and put additional pressure on water and soil resources. Firm
data on the extent and severity of land degradation and its impact on production potential for
most of the world are not available, but the recent overview, although still qualitative in
economic terms, confirms significant degradation and loss of arable land, especially in
Africa Studies disagree on the extent to which intensification use affects land degradation.
Competition for agricultural resources for other uses may also affect the supply and price of
land for agriculture. Carbon sequestration, biomass energy production, forest product
production, the potential development of new non-food agricultural products, and removal of
agricultural land from production for other cavironmental objectives will all likely affect the

amount of land available for food production.
Water supply and irrigation. Inrigation has contributed significantly to increased production in

the past. Currently, 17% (253 million hectares) of global cropland is inrigated, but this 17% of land accounts for more than one-third of total world food production. An estimated additional 137 million hectares have the potential to be irrigated, but the cost of doing so may be prohibitive. Current water systems in many developing countries achieve low efficiencies of water distribution, and average crop yields are well below potential. There are environmental and bealth-related effects of irrigation such as soil salinizatiou and the spread of water-borne diseases that may limit further expansion. Major factors contributing to these inrigation problems in both developing and developed countries are: un-priced and heavily subsidized water resources; inadequate planning, construction and maintenance of water systems; unassigned water rights of rules that limit the transfer of rights; and conflicts between development and distribution goals. Solutions to these problems me available in most cases and a recent study found that investments in irrigation have boca a last us profitable as investments in other agricultural enterprises. Changes in potenti-l antigation water supply due to climate change have not, with few exceptions, generally been integrated into agricultural impact studies. • Future yield growth. Assumed continuation of yield increases due to improving technology

and further adoption of existing tochnologies is uncertain. Gaps betweca actual and potential

yield me cited as evidence of unexploited production potential but potential yields are rarely, if ever, attained in practice. Realization of improved varieties depends on continuation of agricultural research and crop breeding systems and the exchange of germplasm Future economic development. The impact of climate change on human populations in terms of famine, chronic hunger, health, and nutrition will depend on bow and whether currently poor areas develop over the next 20 60 50 years. The future path of development of currently vulnerable countries remains uncertain. Policy failures, wars, and political and civil unrest are identified causes, but correcting these problems has proven difficult. Lagging agricultural development has been identified as a consequence of significant policy distortions in many developing countries, conflicting with the industrial sector, and limiting the ability of the

broader economy to grow. The challenges presented by non-climate change factors to future agricultural production are immensc. Basic data on the current extent of soil degradation on crop production, the use of pesticides and chemicals, and the production practices used in different parts of the world are poor ar anecdotal. Thus, projecting the effect of possible additional degradation and pollution problems on agricultural production is far from certain. Whether the challenge of meeting future world food needs is met wil depend on the world's commitment to agricultural research, particularly research that contributes to yield growth while maintaining resource quality, to correcting agriculaural and resource policies that distort individual incentives and contribute to misuse of resources, and to efforts to ensure that the poor have the income or other rights to food. Optimism in this regard is largely based on the observation thal, historically, agriculare and agricultural rescarch have responded to the challenge of a rapidly growing population. Major modeling studies assume a continuation of those historical trends. In fact, these trends depend on continued commitment of resources by private firms and the public toward solving the technical, economic, resource, and environmental problems we know exist today and those of which we are not yet aware. Thus, whether world food production is adequate in the future is only secondarily an exercise in projection; it depends in large part on what we choose to do. Projecting what these choices will be was beyond the scope of the PCC assessment and therefore the relatively optimistic IPCC projections must be understood to be focusing on a relatively narrow aspect of matters relating to the world's ability to feed itself.

4. Dr. Michaels testified that the climate models most heavily cited by the IPCC 1992 supplementary report on climate change were known to contain large crrors at the time of adoption of the Framework Convention on Climate Change and that such errors were not disclosed with the result that the model's uncertainties were not considered in the debate surrounding this issue. Please respond to this statement. Answer: The accusation of Dr. Michael is completely unfounded. The 1992 PCC assessment carefully described how the models performed, including what the models can and cannot do. The large majority of scientists, unlike Dr. Michaels, believe that the GCMs are quite good in simulating many features of the current climate system, hence are useful fa policy formulation. The assessment showed how the models are quite good in simulating climate at large spatial scales, but not a small spatial scales. The 1992 IPCC assessment used a wide variety of models to project climate change, including then newly developed coupled ocean-atmosphere GCMs from the Geophysics Fluid Dynamics Laboratory (USA), Max Plank Institute (Germany), National Center Atmospheric Research (USA), and United Kingdom Meteorological Office (England). These coupled ocean-atmosphere GCMs were used to perform transient, i.c., time dependent calculations. In addition, cight atmospheric GCMs and mixed-layer occan models were used to perform equilibrium calculations.

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